RE: 1220 loud PL tone
Hi, Andy
I haven't fully resolved the problem. Someone had suggested that there
was a fix in the form of extra bypass capacitor(s) somewhere. I
contacted Ten Tec and they did not know of such a fix. The PL tone
is louder on high power than on low, which leads me to believe that
it is related to current dreain in the final or stray RF. I was able
to reduce it a bit by adding extra grounds between the main circuit
board and the final amplifier board. I also added a solder lug to the
back shield at the Q19 mounting hole and soldered it to the final amp
PC board ground. You should have the big 4700 uf cap at C86, this will
help too. All this helps but did not eliminate the problem
completely.
Even making a "cover" over the gap between the back shield and the final
board has an effect, though I didn't leave this in. There just seems to
be a lot of stray current, DC and RF floating around the chassis
when in the high power mode. How this affects the amplitude of the PL
tone, I'm still not sure. The one thing that I didn't try is shielding
the display board as some builders of the 1254 receiver have done.
The display drive signals put out a buzz, too which may be at the
same frequency as the PL tone. There is certainly a sneak path
somewhere, but I just haven't isolated it!
Keep trying, and let me know what you find.
73, Bob WB2VUF
KA2UQW@aol.com wrote:
>
> Hi Bob,
>
> Name here is Andy, KA2UQW. Saw your message about the 1220 on the
> reflector at contesting.com. I just finished building the 1220, ran into
> same
> trouble as you. Have talked to ten-tec about it too. Wonder, have you found
> a
> fix? I've reduced it a bit but not much. Rig still apart on my bench.
>
> Andy
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