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Curious buzzing sound on AM car radio

S

Spooky

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
 
P

Porky

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.
 
D

Dave Plowman (News)

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.

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.
 
M

Mark

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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