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Better OTA signal at night?


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10 replies to this topic

#1 OFFLINE   slice1900

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Posted 15 October 2013 - 11:13 PM

I've noticed that late at night I'm getting better signal than I do during the day, and I'm curious why. There are only 4 stations I really care about, and luckily they are all located in approximately the same direction. At night I get solid 100% signal quality on three of them and one varies between 96 and 100% with occasional dips to 90%. During the day three of them are still 100% and the other varies from 77% to 87%.

 

These numbers are good enough, so it isn't a serious issue, I just wonder why. As best as I can tell from the ground, my antenna is aimed directly at the three with the 100% signal, making it about 15* away from the one that sees slightly lower reception. So it makes sense that one is the weakest, due to the aim and the fact that station is about 50 miles away versus 35 or so for the rest. Perhaps I could fix this by having it aimed more towards the weaker one.

 

It may be that all of them get slightly weaker during the day for some reason, but the others are still strong enough that I see 100% no matter what. I'm wondering if it is possible something is affecting this one since it is VHF channel 7 and might have some source of interference during the day at frequencies just below it. The antenna (some channel master 7xxx model I believe) was installed in 2005, so it is designed for VHF as well as UHF - it used to receive a VHF low analog station just fine when first installed.


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#2 OFFLINE   sregener

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Posted 16 October 2013 - 04:46 AM

Nighttime reception is best.  There are a couple of reasons for this.

 

First, the sun is a significant source of radio noise, including at television frequencies.

 

Second, the troposphere is a layer of the atmosphere that allows radio transmissions to pass through during the day, but frequently bounces them back towards earth at night.  You will notice this effect most strongly on nights that are crystal clear (no clouds.)

 

If your daytime reception is trouble-free (no dropouts or pixelation) then you have nothing to worry about.  It is normal.

 

Signal meters that report 100%, etc. are really reporting an error rate and not a reception strength.  Because of forward error correction (FEC), the picture stays perfect even at 70%.  But as the errors increase, the odds of an occasional picture glitch increase.  But if you're at 100%, there's no way to tell just how much signal you'd need to lose to start seeing a problem, as a just barely perfect signal is indistinguishable from one that is 10x as strong.


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#3 OFFLINE   SayWhat?

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Posted 16 October 2013 - 05:38 AM

I found the best in the early morning around 4 or 5 AM.  I'd get signals from distant stations (close to 100 miles) that I couldn't get any other time.

 

Something crapped out, either the impedance coupler or the mast mounted amp, so I don't get anything at all right now.  Just haven't bothered to pull the whole mess down and work on it.


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#4 OFFLINE   KyL416

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Posted 16 October 2013 - 10:43 AM

Of course that sometimes backfires in cases where the FCC thought it was a good idea to have neighboring markets use the same channel. i.e. here in NEPA WBRE and WYOU are on the same number as WPIX and WNET so on nights with a lot of boost we lose them completely, people in Philly's southern suburbs have the same problem since WTXF is on the same channel as WMPT in the Baltimore market.

#5 OFFLINE   AirShark

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Posted 16 October 2013 - 10:47 AM

Nighttime reception is best.  There are a couple of reasons for this.

 

First, the sun is a significant source of radio noise, including at television frequencies.

 

Second, the troposphere is a layer of the atmosphere that allows radio transmissions to pass through during the day, but frequently bounces them back towards earth at night.  You will notice this effect most strongly on nights that are crystal clear (no clouds.)

 

If your daytime reception is trouble-free (no dropouts or pixelation) then you have nothing to worry about.  It is normal.

 

Signal meters that report 100%, etc. are really reporting an error rate and not a reception strength.  Because of forward error correction (FEC), the picture stays perfect even at 70%.  But as the errors increase, the odds of an occasional picture glitch increase.  But if you're at 100%, there's no way to tell just how much signal you'd need to lose to start seeing a problem, as a just barely perfect signal is indistinguishable from one that is 10x as strong.

 

EXCELLENT answer.



#6 OFFLINE   Stuart Sweet

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Posted 16 October 2013 - 10:52 AM

I also vaguely recall that some stations are allowed to boost power at night.
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#7 OFFLINE   slice1900

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Posted 16 October 2013 - 11:17 AM

Thanks for the answers, that makes perfect sense. If/when I am ever up on that roof I may see about turning the antenna 15* or so towards the weaker/more distant station to see if I can get them all locked in at 100% during the daytime, but it isn't a huge concern.

 

I resolved most of the issues I had been occasionally having with that station not quite coming in perfectly during poor conditions by adding a 25 watt GC amp. Since the signal is being split 32 ways it was losing a bit. The funny thing is that the amp even improved the signal strength (as reported by a Directv receiver, so I know it is really quality/BER) versus directly connecting the antenna output to a single receiver. Not by a lot, but I wasn't expecting that result since it is just a regular amp rated at 7 db of noise installed inside after ~30 feet of cable, not a special ultra low noise preamp on the mast.


Edited by slice1900, 16 October 2013 - 11:18 AM.

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#8 OFFLINE   Nick

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Posted 18 October 2013 - 12:30 PM

Signal-wise, you are blessed. If it ain't broke, don't fix it!


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#9 OFFLINE   slice1900

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Posted 18 October 2013 - 01:30 PM

I would, but some damn perfectionism inside me makes me think I should be able to find a way to get them all locked in at 100% day and night! !rolling


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#10 OFFLINE   Davenlr

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Posted 18 October 2013 - 08:33 PM

If you want to see how well the night time signal is carrying in your part of the country, here is a real time map of signal propagation: http://aprs.mountainlake.k12.mn.us/

 

Here is a site with predictions for the near future: http://www.dxinfocen...opo.html#hour24


Edited by Davenlr, 18 October 2013 - 08:34 PM.

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#11 OFFLINE   slice1900

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Posted 19 October 2013 - 01:21 AM

That first site looks like it might be something more for amateur radio. At least the call signs in that link look like amateur radio, and it didn't recognize any TV stations I added.

 

The second link with the troposphere info is interesting. I remember when I was a kid that I was fascinated with seeing stations from far away once in a while when the conditions were just right. We'd get channel 10 from Quincy, IL (150 miles away) often, but once I recall seeing a channel (channel 4 or 5 I think?) from New Orleans (~1000 miles) coming in crystal clear, as good as the local PBS station that had a tower a few miles away. On another occasion I remember seeing a channel from somewhere in Saskatchewan.

 

That sort of thing probably doesn't happen these days with digital TV, but even if it does likely hardly anyone would notice since no one is randomly flipping through the channels like I did as a kid before we got cable...

 

I do recall seeing that sort of freak reception more often at night. Not sure if that was because conditions for it were better then or because I was too busy doing other stuff during the day so I was only bored enough to flip through the dial at night :)


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