[TMC] GPR-90 RXD Tuning

[Richard Knoppow]

     The GPR-90RXD has a tuned first RF stage unlike the 
original GPR-90 which has a broad-band input. I don't have 
either kind of receiver so must ask of someone who does.  It 
appears that the first IF of the RXD is not tracked with the 
LO as in most receivers but must be manually peaked with the 
"antenna tuning" knob. Is this the case?  Another puzzle: in 
the original GPR-90 the antenna tuner is actually in the 
grid of the second RF so it can't peak the antenna tuning 
except for the broadcast band where the first RF is not use. 
In the RXD version the antenna tuning cap is in the grid of 
the first IF in the conventional way, but again, there is no 
additonal section on the main tuning cap so it appears the 
antenna peaker is the sole tuning for the first RF.  Of 
course a lot of receivers and transceivers these days have 
manually tuned pre-selectors.  I am not sure when this 
started with modern receivers but the Collins S line must 
have been about the earliest.
     Another question:  The GPR-90 is sometimes criticized 
for having poor overload rejection. It would appear that the 
addition of another tuned circuit in the RF was to remedy 
this.  Is this the case.



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