[Boatanchors] General question...frequency shift with RF gain

[Al Klase]

John,

I think Dale's assessment of the cause is correct. I just fired up my 
NC-100, and listened to some 20-metter CW (AVC off). I'd call any 
frequency change with RF gain setting negligible. There is perhaps just 
a hint of a shift in the first couple of degrees of gain reduction from 
maximum. That would be where the change in current draw of the 
gain-controlled stages would have the greatest effect on supply voltage.

If I did have a significant problem, I'd swap out the local-oscillator 
and BFO tubes before I did any serious digging around. There is also the 
possibility, that with cheaper receivers, they all do this.

Thanks for bringing this up, I hadn't had the old painted lady on the 
air for quite some time.

Al

Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

On 1/15/2016 11:15 AM, Dale Parfitt wrote:
> While I have never experienced this I would wonder if changing the RF Gain changes the current drawn by the front end stages that are controlled by the AGC line. This may change the loading on the  receiver's HV supply.
> That little change may then cause a change in the RX VFO voltage, thus causing a small frequency shift. Easy enough to check with a good voltmeter.
>
> Dale W4OP
>
> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of John Saxon via Boatanchors
> Sent: Friday, January 15, 2016 10:55 AM
> To: Boatanchors Mail List
> Subject: [Boatanchors] General question...frequency shift with RF gain
>
> On the Hallicrafters list a fellow reported a receiver that shifted frequency with RF gain adjustments.  Several folks responded that they had had a similar experience. I am having the same issue with a National NC-101X.  Just out of curiosity:  Is a frequency shift with RF gain adjustment common?  uncommon?  in-between?
> Just wondering...
> --JohnK5ENQ
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