[Elecraft] K2 RX audio output - again

[Jack Smith]

Geoff:

At least my Racal RA6790/GM labels the front panel control "IF Gain."

As a side note, I find the RA6790/GM to have the best ergometrics of any 
receiver I've owned, although not the best AGC action.

Jack K8ZOA

Geoffrey Mackenzie-Kennedy wrote:
> Ron AC7AC wrote:
>
> Going waaaaaay back to when I was first building receivers, that RF gain
> actually controlled the gain of the RF amplifier (preamplifier in modern
> jargon) at the input to the receiver as well as the gain of the 
> intermediate
> frequency (i.f.) amplifiers ahead of the detector. Nowadays in
> state-of-the-art receivers like the K2 we control the gain at the 
> input by
> switching the rf amplifier (preamp)into our out of the signal path or 
> we can
> add an attenuator (ATT) at the input to reduce the signal gain 
> reaching the
> receiver. The RF gain now controls only the gain of the i.f. 
> amplifier, but
> the term "RF Gain" is still used to describe that control (after all, the
> intermediate frequency is still an RF signal).
>
> -------------------------------------------------------------------------
>
> Digressing from the subject of audio output for a moment, having the "RF
> Gain" control the gain of the IF amplifier only can lead to some
> undesireable effects unless the IF amplifier design is done very 
> carefully
> using suitable devices. The problem is that the linearity of some of the
> more popular low cost amplifier chips actually gets worse as their gain
> starts to be reduced, although some types of these chips will recover 
> as the
> gain is further reduced. Assuming a situation where the Preamp is 
> "Off" and
> the Attenuator is "In" leaving two or more signals are in the 
> passband, some
> strong and the one that you want is weak, any negative effect on 
> linearity
> caused by changing gain is of course unwelcome. The overall effect is
> determined by the receiver's Gain Distribution and the characteristics of
> the stages both before and after the controlled IF amplifier.
>
> Many modern (not ham) HF receivers designed to handle *very* strong 
> signals
> while allowing copy of an adjacent signal close to the noise still do use
> "RF Gain" to control some type of front end variable attenuator, and a 
> strong
> RF amp with fixed but very low gain embedded in reasonably high loaded Q
> variable frequency tuned circuits. But these receivers consume a lot of
> power.
>
> 73,
> Geoff
> GM4ESD
>
>
>
>
>
>
>
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