Digital television and the sun

Does it get hot where you live? Are you using an old antenna/pre-amp, and/or old/cheap cable for your downlead?

I get the same effect, sometime I must get up on the roof and put up a yagi with better, ie reduced rearward lobe/ higher forward lobe responses.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I can not say for sure but there is station that they must change direction of antennas from night to day or wise versa because of signal propagation which interfere with other networks FCC regulation sorry KA2AYS

This is plausible (in principle), but at the frequencies at which digital TV operates, there isn't much difference between day and night propagation.

That only applies to AM radio stations.

All TV stations (analog and digital) are licensed for the same technical facilities 24/7.

I wonder if the OP's problems stem from interference from some device that's only operated during the day? (say, neon lights at a nearby store? Or a factory with large motors?)

Does *analog* reception change from day to night - do you get snowy daytime reception, or funny patterns, etc., etc.?

I have only been receiving digital tv for a few days. It has been very hot and humid here, could that be causing the problem? As for analog reception, it works well day and night. I use the same Channel Master roof top UHF/VHF antenna and coax cable for analog and digital. FWIW the stations I am trying to receive are in Indianapolis and I am in Bloomington IN.

Water infiltration into a coax cable can cause signal loss. I suppose it's possible you've gotten rainwater into the coax (due to inadequate sealing of the F connector on the end) and that high temperatures change how the moisture affects signal attenuation.

Hmmm. That would see to rule out simple temperature change or signal strength, then.

ATSC digital signals are relatively sensitive to multipath (the same phenomenon which generates "ghost" images on analog TV). Possibly there's more multipath being generated in your area during the day, as a result of (for example):

- More airplanes flying through the "field of view" between you and the transmitter

- More wind, causing tree branches and leaves to move around nearby

- More surface vehicles (trucks, ships) travelling nearby

The idea that there might also be a locally-generated source of interference which is more active during the day is also a good one. Are you seeing "sparkles" on the weaker analog channels (from impulse noise), or "herringbone", or something like that?

Ducting affects signals in the TV spectrum much more at night than at daytime.

As Dave suggests, take a careful look at your analog reception. Especially the weaker stations - channel 29? channel 49? The appearance of any interference on analog reception is a clue to the nature of what might be affecting the digital.

Are *all* digital stations affected or only some of them? (channel 8's digital is on a very different frequency from the other Indianapolis stations)

Do you have a preamp on your antenna? Outside? Do neighbors have preamps? We once had an interference problem in a small town when someone's preamp malfunctioned & began acting as a small transmitter. It was thermally-related - would only malfunction when it was cold. (i.e., at night...)

This too applies only to AM radio. No TV or FM station in the U.S. or Canada is required to reduce power at night.

(and I'd be 99% sure that applies to the rest of the world as well)

Oh, $DEITY, those preamps and distribution amps can be utterly evil.

As you note they'd prone to oscillation, which can generate all sorts of interference. A couple of boat-born "active TV antenna" amplifiers managed to knock out GPS reception in the Moss Landing area in California for quite some time, which was not a good thing for ship and boat captains who depend on GPS to get them safely through the fog!

I've also had problems with amps of this sort when there's a radio transmitter nearby... the strong signal from a transmitter will saturate the amplifer, causing interference and signal loss on all of the channels going through the amp.

That's a VERY good point, and it brings up another question for Chuck B: when the digital reception is messed up, does it *stay* messed up continuously, or does it work OK for awhile and then go bad & then come back again?

Most radio transmitters either operate continuously day and night, or operate intermittently. (I talk for a few seconds, then let go of the mike & let the other guy talk) If the interference is intermittent, maybe it's coming from a transmitter at a business that only uses it during the day? (construction firm, factory, etc.)

If there is an amplifier, it might be worthwhile taking it out of the circuit for awhile. You might lose some channels altogether but if it allows the stations that do come in to continue to come in during the day then you have a pretty good lead.

ybe

If you could borrow another tv set, it would be worthwhile to see if it too fails. There are differences in propogation characteristics from day to night that do affect the UHF frequencies. With a good strong signal, they will not be apparent. But with digita signals and receivers, it is an all or nothing situation, sorry.

Bob Hofmannl

On Sat, 19 Jul 2008 13:06:21 -0400, Chuck B. put finger to keyboard and composed:

Can you see a big difference in the numbers for day/night signal quality in your TV's or STB's menu? Are you splitting your signal between two or more TVs? Are your stations on different bands, eg analogue on VHF and digital on UHF ???

- Franc Zabkar

Most Indianapolis digitals are UHF, the exception is CBS which is on digital VHF channel 9.

Four of the six most popular Indianapolis analog stations are VHF channels