Strange reception experience

[SeaMist]

Hi,
My radio in my 2011 defender was working ok on AM and FM. After I had a snorkel installed the AM reception on distant stations was much worse. I have worked out that I now have alternator noise. It's on AM only and while present well in the background on a close station it is quite unobtrusive. On a distant station e.g 3LO from where I live it has made reception unusable, when before it was slightly hissy but usable. CD playback is unaffected as is FM. Any ideas?

[superquag]

Did the bonnet originally have an earth strap, - body to bonnet? - Has it been disturbed or moved?

[rovers4]

On my Def, I had to remove the antenna to install the snorkel, and then put it back again, afterward.

Is yours the same?

In either case, the antenna mount is a vital part of the antenna electrical circuit. There must be a perfect connection between the braid or shield of the cable, via the mounting hardware to the vehicle body.

If any disturbance occurs, even if just a bump while the mount isn't absolutely secure, the connection can be disturbed.

Oxidation of the underside of the guard occurs and the teeth on the mount can't touch adequately on the metal.

A wire brushing of the inside of the guard where the antenna fits is required and then a trial run to see if when the mount is tightened that the noise disappears significantly, if not totally.

The noise comes from the vehicle alternator and is in the same form as the A.M. stations, hence you hear it.

F.M. is a different form of signal and noises like the above get eliminated.


Rovers4.

[superquag]

X2 ..... Been there-Done that !

[Rurover]

Rovers4 is right on the money.
The wire part of the antenna is only the top half of the receiving element. The bottom part is the so called "ground plane", which uses the vehicle's bodywork as part of the antenna.

It's important to get a good electrical connection between the antenna base and the bodywork (a bit like an earth connection in an electrical circuit) to get that ground plane working properly.

I inserted a small stainless steel screw through the antenna base into the fender top to make sure I had a good connection.

Alan

[SeaMist]

Thanks guys, I'll try that! :)