# ASK DBSTalk: 921 vs. 811 OTA Performance



## mraub (Mar 5, 2004)

Our NBC affiliate turned on their HD transmitter in time to show what little HD Olympic coverage NBC is offering. My 921 doesn't seem happy with their signal, though the 811 likes it just fine.

On the 921 I get brief video breakups and loss of audio a couple of times a minute; very distracting. The signal strength meter is between ~75-80 and stays green. I also have a 811 hooked to the same antenna, with about 30-40 feet of extra RG6 and a pair of diplexers between the 921 location and the 811 location, so I'd guess I'm getting 2-3 less dB signal to the 811. The 811 never breaks up, either audio or video. (I don't diplex the OTA to the 921--I was able to run a separate coax to it).

Is the 811 OTA receiver simply superior to that in the 921 or could there be other causes. The engineer for the NBC station seems willing to work with people to improve the quality of picture received (through adjustments to the HD encoder) but I don't really know what to suggest to him to get rid of the 921 dropouts.

Any suggestions?

MIKE


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## Mark Lamutt (Mar 24, 2002)

It'd be useful to know where you are, Mike, and what your NBC station call letters are. Then we can compare with other 921 users in your area.


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## mraub (Mar 5, 2004)

Good point, Mark. I'm in Champaign, Illinois. The NBC station is WICD and their HD channel is 41-1. Others who live much further from the tower than I report much stronger and more stable signals using antenna having less gain than what I've tried.

It's fairly cool this evening and I'm headed back to the attic to try something different.

MIKE


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## emathis (Mar 19, 2003)

I live in Albuquerque, NM and my NBC affliate also just turned on HD in time for the 24 hour olympic channel. I also have the breakup of video and audio that mraub is having, but my reciever is an 811. Don't no if this is any help, but it is strange that his 811 isn't having the same problem. I just remembered, I could try the built-in tuner in my Mits and see if it has the same problem. I will get back to you.

P.S. Guess what, the built-in tuner is not breaking up like the 811.


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## boylehome (Jul 16, 2004)

mraub said:


> Our NBC affiliate turned on their HD transmitter in time to show what little HD Olympic coverage NBC is offering. My 921 doesn't seem happy with their signal, though the 811 likes it just fine.
> 
> On the 921 I get brief video breakups and loss of audio a couple of times a minute; very distracting. The signal strength meter is between ~75-80 and stays green. I also have a 811 hooked to the same antenna, with about 30-40 feet of extra RG6 and a pair of diplexers between the 921 location and the 811 location, so I'd guess I'm getting 2-3 less dB signal to the 811. The 811 never breaks up, either audio or video. (I don't diplex the OTA to the 921--I was able to run a separate coax to it).
> 
> ...


I believe is that the signal strength that you show is really low as compared to 100-125. I had the same problem with such a low signal on my 921. I put in an in-line RF amplifier. It boosted my signal strength and eliminated my problems. 85-95 can still show some pixelation and dropouts.


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## mraub (Mar 5, 2004)

boylehome said:


> I believe is that the signal strength that you show is really low as compared to 100-125. I had the same problem with such a low signal on my 921. I put in an in-line RF amplifier. It boosted my signal strength and eliminated my problems. 85-95 can still show some pixelation and dropouts.


I already have a good Channel Master UHF preamp in the line, but no matter what antenna I try I can't get above about 80 on the meter. I even hooked up very long folded reflector UHF antenna that's susposed to give about 17 dB gain. That antenna plus the preamp ought to have blown the meter off the chart, but still about 80. I tried a small Silver Sensor clone to make sure the problem wasn't signal overload and couldn't lock on the signal.

I may just be in a dead area for the station's signal. I'm going to call the station engineer tomorrow to see if he can help.

Thanks for all the suggestions.

MIKE


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## mraub (Mar 5, 2004)

I tried one more thing which seems to work--kinda. I unhooked the high gain antenna and connected a medium gain corner reflector having probably about 8 dB gain. When I tune to NBC the picture is very pixelated and sometimes goes to the black "Acquiring Signal" screen. This lasts for about 20 seconds and then the 921 gets a solid lock. I watched for about 1/2 hour and the picture never broke up once. Why the 921 will finally lock when fed with a lower gain antenna is something I can't explain. Signal strength remains ~80-85.

Will the fact that it takes 20 seconds to lock on this OTA signal affect my ability to record from this channel. In other words does the 921 ignore or cancel a timer if it doesn't immediately lock the signal or does it just record what the tuner produces, whether it's garbage or a clean signal? I can live with a bit of garbage before a program begins, since I usually set the timer to start 1 minute before the scheduled start time of the show.

MIKE


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## SimpleSimon (Jan 15, 2004)

mraub said:


> Will the fact that it takes 20 seconds to lock on this OTA signal affect my ability to record from this channel. In other words does the 921 ignore or cancel a timer if it doesn't immediately lock the signal or does it just record what the tuner produces, whether it's garbage or a clean signal?


That's a darn good question.

Love to know the answer as soon as you can tell us.


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## boylehome (Jul 16, 2004)

mraub said:


> I tried one more thing which seems to work--kinda. I unhooked the high gain antenna and connected a medium gain corner reflector having probably about 8 dB gain. When I tune to NBC the picture is very pixelated and sometimes goes to the black "Acquiring Signal" screen. This lasts for about 20 seconds and then the 921 gets a solid lock. I watched for about 1/2 hour and the picture never broke up once. Why the 921 will finally lock when fed with a lower gain antenna is something I can't explain. Signal strength remains ~80-85.
> 
> Will the fact that it takes 20 seconds to lock on this OTA signal affect my ability to record from this channel. In other words does the 921 ignore or cancel a timer if it doesn't immediately lock the signal or does it just record what the tuner produces, whether it's garbage or a clean signal? I can live with a bit of garbage before a program begins, since I usually set the timer to start 1 minute before the scheduled start time of the show.
> 
> MIKE


Just an Idea, and it worked for me. Use a hi-gain directional fringe antenna with rg6 meshed shield cable (Omni-directional antennas really suck for digital reception.) Keep the cable as short as possible. Avoid the pre-amp as it picks up all kinds of other signal which will degrade the true digital signal. Use a "clean" in line amp about six feet from the receiver. Don't use any splitters (they can reduce db gain by a bunch!) Try raising or lowering the antenna on its mast to a point that it sees the sweet spot. Believe it or not, sometimes lowering it helps. The NBC channel that your having trouble with, what is the digital channel number? I've discovered channel 20 is weaker when using full spectrum UHF antennas. There may be other factors like reflected signal from a water tower, building or whatever. There may also be some nearby radio transmissions producing harmonics causing interference to your signal. Lastly, the station may be broadcasting low power. In my area this seems to be the norm. good luck mraub.


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## Mark Lamutt (Mar 24, 2002)

Another thing - get the antenna out of the attic and put it on the roof where it belongs. That may make 5-10 points of signal strength difference right there. And, believe it or not, you can live 3 miles from the tower and be in a mostly dead spot. Transmissions are aimed "out", not "down", so there's a point that the closer you are to the tower, the worse your signal is going to be. And, the "sweet spot" is true - in Denver, my sweet spot for getting our lowest power station is literally 2" horizontally x 1" vertically. If my antenna moves out of that exact alignment, I lose the station.


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## mraub (Mar 5, 2004)

The previous two posts contain excellent advice for antenna placement. I kind of took the route of least resistance and used the coax put in the house when it was built, which was probably RG59. The thought of trying to fish some fresh RG6 from the attic (or roof if I put the antenna there) to the basement was more that I wanted to consider, unless I couldn't get what I had to work. 

My NBC station transmits on channel 41-1 and yes they are still low power. Most of my stations are in the opposite direction and I use a attic mounted Winegard Sqareshooter for them. So far I've been to get 100% reliable reception from a station ~60 miles away, but which at full power. I may end up getting another Squareshooter and aim in the NBC station's direction. I know the Squareshooter sounds like snake oil, but the darn thing works like gangbusters.

MIKE


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## mraub (Mar 5, 2004)

I set up a timer for my slow to lock OTA station and it recorded just fine. I fast forwarded past the acquiring lock garbage and the rest of the recording was fine.

MIKE


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## SimpleSimon (Jan 15, 2004)

Thanks for the info!


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## jamullian (May 7, 2004)

I have long suspected that when KNSD San Diego upped their xmit power, and my 921 lost all capability of locking on to the signal - though it did start showing green after L187 - it was something to do with adjoining channels and interference.

Now there is a (caveat: faitly technical) article on the subject of DTV receivers and why they have exactly this problem at http://www.tvtechnology.com/features/digital_tv/f_DTV_interference.shtml

which seems to give credence to my theory. (Other, dedicated, OTA receivers I have tried do not have this problem).


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## boylehome (Jul 16, 2004)

mraub said:


> I may end up getting another Squareshooter and aim in the NBC station's direction. I know the Squareshooter sounds like snake oil, but the darn thing works like gangbusters.
> MIKE


The Squareshooter SS2000 may be the fix. It has at least a 12db gain over the SS1000, and the research I've done with the information that is available, suggests that this is the hot ticket for HD channels. I just may get one after I find a few more reviews. Change out that old cable.


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## tahoerob (Mar 22, 2003)

I do not remember which forum had the info, but I read that the OTA tuner chip in the 811 is BETTER than the chip in 921.


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## mraub (Mar 5, 2004)

boylehome said:


> The Squareshooter SS2000 may be the fix.


Doesn't the SS2000 have a built in preamp? I wonder if that would cause problems with the ~25 dB gain preamp I already have in the line.

Anyway, over the past few days the 921 has been locking on the NBC station immediately. They may have made some adjustments to their HD decoder.

MIKE


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