[Elecraft] Why no IF shift ?

[N2EY at aol.com]

In a message dated 8/7/06 7:03:01 PM Eastern Daylight Time, 
hubby2k at hotmail.com writes:


> I imagine one
> could shift the bfo frequency along with the tuning to give the effect of IF
> shift, if one had a place to put another knob. 
> 

The venerable Collins 75A-4 of a half-century ago, possibly the first 
receiver to have the feature, implemented the feature that way - mechanically! When 
you turned the knob, the PTO assembly rotated one way, changing the LO 
frequency and the BFO pitch control rotated to change the BFO frequency the same 
amount, but in the opposite direction. The method's success depended on the 
absolute linearity of the Collins PTO and BFO tuning. Quite a challenge even though 
the PTO and BFO tuned only single ranges for all bands.

btw, Collins called it "bandpass tuning" IIRC.

The same concept could be employed in the K-2, but it would require software 
that would figure out how to move the LO one way and the BFO the other way by 
exactly the same amount. And the software would have to do it on all bands and 
all frequencies on those bands!  

Most "other" rigs implement IF shift by an extra conversion step after the 
first fixed IF. This means there's a lot of gain and stages between the antenna 
and the sharp selectivity "knothole". No thanks.

IMHO, IF shift is of limited use in a CW receiver, and not worth giving up 
having the filter right up against the first mixer.

73 de Jim, N2EY