Minneapolis/St. Paul - Ch. 11-1 Reception Issues - Page 2 - AVS Forum
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post #31 of 44 Old 01-25-2014, 01:25 PM
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Your TVFool results clearly show SIX or more VERY Strong TV signals...plus over a DOZEN VERY Strong FM signals (enter your location into www.fmfool.com)....so YES, you need an FM Band Reject Filter on the input of the Distribution Amplifier. To estimate signal levels on the input of the DistroAmp:

Sip = Pwr (dBm) - Attic Loss (est 13 +/- 6 dB) + Antenna Gain (est 5 dBd for ANT751) - Balun Loss (est 0.5 to 1.5 dB) - Balun-to-DistoAmp Cable Loss

Now compare these strong levels to the calculated Sip levels in the Overload Spreadsheet, line 68 (for SIX strong signals). I estimate Sip = -30 dBm (give or take a few or more dB) which would degrade the Spurious Free Dynamic Range on all except the lower Gain Winegard models....which MIGHT be marginal, depending on how much Attic Loss you REALLY have and inaccuracies in TVFool predictions.

HOWEVER, since manufacturer's aren't interested in providing meaningful overload specs for Distribution Amps, we really don't KNOW whether they are as good as the lower Gain Winegard Preamps....maybe....maybe not....

So it's worth doing a Trial and Error Test, inserting small amounts of attenuation prior to the DistroAmp. Since Intermodulation Distortion Noise levels are reduced by 3 dB or EVERY 1 dB of Insertion Loss, inserting a few dB of Attenuation, such as a spare RF Splitter (typ 3.5 dB Loss), will reduce IMD Noise by 10.5 dB....and a 6 dB Attenuator will reduce IMD Noise by 18 dB....which is probably more than is needed at your location so that the the weak signals are no longer degraded by the IMD Noise levels.
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post #32 of 44 Old 01-25-2014, 01:55 PM - Thread Starter
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Quote:
Originally Posted by holl_ands View Post

Your TVFool results clearly show SIX or more VERY Strong TV signals...plus over a DOZEN VERY Strong FM signals (enter your location into www.fmfool.com)....so YES, you need an FM Band Reject Filter on the input of the Distribution Amplifier. To estimate signal levels on the input of the DistroAmp:

Sip = Pwr (dBm) - Attic Loss (est 13 +/- 6 dB) + Antenna Gain (est 5 dBd for ANT751) - Balun Loss (est 0.5 to 1.5 dB) - Balun-to-DistoAmp Cable Loss

Now compare these strong levels to the calculated Sip levels in the Overload Spreadsheet, line 68 (for SIX strong signals). I estimate Sip = -30 dBm (give or take a few or more dB) which would degrade the Spurious Free Dynamic Range on all except the lower Gain Winegard models....which MIGHT be marginal, depending on how much Attic Loss you REALLY have and inaccuracies in TVFool predictions.

HOWEVER, since manufacturer's aren't interested in providing meaningful overload specs for Distribution Amps, we really don't KNOW whether they are as good as the lower Gain Winegard Preamps....maybe....maybe not....

So it's worth doing a Trial and Error Test, inserting small amounts of attenuation prior to the DistroAmp. Since Intermodulation Distortion Noise levels are reduced by 3 dB or EVERY 1 dB of Insertion Loss, inserting a few dB of Attenuation, such as a spare RF Splitter (typ 3.5 dB Loss), will reduce IMD Noise by 10.5 dB....and a 6 dB Attenuator will reduce IMD Noise by 18 dB....which is probably more than is needed at your location so that the the weak signals are no longer degraded by the IMD Noise levels.

 

Wow, great info...thanks!  I'll be doing the trial and error testing once the attenuators show up.  I'm assuming, between the 6, 10, 12, & 16 that I bought, I should be able to dial it in.

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post #33 of 44 Old 01-25-2014, 05:12 PM - Thread Starter
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Ok, so absolutely nothing has changed with the setup and the pixelation is happening more.  I know that time of day plays into signal so is it possible that the signal could be getting stronger at night therefore overloading the system moreso than during the day?

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post #34 of 44 Old 01-26-2014, 10:43 AM
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....so is it possible that the signal could be getting stronger at night therefore overloading the system moreso than during the day?

Perhaps, if the issue is indede due to some sort of interference, the SOURCE of the interference may be increasing.

If you've installed 10-20 dB of attenuation at the RF input and the symptoms are still occurring, it's a fairly save conclusion that the interference is not coming into the set via the coaxial cable. That leaves less obvious sources of ingress including possible USB or HDMI inputs (unplug any such connections and retest) or, perhaps, there is a very strong, very local source of I in or very close to your home. To test for in-home sources, turn off all circuit breakers except the one servicing the TV set and retest. If it still exists, then use an extension cord to feed power from an alternate circuit while shutting off power to the original circuit that powered the set. This way, you can determine if any of the devices powered by circuits within the home are responsible.

If in-home testing doesn't work, then look outside. There may be noisy power lines, streetlamps, or neighbors with electrical or electronic devices that might be producing RFI. Try tuning in an AM radio to an open frequency around 900 KC and see if there's lot of noise. This is a good indicator of power system noise.
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post #35 of 44 Old 01-26-2014, 12:28 PM
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A Good Antenna Coax GROUND is important to guard against interference pickup.

A Good CATV Coax GROUND (for Internet) is also important....and sometimes a CATV GROUND LOOP ISOLATOR is needed:
http://www.amazon.com/TII-220-Ground-Isolator-applications/dp/B0070Q6URO/ref=pd_cp_e_0
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post #36 of 44 Old 01-26-2014, 12:31 PM - Thread Starter
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Perhaps, if the issue is indede due to some sort of interference, the SOURCE of the interference may be increasing.

If you've installed 10-20 dB of attenuation at the RF input and the symptoms are still occurring, it's a fairly save conclusion that the interference is not coming into the set via the coaxial cable. That leaves less obvious sources of ingress including possible USB or HDMI inputs (unplug any such connections and retest) or, perhaps, there is a very strong, very local source of I in or very close to your home. To test for in-home sources, turn off all circuit breakers except the one servicing the TV set and retest. If it still exists, then use an extension cord to feed power from an alternate circuit while shutting off power to the original circuit that powered the set. This way, you can determine if any of the devices powered by circuits within the home are responsible.

If in-home testing doesn't work, then look outside. There may be noisy power lines, streetlamps, or neighbors with electrical or electronic devices that might be producing RFI. Try tuning in an AM radio to an open frequency around 900 KC and see if there's lot of noise. This is a good indicator of power system noise.

 

I've done all of this already and unplugged anything that created buzzing with the AM radio.  After adding in attenuation into the line, I've seen improvement so I'm sticking to this road for the time being.  I'm anxious for the attenuators to arrive so I can tinker around with them.  I'm guessing that my LG has a more sensitive tuner in it and that's why it's being affected and the Vizio isn't.  So far I've only introduced -10db of attenuation into the system as that's all I can muster with the supplies I had on hand.  

 

As for USB/HDMI, I haven't had my HDMI plugged into anything for this entire time and I don't have any USB device plugged in either.

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post #37 of 44 Old 02-08-2014, 03:20 PM - Thread Starter
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Sorry I kinda went missing for a bit.  Well, the attenuators didn't do squat except make the rest of the channels weaker.  I'm just been trying to ignore it and learn to deal with it, but since the Olympics have started I have started watching NBC a lot more and it's bugging me again.

 

With that being said, I did some more searching and it appears there are A LOT of complaints out there about local NBC affiliates.  I've seen a lot of issues leading back to their 11.2 channel that they recently (last few years) started broadcasting.  Would that make sense?  

 

I would be a little more comfortable with it knowing it's not anything wrong with my setup.  It still confuses me as to why my other TV would pick up NBC just fine though.

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post #38 of 44 Old 02-08-2014, 03:51 PM
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Yeah....as I said above, 6 dB Attenuation (18 db reduction in IMD Noise) might be at the UPPER limit of how much attenuation you need. Try 3 dB up to about 7.5 dB (4-way splitter).
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post #39 of 44 Old 02-08-2014, 05:34 PM
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Quote:
Originally Posted by WRX1986 View Post

Ok, so absolutely nothing has changed with the setup and the pixelation is happening more.  I know that time of day plays into signal so is it possible that the signal could be getting stronger at night therefore overloading the system moreso than during the day?

Looking at your TVFool results, I'm guessing you are located close to and just west of the Mississippi River. In the TVFool map function, I moved the pointer until I got 12.7 mi and 123 deg for KARE. Then I turned on the 'Show lines pointing to each transmitter'. The line for KARE goes right over the Mississippi River. Water is a good reflector of TV signals so you are getting a multipath reflection off of the water. Your Vizio is able to compensate for this multipath signal but your LG cannot since it may have an older generation tuner. Also the strength of this multipath signal will vary depending on the roughness of the surface of the water. A smooth surface is the worse case.

One way to check if this is the cause of your problem is to raise or lower your antenna.
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post #40 of 44 Old 02-08-2014, 09:45 PM - Thread Starter
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Looking at your TVFool results, I'm guessing you are located close to and just west of the Mississippi River. In the TVFool map function, I moved the pointer until I got 12.7 mi and 123 deg for KARE. Then I turned on the 'Show lines pointing to each transmitter'. The line for KARE goes right over the Mississippi River. Water is a good reflector of TV signals so you are getting a multipath reflection off of the water. Your Vizio is able to compensate for this multipath signal but your LG cannot since it may have an older generation tuner. Also the strength of this multipath signal will vary depending on the roughness of the surface of the water. A smooth surface is the worse case.

One way to check if this is the cause of your problem is to raise or lower your antenna.

 

Hmmm...never thought of this.  I'm actually very close to the river.  The LG is from '09 I think, so it does have an older tuner.  I'm assuming raising the antenna would help in this case?  Unfortunately, that's not really an option right now since it's hung in my garage rafters and as high as it will go.  My one question about this is that pretty much all the channels I'm receiving are broadcasted across the river, so why is it only happening with NBC?

 

Is there any way it could be the fact that Kare11 (local NBC) is 1080i and has a subchannel in 480i...maybe there's not enough bandwidth?  I've seen a lot of posts about this.  Main reason I ask is because the only other VHF channel is FOX and their HD is broadcasted in 720p with their subchannel in 480i and I have absolutely no issues with that.

 

Here's a post I found that sounds awfully familiar to my issue:

"Doesn't running more subchannels cut down on the bandwidth too? Some of our local affiliates are running like 4 subchannels. They have the HD content, then a 4:3 channel, then a weather radar channel and then some other crap all on the same main channel, like using 41.1, 41.2, 41.3, 41.4. During the Superbowl enough local people here complained that the local station turned off all subchannels except for the HD channel and we could all tell a huge difference in quality over their regular output, but the next broadcast day they turned all the other crap back on and quality went down. During football season I could tell a huge difference between ABC's 720p and CBS's 1080i football broadcasts. The CBS broadcast would get pixelated durning fast motion shots and look awesome during stills. ABC's 720p looked good all the time. I guess that is the difference between progressive and interlaced, but mainly I think the bandwidth available isnt really enough to support the 1080i because it has twice as many pixels as 720p. Even during the superbowl with the subchannels turned off and the station was at 100% power I could still notice some slight pixelation from time to time."

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post #41 of 44 Old 02-08-2014, 09:53 PM - Thread Starter
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Originally Posted by holl_ands View Post

Yeah....as I said above, 6 dB Attenuation (18 db reduction in IMD Noise) might be at the UPPER limit of how much attenuation you need. Try 3 dB up to about 7.5 dB (4-way splitter).

 

I used another 2 way splitter in the line to get a total attenuation of 7dB...still pixelation.

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post #42 of 44 Old 02-09-2014, 08:11 AM
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Hmmm...never thought of this.  I'm actually very close to the river.  The LG is from '09 I think, so it does have an older tuner.  I'm assuming raising the antenna would help in this case?  Unfortunately, that's not really an option right now since it's hung in my garage rafters and as high as it will go.  My one question about this is that pretty much all the channels I'm receiving are broadcasted across the river, so why is it only happening with NBC?

The effects of multipath interference is dependent on the transmit frequency. Each station uses a different transmit frequency, therefore the wavelengths are different. If the two signals (direct and reflected) arrive out-of-phase then you have signal cancellation. KARE happens to use a frequency that has some signal cancellation. If you were to move the antenna higher or lower then some other stations may have pixellation.

I would at least try lowering your antenna to see if it makes any change. Your question about subchannels can best be answered by more knowledgeable posters.
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post #43 of 44 Old 02-26-2014, 06:29 PM
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I have an HDTV antenna on the roof for our large tv and a rabbit ear version in the bedroom. Found this solution by accident but we were able to watch the Olympics on KARE 11. With the bedroom antenna turned the "gain" to zero. KARE came in great where with the gain on we were not getting any signal. Tried it on the outside antenna but had to unplug the antenna electrical plug in. Using just the antenna with no electric picture was fine. Plugged it back in and no signal. Out of 42 channels KARE was the only one we were not getting a signal for with the gain on.
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post #44 of 44 Old 02-27-2014, 03:39 AM
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Sounds like you're using amplifiers in ares where the signals are too strong and the amps are overloading.

Ditch the amplifiers/amplified antennas and go passive only.
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