# OTA signal strength too strong?



## JerryMeeker (Sep 20, 2007)

I have an OTA AM21 tuner connected to a HR-24. I am quite close to the antenna farm here in Austin, several miles with a clear line of site. The OTA signal strength meters all read 100%. The problem is that rather than a pristine signal, I experience signal break-up quite frequently. A friend suggested that my signal may be too strong, and recommended that I install coax signal attenuators to try and solve the problem.

Is anyone familiar with signal strength issues causing OTA signal break-up? Is an attenuator the right direction to go?

Thanks for any advice.


Sent from my iPad using DBSTalk mobile app


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## gov (Jan 11, 2013)

Yeppers.

Attenuators are made in various 'sizes'.

IIRC, 3dB, 6dB, 9dB, 10dB, 12db, and 20dB.

And they are threaded male and female so they can be stacked up for different values.


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## mwdxer (Oct 30, 2013)

I did not know there was over kill in signal with digital. Here I have translators at 12 miles away running 1 KW to 6 KW ERP and I get 98-100% on all 5 signals. I am using a high gain UHF yagi too. But it seems to work well.


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## RBA (Apr 14, 2013)

Near the antenna farm maybe the problem and strong signals may also be the problem, but not as you expect You maybe experiencing interference from reflected signals, used to be called ghosting in analog days. Are you using a TV antenna, rabbit ears? Try stripping about 6" of coax cable off the center conducter and screwing that into the AM21, it will weaken the signal.


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## o7RAVENS (Oct 28, 2007)

If your antenna is to close to the wall of your house it could cuise trouble. Just a thought.


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## hasan (Sep 22, 2006)

JerryMeeker said:


> I have an OTA AM21 tuner connected to a HR-24. I am quite close to the antenna farm here in Austin, several miles with a clear line of site. The OTA signal strength meters all read 100%. The problem is that rather than a pristine signal, I experience signal break-up quite frequently. A friend suggested that my signal may be too strong, and recommended that I install coax signal attenuators to try and solve the problem.
> 
> Is anyone familiar with signal strength issues causing OTA signal break-up? Is an attenuator the right direction to go?
> 
> ...


You can buy nice variable attenuators at Radio Shack, or if not them, from Monoprice.com. This is what you want: 75 Ohm variable attenuatior. A fixed attenuator may not work, while the variable ones most likely will. It is also highly likely that your problem is not strong signal overload, but rather multi-path distortion which the AM21s don't handle all that well (all though they do better than the original HR20-700 did. I've been through this entire process in 2007 when we were testing the HR20-700. I had calibrated attenuators, phase shifters, etc, all playing around trying to figure out why strong signals were causing so much trouble.

in the end, the cheap variable attenuator from Radio Shack (which may not be available any more, but Monoprice should have it) did the most to ameliorate the problem. I have had, for years, 100% signal strength on all channels, and no dropouts whatsoever. We are 26 miles from the transmitter complex over open terrain, with the transmit antennas at 2200'.

Get the attenuatior, put it in line:

1. Reduce the signal level from your antenna to the point where the signal quality meter of the HR box just begins to drop below 100%. Then take it back up just a tiny bit. This should be the sweet point.

This should reduce the reflections enough (if they are the problem) enough that the tuner can discriminate between them and the desired signal. If that doesn't work, you need a directional antenna that will reduce off axis signals.

One other important point is that the AM21 *does not measure signal strength*. It measures a variant of BER or bit-error-rate, which is a measure of signal QUALITY not Quantity. Moving the antenna around not only changes strength, but also may change the bit-error-rate because reflections are being either increased or decreased.

In the end, you want a STEADY (no jumping up and down) signal quality of 100%....or whatever high percentages is absolutely stable. Moving up and down a few percent is fine, but seeing 10% jumps in signal quality on the HR box meter is going to result in problems.

Hope this helps.


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## harsh (Jun 15, 2003)

The problem may be too strong a signal but more often it is that you're getting too strong an alternate signal (multipath). AGC circuits are pretty good about squashing a hot signal but when you get a signal that is out of phase with the primary signal, your goose is cooked.

Attenuators may fix the problem by quieting the out of phase signals. Using a more directional antenna may be a better option if there are stations far away that you don't want to lose access to.


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## JerryMeeker (Sep 20, 2007)

Good advice from everyone, thanks. I will look into the Monoprice attenuator. As for the antenna, it is installed on top of my chimney, pointing at the antenna farm (all Austin TV stations have antennas in the same farm, so the antenna requires not pointing adjustment).


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## TomCat (Aug 31, 2002)

Here is an example of what Hasan is talking about (attached). RatShack restamps them with their part number.

But the concept of this reducing multipath is flawed. An attenuator reduces both the main lobe and reflections by the same amount, and there is no threshold that you can scoot the lower signals beneath. Bottom line, if you reduce both desired and undesired signals with an attenuator you reduce them the same amount, which means the ratio of signal to interference stays exactly the same. So it will not reduce multipath ratios, meaning it has no effect on reducing aggregate multipath interference.

How an attenuator can be of help is when the incoming signal is so strong that it overloads the front end, which causes the signal to splatter in time and frequency and raises the noise/interference floor locally. The end goal is to get the high pulses (ones) and the low pulses (zeroes) to be distinguishable from each other in the digital bitstream that is the video PID in the transport stream once demodulated to baseband and demuxed by your STB's tuner, just before that is fed to the decoder.

Multipath destroys that by overlaying new copies out of time, but too strong a signal does pretty much the same thing when the signal is above the window of operation (in the wrong or curved part of the transfer curve) where PN junctions go non-linear. That creates intermod interference that can thwart reception in a very similar way to how multipath does it, but it only does it if the signal is too hot.

So the idea is to get into the sweet spot of that window of operation. Hook up the attenuator and rotate the knob until there is no attenuation (min). Go to the channel strength screen (signal quality, actually). Add attenuation slowly bit by bit and see if the signal goes up or down. If the signal goes down, you did not have too strong a signal, and you do not need the attenuator. Take it back and get your money back.

But it the signal is too strong, as you add attenuation, the reading will actually start to rise. Add attenuation until it starts to go back down, then split the difference, not much different than how you dither during dish aiming.

You can leave the attenuator in line, but tape over the knob so kids and pets don't reset your careful level setting. I also have an FM trap in line, because there are 17 very strong FM stations coming from the same azimuth as where my OTA signals originate, and they compete. Having the FM trap switched in gives me about 5 more clicks on the quality meter.

Apologies for the focus; my ancient iPhone does not take good pics.


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## veryoldschool (Dec 10, 2006)

Hell must have just frozen over, since I agree with TomCat. :eek2:

If the problem turns out to be multipath, changing where the antenna points may help to reduce it.

For maximum gain you want to have it point towards the transmitter, but if the direction of the multipath signal is such that you can turn the antenna off angle from the transmitter, you may drop the multipath more than the main "path" due to the antenna "lobe" pattern.


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## NR4P (Jan 16, 2007)

I agree with others and likely a multipath problem. More often from indoor/attic antennas vs. outdoor ones.

If attenuation can't solve it, try pointing the antenna in a different direction as VOS suggests. Since you are so close, turn the antenna 45, 90 or even 180 degs. You should have plenty of signal and it may solve some of the multipath.

A sign of multipath is when you look at the signal strength indicator in the off air menus, see something high like 90% or 100% and then all of a sudden a brief drop to 60% etc. That's multipath assuming all connections are good.

And one other thing. The antenna farm may also have FM radio stations there too. And your TV antenna brings that in. Radio Shack once sold an FM trap. That solved a problem for me a few years back.


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## slice1900 (Feb 14, 2013)

Is the FM trap to prevent harmonic frequency interference? Or does a strong FM signal affect reception of a weaker UHF station by overpowering the tuner or something?

Since I have my signal split 32 ways, I have a 25db distribution amp inline with my antenna. It has a switch for the FM trap marked "in" and "out", and I remember when I tried both settings (since it isn't obvious to me which one enables the trap) one setting produced slightly lower signal quality readings so I used the other. As there are some fairly strong FM stations in line with the direction my antenna is pointed, should I enable the trap (if it isn't already) even if it lowers the apparent signal quality a tiny bit?

When I was investigating other issues I had a script running on my wireless router taking signal quality readings off a receiver once per second and recording them to a file. When I tried that on my OTA signal for curiosity's sake I observed momentary blips where the quality would drop noticeably for a second or two. Occasionally the way to down to 25 (which is what the AM21 shows for "no signal") I thought it might be the amp or its power supply, but it was unchanged when I bypassed it for that receiver. I guess that's multipath, from a plane or atmospheric disturbance, and there's nothing to be done about it? The picture will briefly pixellate for a moment once in a while, and while I never tried to correlate that with the signal readings, I assume that's what I'm seeing.


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## hasan (Sep 22, 2006)

Your antenna probably has unity gain at the FM frequencies, so I wouldn't worry too much about it, just the raw power output of the FM station itself. The issue isn't the absolute value of the signal quality, once the signal is strong, it is *variation*. In other words, there is no difference in performance whatsoever with a quality level of 80% vs 100% if the percentage level is relatively constant. In other words let's say the signal level is staying constant within 3%. That would be fine. However, if the meter shows sudden variations of greater than 10%, I would be concerned that I have multi-path distortion that cannot be dealt with. Again, the issue is sudden variation, not variation from daytime to evening or early morning. Signals can become quite strong AND stable in the quiet times of the atmosphere, so let's leave that consideration out.

I'm not all that impressed with the FM traps built in to the preamp you rtalking about. I'm guessing it is an antenna preamp that you have re-purposed as a distribution amplifier (which is fine...in fact, more than fine, as it should be vastly superior to most distribution amplifiers which are not designed to have low noise front ends). The FM traps in those things, however leave a lot to be desired. If I discovered that an FM station was causing me problems, I would make my own notch filter (which is quite easy). To do this you need: the actual fm frequency of the problem FM transmittter, the velocity factor of the coax you are going to use, and a 75 ohm T with F connectors (or a soldering iron).

I use exactly that setup to notch out 144.39 MHz from my 2 meter ham transmitter that just kills RF channels 5, 8, 11 and 13. The AM21 tuner is fairly easy to overload with a local 2m transmitter, even if the transmitter is perfectly clean. the ront end of the AM21 is just not that strong.

Momentary drops to 25 would indicate to me that something is interfering with the AM21...just like what I described above, unless those momentary drops are constant (by that I mean happening all the time, not being separated by several seconds. If they are happening all the time, it is most likely multi-path, in which case, the best solution is a directional antenna, and moving it around a bit to put the reflection down a sidelobe of the antenna. Now, FM overload (from a commercial station) could cause similar symptoms and in that case, the variable attenuator previously described could eliminate the problem.

Start with the variable attenuator and be sure to put it BEFORE the 25 dB amp (put it at the input). Adjust it to see if you can kill the sudden drops.

Let us know how it comes out. It could be RF interference from a consumer device, fundamental overload, or FM adjacent channel interference. In each case the cure and approach might be a little different, but the variable attenuator will be a big help along the way (and they are cheap)


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## veryoldschool (Dec 10, 2006)

hasan said:


> I'm not all that impressed with the FM traps...


Not sure if you remember back in the HR20 days and the poster who used 3 traps cascaded.


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## hasan (Sep 22, 2006)

veryoldschool said:


> Not sure if you remember back in the HR20 days and the poster who used 3 traps cascaded.


Some of my most fun experiments were with the HR20 and its OTA capabilities! I'd have to have my memory jogged with the 3 cascaded traps, but if done properly, they would work fine. I haven't seen any of the built-in traps (more properly band-stop filters) in the mast mounted preamps do as well. I played with mine, to little positive effect, but never managed to get one on a spectrum analyzer, which I'm sure would have been very revealing. To this day, I still use the same preamp (Channel Master C-7777 and variable attenuator that we were playing with to get the HR20 to behave properly. The AM21 is considerably better when it comes to multi-path than the HR20 was. It also has better dynamic range and is much less vulnerable to impedance bumps. (Although in their final firmware tunings, they got it pretty darn good, comparing favorably in displaying similar signal quality as my Samsung TV tuner) All in all, I think they have done a nice job with the AM21. I have no idea what differences there are between the 21 and the 21N...because I still have the original two I started with. One on each HR24 here. I left the HR44 alone, except for adding a 2 TB WD20EURX and Max 5 TT Enclosure on.

If it was you who did the cascaded filters, I apologize for not remembering, and would appreciate you reminding me of the findings.

One thing I didn't accept at the time was the mpeg-4 could in any way approximate the gold standard of OTA mpeg-2. Either they have gotten better at it, or my eyes are not as good as they used to be, but now I really, really have to look at specific elements of the picture to see what used to be obvious to me. Amazing what 7 years can do, eh?

Nice to hear from you again!


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## slice1900 (Feb 14, 2013)

hasan,

Thank you for the detailed response. The amp I'm using is a GC32-3091 VHF/UHF/FM amp, rated at 25db/23db VHF/UHF gain and 6.5db/6db UHF/VHF NF. I guess I refer to it as a distribution amp due to the rather large amount of gain, but technically it isn't one. Would switching the FM trap in/out and seeing if there are differences in the signal dropouts provide any clues to whether FM has anything to do with what I'm seeing? Even if the FM trap in the amp isn't all that good, presumably it would attenuate the FM signal to some degree.

If it turned out FM was a problem, can one buy an inline FM trap that works better than the one built into my amp? Since I don't need VHF lo a filter that just dropped everything below VHF hi would be fine, but I've never seen one. You'd think they make them, since many areas no longer have any VHF lo stations.

I'll try attenuating the signal before the amp as you suggest and see what happens. What I see now are long periods of stability with little change in the signal. In the summer I see a difference between day/night readings, but hour to hour the readings are stable. What I observed more recently with the second to second readings was that would suddenly drop, sometimes 10%, sometimes 30%, and sometimes all the way to 25. Such drops seem to last 1-5 seconds. Sometimes it happens more frequently than others, but rarely do I see more than a handful of occurrences within the space of an hour.

When I tried measuring two stations simultaneously on two different receivers, there was a correlation in the interference between two VHF lo stations - channels 7 and 9 experienced drops at the same moment. I didn't observe such correlation between two UHF stations, or between a VHF and a UHF station. I don't know if that provides any clues, but I thought it was interesting.


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## veryoldschool (Dec 10, 2006)

hasan said:


> If it was you who did the cascaded filters, I apologize for not remembering, and would appreciate you reminding me of the findings.
> 
> Amazing what 7 years can do, eh?
> 
> Nice to hear from you again!


No it wasn't me, but I tend to remember any & every thing about RF.
We had "some fun" back then eh?
!rolling


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## hasan (Sep 22, 2006)

slice1900 said:


> hasan,
> 
> Thank you for the detailed response. The amp I'm using is a GC32-3091 VHF/UHF/FM amp, rated at 25db/23db VHF/UHF gain and 6.5db/6db UHF/VHF NF. I guess I refer to it as a distribution amp due to the rather large amount of gain, but technically it isn't one. Would switching the FM trap in/out and seeing if there are differences in the signal dropouts provide any clues to whether FM has anything to do with what I'm seeing? Even if the FM trap in the amp isn't all that good, presumably it would attenuate the FM signal to some degree.
> 
> ...


http://www.winegarddirect.com/viewitem.asp?d=Winegard-FT7500-75-Ohm-FM-Trap-Fixed-(FT7500)&p=FT7500

This is an in-line band stop filter that claims it will reduce the ENTIRE fm band by 26 dB. That is very good. There is no specification for insertion loss, but there is a bit of a warning:

but it can actually reduce signal on VHF channel 6.

This means that if you are receiving RF Channel 6, you could lose a bit of signal from it. RF channel six is on the edge of the FM band, or at least close enough to the filter skirts to cause some attenuation. 

As far as using your existing fm trap switch to determine what might be going on: if you know which way is "on" and it causes the rate of the jumping of signal quality to lessen, then yes, you may be headed in the right direction.

The description of the readings you report really could be either overload caused by a transmitter (like my ham radio example) or the nearby FM Radio transmitter, but it is also characteristic of multi-path. My bet is multi-path. If you put the attenuator on and no matter where you set it, the jump rate doesn't change, then it is more likely multi-path than overload. You can also try to bypass the preamp altogether and see if the jump rate (this is the rate at which the signal quickly goes up and down) is effected. A change here would point at overload.

So, as long as you have an attenuator and you can check before and after with the fm switch on your preamp, you can get a pretty good idea what is going on.

My bet is multi-path, as it is much more common than overload, unless your preamp is just killing things. Hopefully, your preamp is NOT feeding one of the AM21 boxes directly...that would be way too much signal. The AM21 needs to be fed like this:

Antenna > Variable Attenuatior > Preamp > Splitter > AM21

Your remarks:channels 7 and 9 experienced drops at the same moment.

Reflections (Multi-path) vary by frequency so 7 and 9 may show profound multipath, while UHF 19 shows none and Low Band VHF 5 shows little to none. 

Use your worst case jump rate channels for your testing.

Let us know, it's most interesting for us RF guys!


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## hasan (Sep 22, 2006)

veryoldschool said:


> No it wasn't me, but I tend to remember any & every thing about RF.
> We had "some fun" back then eh?
> !rolling


I'll Say! Fond memories.


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## TomCat (Aug 31, 2002)

slice1900 said:


> Is the FM trap to prevent harmonic frequency interference? Or does a strong FM signal affect reception of a weaker UHF station by overpowering the tuner or something?
> 
> Since I have my signal split 32 ways, I have a 25db distribution amp inline with my antenna. It has a switch for the FM trap marked "in" and "out", and I remember when I tried both settings (since it isn't obvious to me which one enables the trap) one setting produced slightly lower signal quality readings so I used the other. As there are some fairly strong FM stations in line with the direction my antenna is pointed, should I enable the trap (if it isn't already) even if it lowers the apparent signal quality a tiny bit?
> 
> When I was investigating other issues I had a script running on my wireless router taking signal quality readings off a receiver once per second and recording them to a file. When I tried that on my OTA signal for curiosity's sake I observed momentary blips where the quality would drop noticeably for a second or two. Occasionally the way to down to 25 (which is what the AM21 shows for "no signal") I thought it might be the amp or its power supply, but it was unchanged when I bypassed it for that receiver. I guess that's multipath, from a plane or atmospheric disturbance, and there's nothing to be done about it? The picture will briefly pixellate for a moment once in a while, and while I never tried to correlate that with the signal readings, I assume that's what I'm seeing.


The trap does both; it can prevent the tuner and agc from being swamped if the FM signal is that strong, and it can prevent intermod created by mixing those frequencies with others. It is always better to receive a signal that is not in the presence of competing signals, whether those competing signals are on the same frequency, adjacent frequencies, or even not (because the mixing can still create harmonics on frequency). A good FM trap is probably slightly better than a VHF/UHF rolloff filter, and in most markets some DTs have gone back to a hi-V channel anyway. RatShack still sells one for about 8 bucks, and Monoprice and others probably have them.

The "3091" appears almost identical to the distribution amp that RatShack sold for years, up until a few years ago. It has a great low noise figure and the trap is pretty good; that is probably identical to the amp and trap I am using, in fact.

An antenna preamp is usually quite different. They do much the same thing, but the window of operation is at about -25 to -35 dBmV for a preamp. The CM7777 is a great example of a good one. A distribution amp is something you want to hit at a much higher level, around 10 to 15 dBmV, and you can go even lower with ATSC signals because noise is much less a factor. So, you can't substitute one for the other, because they do very different jobs.

I do agree that multipath is more likely the issue, and offsetting the aiming of the main lobe can indeed force the reflected interference into a dead spot which can lower the interference ratio between the two, and is good advice. But you can try the attenuator/FM trap route pretty cheaply and quickly, while to lower multipath you have to move the antenna, raise the antenna, or get a better (more-directional) antenna (or a TV with a newer tuner).

For "perfect" reception, you should still see one minor glitch every 24 hours. If you watch TV 2 hours a day that's then one glitch every 12 days. Even good reception may yield a glitch once an hour. Acceptable reception may yield 2 or 3 glitches an hour, and anything that glitches more than that is probably not acceptable. But, you will still see perfect pictures between the glitches. For analog, it is constant PQ degradation as reception gets worse.

Another possibility is too low of a signal, but that is not likely in this case. You have to have a signal that is 15 dB above the noise floor (but 20 works better because atmospheric stuff modulates the level up and down a bit, meaning 15 now may be 13 an hour from now, and 20 gives you fade margin). This usually only happens when you have flat terrain, no obstructions, and are 35 miles or better from the towers. That is when a preamp comes into play. Still, for perfect analog reception that ratio had to be 46 dB.


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## slice1900 (Feb 14, 2013)

hasan said:


> http://www.winegarddirect.com/viewitem.asp?d=Winegard-FT7500-75-Ohm-FM-Trap-Fixed-(FT7500)&p=FT7500
> 
> This is an in-line band stop filter that claims it will reduce the ENTIRE fm band by 26 dB. That is very good. There is no specification for insertion loss, but there is a bit of a warning:
> 
> ...


OK, I'll keep that Winegard trap in mind if it turns out FM has something to do with what I'm seeing. Obviously I don't care about losing RF channel 6 so it would work perfectly for me if it turns out I have a need to block FM. I actually have enough signal power that everything works (in clear weather at least) through the 32 way split without the amp, so a db or two of insertion loss wouldn't matter at all.

In order to test all your ideas more efficiently I think I'll try the following, let me know what you think. I can set up a script to tune each of two receivers to the same channel overnight for about 8 hours (unless I move receivers around I don't have two located where I can do 24x7 testing on them) and record signals from both every second and directly compare to see whether there's a difference based on the test conditions. That should eliminate any potential variability due to weather conditions.

Test #1: I'll add a 2 way splitter in front of the the amp, so one receiver bypasses the amp and 32 way split as a "control" and the other is fed via the amps and 32 way split as normal. This will show if the presence/absence of the amp causes any noticeable changes.

Test #2: I'll try the "opposite" setting for the FM trap on the amp compared with test #1. I don't know which setting enables or disables the trap, but if there's no difference observed between the two, I can probably eliminate FM as a concern.

Test #3: I'll add more splitters between that 2 way and the amp to further attenuate the signal entering the amp in 3.5db increments and see if that makes any difference, and if so where the "sweet spot" is.

I don't really know what channel has a higher jump rate, as I never thought to count the number of signal interruptions and compare between channels, but I'll try them with several channels including my strongest and weakest to see if that matters.

It might take a few weeks to run through all the scenarios, but hopefully I'll end up with some interesting data.


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## slice1900 (Feb 14, 2013)

TomCat said:


> For "perfect" reception, you should still see one minor glitch every 24 hours. If you watch TV 2 hours a day that's then one glitch every 12 days. Even good reception may yield a glitch once an hour. Acceptable reception may yield 2 or 3 glitches an hour, and anything that glitches more than that is probably not acceptable. But, you will still see perfect pictures between the glitches. For analog, it is constant PQ degradation as reception gets worse.
> 
> Another possibility is too low of a signal, but that is not likely in this case. You have to have a signal that is 15 dB above the noise floor (but 20 works better because atmospheric stuff modulates the level up and down a bit, meaning 15 now may be 13 an hour from now, and 20 gives you fade margin). This usually only happens when you have flat terrain, no obstructions, and are 35 miles or better from the towers. That is when a preamp comes into play. Still, for perfect analog reception that ratio had to be 46 dB.


So "perfect" isn't perfect, I guess, and you can't avoid some glitches? I know I see more than one glitch per 24 hours, but usually not as high as one glitch per hour (though the number of glitches was variable as I recall, there could be a half dozen or more in an hour, and then go hours with none)

I'm pretty sure low signal isn't the problem, according to tvfool.com the furthest station I care about is just under 50 miles away, but the noise margin is 40 db. I'm not sure what model my antenna is, I know it is a Winegard. It might be a 7080 or 7695, it looks very similar to both. Not the top of the line, but pretty good. There are no trees in the area blocking reception, and the terrain in the immediate area is flat in the direction it is pointed.


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## NR4P (Jan 16, 2007)

For what its worth, I rely on OTA for most local TV viewing. Some stations are 2 miles away, some about 15 miles and others about 50 miles.
I hardly ever see a glitch, dropout or other issues. Rain never affects any reception (Hurricanes not included in that "never" statement).

if there is a strong lightning storm, that will affect the stations 50 miles away, assuming the towers don't take a hit and go off air briefly.
Once in while a low flying plane or helicopter will affect the distant stations too, but briefly. 

In summary, I probably see a minor glitch 1x or 2x a month. OTA can be nearly perfect with a good antenna and distribution system.


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## hasan (Sep 22, 2006)

Once or twice per second every second or two of at least 10% would cause me concern. Just watching the signal meters on the appropriate channels should tell you a lot about what is going on.
If the jump rate is < 3% then there is no problem. If you see that drastic 50% or greater reduction periodically, that is a big problem. Commercial FM interference should be pretty constant.

You have an interesting problem and some good ways to test it. Let us know!


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## hasan (Sep 22, 2006)

NR4P said:


> For what its worth, I rely on OTA for most local TV viewing. Some stations are 2 miles away, some about 15 miles and others about 50 miles.
> I hardly ever see a glitch, dropout or other issues. Rain never affects any reception (Hurricanes not included in that "never" statement).
> 
> if there is a strong lightning storm, that will affect the stations 50 miles away, assuming the towers don't take a hit and go off air briefly.
> ...


He has a real problem, that you and I don't see. I have sigs @ 100% all the time at 26 miles over open terrain. The transmit towers are at 2200 feet and my antennas are up about 30', moderately sized vhf/uhf combos. I have a CM-7777 preamp as my distro amp with a variable attenuator on the input. I think I'm currently split about 8 ways on the preamp output. I can still kill several channels with my 144.390 transmitter if I don't have my 144.39 stub connected.


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## JerryMeeker (Sep 20, 2007)

I ordered a variable signal attenuator on Ebay, and after about three weeks, it finally arrived from the Far East today. I am extremely disappointed, it is a total POS.










I was expecting screw-on BNC connectors, and look what I got. The metal back plate fell off the first time I handled it. I guess you get what you pay for. Back to the drawing board.


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## TomCat (Aug 31, 2002)

There is no such thing as a "screw-on" BNC. The bayonet nut connector (which goes by other names as well) has a pair of bayonet type locking notches that mate with two perpendicular poles onto a female bulkhead connector.

The pic I posted earlier has what you should have expected, which is a female F connector on either end. That's a true screw-on, I just hope you were not the one screwed.

But I can't tell what the heck that thing is; it looks sort of like a push-on male F, and if so, you could probably still use it by adding an F-81 barrel connector (dual female F).


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## veryoldschool (Dec 10, 2006)

TomCat said:


> There is no such thing as a "screw-on" BNC.


Guess you've never seen a TNC connector: http://en.wikipedia.org/wiki/TNC_connector


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## peds48 (Jan 11, 2008)

veryoldschool said:


> Guess you've never seen a TNC connector: http://en.wikipedia.org/wiki/TNC_connector


Are these real "screw on" (like coax) or twist on? (like BNC)

can't tell from the picture


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## veryoldschool (Dec 10, 2006)

peds48 said:


> Are these real "screw on" (like coax) or twist on? (like BNC)
> 
> can't tell from the picture


They're a threaded BNC "as in" the same size as BNC with threads.
They're 50 Ohm, so you wouldn't see them with 75 Ohm coax.

Sometimes TomCat is just wrong. :wave:


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## JerryMeeker (Sep 20, 2007)

@TomCat, yes, I should have said "F-Type" connector, which is what I was expecting. The actual connector is what I believe is called a "Push-On" connector, and I am going to try this adapter from Radio Shack: http://www.radioshack.com/product/index.jsp?productId=2103581.


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## JerryMeeker (Sep 20, 2007)

Problem solved. The Radio Shack adapter is what I needed.










I have installed the attenuator and adjusted the signal strength as per the advice provided earlier in this thread. Of the primary OTA broadcast signals here in Austin, four of five register a 100% signal, while the fifth (FOX) registers somewhat lower. I adjusted the attenuator until the signal dropped just below 100%, and than tweaked it back up to 100% so that the adjustment is right on the edge. Unfortunately, this lowers the FOX signal to only 25%, and the AM21 won't pull the signal in. Well, four out of five is not bad.

I will record some OTA programs this evening to see if the signal dropouts I have been experiencing have been resolve by attenuating the signal. I'll report back.


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## TomCat (Aug 31, 2002)

veryoldschool said:


> They're a threaded BNC "as in" the same size as BNC with threads.
> They're 50 Ohm, so you wouldn't see them with 75 Ohm coax.
> 
> Sometimes TomCat is just wrong. :wave:


As are you. And saying that implies that I am correct most of the time.

BNCs are available as both 50-ohm and 75-ohm, and you can tell them apart because the dielectric is shaped differently. So you are wrong about that, too. We used to use 50-ohm, but digital video will not work with them, so we went to 75-ohm.

And a TNC is not a BNC, they are different connectors that are different sizes, and are used for different purposes. In my professional life I use both all the time. SomeTNC's use a similar locking bayonet/nut connection, but otherwise they are no more like a BNC than they are like any other connector. Most of them don't even use that. You can go on to Google Images and see that there are numerous different versions.

I have attached a pic of 50 and 75-ohm BNC's as well as a screw-on TNC that I just happen to have in my parts drawer here. So this time, just like every other time, I am right, and you are not.

And even Wikipedia is wrong (gee...that's never happened before). A TNC is not _a version of_ a BNC, it is a different connector with a different name used for different purposes that can sometimes be _similar _to a BNC.

I also looked at a dim blurry thumbnail and was unable to see exactly from that angle what kind it was. I guessed that it looked like a push-on F, and the OP has now confirmed that.

So it appears that all bases are covered which leaves the question "what am I wrong about?" It appears that I am once again wrong about nothing, so that is yet another thing that you are wrong about.

You should be used to that by now.

So, Tom = 1
Wikepedia = 0
VOS = 0


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## peds48 (Jan 11, 2008)

TomCat said:


> so that is yet another thing that you are wrong about.


One thing I have come to learn on these boards, is that VOS is NEVER wrong....


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## TomCat (Aug 31, 2002)

JerryMeeker said:


> ... I adjusted the attenuator until the signal dropped just below 100%, and than tweaked it back up to 100% so that the adjustment is right on the edge. Unfortunately, this lowers the FOX signal to only 25%...


Once again, *if the signal quality level never rises above where it was originally *with the attenuator in line and adjusted, then your signal does not need attenuation. You will need to move the antenna or get a more-directional one to reduce the multipath ratio.


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## TomCat (Aug 31, 2002)

peds48 said:


> One thing I have come to learn on these boards, is that VOS is NEVER wrong....


Whatever gets you to sleep at night; just keep telling yourself this.


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## studechip (Apr 16, 2012)

Not sure if this was suggested yet, but how about an indoor antenna? There will be less signal received, therefore not overloading the tuner.


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## veryoldschool (Dec 10, 2006)

TomCat said:


> And a TNC is not a BNC, they are different connectors that are different sizes, and are used for different purposes.


It never pays to argue with an idiot.

I've had to "mix and match" connector parts between BNC & TNC for flight testing in the Air Force, so you can turn a BNC into a threaded [TNC] connector.


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## veryoldschool (Dec 10, 2006)

peds48 said:


> One thing I have come to learn on these boards, is that VOS is NEVER wrong....


Well, I have been "mistaken", as I'm human, but I also have the memory of an elephant and decades of experiance.


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## peds48 (Jan 11, 2008)

veryoldschool said:


> Well, I have been "mistaken", as I'm human, but I also have the memory of an elephant and decades of experiance.


That's what is is, "mistaken" is not the same as being "wrong" :rotfl:


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## JerryMeeker (Sep 20, 2007)

Well, I have had the signal attenuator in the OTA signal path for several days now. While the signal freeze/pixelation issues have improved, they have not been completely eliminated. The CBS signal is rock solid. The ABC signal exhibits 2-3 signal breakups during a one-hour recording. The NBC signal remains the worst, but it has still improved since the attenuator was installed. 

I will try reducing the signal strength a bit more to see if I can squeeze out additional improvements.


Sent from my iPad using DBSTalk mobile app


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## hasan (Sep 22, 2006)

JerryMeeker said:


> Well, I have had the signal attenuator in the OTA signal path for several days now. While the signal freeze/pixelation issues have improved, they have not been completely eliminated. The CBS signal is rock solid. The ABC signal exhibits 2-3 signal breakups during a one-hour recording. The NBC signal remains the worst, but it has still improved since the attenuator was installed.
> 
> I will try reducing the signal strength a bit more to see if I can squeeze out additional improvements.
> 
> Sent from my iPad using DBSTalk mobile app


Again, on the channels that you get some breakup, are the signals stable, or are they bouncing around, and if bouncing, how much on the signal quality meter?


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## JerryMeeker (Sep 20, 2007)

hasan said:


> Again, on the channels that you get some breakup, are the signals stable, or are they bouncing around, and if bouncing, how much on the signal quality meter?


There is a slight signal strength variation between 97-100% on the ABC and NBC signals. IOW, the signal is not stable. CBS is rock solid.


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## studechip (Apr 16, 2012)

JerryMeeker said:


> There is a slight signal strength variation between 97-100% on the ABC and NBC signals. IOW, the signal is not stable. CBS is rock solid.


I wouldn't think you would get dropouts with signals that strong. Maybe they are too strong still and overloading the tuner.


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## hasan (Sep 22, 2006)

JerryMeeker said:


> There is a slight signal strength variation between 97-100% on the ABC and NBC signals. IOW, the signal is not stable. CBS is rock solid.


That kind of variation is a non-issue, very minor and should not cause drop outs. What I would look for now is an isolated plunge in signal quality. Here is an example:

I can use the signal meters to look at RF Channel 8 and see the signal is stable as a rock at 100%. If I let it sit there for a period of time, say 10 minutes, all of a sudden the signal will take a precipitous drop down to 40%, for about one second or so. Then, it will be stable (perfect) for another ten minutes or so, before doing the exact same thing. In each of these cases, the pix and sound would break up. Obviously, something was causing the front end of the receiver to cave in, or there was a spurious transmission on the same frequency as Ch 8, very close to me. (I found the source, built a notch filter for it, problem solved...it was overload).

What I'm suggesting you do is closely monitor the signal quality meter on a channel where you experience a few drop outs. Keep your eye on it for the length of time that you normally experience your drop outs. I'm betting you will see the signal quality meter plunge, completely correlated with the drop outs you see.

There are two likely causes:

1. RF Overload from a local transmitter.
2. Multi-path caused by airplane refections, or some other variable object.

In the second case, you need a more highly directional antenna so you can move the offending off axis signal further down the slope of the antenna pattern, or you need to move your current directional antenna a bit either way, to force the offending signal to slide down the "sidelobe" slope. If you already have a yagi or log periodic outside (or attic) antenna, then you need to re-point it...deliberately move it off axis from your desired station, hoping to move the offending refection further down the antenna's response. The more you move the offending signal off the "side" of your antenna, the less interference it can cause. The front to side ratio of your antenna is no doubt, at least 100:1 and the maximum reduction in signal is when the antenna is pointed 90 degrees off the front of the antenna.

Let us know what you find...and remind me just exactly what kind of antenna it is you are using, what height it's at, etc.


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## JerryMeeker (Sep 20, 2007)

Thank you, Hasan, for the useful feedback. This is the antenna I have. It is mounted outside at the top of my chimney, which places it 40-50 feet above ground level. I like in the hills of northwest Austin, on top of a hill with an unobstructed direct line-of-sight to the Austin transmitter towers, which are grouped together on a hill approximately five miles away. The antenna is pointed by eye towards the antenna farm.










Cabling is always an area of concern as well. I installed coax cable back in 1996 as an early adopter of DirecTV technology. Several years ago, I noticed some of the original coax was developing corrosion, so I completely replaced all the cable with top-quality RG6 quad-shield coax, and used high-quality compression F-connectors. The cables all have grounding blocks mounted in a junction box to prevent moisture from corroding the connections. So you can see, I have gone to great lengths to deliver a pristine signal to my DVR's and the AM21.

I'll follow your recommendation and watch the signal strength meter, and perhaps tweak the antenna orientation to see if there is an improvement.


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## hasan (Sep 22, 2006)

Nice! Because of contrast, I'm not sure what I am seeing, is that UHF only? I don't see any longer elements for VHF Lo or VHF Mid band. If it is UHF only, that will help with multi-path, because an antenna of that size has a nice tight pattern with very steep side lobes. It will make it easier to drop a refection (source of multipath) off the side. Let us know how you make out. I've always had a deep interest in the RF side of things and love antenna/transmission line theory and practice. I have a bunch of test equipment as well as a large tower in the back yard for my ham radio antennas, which I've been playing with since I was 16 (a long time ago). Anyway, if there is anything I can do to help you out, let me know. I was in on the early battles with the tuners built into the HR20 and it was a ton of fun getting them to perform properly, or at least as well as possible.


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## JerryMeeker (Sep 20, 2007)

^ According to the specs, it is a UHF-only antenna.


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## hasan (Sep 22, 2006)

JerryMeeker said:


> ^ According to the specs, it is a UHF-only antenna.


OK, so I assume you are not trying to get channels lower than 17 on it, because if you are and they are actually on VHF, that antenna could cause you to receive a ton of reflections, because it has no off main lobe rejection when used on VHF frequencies. It would tend to become omni-directional on VHF, which essentially means works equally poorly in all directions and does not discriminate against off angle signals.

In that case (trying to use a UHF antenna for a VHF signal), it has lost all directionality and moving it around to try to get rid of a reflection may not work at all. Hopefully, all your stations are on UHF and in that case, you can move it slightly off center (either direction, you have to experiment) and place the reflection down the sidelobe of the antenna.

i look forward to hearing of your results.


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## veryoldschool (Dec 10, 2006)

hasan said:


> OK, so I assume you are not trying to get channels lower than 17 on it, because if you are and they are actually on VHF.....


Minor corrections:
VHF-lo ch 2-6
VHF-hi ch 7-13
There is no VHF "mid band"
UHF ch 13-69


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## hasan (Sep 22, 2006)

Thanks!


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## JerryMeeker (Sep 20, 2007)

Well, adjusting the attenuator to various settings still has not improved the quality of OTA signals. NBC is especially bad. However, even on the DirecTV NBC feed, I am getting dropouts. I watch the Brian Williams nightly news every day, and it is a rare broadcast that is dropout free. Is this a national issue, or an issue with the Austin NBC affiliate? 


Sent from my iPad using DBSTalk mobile app


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