Interference on Radio when Rear Demist On

[MartinM]

HI

About 4 months ago I had to have the rear windscreen replaced on my 2000 P38.

Now it's getting cold I find the radio reception is seriously downgraded when demisting/frosting the rear screen. Also the demist is missing three of the lines.

Clearly I can go back to the guy who did the windscreen ... but has anyone got any idea whether masking tape round the connectors might cure the problem (apart from the pain of having to remove the surround that is) or is this a "just live with it " P38 quirk I never noticed before.

By the way the last windscreen was not the original ... just don't recall having the radio problem last winter.

Any thoughts appreciated!

Martin

[ramon alban]

Hello Martin,

If your rear windscreen is also used as the radio aerial then there is a loose signal or shielding connection to the local amplifier thereabouts, or one of the local earths is corroded.

If the radio aerial is not connected via the rear screen then there is some interferance being picked up from elsewhere in the car that is not being suppressed.

Perhaps there is a local RF suppression condenser disconnected. Check the integity of all local wiring.

[MartinM]

Thanks for this ... it confirms I need to pull the facia off and investigate

I suspect from what you say that the rear windscreen demist is acting as the aerial (I have a 2000 P38 Vogue) and that when the screen was replaced the spade connectors were incorrectly reconnected.

Its probably going to be the weekend after next before I get time to do this ... but I'll confirm how we solve this in due course!

Martin

Hello Martin,

If your rear windscreen is also used as the radio aerial then there is a loose signal or shielding connection to the local amplifier thereabouts, or one of the local earths is corroded.

If the radio aerial is not connected via the rear screen then there is some interferance being picked up from elsewhere in the car that is not being suppressed.

Perhaps there is a local RF suppression condenser disconnected. Check the integity of all local wiring.

[willfromsussex]

If there are tiny breaks in the lines that are not working, they could be causing the interference where they are trying to conduct.

[David Sparkes]

Errr No.

Go back two paces.

As the 38A left the factory they never used the Heated Rear Window as a radio aerial.

Look at the rearmost windows down the side, both of them. In a 2000 they both have elements in them, these are the radio aerials, one side for VHF, the other side for the other stuff. Which is which I can't recall, especially because LR reversed the arrangement part way through the life of the car. There is probably a Technical Bulletin or two about it.

The RH rear side window also has a single line aerial for the Alarm receiver.

A 'gotcha' is that if someone sticks metallised reflective film over the side windows, this does a good job of keeping the radio signals at bay, as well as the suns heat. A poor radio signal means that local noise is more noticeable.

I quite like the idea that a bad connection within the HRW will arc, and use the rest of the elements of an aerial, but I'm no radio man.

Whether the interferance is due to the technician who fitted the HRW disturbing something else is a matter of conjecture. I've never had to look if the wiring for the radio system and HRW co-exist anywhere.

Each aerial has an amplifier, and they are under the shelves just inside the side windows where the aerials are. I'd expect the HRW wiring to be on the roof, so I wouldn't expect the radio wiring to be disturbed.

Good Luck