[TMC] GPR-90 RXD Tuning

[wb9tow at egr.msu.edu]

Very true John, Sensitivity was king in those days!
But, it was no fun loosing a ZL yesterday AM on 40m CW
due to front end over load by a station 5 kc away!
Yes, 10 dB of attenuation might have saved the qso!
73
Steve

> Hi Steve,
>
> Back in those days, a high premium was placed on HF receiver sensitivity,
> so designers went for low noise figure.  This marketing-based obsession
> continues today in the ham radio market, to the detriment of some
> receivers.  Over most of the HF band, and particularly below 10 Mc or so,
> atmospheric noise is generally the limiting factor, so modern commercial
> and military receivers are usually optimized for dynamic range rather than
> noise figure.  So the old receivers usually had lower noise figures than
> the modern ones.  As such, the GPR-90 has plenty of "excess" sensitivity
> on 40M, so you might want to simply try adding attenuators ahead of the
> receiver to reduce the intermod.  6 to 10 dB of attenuation might do the
> trick, but you could probably add as much as 20 dB attenuation on 40M at
> night, if you have a reasonably efficient antenna, and still have adequate
> sensitivity, but drastically drop the intermod product levels.
>
> 73,
>
> John K9WT
>
>
> ---- wb9tow at egr.msu.edu wrote:
>> Excellent information on the TMC Receivers!
>> Just a present day observation, I use a GPR-90 with
>> GSB-1 on 40m CW about every day. The combination is
>> not too bad depending on the "time of day". I live about 1 1/2
>> miles from a 5KW MW BC station. Their station is off the air
>> at night, which helps reduce the IM....
>> I run a resonant antenna system and an ATU but still
>> find the IM rejection quite poor.
>> I've often wondered if there is a way to improve this design
>> without destroying the value of the rx, but I think the best
>> step is to acquire a GPR-90RXD or GPR-92....
>> 73
>> Steve w8tow
>> >
>
>


Cheers!
Steve


Steve Marquie
B.S. Technical Management
Instructor - BAE Department / Field Op Mgr-EnviroWx
Department of Biosystems & Ag Engineering
Room 126 Farrall Hall
Michigan State University
East Lansing, MI 48824
(517) 355-8128 office
(517) 927-9322 Cell