Curious buzzing sound on AM car radio

Oct 17, 2005 3 Replies
S

Hi All,



I have a Motorola push-button AM car radio which is plagued with a buzzing sound on its audio. It is present at the low end of the medium wave band and it is right across the long wave band too. At first, I thought it was noise coming through the DC power adaptor I was using, but it was still there when I ran it in my car from a DC outlet. The buzz is only present with an antenna is connected and it almost disappears when you place a hand on the top of the radio chassis. I can't pick up this interference on any other radio and my ground connections to the chassis seem fine. I'm at a loss as to where to start fixing this! Any suggestions will be gratefully received.



Regards, Gary



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P

Your antenna lead may have a break in it or something loose at the antenna end. Check the routing of the cable under the dash.

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D

In the AM only days, it used to be the practice to use a thick braided earth strap from the radio chassis to a nearby body ground, even if it had a ground power wire. There was usually a captive 1/4" bolt on the back for this purpose. Think the theory was that RF needs a lower impedance ground than the power lead which may well be grounded someway off at a central point, and pick up interference.

*Why is the man who invests all your money called a broker? Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound.
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M

is it really old i.e. does it have a vibrator type power supply? does it have tubes? or is it all solid state? how about if you drive your car to a field away from power lines and houses?

Mark

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