[TMC] GPR-90RXD stuff

[Richard Knoppow]

    That sounds like what I remember, I may have seen it in the 
archive but don't remember. In any case, I have not heard that 
this was a common problem. To me it sounds like a power supply 
problem rather than a design flaw in the BFO. The BFO arrangement 
in the GPR-90 is a conventional one which should work pretty 
well. The RXD BFO appears to me to be designed so that the BFO 
does not show up in the IF output.
    Most conventional receivers keep the BFO injection low for a 
couple of reasons: one is to prevent coupling, that is, pulling, 
of the BFO and another is to minimize the effect on the AVC. Some 
receivers had a control for injection, actually the SP-600 does, 
supposedly there is some setting that minimizes noise on CW. If a 
product detector can be used it eliminates all this.
    A note: The GPR-90 uses feedback in the audio amplifier. This 
should result in a significant reduction of distortion. The only 
other receiver I know of that does this is the RCA AR-88. Both 
use single ended amplifiers. Single pentode amps have poor 
performance. For instance, Collins specs the audio in the 51J 
series at 1.5 Watts at 15% THD.  That is fifteen percent. 
Checking the specs in the tube handbooks will confirm this sort 
of level although its worse than many similar receivers.
     Since I am thinking about this I have always wondered at 
TMC's advertising approach to hams. I have lost a word I need 
here but the constant complaint that the 90 was not a frequency 
meter, etc was, I think a mistake. Well, it isn't a frequency 
meter but does have excellent calibration accuracy and is very 
stable. I think TMC was telling people it wasn't really a very 
good receiver until people believed it.

On 8/12/2021 6:39 AM, Duncan Brown wrote:
>
> On 12-Aug-21 00:06, Richard Knoppow wrote:
>>
>>    I looked at e-ham net reviews again, they are interesting 
>> because those who hate the receiver do so for reasons that 
>> indicate to me their sets were broken. I thought I saw a 
>> review that said the BFO pulled but couldn't find it.
>
> I never noticed BFO pulling on the GPR-90, but I didn't use the 
> BFO a lot.
>
> The "pulling" comment came from Roy Morgan, K1LKY, here on the 
> TMC list in 2016:
>
> "- You may have noticed that a strong signal will pull the BFO 
> - that is tuning through a strong signal, near zero beat, the 
> tone gets “stuck" at zero beat on either side of zero until you 
> tune away a little bit. This is caused by some sort of feedback 
> or leakage path front the IF section into the BFO oscillator.  
> I don’t know how to fix this. "
>
>
> -have fun,
>
> Duncan
> K2OEQ
> ______________________________________________________________
> TMC mailing list
> Home: http://mailman.qth.net/mailman/listinfo/tmc
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:TMC at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL