#5957 w/ DSP, NB, SSB seems to have developed an RF noise problem.
With the radio setup this way:
> antenna connected to dummy load, DSP off, NB off, AGC off, CW mode,
AUD fully advanced
I get the following symptoms:
> as RF gain is advanced a "frying noise" comes up, reaching about S5
at max RF.
> switching preamp/attenuator in and out doesn't change the problem
"noise." I can hear real RF noise from the dummy load and preamp
increase/decrease on top of the problem "noise."
> changing the XTAL filter setting does change the "noise."
> as the RF control is reduced from max to min, at about 2/3 max a soft
"pop" is heard, the the S-meter reading goes all the way to max [as if
the RF gain were fulling off] and then trails back towards S-0 as it was
before the "pop." Afterwards, the S-meter reading continues to max as
normal. It's as if the AGC were on, but it isn't.
> switching AGC in/out doesn't alter the "noise."
> switching DSP in alters the "noise" as the DSP circuit tries to
handle it. As compared to the no-DSP condition, the "noise" with DSP
comes up as brief static "spikes" that eventually blend into sound of
the "noise" w/o DSP.
> switching NB in/out doesn't alter the "noise."
In view of the above, I'm thinking that this noise is coming from Rcv
Mixer [TUF-1] - Post-Mixer Amp [Q22] circuit area. Nothing before that
seems to effect it, and the XTAL filter definitely reduces it. Any quick
insights or trouble shooting steps that can help me reduce/eliminate
this "noise" would be appreciated.
Thanks much.
...robert
Robert G. Strickland, PhD, ABPH - KE2WY
[hidden email]
Syracuse, New York, USA
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