On Mon, 2007-07-30 at 18:22 -0400, Gary E Norman wrote:
> No, it shouldn't be normal.
> I had a PM-3A years ago that would oscillate like this on receive when the
> dry cell batteries I was using got low. Don't know if it was due to the
> lower voltage or the higher internal resistance of the battery.
> Cured it by switching to a fresh battery. Before getting a new battery, I
> was able to make the oscillation stop by putting an electrolytic capacitor
> across +12V and Gnd.
>
> Gary, W1PG
>
Insufficient battery bypassing has been a classic transistor radio
problem. The impedance of a new battery is so low there's no feed back
but old batteries can lead to audio oscillations. A good electrolytic
(or tantalum) say 50 or 100 Mfd has nearly always been the cure. Just in
some days, it cost more than the battery so makers often left it out.
73, Jerry, K0CQ
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