Can't lock ATSC channel 7 in Tampa Bay, FL

Tekdoc

DTVUSA Jr. Member
#1
[SOLVED] Can't lock ATSC channel 7 in Tampa Bay, FL

For the last 2 months or so I have been unable to receive WFLA over the air in Safety Harbor, FL. Reception on this channel used to be rock solid. My primary antenna is an attic mounted RCA ANT751. I have tried 2 other antennas and 3 different tuners with the same result - nearly 100% signal strength and no signal lock. I installed an FM trap and also tried an inline attenuator with no change. I am able to receive all of the other local channels (including 2 other VHF Hi channels) with no problem. Any thoughts on troubleshooting?
 
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#2
Probably either local electrical interference or attic-induced multi-path.

Try relocating the antenna first. However, since multiple antennas, presumably in different spots, have given the same result, I'd suspect its electronic noise interference.
 
#3
A look at your TV fool would help. Sounds like signal overload, or interference from some other local source of strong RFI. You've tried some of the right things. One thought that comes to mind is a home appliance that could be generating a strong RF spur at that frequency. With an attic antenna you could have an interference source right in your own house. Poorly designed switch mode power supplies are famous for this unwanted attribute. There can be plenty of other things that could cause this even the TV itself.
 

Tekdoc

DTVUSA Jr. Member
#4
The alternate antennas were tested in different areas outside the attic, directly connected to 2 different TVs. I unplugged or cut breakers to everything electrical I could find with no change. I did notice that even with no antenna connected to my HD Homerun tuner I am getting 50% signal strength on channel 7 whereas the other channels show about 15% with no antenna connected.

I live in an end unit condo and the cable lines for half of the building come in from the side of our unit. What is the chance this could be signal leakage from cable TV equipment outside my home?
 
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#6
What is the chance this could be signal leakage from cable TV equipment outside my home?
Very low but possible.

It's far more likely that it's coming from some lighting fixture or electronic device's power supply.

You'd really need a spectrum analyzer to effectively troubleshoot it.
 
#9
We have not seen your TV fool report. In this case an FM fool report might be useful. An FM broadcaster next door, or even a mile away could wipe out one channel like that. It would have to be close to be giving you an increased signal reading on your HD homerun with no antenna.
TVTechnology: Testing for DTV Interference
Keep in mind unlicensed transmission in the FM broadcast band has been know to happen in this country. The most likely cause of your problem is a poorly designed consumer electronic product.
 
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#11
I reread your first post I think someone bought a new light, or other household electronic item that is a RF noise generator. Being in a condo the source of the interference could be further propagated through the electrical wiring. The noise from switch mode power supplies can be frequency specific, and power supplies are not the only source of frequency specific unwanted RF noise that can be found around a household.
 

Tekdoc

DTVUSA Jr. Member
#12
Here's the interference captured by a spectrum analyzer:



Not yet sure if it's coming from inside or outside. Will try to track down source this weekend.
 
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Tekdoc

DTVUSA Jr. Member
#15
I identified the source - my desktop PC. Here's a sweep with the antenna on the desk and the PC powered on:



And with the PC powered off:

 
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Tekdoc

DTVUSA Jr. Member
#17
I am happy to report I didn't have to scrap my PC or buy a new power supply. The culprit turned out to be a 120mm case fan I installed in my PC about 2 months ago. I removed the fan and the interference is gone. Thanks to everyone who posted to this thread. I also want to mention the excellent tools I used: RTL-SDR Receiver along with Gqrx and RTLSDR Scanner software. They were really the keys to tracking down the RFI :D
 
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MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#18
This reminds me of when I was a young kid and I built a "transmitter" that sent morse code to a radio.

It consisted of a battery, a DC motor, a switch and some wire. It had a range of about 1/2 a city block!
 
#19
I'm happy to hear of the pleasant out come. It was good to read about your trouble shooting. As one whose wireless communication interest range from long wave to microwave I'm quite well aware of the amount of RF garbage noise that is generated by by house hold electronics. There have probably been plasma televisions sold in this country that generate enough RFI to wipe out reception of some channels. I currently have a microwave oven sitting 1' away from this computer that will wipe out the wifi connection I'm using. I can't reheat my stale coffee, or pizza and surf the web at the same time. I spent years complaining about a power line that needed a bit more attention to maintenance then it was getting. That problem was never fully resolved. They could quiet the RFI down to an acceptable level, but in six months time without regular maintenance it would be back. They did not like it when I called their power line a spark gap noise generator.
I can imagine the problems that could happen when a neighbor buys something new that is a massive RF noise generator.
Steve
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#20
... The culprit turned out to be a 120mm case fan I installed in my PC about 2 months ago. I removed the fan and the interference is gone. ...
Tekdoc,

Years ago I noticed a faint high-pitched whine on the AM radios in my home and it grew louder and louder every week. Then, the whine broke into my land-line telephone! I took a hand-held transistor radio and tuned it off-station on the AM band and the directional ferrite bar antenna indicated to me that my entire household wiring was 'infected' with the noise signal.

I shut off different circuits at the AC Breaker Box and determined the circuit that stopped the noise and that narrowed the search: sure enough, the case cooling fan in my computer was the source of the noise. Welcome to the club!

Jim
 
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