OTA Signal Fade at Dawn

[spongella]

I've noticed over the past few years that some OTA signals from weaker (and more distant) line of sight stations will decrease from when the sky is dark to first light. For example at 6:00am a TV signal was 53% and by 6:30am it was 0% strength. At 53% the signal was viewable and stable, then started pixielating, then the station had no signal at 6:30am. The antenna was not moved or changed in any way during the fade.

I live in a valley with considerable ground fog at dawn, this may be a factor, not sure. I will try again on a clear morning to see if there is the same fading. Very interesting.

 

[delta_charlie]

I've noticed over the past few years that some OTA signals from weaker (and more distant) line of sight stations will decrease from when the sky is dark to first light. For example at 6:00am a TV signal was 53% and by 6:30am it was 0% strength. At 53% the signal was viewable and stable, then started pixielating, then the station had no signal at 6:30am. The antenna was not moved or changed in any way during the fade.

I live in a valley with considerable ground fog at dawn, this may be a factor, not sure. I will try again on a clear morning to see if there is the same fading. Very interesting.

Hi, might the affected channels be on high VHF? I only get one channel on high VHF and I find it does get wonky when there is any weather around.

Might have something to do with Tropospheric ducting too. VHF and even UHF can be affected.

If you want to learn more try some searched on VHF Tropospheric ducting

Take care, Dale

 

[Jim5506]

Another factor is the SNR. At night the earth shields you from the sun's radiation but with dawn the sun contributes quite a lot to the background noise covering up weaker signals until they are buried in the background.

 

[solarvic]

I do not know that many technical facts about how broadcast systems work but noticed when Nexstar installed thier new tower in Youngstown ohio the stations have a weaker signal. I think nexstar kind of has a monopoly on the youngstown stations. They really bragged about how thier signal was going to be. They have CBS, Fox, ABC and MyTV and a lot of the other stations all broadcast from the same tower. Nextstar also has a lot of stations in Erie so I can,t escape Nextstar. One day this week I only could receive NBC which is suposed to be local owned.

 

[rabbit73]

I've noticed over the past few years that some OTA signals from weaker (and more distant) line of sight stations will decrease from when the sky is dark to first light. For example at 6:00am a TV signal was 53% and by 6:30am it was 0% strength. At 53% the signal was viewable and stable, then started pixielating, then the station had no signal at 6:30am. The antenna was not moved or changed in any way during the fade.
I live in a valley with considerable ground fog at dawn, this may be a factor, not sure. I will try again on a clear morning to see if there is the same fading. Very interesting.

Sounds like temperature inversion.

Is this signal report correct for your location?
RabbitEars.Info

What are the callsigns of the problem channels?

What antenna are you using?

 

[907TECH]

You need more fade margin (more gain, height or whatever). Jim highlights the likely cause it is not unusual at all, signals are decodable, or not. That one is on the threshold probably at your location.

 

[spongella]

From the comments (and I thank all of you) I think the answer is to increase antenna height or get an antenna with more gain.

 

[N6BY]

Is the antenna aimed at the sun when it rises? If so, that will cause a reduction in signal quality.

 

[spongella]

Is the antenna aimed at the sun when it rises? If so, that will cause a reduction in signal quality.

No, it occurs in all directions where the antenna is pointed.

 

[spongella]

Sounds like temperature inversion.

Is this signal report correct for your location?
RabbitEars.Info

What are the callsigns of the problem channels?

What antenna are you using?

Temperature inversions do occur rarely here. Fading occurs only with distant stations such as WPPT. I use rabbitears as a guide, yes. I use one of those 150 mile (more like 50 mile) rotatable antennas. I know they have a bad reputation but mine works for me, with the exception of the aforementioned signal fade.

 

[spongella]

Hi, might the affected channels be on high VHF? I only get one channel on high VHF and I find it does get wonky when there is any weather around.

Might have something to do with Tropospheric ducting too. VHF and even UHF can be affected.

If you want to learn more try some searched on VHF Tropospheric ducting

Take care, Dale

Tropo does occur at this QTH but is rare. Frequency dependence does not seem to be a factor. When tropo does occur I can get stations farther away than usual.

 

[spongella]

Another factor is the SNR. At night the earth shields you from the sun's radiation but with dawn the sun contributes quite a lot to the background noise covering up weaker signals until they are buried in the background.

This seems to be the most plausible explanation.

 

[spongella]

You need more fade margin (more gain, height or whatever). Jim highlights the likely cause it is not unusual at all, signals are decodable, or not. That one is on the threshold probably at your location.

I agree, higher or more gain will be helpful. Coax is only about 13 feet of RG/6 so very little loss.

 

[spongella]

Thanks again for your help.

 

[spongella]

I do not know that many technical facts about how broadcast systems work but noticed when Nexstar installed thier new tower in Youngstown ohio the stations have a weaker signal. I think nexstar kind of has a monopoly on the youngstown stations. They really bragged about how thier signal was going to be. They have CBS, Fox, ABC and MyTV and a lot of the other stations all broadcast from the same tower. Nextstar also has a lot of stations in Erie so I can,t escape Nextstar. One day this week I only could receive NBC which is suposed to be local owned.

I think the last FCC channel repack has definitely affected the reception of some TV stations.

 

[rabbit73]

Temperature inversions do occur rarely here. Fading occurs only with distant stations such as WPPT. I use rabbitears as a guide, yes. I use one of those 150 mile (more like 50 mile) rotatable antennas. I know they have a bad reputation but mine works for me, with the exception of the aforementioned signal fade.

WPPT is a guest on the WBPH transmitter on RF 9.

The "150-mile" antennas do work, but they often break down. You only have a folded dipole for VHF-High and you are not LOS for WPPT/WBPH:

I grew up in a small town in NJ between New Brunswick and Perth Amboy. IIFC, I used to take the train from Plainfield to Flemington to visit a girlfriend. I had a W2 callsign in the early 1950s. I had to go to the FCC office in NYC to take my exam.

I started doing antenna experiments when I was 8; I'm 87 now and still doing them. Using an SDR and a SLM makes it more fun.

 

[Tower Guy]

It is possible that instead of a weaker signal at dawn on your local channel 9 there is another distant channel 9 that gets strong enough to interfere with the local channel 9. This tropo related interference could degrade the signal quality of the local channel 9.

 

[Apologist]

It is possible that instead of a weaker signal at dawn on your local channel 9 there is another distant channel 9 that gets strong enough to interfere with the local channel 9. This tropo related interference could degrade the signal quality of the local channel 9.

I’ve been dealing with a lot since the repack. I would assume this is happening in a lot of places.

 

[TNGuy84]

I have the same effect with the market that's the next closest one to me. From 6pm on, I can get some of the channels I normally can't get during the day with a high signal quality. Once it gets around 7-8 am in the morning, those channels fade out. I've tried going outside in the middle of the afternoon and raising the antenna up manually to see if I catch of glimpse of any increase, and it's pretty much null.