# Not quite Satellite, but OTA related



## bungi43 (Jan 17, 2011)

So I'm about 70 miles outside Chicago. Normally I'm picking up the stations at 85% signal strength or better.

We are under a fog advisory in NW Indiana tonight...and I'm not getting several Chicago stations at all....BUT some stations I'm getting at their normal 90% strength.

Is that normal? What other reasons would I be losing a bunch of stations tonight?


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## RBA (Apr 14, 2013)

bungi43 said:


> So I'm about 70 miles outside Chicago. Normally I'm picking up the stations at 85% signal strength or better.
> 
> We are under a fog advisory in NW Indiana tonight...and I'm not getting several Chicago stations at all....BUT some stations I'm getting at their normal 90% strength.
> 
> Is that normal? What other reasons would I be losing a bunch of stations tonight?


Fog is water droplets suspended above ground level so that is a possibility. What frequency are the missing channels VHF or UHF? How strong is their broadcast, you might check tvfool.com?


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## slice1900 (Feb 14, 2013)

I don't think fog/moisture affects the frequencies for TV signals at all. Maybe what you're seeing is multipathing caused by signals bouncing off cloud layers/temperature inversions? Depending on the location of the TV station some may be more or less prone to this, hence why it is sort of hit and miss with the various stations.


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## Stewart Vernon (Jan 7, 2005)

Fog is essentially a ground-level cloud... how it might interfere with your OTA signals really depends on where your signals are coming from. The farther you are away, the steeper the angle from you to the radiating tower, and the steeper that angle, the longer the signal would be interfered with by that fog.


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## bungi43 (Jan 17, 2011)

That makes a lot of sense. As I said, I'm a good distance from Chicago, but this is the first time in 2 1/2 months since I got my new antenna put up that I've had any issues. It appears to be a bit better this morning, but some of the stations are still struggling (still very overcast here this morning). I'll give it a few days, see what happens.


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## Stewart Vernon (Jan 7, 2005)

Yeah, its a multiple thing since the farther away you are from the broadcast tower, the weaker the signal is you receive... but also the increased angle means it would be in that band of fog longer too... so if you're on a fringe even a little bit of interference might be enough.

The old analog signal was interfered with too... but you might get a marginal signal and decide it was "ok" enough to watch... whereas with digital it's kind of an all or nothing... so while your reception slowly degraded with signal and interference in analog... digital provides a pristine reception up until the point where you suddenly get nothing at all.


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## Laxguy (Dec 2, 2010)

Stewart Vernon said:


> Fog is essentially a ground-level cloud... how it might interfere with your OTA signals really depends on where your signals are coming from. The farther you are away, the steeper the angle from you to the radiating tower, and the steeper that angle, the longer the signal would be interfered with by that fog.


Wouldn't it be the opposite? The closer you are to a tower, the steeper the angle to your antenna? And, yes, the steeper the angle, the further the signal has to travel, but wouldn't that be a matter of a few hundred yards at most?


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## scooper (Apr 22, 2002)

I haven't seen fog per se interfering with OTA reception, but a good enough thunderstorm will. Some of that may be related to causing multipath in the trees and leaves in the forest I live in.


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## Stewart Vernon (Jan 7, 2005)

Laxguy said:


> Wouldn't it be the opposite? The closer you are to a tower, the steeper the angle to your antenna? And, yes, the steeper the angle, the further the signal has to travel, but wouldn't that be a matter of a few hundred yards at most?


It's the angle from the tower that matters... The signal is radiating outward from the top of the tower. If you are living right below the tower the signal is straight down through the hypothetical fog, which is the shortest possible way through that fog's depth. The farther away from the tower you go, the angle from the top of the tower increases and instead of going straight down through the fog, the signal is crossing through it at an angle... that means more time for the signal you receive to be inside that fog.

I can draw a diagram if the words weren't good enough. You kind of have to visualize the tower, your house, and the layer of fog... and see the path the signal travels as you get farther away from the tower to see what I'm talking about.


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## makaiguy (Sep 24, 2007)

The semantic problem deals with which line you are considering as the base of your angle. You are considering the vertical tower as the baseline, thus making a line from the top of the tower to a distant point a *steep* angle approaching 90 degrees.

I think most of us would instinctively use a horizontal "ground" line as our baseline. So from our viewpoint, a line to the top of a distant tower would be a *shallow* angle approaching 0 degrees.


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## Laxguy (Dec 2, 2010)

Thanks, MG, that puts nicely what "angle" I was going from.


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## Stewart Vernon (Jan 7, 2005)

Ok... that's what I wondered... I was using the angle from the tower, using the tower as the baseline... because the "transmission line" was the line in question, traversing the foggy area... so it seemed the most logical angle to use as that is where the transmission originates. I guess that wasn't coming through in the conversation though.


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## SomeRandomIdiot (Jan 7, 2009)

bungi43 said:


> So I'm about 70 miles outside Chicago. Normally I'm picking up the stations at 85% signal strength or better.
> 
> We are under a fog advisory in NW Indiana tonight...and I'm not getting several Chicago stations at all....BUT some stations I'm getting at their normal 90% strength.
> 
> Is that normal? What other reasons would I be losing a bunch of stations tonight?


Despite the long explanations you have been given, unfortunately they are incorrect.

*The Fog was only a symptom of the issue, but it was not the cause.*

TV frequencies do not have that type of attenuation from rain/water that higher frequencies (like Ku and Ka band) have. This can be seen from the fact that you were getting some at normal strength and some not at all. If the Fog was truly the cause, you would have had attenuation to some degree across the entire Spectrum (not particularly even attenuation, but you would not be getting some at Full Strength).

1) At about 70 miles outside of Chicago, are you in the Rensselaer area or further East or West of Rensselaer?

2) Which stations were you getting and which are you not getting?

3) What was the approximate temp at the time?


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