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Old 24-Jun-2016, 9:53 PM   #1
Exchangegeek
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Radio Interference from large Airport?

This is very low priority and I may be chasing a red herring but could the ATL Airport 15 miles away cause signal loss during peak traffic times?

Enclosed, please find my Signal chart and a map of the ATL airport with my path's represented from Antenna.org. You can see that my paths go DIRECTLY above the airport.

I am 29 miles from the antennas and the report shows me at 2Edge but I think I am LOS. Most of the time, I have 70-90% Signal Strength, 90-99% Signal Quality and 100% Symbol Quality, 60-80%. I have a newer DB8 in the attic with less than 10 feet of cable to the receiver. No amplification is used.

However, there are times during the evening and in the mornings on weekdays when the numbers intermittently drop to 40-60% in spurts and the stream starts to chop and fail. Some channels become unwatchable.

My antenna is dry-walled in (not a great decision I made a year ago) so I can't easily change anything out but I am wondering if there is really much I can do. I am happy overall with the reception and just wanted to know if anyone had any ideas.

Many thanks!

-Steve
Attached Images
File Type: png Radar-Digital.png (67.0 KB, 351 views)
File Type: jpg airport.jpg (116.3 KB, 344 views)
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Old 24-Jun-2016, 11:35 PM   #2
ADTech
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It's unlikely that it RFI. If it's actually caused by the traffic at the airport, it's what would have been know in the analog days as as "airplane flutter".
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Old 25-Jun-2016, 12:33 AM   #3
rabbit73
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Welcome, Steve:

Sorry that you are having reception problems. I agree with ADTech, it is more likely the aircraft in the signal path than RF interference. If it were electrical interference, it would have a different timing pattern, but you could check that out with a portable radio that tunes the AM broadcast band.

Thanks for the tvfool image, but a link to the actual report is more useful so that we can click on a callsign to see the terrain profile.

I don't have your exact address, so I derived an estimate of your location from your report to make an analysis. I think I'm pretty close with this report:
http://www.tvfool.com/?option=com_wr...e2cbc42e54ebbf

and I did a signal line map using the tvfool interactive map browser that is close to your map



your map


Quote:
I am 29 miles from the antennas and the report shows me at 2Edge but I think I am LOS.
I did a terrain profile that shows the WSB signal grazing a few peaks on its way to your antenna, so I think the 2Edge designation is justified, especially since the computer simulation doesn't include ground clutter



The proof is, when I raise your antenna to 30 feet, I see LOS for some signals
http://www.tvfool.com/?option=com_wr...e2cb40e510602f
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File Type: jpg ExchangegeekTVFmap.JPG (86.1 KB, 699 views)
File Type: jpg ExchangegeekTVFhismap (2).jpg (186.3 KB, 677 views)
File Type: jpg ExchangegeekTVFp2WSB.JPG (101.2 KB, 669 views)
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Last edited by rabbit73; 25-Jun-2016 at 1:24 AM.
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Old 25-Jun-2016, 1:27 AM   #4
Exchangegeek
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Thank you so much for the replies and the work you did. Rabbit73 the research you did is amazing. The WSB channel as you indicated is certainly my weakest and it has good days and bad days and I am impressed you found that so quickly.

I did read about airplane flutter but didn't want to draw any conclusions as yet so I saved these images for last. Enclosed, please find two images. One shows the airport traffic during my problem times and other shows airport traffic when I have 100% signal quality. I could still be a coincidence but the limited investigative work I have done suggests it may be flutter.

My limited understanding is that I have a couple of options in respect to a tighter focus antenna or multiple antennas but I am pretty happy with what I have for now.

Do you feel my suspicion is correct and is there anything I can do to make the signal more reliable? I can't get to the antenna anymore but I assume raising it and putting it outside would help. Any other ideas?

Thanks again for all your work and the replies. You guys are terrific!

-Steve
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File Type: png Bad Signal - Thurs 8am.png (179.9 KB, 366 views)
File Type: png Good signal - Tues 11am.png (148.8 KB, 371 views)
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Old 25-Jun-2016, 1:46 AM   #5
rabbit73
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Quote:
Most of the time, I have 70-90% Signal Strength, 90-99% Signal Quality and 100% Symbol Quality, 60-80%.
That looks like SiliconDust HDHR readings. Symbol Quality of 60-80% is not good. That is uncorrected errors; your goal is 100%.

The problem is, the FEC (Forward Error Correction) has a limited ability to correct errors. Once that limit is exceeded, you have reached the "Digital Cliff" where you have pixilation, picture freeze, and finally dropout.

If the error correction ability is used to correct errors caused by the poor antenna location in the attic, and to correct errors caused by the terrain diffraction, there is very little left to correct the errors caused by the dynamic multipath from the aircraft.

My antenna is aimed across a street that has a lot of traffic, which causes dynamic multipath from signal interruption, but it only affects the weakest signals. The strongest signals, with few errors to correct, survive unharmed. I can tell the errors are being corrected, because the needle on my signal level meter dips when a vehicle goes by.

If you can get your antenna out of the attic, and higher, you might be able to improve your Symbol Quality.
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Last edited by rabbit73; 25-Jun-2016 at 2:08 AM.
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Old 25-Jun-2016, 2:04 AM   #6
rabbit73
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Thanks for the interesting traffic pattern images. I wouldn't know where to find them, but I agree with your suspicions
Quote:
My limited understanding is that I have a couple of options in respect to a tighter focus antenna or multiple antennas but I am pretty happy with what I have for now.
The tool that is used is to narrow the vertical beamwidth of the antenna by vertical stacking. This is to improve the ratio between the direct signal and the signal reflected from the aircraft. But if the aircraft is in the direct beam, it doesn't work.

The only other idea I have is that some tuners handle multipath errors better than others. Does your TV tuner do better than your HDHR tuner?
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Old 25-Jun-2016, 2:05 AM   #7
Exchangegeek
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That makes perfect sense rabbit73 and I appreciate the information. The flutter does happen more on weaker channels. I also take your point that a stronger signal will have to make fewer corrections. If I can move this higher in the attic or even outside then I should have fewer problems.

You are also spot on with the device! Instead of splitting the signal and sending it throughout to various TVs I bought an HDHomeRun device and connected it to my network. Since my house has wired ethernet, this setup works perfectly so I can watch OTA from my TVs , my computer or my Projector outside. I am impressed with this device and am watching TV on my computer as we speak. I can also monitor the signal live from the device's admin page. I don't know how long the device will last but it works incredibly well.

On a side note, I screwed up my numbers accidentally. All the numbers I posted before are correct, but I accidentally added some at the end that should not be there. 70-90% Signal Strength, 90-99% Signal Quality and 100% Symbol Quality is my typical numbers and results in a perfect picture most of the time.

Enclosed, is a snapshot of my typical signal strength. Most Channels appear as the left image but WSB as you pointed out is weaker and on the right. Right now there is zero flutter so my picture is perfect.

Thanks again for all your help.
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File Type: png signal.png (104.6 KB, 346 views)
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Old 25-Jun-2016, 2:34 AM   #8
rabbit73
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Thanks for the images and the correction

551 is 27
623 is 39

As a first step, try to improve your signal strength by adding a preamp close to the attic antenna; maybe an Antennas Direct Juice.
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Old 29-Jun-2016, 3:15 PM   #9
Exchangegeek
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Last Post of this thread and an update.
I had a couple of amps laying around and I connected one to see what would happen and was not disappointed.
All channels now seem to handle the flutter better. I also gained two channels and my WSB is now error-free. I have watched a few hours of OTA since I connected the AMP and so far so good. This may have been the final little tweak needed.

Many thanks for your help.
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Old 29-Jun-2016, 5:15 PM   #10
rabbit73
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Thanks for the update. Glad to hear that the preamp improved your reception.
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Old 30-Jun-2016, 1:51 PM   #11
skatingrocker17
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I used to live very close to Detroit Metro Airport and I would see strange signal issues often. Jumps from 100% down to 60's would cause a momentary breakup in the signal and it would shoot back up to 100%. Some days it was non-existent and some days it was really bad which probably depends on the path of the airplanes.

It was less noticeable on my VHF stations WJBK and CBET.
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