[TMC] TMC GPR-90

[Richard Knoppow]

----- Original Message ----- 
From: "Lou" <beethoven1 at sbcglobal.net>
To: <tmc at mailman.qth.net>
Sent: Sunday, June 30, 2013 7:33 AM
Subject: [TMC] TMC GPR-90


> What are the electrical and physical differences between 
> the GPR-90 and the GPR-90 RXD and which TMC SSB converter 
> mates with these receivers?

    The RXD has a different RF stage. The grounded grid 
input is replaced with a conventional pentode. The reason 
was evidently to improve the cross modulation and overload 
characteristics, which leave something to be desired in the 
original.  The noise level is about the same.  The RXD also 
has a crystal oscillator with selectible crystals for fixed 
frequency operation similar to the Hammarlund SP-600-JX. 
The front panel is higher than the GPR-90 to clear this 
added device. There is a door above the S-meter for the 
crystals. The RXD also has connections for extrenal high 
stability oscillators for all of the internal oscillators 
again similar to the Hammarlund SP-600-JX17.  This is to 
make it useful for certain types of diversity systems. The 
receiver also has an external connection for the diode load 
and AVC, again for diversity use.
    According the handbook the any sideband adaptor which 
works with the GPR-90 will also work with this receiver.
    There is also a GPR-91RXD which has a wide-band IF to 
adapt it for multiplex telegraph use.
    Handbooks for both types are available from 
http://jptronics.org/radios/  as well as a great deal of 
other TMC data.
    I think the GRR-90 is a rather underrated receiver. The 
RXD front end changes probably fix some of the complaints. 
Whatever else its a very sexy looking receiver:-)


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com