[TMC] GPR90-RXD Receiver & SSB
rrkrr
rrkrr at comcast.net
Sun Dec 14 15:35:18 EST 2008
Bob,
When I got the GPR-90RXD, it had almost detected signal amplitude. The
original owner had not investigated this problem. After tracing signals
with an oscilloscope, I found that the IF output signal was greatly
attenuated in the CW/SSB slide switch that routes the IF signal out to
the GSB-1. There's another "Radio/Phono" slide switch that takes
external audio input for the GPR-90 audio amp - this is also used to
amplify detected audio from the GSB-1.
As I recall, the CW/SSB slide switch is placed in the circuit ahead of
the AM/CW detector, so if the signal doesn't get through the switch,
there is no signal indication and no audio output. The contacts on my
switch were heavily corroded, but the switch worked well after cleaning.
My GSB-1 also needed recapping, as the VFO in it was very unstable. I
got this working too, but was still never really happy with using this
setup for SSB, chiefly because there is no AGC feedback to the receiver
from the GSB-1, so you still have to ride the RF gain control a bit. It
is much better than using the internal detector for CW/SSB.
As for the definition you're looking for: My receiver was completly
unusable before I cleaned the oxidation off the slide switch contacts.
After the contacts were cleaned, performance was probably as good as the
original receiver design. I don't know, but I imagine there might be
some intermediate state where a bit of increased switch contract
resistance resulted in slightly reduced performance. All I'm saying is
it might be worth checking with an ohm meter.
Bob
K4ERR
Robert Nickels wrote:
> rrkrr wrote:
>> Another item to look at is the slide switches on the rear that are used
>> to select the external signal connections to the GSB-1. On the GPR-90 I
>> had, the internal contacts on these switches were corroded. I got a
>> considerable improvement in performance after prying these open and
>> cleaning the contacts.
>>
> Bob, could you define what you mean by improved performance a bit?
> My only complaint in using the GSB-1 with my GPR-90 is that the audio
> level is quite a bit lower when going through the adapter than
> straight out of the GPR-90. I just assumed this was something in the
> audio chain of the GSB-1, which I've never evened opened the cabinet
> on, but maybe I should look at those switches instead. Did you
> notice an improvement in sensitivity, audio, or what? (I'm using the
> common connection to the TMC speaker as per the manual, by the way).
>
> This combination is really great in my opinion, albeit hard to come by.
> 73, Bob W9RAN
>
>
>
More information about the TMC
mailing list