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Heat but not air conditioner?

V

vchimpanzee

In my 1997 Mercury with a rear window antenna (which I have found out is also a defroster) I can have the heat going full blast and never have AM problems. But in the summer I have to run the AC late in the day and it messes up my signal terribly.
 
Antenna is in the glass which is about the temperature of the outside. Put your hand on the glass to check. High temperature expands the glass enough that the loose joint (where the antenna is connected to the antenna lead) or the slight break in the wire in the glass opens. I believe that if you look carefully the antenna is actually a separate run from the defroster.
 
K6JHU said:
Antenna is in the glass which is about the temperature of the outside. Put your hand on the glass to check. High temperature expands the glass enough that the loose joint (where the antenna is connected to the antenna lead) or the slight break in the wire in the glass opens. I believe that if you look carefully the antenna is actually a separate run from the defroster.
Click to expand...
Okay, well, I didn't know that. If I hadn't read that there are antennas in rear windows, I would have thought, once I discovered I had one, that the wires were the rear defroster.

Anyway, why does the heat not affect the signal but the air condtioner does?
 
Two things. First, does this happen as soon as you turn on the AC. Then it could be the AC developing RFI.

Second, a thermostat (like the one you probably have on your wall) has two dis-similar metals with different coefficients of expansion. A change in temperature causes them to bend one way or the other making or breaking the contact. So it you have a loose solder joint cold vs hot (AC on) or hot vs cold (winter - AC off) makes a difference which way the bend goes.

Typically the windshield antenna is used for FM as well as AM. So look for a dipole in amongst the defroster runs.
 
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