[R-390] Spectrum Analyzer

David Wise David_Wise at Phoenix.com
Mon Mar 14 13:41:13 EDT 2011


Nope.  All of the R-390 family's selectivity comes from
LC tuned circuits, mechanical filters, and crystal filters,
and their Q is not affected by AGC.  The tubes around them
might exhibit a variation in input or output admittance,
which affects overall circuit Q and tuning, but it's too
small to notice.

Dave Wise

>-----Original Message-----
>From: r-390-bounces at mailman.qth.net 
>[mailto:r-390-bounces at mailman.qth.net] On Behalf Of Barry
>Sent: Monday, March 14, 2011 9:44 AM
>To: r-390 at mailman.qth.net
>Subject: Re: [R-390] Spectrum Analyzer
>
>> If you have good points to inject and monitor the IF frequency, the 
>> SA display will give you a beautiful picture of the IF 
>> passband.  (Don't forget to turn the radio's AGC off.)
>> 
>> Best regards,
>> 
>> Don
>
>Along the lines of "please don't laugh at me but...", how does 
>the AGC affect the bandpass, particularly its shape.  I 
>thought all the AGC did is change the gain at the various 
>stages so the shape would be the same just translated "up" or 
>"down" depending on the signal.  Is that a horrible way to 
>understand AGC (or its effects on the passband)?
>
>Thanks,
>Barry - N4BUQ (who only wishes he had a nice SA like the one 
>Ben's looking at getting)
>
>________


More information about the R-390 mailing list