Am Aerial problem

Submitted: Monday, Mar 12, 2007 at 15:07

ThreadID: 43163 Views:1700 Replies:3 FollowUps:1

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Rod E B

When I drive under a bridge or a metal gantry the radio on am only (not on fm) lets out a swark or a high pitched beep

I do not get real good reception at the best of time when outside the CBD

do I need a new aerial ,
a better earth
or a new radio

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Reply By: Mike Harding - Monday, Mar 12, 2007 at 15:38

Monday, Mar 12, 2007 at 15:38

>do I need a new aerial
>a better earth

Probably one, or both, of the above.

Mike Harding

AnswerID: 226953

Reply By: Member - Alastair D (NSW) - Monday, Mar 12, 2007 at 15:55

Monday, Mar 12, 2007 at 15:55

Rod,
The effect you describe is common with am reception and there is little you can do about it. It is due to the nature of the distortion of the signal strength around these structures which does not happen with fm. Need to get technical to explain why and won't bother.

Most modern am/fm car radios have a poor am capability. There was a thread some time ago on this where some members named a few brands they thought better. Use the search if you want. Actually it was probably only some of the older units of ~20+ years ago which had quite good am reception.

alastair

AnswerID: 226955

Follow Up By: joc45 - Monday, Mar 12, 2007 at 17:48

Monday, Mar 12, 2007 at 17:48

Inclined to agree with Alastair.
Most of the AM radios these days are there coz they have to provide something that works on AM. In most of civilized Europe, Asia or US, they mostly listen to FM, and you're not too far from an AM station anyway, so sensitivity is not a big requirement. Also, they're not too interested in keeping local interference out, again coz usually the AM signal is high enough to override any interference, so why bother designing something flash.
When you go under the bridge or whatever, the received signal drops right down so that it's not far above the local interference level, and you get the cr@p.
In a decent installation, the receiver is more sensitive, the antenna is well-matched to the radio for best signal pickup, and efforts are made to eliminate local interference either at its source, or in proper filtering and earthing of the system.
Why else does Toyota not bother about the RF cr@p spewed out from its 4.2 Turbo diesel? ;-)
Gerry

FollowupID: 487798

Reply By: Max - Sydney - Monday, Mar 12, 2007 at 18:40

Monday, Mar 12, 2007 at 18:40

Rod

You should live in Sydney with its older tunnels that don't pipe radio signals into them like the new ones do. It'll screech from the moment you get into the domain tunnel or the one under the airport till you get out.

Its always been like that and the same with Australian made cars - AM signals just don't duck under the portal and come inside.

At some intersections too - with radio controlled traffic lights and power lines overhead you get the squaaaark too.

I disagree that Toyota has a poor quality AM reception - certainly the 10 year old 80 series will get FM for up to 30 km from a bush town, but up to 150 km on AM.

The downside is we have to put up with the tunnel /bridge / gantry loss of signal - that's the story of AM signals.

Don't waste money on new antennae or radios or anything - just hack it!

Max

AnswerID: 226993