[MissMontana (OP)]

I get a brilliant TV signal when it's sunny and warm out but when it's cold the reception really deteriorates?  

Why is that?  

(and yes I have v poor quality TV top aerial  [:I])

[tweener]

Temperature and precipitation don't greatly affect the propagation of TV signals.  There is more effect on UHF than on VHF, but it's usually not a problem for either.  However, if you are receiving a station that is a long distance away (> 25 miles) weather may have a significant effect.  

The change is most likely due to something around your house, like the siding or a shed or maybe a hill or cliff reflecting the signals differently when they are cold and wet.  This could create what is called multi-path, where the signal from the station is canceled by the signal that is reflected by some other surface.  

Have you tried moving your antenna to a different location or orientation?  Depending on the type, rotation may help, or you may need to move it a couple of meters.  No guarantees.

The other possibility is that some of your antenna wiring or even your TV may be reacting with the change in temperature and humidity.  Some components can be very sensitive to that if they are not assembled properly (meaning at the factory).  Check all your antenna connectors and make sure they are tight and not corroded.  See if the picture jumps or cuts out when you jiggle each one.  Don't mess with the power connections - that can be dangerous, and it won't be what's affecting your reception.

Otherwise, see if you can get another antenna and try it.  If it does the same thing, it's either the propagation to your house, or your TV.  If it fixes it, be happy!

Be happy anyway.

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John - The Eternal Pessimist.

[neilep]

Johns right (of course ![]).....but I think you may have answered your own question Toni when you say you have a very poor quality TV aerial.....ditch it or try an aerial booster, you can pick one up for about £20 (though these can also just amplify a bad signal).......or even better...if budget allows, get a proper roof mounted aerial and all your reception problems should go away..........cos even if your aerial is not broken, if it's a crap aerial...it will perform crappily happily []...though if the TV is ancient then I suppose the change in weather could have an effect on the TV's components ability to deal with the signal. In 9 out of 10 cases though, I have found that it's poor reception and therefore an aerial problem.
...hang on though....I've just thought....you say the picture is bad during bad weather eh ?...do you notice it happening all the time or intermittently ?...........I guess I'm trying to establish if you are experiencing mains interference....this happens a lot when your boiler kicks in to heat water or heat the house etc.....in bad weather I assume you put the heating on eh ?......

I suppose that is a long shot unless you say so but would be inclined to bear it in mind.

'Men are the same as women...just inside out !'

[chris]

John - why does the quality of radio reception (particularly on MW (AM)) change with weather conditions ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

[tweener]

AM radio uses a much lower frequency (700 to 1100 kHz) than FM ( 88 to 108 MHz) and TV (54 to 216 MHz) and also uses a different modulation technique (amplitude modulation rather than frequency modulation).  These factors make is much more susceptible to interference from natural disturbances, primarily lightning.  Sunspots also affect am and shortwave broadcasts by disturbing the ionosphere.  This causes lots of noise (generated in the ionosphere) and propagation disturbances from the strange reflections and absorptions.

It has advantages that include being able to reflect off the ionosphere and thus travel much farther over the horizon.  

This doesn't really answer your question, but I don't know how to explain it tonight.

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John - The Eternal Pessimist.

[neilep]

John, perhaps you can help me with this one....why when it rains....and I mean when it really pours, do I lose all signal to my satelite dish ?....surely it's just not the fact that the signal can't cut through the rain is it ?...or is it ?....is it a diffraction thing happening here ?

'Men are the same as women...just inside out !'

[tweener]

Yes Neil, it's exactly because the signal can't cut through all the rain.  The downlink operates at 11 GHz.  The dish is fairly small and the satellite is not broadcasting a whole lot of power (relative to ground based transmitters with the whole grid behind them), which means that it is susceptible to outages from rain and even heavy clouds.  If you only have this problem when it really rains hard, count yourself lucky - I've seen some that go down when a cloud passes. They probably weren't set up correctly in the first place.

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John - The Eternal Pessimist.