[CW] Receiver RF Gain

[Richard Knoppow]

    I think it depends on what the purpose is. Generally the 
noise of the imput stage depends on the transconductance of the 
amplifier. However, that assumes the primary source of noise is 
the tube or transistor. Where there is considerable atmospheric 
noise it may result in less cross modulation between signal and 
noise to run the gain lower. The established method of listening 
to CW on a receiver with a diode detector is to run the RF or IF 
level into the diode low. This is based on some assumptions about 
the detector. In most older receivers, that is those without 
product detectors, the distortion of the diode detector depends 
on the ratio of the BFO to the signal level. BFO injection is 
generally kept low to prevent desensitizing the set. Not at all 
an optimum way to detect CW or SSB. A product detector does a 
much better job and may allow higher gain in the RF section. For 
a while I ran my old Super Pro with an adjustable cathode 
resistor in the first RF. I gave up on this because I found it 
did not help the 6K7 tube, which has very good dynamic range. I 
ran some experimental low noise tubes in its place and some were 
improved by having a separate gain control. This was long ago.
    I am not sure I am making any sense.
    OTOH, its not unusual these days to find people re-inventing 
the wheel.

On 10/29/2018 5:53 PM, Ron.K3PID wrote:
> I noticed an article in QST explaining that it is better to run a 
> lower RF gain on your receiver for weak signals and in noisy 
> conditions. WOW! I am thinking that those of us who are seasoned 
> enough to be Elmers must have really fallen down on the job.  
> Just the idea that someone needed to write that article is an 
> indication that we failed to pass on the basic operating skills. 
> My Elmer taught me ( and a lot of others) to run with a 
> relatively high audio gain and then back off the RF gain to drop 
> the noise. It works welll and I’ve been doing it that way for 57 
> years. It works on my computerized Yaesu and just as well on my 
> R-390 or my HQ-180.  I just assumed it was common practice.
> 
> 73
> Ron K3PID
> 
> ______________________________________________________________
> CW mailing list
> Home: http://mailman.qth.net/mailman/listinfo/cw
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:CW at mailman.qth.net
> CW List ARCHIVES: http://mailman.qth.net/pipermail/cw/
> Unsubcribe send email to
> cw-unsubscribe at mailman.qth.net
> Subscribe send email to cw-subscribe at mailman.qth.net
> Support this email list: http://www.qsl.net/donate.html
> 
> =30=
> 

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