[TMC] GPR90-RXD Receiver & SSB

[rrkrr]

Umm, that should be "it had almost NO detected signal amplitude......"

Bob
K4ERR

rrkrr wrote:
> 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
>>
>>
>>
>>     
>
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