# HD tuning problems caused by 942 putting 12 Volts DC on the 8VSB antenna INPUT?



## TVBob (Dec 19, 2003)

Why does the DVR-942 put 12V DC at 150 ma on the 8VSB (antenna *INPUT*) line? I think this is creating ground loops and interference problems. Would a DC Block on the 8VSB antenna connector fix this? If so, shouldn't all DVR-942s ship with one?

I tried a shield breaker, but of course that didn't help because there are many other DC paths to the amp. ground through other shielded cables and components.

I'm using an "HDTV and DTV approved" *Channel Vision CVT-2/4PIA II* 4-way distribution amplifier to feed my OTA antenna to the DVR-942, a Dish 811, my Sony HDTV, and a DVD recorder. I think this DC _output_ voltage created by the 942 is causing some kind of ground loop or feedback in the distribution amp, and that is messing up the signal to the HD tuner in the 942 on certain channels. My 942 displays a very blocky picture on strong terrestrial channels (RF 45.1 and 49.1). If I _disconnect _the 811 and/or TV from the distribution amplifier, the picture looks fine. I never had this problem when a DVR-921 was connected to the same amp.

The 12V is definitely there; I measured it with a voltmeter. Is there any way to turn it off with software or is a DC block the best thing to try at this point? And why did the Dish engineers choose to put 12VDC on the OTA antenna line any way?


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## Parp (Jun 19, 2004)

Maybe it has something to do with the Active Antenna technology that they had on the original spec sheets... No mention of it now though... Been meaning to throw the question out there--what happened to it?


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## jsanders (Jan 21, 2004)

Hi TVBob,

Is the "Channel Vision CVT-2/4PIA II" pictured in your avatar? Doesn't look like it has a pre-amp on there. Maybe my eyes aren't seeing it.

Here is a question for you.... What hapened to your 921 btw? Maybe I shouldn't ask. :lol: 

Anyway, could you check your 811 to see if it is also biasing the 8VSB input? If it is, then that could cause your ground loop. The voltages may never be exactly the same, and you could have a residule current going from the 811 to the 942 (or vice versa) if they both bias for an antenna pre-amp. In that case, a DC block one one of the units would help.


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## TVBob (Dec 19, 2003)

jsanders said:


> Is the "Channel Vision CVT-2/4PIA II" pictured in your avatar? Doesn't look like it has a pre-amp on there.


That's just my _old_ TV antenna. I had to put up a much better antenna to get decent HDTV reception. The amp. is an indoor distribution amp, pictured on this external link.


> What hapened to your 921 btw? Maybe I shouldn't ask. :lol:


I listed it on eBay the day after I hooked up my 942. Unfortunately it sold for far below the going rate. Discussion here.


> Anyway, could you check your 811 to see if it is also biasing the 8VSB input? If it is, then that could cause your ground loop. The voltages may never be exactly the same, and you could have a residule current going from the 811 to the 942 (or vice versa) if they both bias for an antenna pre-amp. In that case, a DC block one one of the units would help.


I'm pretty sure the 942 is the only one putting out any voltage on the antenna line, but I'll check. I'll install a DC block this weekend and report the results here. Maybe that "RF attenuator" that ships with the 942 was supposed to be a DC Blocker, but there was a miscommunication.


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## Mark Lamutt (Mar 24, 2002)

I'll look into this, Bob.


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## Mike D-CO5 (Mar 12, 2003)

TVBob said:


> That's just my _old_ TV antenna. I had to put up a much better antenna to get decent HDTV reception. The amp. is an indoor distribution amp, pictured on this external link.I listed it on eBay the day after I hooked up my 942. Unfortunately it sold for far below the going rate. Discussion here.
> I'm pretty sure the 942 is the only one putting out any voltage on the antenna line, but I'll check. I'll install a DC block this weekend and report the results here. Maybe that "RF attenuator" that ships with the 942 was supposed to be a DC Blocker, but there was a miscommunication.


I am using the rf attenuator that came with the 942 and it has helped my signal. I was getting a strong signal on my CBS station , but my picture kept breaking up and would never stay solid. I put the attenuator on and it fixed my problems with my Cbs station. I am getting no break ups now and the signal is coming in with about 83 strength.

I am also using a inline amplifier from Radio Shack to a perfect vision 4 way splitter. This amplifies the signal great for all my other hd tuners , vcrs, etc and the attenuator seems to cut the strength just enough so it doesn't overpower the reception. It has been working for me for about a week now with no problems.

I would try the atteunator on your antenna port and see if this helps you with your reception problems.


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## ericha (Jan 21, 2003)

A way to be sure to get rid of the DC is to break the DC path. Any kind of high-pass filter should do this. A simple trick for this (and for breaking ground loops) is to use 2 baluns (75 ohm to 300 ohm converters) back-to-back. One converts teh 75 ohm line to 300 ohms, then the 2nd balun converts teh 300 ohm line back to 75 ohms. Because the balun is really a transformer, no dc can get through. The one potential problem with this is that the DC out of the 942 could saturate the core of the balun connected to it, which would keep it from working (at least very well).

The best solution is a dc block, which is just a coupling capacitor, to get rid of the dc. If you also want to get rid of any ground loops (which cause hum, and possibly buzz, which comes from harmonics of the 60 Hz), use the balun trick.


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## TVBob (Dec 19, 2003)

Mike D-CO5 said:


> I am using the rf attenuator that came with the 942 and it has helped my signal. I was getting a strong signal on my CBS station , but my picture kept breaking up and would never stay solid. I put the attenuator on and it fixed my problems with my Cbs station.


The attenuator was not intended for the antenna line on the 942, it was intended for the TV-2 RF output. I measured it. It seems to have a 110 ohm resistor inside.

The signals aren't that strong, but I tried putting the attenuator inline for a few minutes. It made things worse. When I took it out, I noticed that it was very hot, probably due to the 12 VDC that Dish puts across the antenna line.

I confirmed that none of the other receivers, including the Dish-811, have 12V being output on the OTA antenna line like the 942. I tried one side of a Diplexer in the antenna line, and that seemed to help the picture a little, but I could still measure a little voltage coming out of the Diplexer (.1 to .5 volts). More tomorrow after I try the DC blockers.

One question: does anyone else have an 811 and 942 connected to the same antenna? I've noticed the 811's OTA receiver seems to be quite a bit better on weaker signals than the 942's.


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## Bichon (Jun 5, 2003)

TVBob said:


> The attenuator was not intended for the antenna line on the 942, it was intended for the TV-2 RF output. I measured it. It seems to have a 110 ohm resistor inside.


You've made me nervous enough that I've removed mine, even though it was only slightly warm.

Have you measured the Radio Shack attenuators that people are putting on their receivers? Do they get warm too?


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## TVBob (Dec 19, 2003)

Bichon said:


> Have you measured the Radio Shack attenuators that people are putting on their receivers? Do they get warm too?


No, I haven't measured those, but they're probably about the same.

The good news is that adding a single DC Blocker at the 8VSB antenna input of the DVR-942 cured the HD reception problem described above. 

I highly recommend all users of the 942 use a DC Blocker at this connector. Even if you don't use any amplifiers and go straight from a TV antenna into this connector, any short in the antenna line would short the 12 VDC to ground, and that can't be good for the 942.

If you're using a Diplexer to feed this input, you may be OK, because that blocks most of the DC voltage coming out of this connector on the 942. But an extra DC blocker wouldn't hurt. I think Dish should supply a DC Blocker with every 942, unless they can find a way to turn off this voltage with a software upgrade.


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## SimpleSimon (Jan 15, 2004)

My thought is that if the 12VDC being output is "normal" is that it's intended to power an antenna amplifier.

In any event, if it's there by design, there needs to be a way to stop it.


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## Mike Johnson (Jan 16, 2005)

I've confirmed this on my 942. Mine measures 11.9v DC, but there is definitely voltage on the OTA antenna input. I'm putting in a DC block until we hear more about this.


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## StevenD (Nov 6, 2004)

TVBob said:


> The attenuator was not intended for the antenna line on the 942, it was intended for the TV-2 RF output.


The attenuator that comes with the 942 is actualy for the UHF Pro remote antenna.


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## Mike Johnson (Jan 16, 2005)

StevenD said:


> The attenuator that comes with the 942 is actualy for the UHF Pro remote antenna.


No, TVBob is correct. The sticker on the supplied attenuator says, "This attenuator is only for use on output TV2 in special cases. Consult Chapter 2 of the User Manual." Its use is explained in Chapter 12 (not 2), page 117, and the attenuator is color coded yellow to match the TV2 RF output.

The UHF Pro antenna attenuator is _not_ included with the 942. It must be purchased seperately. This is explained on page 85 of the User Manual.


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## the_bear (Oct 18, 2004)

The 12V could explain a LOT of people’s reception problems.


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## jpetersohn (Apr 6, 2005)

SimpleSimon said:


> My thought is that if the 12VDC being output is "normal" is that it's intended to power an antenna amplifier.


I would believe it's normal, my 942 has a label under the 8VSB antenna connection stating "12V 150 mA DC".


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## Mike Johnson (Jan 16, 2005)

That will teach us to not look at the back panel! It couldn't be any more clear. Scott's photo says it all.


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## SimpleSimon (Jan 15, 2004)

mike_johnson said:


> That will teach us to not look at the back panel! It couldn't be any more clear. Scott's photo says it all.


 I would've looked if I had one.


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## normang (Nov 14, 2002)

Where does one find a dc blocker? If from RS, what is the catalog # for reference? Is it really needed in all cases, or as a matter of course if not feeding anything between receiver and attenna.


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## Bichon (Jun 5, 2003)

Yes, Radio Shack sells the DC Block. It is part number 15-1259. Bought one, and a variable attenuator for my 942 this morning. So far, so good.


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## BigFella (Jul 13, 2004)

TVBob et al:
I just purchased a Channel Vision CVT28PIAII, the 8 port version of your DA on ebay and I plan install it this weekend. I plan to take the TV2 out of my 942 and connect to the "modulator" in port of the CVT28PIAII, then connect Comcast basic cable (directly out of the wall jack - no cable box) into the Antenna/Cable in port and distribute via the outputs of the CVT28PIAII to the other televisions in the house. Does anybody see any problems with plan? Does the 12v DC issue come into play here (the CVT28PIAII has it's own power supply)? Will I need to use a DC block, or the TV2 attenuator anywhere in-line?

Thanks!


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## TVBob (Dec 19, 2003)

BigFella said:


> I plan to take the TV2 out of my 942 and connect to the "modulator" in port of the CVT28PIAII, then connect Comcast basic cable (directly out of the wall jack - no cable box) into the Antenna/Cable in port and distribute via the outputs of the CVT28PIAII to the other televisions in the house. Does anybody see any problems with plan? Does the 12v DC issue come into play here (the CVT28PIAII has it's own power supply)? Will I need to use a DC block, or the TV2 attenuator anywhere in-line?


First, are you planning to plug anything into the *8VSB Ant *jack on the back of the 942? If so, put a DC Block on that jack first. As for the TV2 output, there should be no need to use a DC Block on that jack, but you probably should use the attenuator (see Chapter 12 of the 942 manual). I would try the attenuator on the TV2 output jack first (or on the modulator input of the distribution amp). If the signals on the other TVs all look good, keep it there. Otherwise, remove it and see if there is any improvement.

One other point: if you're _not_ using the TV2 Out jack, put a 75 ohm _*terminator* _on it. It won't affect the 942, but it will prevent interference to nearby TV receivers. A terminator is not a DC block and it is not an attenuator. Radio Shack catalog no. 15-1156 is an example of a (overpriced) terminator. 

You should put a terminator on each unused output of the distribution amplifier as well. *But do not use a terminator on the 8VSB Ant output unless you have a DC Block underneath it.* That 12V DC will just heat up the terminator and eventually it may fail.


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## BigFella (Jul 13, 2004)

TVBob said:


> First, are you planning to plug anything into the *8VSB Ant *jack on the back of the 942? If so, put a DC Block on that jack first. As for the TV2 output, there should be no need to use a DC Block on that jack, but you probably should use the attenuator (see Chapter 12 of the 942 manual). I would try the attenuator on the TV2 output jack first (or on the modulator input of the distribution amp). If the signals on the other TVs all look good, keep it there. Otherwise, remove it and see if there is any improvement.
> 
> *Nothing into the 8VSB ANT jack yet - later on though. I just have to save my pennies for a good, deep fringe directional antenna. I only live 30-40 miles from the transmitter towers, but there are a lot of mountains in the way. I take it the DC Block will come into play at that point. Can I still use an amplifier for my antenna if necessary?*
> 
> ...


*Understood*

Thank you TVBob!


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## normang (Nov 14, 2002)

Bichon said:


> Yes, Radio Shack sells the DC Block. It is part number 15-1259. Bought one, and a variable attenuator for my 942 this morning. So far, so good.


Cool, the question still is, if there is nothing between the antenna input and the antenna itself, is a blocker needed? Or should one be installed as a matter of course if that current isn't going to power anything on that cable line?


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## TVBob (Dec 19, 2003)

BigFella said:


> Can I still use an amplifier for my antenna if necessary?


Sure, but use that DC Block.


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## TVBob (Dec 19, 2003)

normang said:


> Cool, the question still is, if there is nothing between the antenna input and the antenna itself, is a blocker needed? Or should one be installed as a matter of course if that current isn't going to power anything on that cable line?


I would install one in all cases. It's always possible for a DC short to be created in any coax line. I don't know if a DC short will blow an internal fuse in the 942, or cause no harm at all, but I'm not willing to experiment.

I'd suggest spending the $2-3 on a DC Blocker. Then you don't have to worry about some critter chewing all the way through your antenna coax, shorting the 12V DC to ground.


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## Jeff McClellan (Apr 22, 2002)

So let me ask the stupid question. Are you saying the input for the OTA antenna is putting out power. So if you were to hook a pre-amp up, and not use its inside power supply, the 942 would actually sent current up ti it to make it work. Thats my stupid question. But if that is true, it explains some things.


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## jpetersohn (Apr 6, 2005)

JEFF M said:


> So let me ask the stupid question. Are you saying the input for the OTA antenna is putting out power. So if you were to hook a pre-amp up, and not use its inside power supply, the 942 would actually sent current up ti it to make it work. Thats my stupid question. But if that is true, it explains some things.


Assuming that the preamp uses 12V DC with less than 150mA draw, then yes.
I believe some Winegard antenna preamps use AC?


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## Mark Lamutt (Mar 24, 2002)

Got this last week:

The 12 volt DC output was going to be for support of the 909 active antenna protocal, but support for that has been scrapped. Future 942s will NOT have the 12 volt DC being sent out of the 8VSB port.


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## Mike D-CO5 (Mar 12, 2003)

Could this 12 volt dc output cause problems with reception on say strong channels? I have interference at night for my strongest station in my area , but only at night and early mornings. This didn't happen on my 921 receiver.


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## cebbigh (Feb 27, 2005)

Mark Lamutt said:


> Got this last week:
> 
> The 12 volt DC output was going to be for support of the 909 active antenna protocal, but support for that has been scrapped. Future 942s will NOT have the 12 volt DC being sent out of the 8VSB port.


My 942 is shipping to me now. Will it likely have the 12 volt DC on it? Is there any reason to not block the DC?


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## normang (Nov 14, 2002)

Does The DC Blocker introduce any signal loss to perhaps compensate for?


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## Mark Lamutt (Mar 24, 2002)

Honestly, I see no reason to NOT block the voltage, and I see no reason TO block the voltage, unless you're concerned about the little bit of heat generated. I could probably be convinced why it should be blocked if someone had a good explanation of it, but a 12 volt signal, as far as I know, should have absolutely no affect on signal reception at all. If it did, then mast mounted antenna amplifiers would cause exactly the same problem, with their power inserters.


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## Jeff McClellan (Apr 22, 2002)

Well here is what I do know. I can put my older model Winegard pre-amplifier on the mast and run it directly to the 942. And the power sent from the 942 will work the pre-amp. Signal strength increases by about 10 to 15 percent. So it will work some pre-amps. The station I was having all the breaking up with and had low signal strength, comes in flawless. So what effect this has on it without the pre-amp, I dont know. The only way I can find out is to install a DC block and remove the pre-amp. But my guess is that some of what we have seen is directly related to this.


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## waltinvt (Feb 9, 2004)

Ok, expanding on that: if the 12v from the 942 can run the pre-amp on the mast, should the plug-in part of the amp NOT be used ? In other words, is it possible that having both active will provide too much power and adversly effect the signal ?

The reason I ask, is that I just replaced my 811 with the 942 and with the 811 there were about 4 OTA stations that I'd get a lot of signal activity. Not quite enough to lock but the meter would hang around 49% with occasional spikes up to 60-65%. With the 942, I don't get even a flicker of signal for those same stations.


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## Jeff McClellan (Apr 22, 2002)

I dont use the plug in part. I power the preamp directly from the 942. And it works.


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## waltinvt (Feb 9, 2004)

JEFF M said:


> I dont use the plug in part. I power the preamp directly from the 942. And it works.


Quickest I ever got a response  Good morning.

So do you think it's possible that leaving my amp plugged in could actually interfere or reduce the signals somehow ? I'll check it out on mine later but just thought you may have had yours plugged in at one time and noticed a difference.


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## Jeff McClellan (Apr 22, 2002)

Mine is better without it.


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## waltinvt (Feb 9, 2004)

JEFF M said:


> Mine is better without it.


Cool - I'm going to try it later. Now, this is probably a dumb question but do you think there would be any advantage to removing it entirly and running the "pre-amped" coax directly into the 942 versus just unplugging it ?


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## Bichon (Jun 5, 2003)

waltinvt said:


> Cool - I'm going to try it later. Now, this is probably a dumb question but do you think there would be any advantage to removing it entirly and running the "pre-amped" coax directly into the 942 versus just unplugging it ?


If you just unplug the A/C from your antenna power injector without removing it the antenna line, it probably won't work. Antenna power injectors typically have a DC block on the equipment-facing side to prevent sending power back into your gear.

Before removing the power injector and powering your amp with the 942, I'd confirm that voltage and polarity match those supplied by the injector, either by checking the specifications, or with a multimeter.


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## waltinvt (Feb 9, 2004)

Bichon said:


> If you just unplug the A/C from your antenna power injector without removing it the antenna line, it probably won't work. Antenna power injectors typically have a DC block on the equipment-facing side to prevent sending power back into your gear.
> 
> Before removing the power injector and powering your amp with the 942, I'd confirm that voltage and polarity match those supplied by the injector, either by checking the specifications, or with a multimeter.


OK, now you're getting a little over my head. I'm not sure how to find that information. I'll try looking on the base unit later if I can't find the manual. It was just installed new 6 months ago if that's any help.

I'm wondering now if maybe the power coming from the 942 is actually blocking out the power from the amp - effectivly cancelling out any of the amp's signal boost? This could account for me no longer getting any signal activity for those distant channels that I was getting with the 811. Like I said, even though they wouldn't lock, I was at least seeing a steady 49% and occasional spikes in the 60s with the 811 but not a flicker with the 942.


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## cebbigh (Feb 27, 2005)

I know my cm7775 power source outputs 18 volts dc. I think the other cm777x series use the identical power source. I've already gotten my dc block from radio shack for when my 942 arrives this week. Has anyone who used the dc block (who doesn't have a good match with the 12 volts dc for their amp) seen a reduction in signal quality after using the block?


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## Jeff McClellan (Apr 22, 2002)

I run the coax, straight from the 942 up to the pre-amp. From their to the 4228. It works, my signal jumped greatly. I then installed a in-line Attenuator at the reciever. This did away totally away with the blocking or multi-pathing problems I was having.


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## cebbigh (Feb 27, 2005)

JEFF M said:


> I run the coax, straight from the 942 up to the pre-amp. From their to the 4228. It works, my signal jumped greatly. I then installed a in-line Attenuator at the reciever. This did away totally away with the blocking or multi-pathing problems I was having.


Does your Winegard normally power from a 12 volt 150 ma dc source? Have you noticed any heating of the attenuator?


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## TVBob (Dec 19, 2003)

JEFF M said:


> I dont use the plug in part. I power the preamp directly from the 942. And it works.


Does it really? I thought most mast-mounted preamps required more than 150ma of current, which is all the 942 can supply. If your preamp needs to draw more than 150 ma at 12VDC, the 942 could be damaged. Check the pre-amp specs carefully, especially the power supply output voltage and current.


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## cebbigh (Feb 27, 2005)

For what it is worth, for grins I attached the rs 15-1259 dc block to my 921's 8VSB port just to test if it produced any signal loss and saw no change. I know the 12 volt dc power is only a concern (or perhaps non-concern or even blessing in disguise for some) for the 942 but I just wanted to see what would happen because I'm going crazy waiting for my new unit to arrive.


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## TVBob (Dec 19, 2003)

waltinvt said:


> This could account for me no longer getting any signal activity for those distant channels that I was getting with the 811. Like I said, even though they wouldn't lock, I was at least seeing a steady 49% and occasional spikes in the 60s with the 811 but not a flicker with the 942.


I have both connected to the same antenna via a distribution amplifier, and the 811 definitely seems to do a better job than the 942 if there is any multi-path present in the signal.

I wonder if there are any plans to improve 942's HD tuner with a software upgrade the way the 921's tuner was improved over time?

I would rank OTA HD tuner quality as follows, based on my experience using all of these HD receivers at my location (50 miles from the main tower). Ordering from best to worst:


Dish 811
Sony KD34XBR-2 built-in HD tuner
DVR 921 (in May, 2005)
DVR 942 (locks on much faster than the 921 though)
Dish 6000 (much worse than all of the above)
One very curious problem is *that changing channels on the 811 seems to affect my OTA signal quality on the 942!* I have a DC block on both, but somehow the 811 causes interference on the 942.

Specifically, if the 811 is tuned to Ch. 005-01 then Ch. 005-01 will also look great on the 942, but if I tune the 811 to any other OTA HD channel, the 942 reception on Ch. 005-01 gets all blocky and unwatchable.

So, installing the DC blockers cured only some of my reception problems. Perhaps the DC voltage damaged something in my preamp, causing crosstalk between the receivers now? I'm out of ideas. One can only hope for a software upgrade to the 942 OTA receiver that makes it less susceptible to interference and multipath.


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## TVBob (Dec 19, 2003)

JEFF M said:


> I run the coax, straight from the 942 up to the pre-amp. From their to the 4228. It works, my signal jumped greatly. I then installed a in-line Attenuator at the reciever. This did away totally away with the blocking or multi-pathing problems I was having.


An attenuator on the 8VSB Antenna port of the 942 will burn up most of the 12 VDC as heat and very little voltage will get to your preamp. The attenuator is just a DC resistor. A DC Block at the 942 (a capacitor) would be much better and it won't burn up any power as heat. Signal loss through the DC block should be negligible.

*You should only power your mast-mounted antenna preamp with the power inserter that was made for it, not the 942*, unless the pre-amp wants 150 ma or less at 12VDC.


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## normang (Nov 14, 2002)

Well. I received my 942 and so far so good. my OTA is fine, I get better signals and more channels with the 942 than with my 811. While I know that measuring signal based on the display is more or less apple & oranges, my initial feel is that the 942 is better than the 811 it replaced. 

Since OTA has so many variables, its really tough without some real test gear as to whether there are differences between one 811 vs another or really any differences from the 811 to the 942.

My only issue so far is that I want to use single mode, and send tv2 to my other inputs so that I get full screen SD on my 4:3 HDTV. But because TV2 in single mode is squished, its not possible at the moment. Hopefully 226 will address that..

more later


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## Jeff McClellan (Apr 22, 2002)

First, I am not trying to act like I have the answer's or even know what I am doing. I have just been trying to figure out the best set up. In the beginning, on a weaker station, I was getting the blocking and breaking up, and green lines. I am fairly sure it was due to some strong stations in the same direction. They were coming in near 100 percent power, while the PBS I was trying to hit came in around 60. Didn't take much wind or adverse weather conditions to knock it out. I tried the amp using its on power supply. It added signal strength, but only made the breaking up worse. I then read here about the 12 volts being put out by the 942, so I figured I had voltage going to the power supply, bad, and power going to the pre-amp.

So I did away with the power supply and my signal gain is still there. I am even pulling in a digital station from Greensboro at 60 percent, 90 miles away. But, the one station I wanted still had blocking. I then installed the attenuator to hopefully keep the stronger stations from killing the one I wanted. It worked! I dint know how or why, but it works. I would like to try putting a dc block on the back of the 942 and take the pre amp off to see what will happen. I think it might fix the blocking, but I will lose signal. I went from 60 to 72 with the 942 powering the pre amp. So, you can think what you want, but this older vhf.UHF low gain Weingard amp works well with the 942 powering it. Isn't that what the original intent was with the 942.


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## Jeff McClellan (Apr 22, 2002)

I am going to install a dc block later today and unhook the preamp. I will let you know what happens. Also my 2nd remote that has the uhf antenna, wont work unless you hit a sweet spot pointed at the roof of the room. It is only about 40 feet away from the reciever in another room. Would adding a attenuator help this. I currently have the small antenna installed on about 10 feet of coax mounted at the ceiling of my den. It looks like crap. How or what will fix the short range needed for this. My daughter has pretty much become frustrated with it and wants cable back. FAT CHANCE!


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## Bichon (Jun 5, 2003)

I'm not sure if anyone cares, but I thought I'd describe the OTA setup that works well for me. I have a 4248 antenna in the attic, with a mast mounted 7777 preamp. That runs down to my home theater, where it is connected to ChannelMaster power inserter. The output of that goes to a two-way splitter. One leg of the splitter goes to the HDTV card in my home theater PC, the other leg goes to a R/S variable attenuator. The attenuator is connected to a DC block, which is connected to the 942. This setup is in Freehold NJ, pointed at Philadelphia, I'd guess about 50 miles away. As a bonus, I also pick up WNJT from Trenton, which is in roughly the same direction.


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## Jeff McClellan (Apr 22, 2002)

Well I care. I am going to hook up the dc block and run a short peice of cable to the real power supply for the weingard pre-amp. Like you, I am going to leave the attenuator in place. I am hoping with this setup, I will get great range and no blocking from close by stations that are strong. The more we try, will only benifit others. I do agree now that letting the 942 power anything, cant be good.


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## Mike D-CO5 (Mar 12, 2003)

normang said:


> Well. I received my 942 and so far so good. my OTA is fine, I get better signals and more channels with the 942 than with my 811. While I know that measuring signal based on the display is more or less apple & oranges, my initial feel is that the 942 is better than the 811 it replaced.
> 
> Since OTA has so many variables, its really tough without some real test gear as to whether there are differences between one 811 vs another or really any differences from the 811 to the 942.
> 
> ...


 A work around I have used that works for me; Set your tv to 4 x3 2 format. It makes the second sd tv look right and it makes you be able to change the formats on your ota stations as well as your hd stations. Also the picture format in stretch mode is the exact same mode for normal in 16 x 9 mode . I have been using mine in this mode since the first day and if there is some sd satellite show I need to change the format on to fit the screen, I just change for that show to 16 x 9.


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## Bichon (Jun 5, 2003)

Mike D-CO5 said:


> A work around I have used that works for me; Set your tv to 4 x3 2 format. It makes the second sd tv look right and it makes you be able to change the formats on your ota stations as well as your hd stations. Also the picture format in stretch mode is the exact same mode for normal in 16 x 9 mode .


Be aware that the work-around that Mike proposed results in a 33% reduction in vertical resolution. That means your HD picture will be 1920 x 720i instead of 1920 x 1080i, or 1280 x 480p instead of 1280 x 720p. I find the difference in picture quality pretty noticable on my 58" TV.


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## TVBob (Dec 19, 2003)

JEFF M said:


> I am going to install a dc block later today and unhook the preamp. I will let you know what happens.


If you place a DC block right on the back of the 942, then you can add an attenuator or a pre-amp or both without worries.


> Also my 2nd remote that has the uhf antenna, wont work unless you hit a sweet spot pointed at the roof of the room. It is only about 40 feet away from the reciever in another room. Would adding a attenuator help this. I currently have the small antenna installed on about 10 feet of coax mounted at the ceiling of my den.


An attenuator _attenuates_ (reduces) the signal, so that would make things worse. You need to locate the little UHF remote antenna far away from any electronics that could generate radio noise on 369.5 MHz, which is the frequency used by the remotes. Such noise could be overwhelming the UHF signal from the remote. But of course the antenna also has to be "in the clear" and not shielded by heavy metal objects or surrounded by shielded cables. Of course make sure you are using the blue "#2" remote in the other room since the green #1 remote is IR only I believe.

If you can borrow a portable scanner that tunes to 369.5 MHz, you can check nearby computer monitors, your TV, touch lamps, fluorescent lights, etc. to see if they are generating any radio noise on that frequency. Please let us know what you discover.

Also, any large metal objects such as refrigerators, speakers or TV sets located between the remote and the receiving antenna could attenuate some of the signal, making the remote less reliable. FWIW my "remote" remote works better with the 942 than it did with the 921, so maybe the 942's UHF remote receiver is more sensitive than the 921's. If it's _too_ sensitive, a UHF attenuator just might help.


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## normang (Nov 14, 2002)

I'll have to give that idea a look and see how it goes. It would be nice to use single mode instead of having to switch remotes depending on whether your watching SD or HD.

I also installed a blocker from RS, my antenna is internal and can be touched, so to eliminate the possibility of a short of any kind, the blocker is cheap protection and didn't seem to interfere at all with the reception..

So far I've only have had a few hours to watch and check things out last night, but things look pretty good on the OTA front.


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## cebbigh (Feb 27, 2005)

JEFF M said:


> Well I care. I am going to hook up the dc block and run a short peice of cable to the real power supply for the weingard pre-amp. Like you, I am going to leave the attenuator in place. I am hoping with this setup, I will get great range and no blocking from close by stations that are strong. The more we try, will only benifit others. I do agree now that letting the 942 power anything, cant be good.


I'll be interested in the results. Have you ever used the seperate power supply with the 942 or were you attentive to details and start off using the power from the 942? If I hadn't seen this thread I would have likely initially hooked up the undampened dc coming from the box to an attenuator to my jointenna and then to the two seperate power supplies working my two antennas. I don't know for sure but I think that could have gotten pretty ugly. (If you wonder why I have two power supplies, its because it took me months to get a sweet spot where I could pull in my local abc station using a cm4248. Once I got it reasonably well I decided not to move that antenna no matter what and the pole mounted amp on my chimney was out of reach. I needed a seperate cm4228 to pull in my fox station which transmits from a different direction.)


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## waltinvt (Feb 9, 2004)

This whole thread has got me really confused now. 

What I'm getting is that the latest consensus is that you should use a dc block at the 942's antenna in connection before hooking up the coax that has a powered amp.

The "things might get ugly" line really makes me nervous .

What about those of us whose units were installed without a dc block and did or do currently have a pre-amp and powered base unit installed ? What possible damage could we have and how can we tell?

All I know for sure is that with the 811 there were a couple of stations that looked real promising, like occasional signal spikes in the 60s but only locked once or twice. Still, enough so I was considering relocating / raising my antenna to try and get them. With the 942 I haven't been able to get even a flutter on those stations whether using the amp's base unit, shuting it off or removing it entirely.


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## Jeff McClellan (Apr 22, 2002)

I wont know until tonight. Yes, I started off with just the pre-amp and the weingard power supply. Alot of breaking up which I attributed to multi-pathing. The funny thing is, it wouldn't do it when I connected the same setup to my Sony's internal tuner. Clear as a bell. So I did away with the pre-amp completely, and it fixed the problem. Of course I couldn't pull 2 stations in. I then hooked the preamp directly to the 942 and regained the signal strength back, but blocking occurred. I read where others used a attenuator to help with the over powering of strong close stations. At this point it worked completely. This is where I am at currently and happy. But it still bothers me the 942 is powering my preamp.

So the test tonight is use the dc block, male,female, hook the male female attenuator to it, then run coax to the weingard power supply to power the pre-amp. What do I expect to accomplish? I dint know. I think if anything I may gain some more signal, reduce blocking or multipathing and take the 942 totally out of the equation. A more stable operating environment. This is why I am sure newer 942s wont have this feature. Or, I may just blow the whole house up. I know one thing, I ain't climbing back on the roof tonight. 

One last thing I may try is using the dc block and attenuator, and taking the pre amp out. I have locals that are at 100 percent even without a pre amp using the cm 4228. But our towers are all over the globe. So I have everything needed and will post around 5 my results.

I think the block and attenuator will correct most peoples issues. And if you need a pre amp, then fine add it and you wont see the issues we have seen of late.


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## HobeSoundDarryl (May 15, 2005)

Yes, could someone who has put in the DC block comment on whether it made signals that they could not lock (but should have been able to lock) come in fine? I have a local channel that has always been a solid channel on the old Voom and D* boxes. Since I switched to the 942- everything else staying the same- that channel will come in for about half a second and then be gone (yellow screen, signal loss message, etc.). 

What i'm wanting to see is someone posting that after they put in the DC block on a preamped antenna, a local channel that was not locking is now coming in.

Also, like many other posters, I was formerly able to lock some DTV channels beyond my immediate local market. But now, I can't even get the slightest hint of their signals in the signal scans. Did installing the DC block on a preamped antenna open up the world of not immediate local DTV channels to anyone?

Please advise!


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## Bichon (Jun 5, 2003)

waltinvt said:


> What about those of us whose units were installed without a dc block and did or do currently have a pre-amp and powered base unit installed ? What possible damage could we have and how can we tell?


No damage at all. As I said earlier in the thread, the power supply for your pre-amp should have a DC block built in, such that power is applied to the coax going up to your antenna, but blocked from the coax connected to your equipment.

The potential for damage occurs when connecting an attenuator directly to the 942 without a DC block. Since the resistance of the attenuator is applied across the 12 volt supply, it could hurt the 12 volt supply in the 942 or cook the resistor in the attenuator. Most likely it will do neither, and just cause the attenuator to get a bit warm.


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## Bichon (Jun 5, 2003)

HobeSoundDarryl said:


> Yes, could someone who has put in the DC block comment on whether it made signals that they could not lock (but should have been able to lock) come in fine?


The DC block by itself makes no difference in reception. WHYY, which came in fine on my 6000 (and comes in fine on my HTPC), would still break up and cut out. The DC block with an attenuator, on the other hand, fixes the problem.


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## TVBob (Dec 19, 2003)

JEFF M said:


> Yes, I started off with just the pre-amp and the weingard power supply. Alot of breaking up which I attributed to multi-pathing. The funny thing is, it wouldn't do it when I connected the same setup to my Sony's internal tuner. Clear as a bell.


Same here. The Sony tuner must reject multipath much better than the 942 tuner. Same goes for the 811. Hopefully Dish can address this with a software upgrade. That's the real underlying problem here. The 942 OTA tuner just needs work. In my case the DC block fixed signal reception problems on just _one _channel (Digital 045-01).

It doesn't make much sense to use an attenuator AFTER a pre-amp. so I don't know why that would make things any better unless it is reducing a secondary signal below some threshold that is critical to the 942.

Perhaps the pre-amp itself is being overloaded by strong signals, causing "intermod." In that case an attenuator between the _antenna _and the pre-amp antenna input might help. Better yet, don't use a pre-amp at all if you've got strong signals. If your TV towers are "all over the globe", you need an antenna rotator or an antenna switch you can use to select different antennas for different stations. A pre-amp can't fix multipath, and it could make things worse.

If you can use your analog TV tuner to tune to an _analog _UHF station in your area, you should be able _see _what the attenuator and preamp are doing to your UHF signals. Choose an analog UHF channel number that is close to the digital RF channel no., and hopefully on the same broadcast tower. If you see lots of strong "ghosts," that's multipath and some HD tuners deal with it much better than others.


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## cebbigh (Feb 27, 2005)

waltinvt said:


> The "things might get ugly" line really makes me nervous .


Sorry. Didn't mean to make anyone nervous. How about "messed up" instead of ugly? I don't think anyone has reported damage to their equipment. I'm no electrician, but how much damage could 12 volts 150 ma dc do? I do think it makes the most sense for signal quality to use the dc block in most cases. I think the 12 volts has no current reason to be there. TVBob did us all a favor by pointing it out to us.


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## Jeff McClellan (Apr 22, 2002)

[QUOTE=
It doesn't make much sense to use an attenuator AFTER a pre-amp. so I don't know why that would make things any better unless it is reducing a secondary signal below some threshold that is critical to the 942.

That is what it does, it eliminates the domination of the stronger signal. The 942s tuner is timid.. I have a rotor, just trying to pull some distant locals in. OOPS, they aren't in my DMA.


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## Jeff McClellan (Apr 22, 2002)

Well those weak 12 volts give my preamp a jolt. So they may not curl your hair but, they gave me a 72 over a 61 on a distant hd-pbs station 45 miles away.


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## Bichon (Jun 5, 2003)

TVBob said:


> It doesn't make much sense to use an attenuator AFTER a pre-amp. so I don't know why that would make things any better unless it is reducing a secondary signal below some threshold that is critical to the 942.


It may not make much sense, but it's the only thing I've found that works. I'm about 50 miles from the towers, and my antenna is in the attic, so I'm certainly not overloading anything with strong signals. I'm using a variable antenuator between the preamp and the 942, and found that there is a narrow sweet spot on the dial that works. Too much signal, and WHYY breaks up. Too little, and WYBE (don't think they're at full power) is lost.


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## TVBob (Dec 19, 2003)

FWIW, there's some good info. about antennas, pre-amps, DC blockers, and attenuators that we should all review:

http://www.hdtvprimer.com/ANTENNAS/basics.html

I stand corrected; sometimes it _is _appropriate to use an attenuator after a pre-amp. Which "variable attenuator" are you using? Maybe I should try it.

The pre-amp noise figures published on this web site are most interesting (the table displays fine with Internet Explorer, but not with FireFox for some reason).


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## cebbigh (Feb 27, 2005)

TVBob said:


> FWIW, there's some good info. about antennas, pre-amps, DC blockers, and attenuators that we should all review:
> 
> http://www.hdtvprimer.com/ANTENNAS/basics.html
> 
> ...


Some of that hdtvprimer was over my head at first reading. But I thought this was interesting:

"The Radio Shack attenuator will not pass DC and thus must not be inserted between the mast-mounted amplifier and its power injector."

I'm not sure if that is referring to all rs attenuators. I suspect it is referring mainly to the simple 6db attenuator that most people have found productive. That would explain (I think) why it works. It negates the 12 vdc output by the 942. That doesn't mean that blocking dc is what it's designed to do. I'd still use the dc block and then experiment with either no attenuator or the variable or fixed attenuators to see what works best.


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## JohnT (Aug 15, 2004)

Bichon said:


> It may not make much sense, but it's the only thing I've found that works. I'm about 50 miles from the towers, and my antenna is in the attic, so I'm certainly not overloading anything with strong signals. I'm using a variable antenuator between the preamp and the 942, and found that there is a narrow sweet spot on the dial that works. Too much signal, and WHYY breaks up. Too little, and WYBE (don't think they're at full power) is lost.


Bichon, I think your attenuator might be helping with a strong signal from WLNY-TV (analog) on Long Island. Both WLNY and WHYY-DT broadcast on channel 55, and from your location, they're about 180 degrees apart. WHYY-DT broadcasts at 87kW, and WLNY-TV broadcasts at 5000kW.

FWIW, I could never get a signal from WHYY-DT using my ChannelMaster 4228 and 7777 pre-amp from my attic in Freehold. WYBE-DT reception was always sporadic, although they're licensed for 500kW.

I swung my antenna back around toward NYC a few months ago, and found reception had improved significantly. If you haven't tried the NY stations, it might be worth a shot.

BTW, howdy, neighbor!


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## jsanders (Jan 21, 2004)

TVBob said:


> It doesn't make much sense to use an attenuator AFTER a pre-amp. so I don't know why that would make things any better unless it is reducing a secondary signal below some threshold that is critical to the 942.


Yep, that is a stupid thing to do, normally wouldn't do anythng at all because the pre-amp amplifies noise as well as signal, and that is an ideal case with a noise figure of 1. In practical cases, the pre-amp generates extra noise on its own. Putting the attenuator right after a pre-amp won't do anything to the signal to noise ratio, as it will attenuate the amplified signal, and attenuate the amplified noise. If you happened to be at the end of a long cable run with a line loss that perfectly matched the the amplification of the pre-amp, then an attenuator at the end of this cable run would do something. You can't attenuate thermal noise (in this case, amplified noise attenuated by the cable run to the noise floor), so in this instance, the attenuator would reduce the signal to noise ratio.


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## TVBob (Dec 19, 2003)

For those of you following only this thread, JEFF M has just reported in a new thread that using a DC Block and pre-amp with _no _attenuator works best. In conclusion, use a DC Block on the 8VSB Antenna line, and use the supplied attenuator only for its intended purpose: on the TV2 RF output when you are feeding TV2 directly to a remote TV without any splitters in between.


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## cebbigh (Feb 27, 2005)

Too bad JEFF M's post wandered off to another thread, it really looks like he intended it to post to this one. Glad to hear he is apparently having outstanding results. Just found out my 942 arrives tomorrow (go figure... off M,T,W and the thing will be here Thurs). I plan to try three configurations. 942 to dc block 1) without attenuator and 2) with the simple rs 6db attenuator and 3) with the variable attenuator then to the jointenna then to the power. My guess ahead of time is that it will work best without any attenuator because that is how I get the best results with the 921. Seems to me Dish could help their image by getting out in front on this. Until they actually fix the problem on future boxes they could start including dc blocks with the existing stock of 942's and do something to inform those who already have 942's know that there is something simple they can do to make the OTA work better. There has got to be more than a few 942 users out there who don't faithfully follow these threads.


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## Bichon (Jun 5, 2003)

TVBob said:


> For those of you following only this thread, JEFF M has just reported in a new thread that using a DC Block and pre-amp with _no _attenuator works best. In conclusion, use a DC Block on the 8VSB Antenna line, and use the supplied attenuator only for its intended purpose: on the TV2 RF output when you are feeding TV2 directly to a remote TV without any splitters in between.


That would be good advice if everyone had exactly the same reception situation as JEFF M. The DC block by itself did nothing to improve my situation. Only the variable attenuator, carefully adjusted, allows me to receive both WHYY and WYBE glitch free. It's a 942 thing, since both channels come in glitch free without an attenuator on both my Dish 6000 and my HTPC.


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## Bichon (Jun 5, 2003)

JohnT said:


> Bichon, I think your attenuator might be helping with a strong signal from WLNY-TV (analog) on Long Island. Both WLNY and WHYY-DT broadcast on channel 55, and from your location, they're about 180 degrees apart. WHYY-DT broadcasts at 87kW, and WLNY-TV broadcasts at 5000kW.
> 
> FWIW, I could never get a signal from WHYY-DT using my ChannelMaster 4228 and 7777 pre-amp from my attic in Freehold. WYBE-DT reception was always sporadic, although they're licensed for 500kW.
> 
> ...


Howdy neighbor! That sounds like a reasonable explanation about WHYY. Oddly enough, my Dish 6000 and HTPC have never had any trouble getting it rock solid.

Last time I had my antenna pointed toward New York was prior to 9/11. At the time, I got much better reception from Philly. Since I'm now getting perfect reception and lots of channels: KYW, WCAU, WPVI, WTXF, WPHL, WHYY, WNJT, WPSG, WWSI, WUVP, WFPA. I don't know if I'd be gaining or losing channels by repointing at New York. What channels are you receiving?


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## Mike D-CO5 (Mar 12, 2003)

I am using the cheap 6db attenuator form Radio Shack and it is plugged into the back of the 942 ota port. I am also using a terk 44 clip on antenna on my sat dish. From the tv side of the diplexor I have a coax plugged into a Radio Shack inline amplifier with dc block that comes with it built in to the end. From that line , I have it plugged into a perfect vision 4 way splitter and have it run to my tv with hd tuner, my vcr with analog tuner, my LG upconverting dvd player with hd tuner, and to my 942 . 

I am getting a great signal on all three of my digital stations on my 942:

Nbc 75 - 78
Cbs 80 - 85
Abc 78 - 83

I have tried without the attenuator and I get break ups on my strongest signal with Cbs. So the attenuator is a must for this to work for me. I get more problems with the 942 than any other hd tuner I have , so I know it is the 942 ota tuner that needs some work . I also live near the coast so I am suffering from the " skip issue" . I did some research on the subject on the internet and this "skip issues" effect my area , especially in the Spring and the Fall when there is great differences in the temp at night vs the day. This is where I get distant signals from Channels from other far away areas , for a short time, that screw up my local ota stations. I had these exact issues a couple of weeks ago when the temperature at night was running 50 - 60 and during the day it would go to 80-85. It would screw my signal up on my strongest Cbs station from 8:00pm - 8:00am . So there will always be problems with this and any digital signals in my area. 

Still over all , the attenuator and inline amplifier and dc block seem to have fixed my ota tuner problems for now. Not that I wouldn't like to see more software updates like the 921 got to fix the ota tuner problems.


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## TVBob (Dec 19, 2003)

Mike D-CO5 said:


> I am using the cheap 6db attenuator form Radio Shack and it is plugged into the back of the 942 ota port. I am also using a terk 44 clip on antenna on my sat dish. From the tv side of the diplexor I have a coax plugged into a Radio Shack inline amplifier with dc block that comes with it built in to the end. From that line , I have it plugged into a perfect vision 4 way splitter and have it run to my tv with hd tuner, my vcr with analog tuner, my LG upconverting dvd player with hd tuner, and to my 942 .


I can't follow this this description completely but I think you're saying you have an attenuator between your 942 and your splitter. Have you tried using _only_ a DC block on the back of the 942 _instead_ of the attenuator? If you still have problems in this configuration, try *unplugging the other HD tuners* from the splitter, or better yet go straight from the amplifier to the 942 (with the DC block), just to see what happens. In my case I've proven that selecting specific HD channels on my 811 OTA tuner causes interference to my 942 HD tuner (some type of crosstalk problem I have yet to solve).

You probably had success with this because the resistor in the attenuator reduced the DC voltage coming out of the 942. Without it that DC voltage travels through the splitter to your other HD receivers and the pre-amp (not good).



> I have tried without the attenuator and I get break ups on my strongest signal with Cbs. So the attenuator is a must for this to work for me.


JEFF M reported that replacing the attenuator with a DC block worked best. I bet this will work for you too, and generate less heat.


> I get more problems with the 942 than any other hd tuner I have , so I know it is the 942 ota tuner that needs some work.


I agree! Do we have to file a "bug report" to get Dish to recognize this problem or are they already aware of it? Are there any changes to the OTA HD tuner with L226? Ch. 005-01 is more solid for me tonight but that may just be coincidence. Ch. 048-01 still will not lock on the 942, even though it is solid on the 811 with a reading of 80 or more.


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## Mark Lamutt (Mar 24, 2002)

Fixing some of the multipath issues with the 942 OTA tuner is definitely on the radar, but I don't believe anything's different in this regard in L226.


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## Mike D-CO5 (Mar 12, 2003)

TVBob said:


> I can't follow this this description completely but I think you're saying you have an attenuator between your 942 and your splitter. Have you tried using _only_ a DC block on the back of the 942 _instead_ of the attenuator? If you still have problems in this configuration, try *unplugging the other HD tuners* from the splitter, or better yet go straight from the amplifier to the 942 (with the DC block), just to see what happens. In my case I've proven that selecting specific HD channels on my 811 OTA tuner causes interference to my 942 HD tuner (some type of crosstalk problem I have yet to solve).
> 
> You probably had success with this because the resistor in the attenuator reduced the DC voltage coming out of the 942. Without it that DC voltage travels through the splitter to your other HD receivers and the pre-amp (not good).
> 
> JEFF M reported that replacing the attenuator with a DC block worked best. I bet this will work for you too, and generate less heat. I agree! Do we have to file a "bug report" to get Dish to recognize this problem or are they already aware of it? Are there any changes to the OTA HD tuner with L226? Ch. 005-01 is more solid for me tonight but that may just be coincidence. Ch. 048-01 still will not lock on the 942, even though it is solid on the 811 with a reading of 80 or more.


I have never tried the dc block on the back of my 942 because then my inline amplifier doesn't work when you remove the dc block. I have tried to plug just the amplifier with the dc block into the back of the 942 with the amplifier without the atteunator but I suffered breakups.

Maybe I can try to explain it better. The antenna line is run into a inline amplifier with a dc block built in , and from there into a 4 way splitter and from the splitter , one line is run to my 942 which has a atteunator plugged directly into the back of the 942 on the ota antenna port. This has worked best for me.

I have had significant problems a couple of weeks ago with tropo ducting or skipping ;where the distant stations from far away states come in strong and interfer with my ota locals. This happens in the spring and the fall and in my area near the coast when there are large variences in the temperature from morning /day/night. A couple of weeks ago we were having 50s and 60s at night and during the day 80-90s. I suffered breakups on my strongest channel 6.1 cbs station which prompted me to add the inline amp/dc block/ and the atteunator.

I have read that tropo ducting effects other parts of the country as well except mountain areas where it is blocked by the mountains themselves. I think more people ought to be aware of this issue. This might be the cause of some of the problems that people with the 942 are suffering from recently. That being said I still think they need to do more software updates like they did for the 921 , to strengthen the sensitivity of the tuner. When I had the 921 for most of last year , I had good locks on my three digital stations with little or no breakups and I attached no amp or atteunator with the 921.


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## Rob Glasser (Feb 22, 2005)

I picked up the DC block from Radio Shack last night. Removed the 6dB inline attenuator, installed the DC Block and all is still well. Still no breakups and slightly (like 1 - 2%) better reception on the signal meter. Looks like the issue is not multipath for me but the DC running through the cable. Since the HDTV Primer site indicates that the attenuator does not pass DC I'm guessing either device will work, but I think I'll stick with the DC Block since it was designed for it. My local FOX affliate was the channel I was having the most problems with and I watched about an hour of Simpsons reruns last night with not a single problem.

Thanks for the help.

Rob


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## HobeSoundDarryl (May 15, 2005)

So robglasser, please clarify...

Are you saying that prior to inserting the DC block you were having problems with the Fox channel reception? You thought it might be a multipath problem? But after inserting the DC block, it now comes in just fine?

I tried taking my own RS attunator out of the path last night and noticed that all the channels I was getting are still coming in just fine too (with slightly higher power readings). I am still having a lot of problems with 1 local, and i have felt that it is a multipath problem as other people in the area with other boxes are having success getting that channel (not to mention I was getting that channel on the old Voom and D* boxes- all other things remaining the same). 

I haven't yet made it to RS to pick up a DC block, so your answer may move me to do so sooner than later. I do know that there is power as I can see a small spark when I touch the cable out of the antenna jack to the metal connector I used in place of the attenuator.

Please advise.


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## Rob Glasser (Feb 22, 2005)

HobeSoundDarryl said:


> So robglasser, please clarify...
> 
> Are you saying that prior to inserting the DC block you were having problems with the Fox channel reception? You thought it might be a multipath problem? But after inserting the DC block, it now comes in just fine?
> 
> Please advise.


Without an attenuator or a DC Block I was having problems with Fox. It would expierence quick video and audio breakups every few minutes.

Both the attenuator and the DC Block fix the problem. With the attenuator I get a slight, and I mean very slight, reduction in signal strength across the board. With the DC Block I do not. This leads me to believe that my issue was NOT multipath, but instead the DC voltage running out of the receiver.

Hence, I am now using the DC block instead of the attenuator since it is the device that was really designed to accomplish what I need.


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## TVBob (Dec 19, 2003)

Mark Lamutt said:


> Fixing some of the multipath issues with the 942 OTA tuner is definitely on the radar, but I don't believe anything's different in this regard in L226.


Agreed since my multipath problem with 048-01 is still there in L226, but my Ch. 005-01 (RF 029-01) crosstalk problem seems to be gone.

From the L226 release notes:




> Off-air DTV tuning enhancement to reduce loss of signal occurrences and macroblocking under good signal cases


 

*Macroblocking* is the technical term for "pixelating".


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## Bichon (Jun 5, 2003)

This is to JEFF M., robglasser, and others who have installed a DC block within the past 24 hours and have reported that it fixed their problem: The release notes for 226 software indicate that a change was made to improve OTA reception. This leads me to wonder whether it was the software change, and NOT the DC block that fixed the problem for you. If you're up for an experiment, I'd be curious to hear whether removing the DC block causes the problems to return.


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## Rob Glasser (Feb 22, 2005)

Bichon said:


> This is to JEFF M., robglasser, and others who have installed a DC block within the past 24 hours and have reported that it fixed their problem: The release notes for 226 software indicate that a change was made to improve OTA reception. This leads me to wonder whether it was the software change, and NOT the DC block that fixed the problem for you. If you're up for an experiment, I'd be curious to hear whether removing the DC block causes the problems to return.


I can tell you already that the answer is Yes. I tested it last night, removing both the attenuator and the DC block causes signal break up, replacing either one fixes it. Both act as a DC Block. I figured if it was a multipath issue then the DC Block would not have fixed my problem. Since both the attenuator or the DC block fix my issue then it is a interference issue caused by the DC current on the line. Blocking that from the line and antenna fixes my issues. I don't think I had L226 yesterday afternoon, since I think the TV had been on most of the day when I got home, but can't say for sure. I'll test again tonight to see if L226 did make any difference though.


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## TVBob (Dec 19, 2003)

Mike D-CO5 said:


> I have never tried the dc block on the back of my 942 because then my inline amplifier doesn't work when you remove the dc block.


I don't understand this. Maybe when you use the term "DC Block" you are referring to the black wall cube that supplies DC power to your amplifier? That's not a DC blocker, that's a power supply. Or maybe your system uses an inline DC power *inserter *to send power up the coax to a mast-mounted pre-amp?

What make/model of amplifier are you using? Is it an indoor distribution amp. or a mast-mounted pre-amp with a power inserter?


> Maybe I can try to explain it better. The antenna line is run into a inline amplifier with a dc block built in , and from there into a 4 way splitter and from the splitter , one line is run to my 942 which has a atteunator plugged directly into the back of the 942 on the ota antenna port. This has worked best for me.


OK, this makes more sense, but what do you mean by "built-in DC block"? Is that a DC blocker on the antenna input of the amplifier or are you referring to a DC power inserter? Maybe you can post a picture.

I think you'll find that if you replace the attenuator at the back of the 942 with a *DC blocker* (a small silver cylinder that looks very much like an attenuator but is labeled "DC Block"), your signal will improve. The attenuator is just _reducing_ the signal to your 942. It also reduces, but does not eliminate completely, the DC voltage coming OUT of the 942 and from there into your other equipment through that 4-way splitter. Your other equipment does not expect DC voltage on the antenna lines. Such voltage (though small) may interfere with the operation of your inline amplifier, and that's what is causing the reception problems. So try a Radio Shack DC Blocker instead of that attenuator, and leave everything else alone. I think you'll be quite pleased with the result. The amplifier or power inserter needs to be plugged into a separate power source of course.


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## Mike D-CO5 (Mar 12, 2003)

The inline amplifier comes with a dc block ( printed on the outside of the switch - clearly says DC block) connected to the inline plug. You can take it off and when you do the amplifier quits working. I got it at Radio shack for like $34.99 . It says that it boosts signal by up to 10db for catv, satellite, for antennas. I do have it plugged in as it comes with a plug in source . It also is supposed to minimize signal loss caused by in -line devices or long runs of 100 ft. You can locate one on the Radio Shack website under TV /Satellite and then under amplifiers. Catalog #15-1170. 

Without the inline amplifier for the inside of your home, my signal drops and I suffer from macro blocking and pixelation . 

Without the inline amplifier I get the following signal strengths:
Abc 69-71
Cbs 73 -75
Nbc 69-70 

With the inline amplifier I get the following signal strengths:
Abc 78-81
Cbs 80-85
Nbc 75-78 

Also without the attenuator I seem to suffer from drop outs on my strongest Cbs station even with a good signal of 80 . So I kept both the attenuator and inline amp going. I might try the dc block just to see what happens, but I think there is already one on the line with the amplifier. 

The new software update might have helped to . The readings I got with the amplifier were the ones I got after the software update. Before the update I still got a decent signal but it didn't ever get as strong as it is today. Now that the temperature is staying in the 70's at night and even higher during the day- 90's, I am not suffering any tropo ducting or skipping as I was a few weeks back when I bought the inline amplifier and atteunator. Still I feel they have helped. 

I will look for a DC block next time I go to Radio shack and see if it helps. If it does help I will report back.


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## TVBob (Dec 19, 2003)

Mike D-CO5 said:


> Catalog #15-1170.


*THANK YOU*. Now I understand everything.:hurah:

The manual for this interesting mast-mounted amplifier / power inserter combo may be downloaded here. The RS amp. includes a DC blocker designed to be installed between the _antenna_ and the silver mast-mounted *amplifier*. The black *power inserter *is placed inside between the TV receiver and amplifier to feed *12V DC at 200 ma* to the sliver 10 dB amplifier up on the mast.

Note the voltage! In theory you should be able to power this Radio Shack amplifier with your 942 alone (200 ma is a little higher than the 150 ma rating of the 942's antenna connector, but it just might work if your coax run isn't hundreds of feet long).

Before you get that attenuator, if you want to experiment, try *unplugging and removing the black power inserter* _and _attenuator and just plug your antenna line (the one with the silver amplifier at the far end) straight into the back of your 942 (*no splitters, attenuators or blockers*). Does the amp. still work? It may not work at all, and without the splitter your other devices won't have any signal, but it would be nice to know.

If you're doing all of this indoors and the silver amplifier component isn't up at your antenna, well, you'd be better off with a better amplifier. This 10 dB amp. has a noise figure of 7.5 dB meaning you're really getting only a modest 2.5 dB in "real" gain. Your 4-way splitter introduces 7-8 dB of loss in each line so your amplifier really isn't powerful enough to compensate for the loss in the splitter.

Technical details of this and other amplifiers may be reviewed at this external link. Note this web site says your amp uses *20 VDC* on the coax, has a noise figure of 6 dB and a gain of 12 dB (on Ch. 30), so it doesn't agree at all with what I see in the Radio Shack manual. 

To repeat, if you just install a new Radio Shack DC blocker at the back of the 942 and remove the attenuator, I think you'll find everything works well. If you need even better performance, use a better 4-way distribution amplifier (with built-in 4-way splitter) or a better mast-mounted pre-amp. You'll still want the DC block on the back of the 942 in all of these cases.


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## HobeSoundDarryl (May 15, 2005)

Well all of this inspired me to finally make the trip to RS and pick up a DC block in hopes that it would solve a problem getting one problematic channel. My setup is a large directional UHF antenna mounted outside, a winegard 4700 preamp, a channel master rotor, and the 942. I know my 942 has the DC power issue because I could get a small spark when the exposed end of the cable touched metal. 

I unhooked the cable from the 942 and mounted the DC block there. In general signal strength for all locals dropped a few points (???) and the problematic channel problem was NOT resolved (but the spark was extinguished!!!). So then I inserted an RS attenuator between the premap power block and the DC block and tried various settings. Still no problematic channel success. 

Then, with both options I tried rotating the antenna a few degrees at a time for the full 360 degree range of the rotor. Still no success with the problematic channel. 

Now here's the kicker. My old Voom box and my older D* box could both lock the problematic channel with everything else in the setup remaining the same. Thus, the 942 is apparently simply inferior at handling multipath (or whatever the problem is for me) to older technologies from the other players. Hopefully, a future software upgrade will focus on making the over-the-air reception work better.

And, by the way, I know the problematic channel is currently being recieved successfully by others in my area.

Secondly, I hoped that maybe this would help lock in slightly more distant stations from beyond my nearest locals. Both older DTV boxes could do this for several channels from 2 other nearby cities. However, the DC block and/or attenuator testing made no difference for me whatsoever in getting any signal at all from more distant stations (beyond my local market)- not even a peep of a reading on the local channel signal strength screen.

Net result- nothing tangibly gained at all (unless you count that lack of a spark). It has apparently made a difference for others, so I guess it is like many other things in over-the-air reception (you just have to try it with your setup and see what happens).


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## Rob Glasser (Feb 22, 2005)

When I got home tonight I checked my 942 and I do now have L226 for sure. To test any OTA changes they made I decided to remove the DC Block from the back of the receiver and just plug the antenna directly in. I did that and watched about 15 minutes of FOX and didn't notice any problems. Signal strength didn't seem to change at all with or without the block. I don't trust my signal yet without the block so I put it back on for future recordings, but will try and watch more with it off over the next week. Perhaps L226 did indeed fix some of the issues I was seeing before. Time will tell.


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## TVBob (Dec 19, 2003)

HobeSoundDarryl said:


> Net result- nothing tangibly gained at all (unless you count that lack of a spark). It has apparently made a difference for others, so I guess it is like many other things in over-the-air reception (you just have to try it with your setup and see what happens).


Thanks for trying it, and reporting the results. All data points are helpful. What RF channel is giving you troubles? For me it's still RF 049-01 and -02.

*Update!* Suddenly _all _channels a working great for me, even 049-01, with and _without _the DC blocker. I wonder if this will last? Maybe atmospheric conditions are just right tonight. Maybe some local noise source just went away.

At this moment I can't replicate any of the problems I originally reported before using the DC blocker, even when I take everything out and put things back the way I started. I think L226 has something to do with this, since the OTA receiver was improved by this release. But I put the DC blocker back in for now. I also see a little reduction in signal "strength" on some channels with the DC blocker, but I'm keeping it in since I don't want any DC to enter my distribution amplifier.

I sure can't wait for all of my local channels to be in HD _on the satellite_ so I don't have to mess with these crazy HD reception problems any more.


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## waltinvt (Feb 9, 2004)

TVBob said:


> Thanks for trying it, and reporting the results. All data points are helpful. What RF channel is giving you troubles? For me it's still RF 049-01 and -02.
> 
> *Update!* Suddenly _all _channels a working great for me, even 049-01, with and _without _the DC blocker. I wonder if this will last? Maybe atmospheric conditions are just right tonight. Maybe some local noise source just went away.
> 
> ...


This is probably totally off-the-wall speculation but I wonder if Dish sent something out yesterday early evening. I have heard that they can and do sometimes send minor software "adjustments" without notice and they can go through with or without your permission. This is why I wonder:

I got 226 yesterday morning but didn't have time to fool with it until about 5pm est.

One weird thing I noticed that had not ever happened previously, was I was getting a solid blue narrow rectangle with rounded ends in the lower left of the screen. It would come up with a "pause" press, "guide" and various other menu screen changes.

I could only get rid of by doing a "swap" to the other tuner and back. It was a real pain. A hard reboot but didn't stop it from happening. It ticked me off because I was going to transfer some of my drv stuff to my dvd recorder but it would show up in the recorded image there.

Then a couple hours later (maybe 7pm est) it stopped for no apparent reason. Try as hard as I could, I could not get it to happen again. I'm going to post an new thread to see if anyone else experienced this.


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## Bichon (Jun 5, 2003)

HobeSoundDarryl said:


> And, by the way, I know the problematic channel is currently being recieved successfully by others in my area.


Instead of saying "problematic channel", why not identify it?

If the Dish/Eldon engineering folks are using our reports in their development efforts, I figure we ought to be giving them the information they need. Perhaps that "problematic channel" has a PSIP problem, or is broadcasting at lower or higher power, or has its transmitting antenna in a different place, etc.


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## jsanders (Jan 21, 2004)

Eldon has no contribution in the 942 development.


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## Bichon (Jun 5, 2003)

jsanders said:


> Eldon has no contribution in the 942 development.


Who engineered (and builds) the 942?


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## Jeff McClellan (Apr 22, 2002)

Bichon said:


> Who engineered (and builds) the 942?


Only, "The Best of the Best"


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## Mark Lamutt (Mar 24, 2002)

The 942 is developed here in Denver.


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## cebbigh (Feb 27, 2005)

I have only had my new 942 up and running for a few hours of real usage. (Installed it yesterday after work and had it activated this morning before leaving for work.) I've tried using the dc block and also without. I seem to get better results using the block but without equipment and in this short a period of time I can't say for sure. I have to think that L226 is downloaded here because I just set up. Just speculating, but if L226 eliminates the need for the dc block does it mean the 12VDC is no longer being output from the 8vsc? I don't have a means of measuring that. Has anyone else rechecked?


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## TVBob (Dec 19, 2003)

cebbigh said:


> Just speculating, but if L226 eliminates the need for the dc block does it mean the 12VDC is no longer being output from the 8vsc?


I just checked and the 12V is still there. I don't think they are going to be able to turn this off with a software change. We've already heard from Mark that newer versions of the 942 won't have the 12VDC output (in other words, there is going to be a minor _hardware _change).

Prior to L226, I believe the 942 was quite sensitive to any noise on the antenna line. My theory is that the DC voltage output by 942 could interact unfavorably with an inline amplifier or any other TV receiver sharing the same antenna line through a splitter. Adding the DC block removes this unwanted interaction, and any interference caused by a ground loop.

Now, L226 seems to handle interference better for some, worse for others (see this poll). That's why the picture may look fine even without the DC block. But since the DC block does no harm, and since the 12 VDC _could_ do some harm, I see no reason not to have the DC Block in all installations of the 942, even if you go straight to an antenna with no splitters or inline amplifiers. That way even a short circuit in your coax or antenna won't do any harm to the 942.


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## HobeSoundDarryl (May 15, 2005)

My "problematic" local channel is NBC affiliate 5 (DTV is UHF 55, remapped down to 5-1). It is a problem for more than just the 942 for some locals, but other boxes seem to work fine. My own former boxes (Voom & D*) both could do a better job with it than the 942 is so far (DC block or not).


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