[Elecraft] Filter Challenged...I'm so confused

[Wallace, Andy]

> -----Original Message-----
> From: Ron D'Eau Claire [mailto:rondec@easystreet.com]
> 
> The K2 stores BOTH the filter and the BFO frequencies associated with
> each filter "position". It uses both the filter selection and BFO
> frequencies for FL1 in transmit, so unless you play with the "main
> tuning" having different settings for the BFO in FL2, 3 and 4 will not
> affect the transmitted signal at all.  

Really? So let's say I am tuned to a SSB station on 7200 kHz. 
With FL1 set to pass 400-2400 Hz, things sound fine. However, I
decide to switch in FL2, which I've set to use the OPT1 filter 
shifted 300 Hz higher, as a sort of passband tuning. Doesn't this
mean I need to tune the main tuning down 300 Hz to "zero beat"
the station? And once I do that, am I not going to transmit
(through OPT1) 300 Hz off?
 
> When I answered this question yesterday I failed to mention that what
> you are describing is CORRECT in other rigs. In the K2, the Local
> Oscillator frequency is shifted automatically by the firmware when you
> change the BFO frequency to compensate! 

OK, so 7200 kHz would really be 7200 kHz in that case. I guess
that is sensible -- I don't have the KSB2 yet but zero beating
WWV doesn't change when I use FL1-4 in receive mode USB/LSB.

> I'm so used to that "effect" that I forget it's there. Lou, 
> W7HV brought
> that to my attention this morning. Thanks Lou! 

OK, so (as usual!) I have nothing to fear and I won't be outside
of the transmitting station's passband no matter what I
do with my filters for "passband tuning." And yes, I understand
that OPT1 needs to be set perfectly because it's used in the 
transmit path. 
 
> There used to be an
> excellent write up on the Elecraft reflector by Wayne on how the K2's
> system works called "The Mechanics of CAL FIL" that goes into great
> detail. I might still be there, but for me finding something under the
> "Builder's Resources" on the web site is harder than fining a 1/4 watt
> resistor in the bottom of my junk box. 

It is still there. 

http://www.elecraft.com/Apps/new_fil_docs/CAL_FIL_mechanics.htm

-Andy