Why is reception better at night? - AVS Forum
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Old 08-16-2004, 02:16 PM - Thread Starter
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Why is my OTA digital TV reception better at night? I get all channels at night but have problems with half of them during the day. I mainly watch at night, but I am surprised that solar radiation would effect digital signals. Anyone have a good explanation?

IB
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Old 08-16-2004, 02:30 PM
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Well, the sun is a source of RF noise. That is one impact.

Another is that as the earth heats, the waves rise from the surface. These can refract and deflect signals that are particularly weak.

Once fall arrives, the angle of the sun will be lower for those of us in the US, and you'll likely have less difference in reception between day and night.

For me, reception improves significantly within 5 minutes of sunset. It typically stays good in the morning until 10 or 11.
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Old 08-16-2004, 06:04 PM - Thread Starter
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Thanks. That makes sense. I hope the 5th generation tuners will eliminate the difference.

IB
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Old 08-16-2004, 07:08 PM
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Thats the nature of TV broadcasts in the VHF and UHF band, the tuner generation doesn't matter. If you are close with direct line of sight you won't have such issues, its only when you are expecting the signals to bend from a long distance that you are depending on atmosperic condtions to help and heating of the atmosphere changes things.
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Old 08-16-2004, 07:49 PM
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I used to be interested in DX'ing the AM/LW and SW radio bands, so I'm not at all surprised that reception on the UHF TV band would improve after sunset. Used to be able to pull in AM stations from all around the US/Canada -- and even a couple from South America -- here in Minnesota back in the mid-to-late '80s. But there's enough interference and poorly shielded electronics now to make that a much more difficult endeavor.

Also, although HD programming is encoded digitally the information being transmitted is analog. It's not so much different from using a dial-up modem to access the Internet -- you're modulating digital data for carriage over an analog medium (the POTS phone service, UHF transmission, etc).
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Old 08-17-2004, 06:19 AM
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This is a fairly common phenomenon with UHF DTV reception and you would think it would be better understood. I don't know what it is for sure but I know what it isn't. There are a few problems with the sun noise theory. The broadband radio noise emitted by the sun is measured every day at several locations and published by NOAA;

http://www.sec.noaa.gov/ftpdir/lists/radio/rad.txt

Using yesterdays values as an example and a 12 dB gain antenna the peak solar noise value at 610 MHz would only be -114 dBm. At this frequency this is below the thermal noise floor and far too small to have an impact. Additionally, the disk of the sun is only 1/2 degree making it a point source radiator when compared to any practical UHF antennas. In other words you would need to point your TV antenna directly at the sun to receive even this minuscule noise level. The levels of solar radio noise also do not change significantly with the season.

The day/night variation is most likely caused by changes in the troposphere caused by heating and cooling but UHF tropospheric propagation is poorly understood.
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Old 08-17-2004, 07:45 AM
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The main thing affecting RF propagation is ionization in the appropriately-named ionosphere. The higher the ionization level, the higher the frequencies that can be reflected back (also called 'skip'). The sunlit side of the earth is much more ionized than the night side, thus greater propagation. UHF frequencies are well above what usually gets reflected; however they can be bent (refracted.) What might be happening is that you're getting enough signal from distant stations during the day to affect your reception of local stations.

Just guessing...
http://www.tpub.com/content/et/14092/css/14092_20.htm
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Old 08-17-2004, 08:27 AM
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Quote:
Originally posted by djs
UHF frequencies are well above what usually gets reflected; however they can be bent (refracted.) What might be happening is that you're getting enough signal from distant stations during the day to affect your reception of local stations.
djs;
Your statement concerning reflection of UHF frequencies by the ionosphere is absolutely true but even refraction ceases to be significant at anything over about 100 MHz so unfortunately that can't explain it either.
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Old 08-17-2004, 12:02 PM
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On a day-by-day basis, you're probably right. During solar storms however, wild things can happen - many years ago, I carried out a ham radio conversation at 144MHz over a distance of several hundred miles. This is unusual, but not rare.

Another explanation: some radio stations change power output between day and night - don't know if TV stations do this or not.
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Old 08-17-2004, 02:12 PM
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Quote:
Originally posted by djs
On a day-by-day basis, you're probably right. During solar storms however, wild things can happen - many years ago, I carried out a ham radio conversation at 144MHz over a distance of several hundred miles. This is unusual, but not rare.

Another explanation: some radio stations change power output between day and night - don't know if TV stations do this or not.
Many people try to equate their experience with radio to television. The frequencies, with the exception of FM, just don't match. Shortwave can and does cover great distances. AM does bounce off a layer of the atmosphere at night, giving it great range (and leading to very few "full power" stations after sunset.) UHF especially is very different from either of the above.

Most television stations do not change power at night, since the reason for doing so (co-frequency interference) simply doesn't exist in the same manner it does at 1500Hz.
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Old 08-18-2004, 05:01 PM
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It is due to temperature inversion layering of the troposphere. At least this makes as much sense as anything else I've read. Known as *tropospheric enhancement*, it is distinct from tropospheric ducting. See http://www.iprimus.ca/~hepburnw/dx/tr-modes.htm
for a more detailed explanation.
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Old 08-18-2004, 05:33 PM
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Quote:
Originally posted by NightHawk
Using yesterdays values as an example and a 12 dB gain antenna the peak solar noise value at 610 MHz would only be -114 dBm. At this frequency this is below the thermal noise floor and far too small to have an impact. Additionally, the disk of the sun is only 1/2 degree making it a point source radiator when compared to any practical UHF antennas. In other words you would need to point your TV antenna directly at the sun to receive even this minuscule noise level. The levels of solar radio noise also do not change significantly with the season.
Right on and thank you. Somebody finally put that old wive's tale to rest. I guess I will stop pointing my antenna at the sun. :D

I've run out of witty sayings...
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Old 08-18-2004, 06:55 PM
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I have very little variation between night and day.... Check your connections as the sun may be causing heat expantion of your conection.
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Old 08-19-2004, 07:41 AM
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cpcat,

Great link! I think I'm almost convinced.
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Old 08-20-2004, 08:16 AM
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Quote:
Originally posted by NightHawk
Great link! I think I'm almost convinced.
Last night was calm, and I was getting a 20kw digital from 75 miles reliably. 1000kw digitals looked near-perfect. I had noticed in the past that windy nights didn't seem as good for long-distance reception, but didn't attribute it to a disruption of rising heat.

It will take a longer evaluation before I'll be certain of predicting reception.
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Old 08-20-2004, 09:15 AM
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Another very good in depth explanation with pictures is available at www.dxfm.com , and then in the upper left corner of the home page click "Signal Propagation." Girard Westerberg is a TV-FM DXer and radio engineer.

Steve
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Old 08-20-2004, 11:10 AM
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Quote:
Originally posted by inky blacks
Thanks. That makes sense. I hope the 5th generation tuners will eliminate the difference.

IB
If the signal is not getting to you during the day, there's nothing an newer receiver can do to resolve it...

Matt
Please don't PM me with technical questions that should be posted in the forum.
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Old 08-20-2004, 12:04 PM
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Quote:
Originally posted by mjones73
If the signal is not getting to you during the day, there's nothing an newer receiver can do to resolve it...
While technically true, the problem most of us have who rely on Tropospheric Scatter and Enhancement is that we get *some* signal during the day, just not *enough* for digital reception. For instance, I can watch a snowy color signal with stereo sound from analog stations that are impossible to lock onto with similar, or even superior, digital counterparts. Sometimes, the analog signal looks quite good before a digital lock occurs.

There have been rumors that the 5th-generation chipset does a better job at "recreating" data than 4th-generation chips, and if that plays out, we'll all be happier. I've heard claims of the 5th-gen chip needing 1/4 the signal strength of 4th-gen chips, but that hasn't been confirmed. It may be in reference to multipath situations, where the 5th-gen has a distinct advantage.
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Old 08-20-2004, 01:13 PM
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I might be the only exception, but where I live, I seem to have a better reception during the day. The early evening seems to be worst and it gets better late night.

Hong.

i have great faith in fools -- self confidence my friends call it. -- edgar allan poe
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Old 08-20-2004, 05:03 PM
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Do you have birds roosting on your antenna at night?:D
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Old 08-20-2004, 05:50 PM
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Do you have birds roosting on your antenna at night?
I sure do, and during the day, too. I have to hose off my driveway about once per week. I thought about putting up one of those fake owls but I don't think that really works. Can't say I'll be sorry to see 'em go south.
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Old 08-20-2004, 10:27 PM - Thread Starter
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My set is a Toshiba 51HX93 with what I think is a built in 4th generation LG ATSC tuner. Sometimes I get all channels during the day and other times just half of them. At night it is much better but I am suddenly having problems with CBS at night as well. The worst part is that if I do not get a strong signal my receiver chip loads up and the set goes black after a few seconds of trying to move around the antenna. Then I have to turn off the set and unplug it as well to clear the memory.

Do other people have this problem or is my set defective?

IB
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Old 08-21-2004, 07:53 AM
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Quote:
Originally posted by inky blacks
The worst part is that if I do not get a strong signal my receiver chip loads up and the set goes black after a few seconds of trying to move around the antenna. Then I have to turn off the set and unplug it as well to clear the memory.

Do other people have this problem or is my set defective?
It's at the very least a defect in the Toshiba's tuner. My Samsung SIRT-151 has the annoying habit of losing audio from time to time. This occurs only after a digital artifact (i.e. errors where the FEC breaks down) and corrects itself only after another artifact. Makes recording of HD programming hard on "borderline" stations, as I never know if I'll get great picture and no sound.
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Old 08-21-2004, 11:09 AM - Thread Starter
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Quote:
Originally posted by sregener
It's at the very least a defect in the Toshiba's tuner.
Does anyone know if this is something a repair man can fix by changing a chip, or is it endemic to all the Toshiba RPTVs with tuners?

IB
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Old 08-23-2004, 01:46 PM
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Guy's here in Green Bay Wis. the local stations are not broadcasting at full power all day long to save money. They boost power during prime time hours. Testing is also going on here as one day you get 90% signals and the next 80% and drop outs. I tried to tune my antenna only to totally lose my NBC station. I gave them a call only to find out they are having problems. I have Voom for locals and I am going nuts trying to pinpoint why my locals drop in and out. Signals drop from 95% to 60% and break up I am only 10 miles form the towers. Voom upgraded my antenna and still I have issues. You will have the best luck aiming the antenna during prime time hours at least here in Green Bay anyway. Signals swings are a pain with the voom reciever. I see that Zenith has an attenna that advertises HDTV and multipath corrections. Its an UHF model GEMDTV1 sold at Fleetfarm for $69.00 has anyone had success with this attenna?

HDTV is clear get the picture
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Old 08-23-2004, 07:27 PM
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Quote:
Originally posted by djs
Do you have birds roosting on your antenna at night?:D
If you do you need to teach them to sit at log-periodic spacings :D :D :D

I've run out of witty sayings...
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Old 08-24-2004, 09:15 AM
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Last night was breezy and UHF reception was atrocious. Analogs faded in and out like they do in daytime. Digitals from long-distances wouldn't lock. It wasn't multipath from trees, either - these signals are too weak for ghosting. On the analogs, you could see the picture go from good to bad and it was all "snow."

More and more, I'm buying the enhancement theory.
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Old 08-24-2004, 12:49 PM
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Quote:
Originally posted by sregener
Last night was breezy and UHF reception was atrocious. Analogs faded in and out like they do in daytime. Digitals from long-distances wouldn't lock. It wasn't multipath from trees, either - these signals are too weak for ghosting.
Wind is an additional factor independent of day or night reception. I'm not sure why you wouldn't consider it tree and leaf induced multipath. It dosen't take much movement of either the antenna (TX or RX) or a reflecting surface to corrupt the 8VSB digital signal.
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Old 08-25-2004, 12:57 PM
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Quote:
Originally posted by NightHawk
Wind is an additional factor independent of day or night reception. I'm not sure why you wouldn't consider it tree and leaf induced multipath. It dosen't take much movement of either the antenna (TX or RX) or a reflecting surface to corrupt the 8VSB digital signal.
Well, I can't speak for the transmitting antennas, but I assume they are very heavily guyed and any difference at 75+ miles would be minor. The receiving antenna just plain doesn't move, period.

I'd buy the tree and leaf multipath if I could see it on analog channels. But what I was seeing was a very distinctive fading-in fading-out pattern. It nearly matched my daytime reception for long distance situations. Unless the trees were all swaying in a regular motion, I think I can rule out tree reflections.
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