[Elecraft] Re: KX1 IF filter tuning?

[Jeff Stai WK6I]

At 05:16 PM 12/8/2003, Wayne Burdick wrote:


>Jeff Stai WK6I wrote:
>> 
>> OK, here goes... has anyone put their KX1 on to Spectrogram to look at the filter shape? I have...
>
>Hi Jeff,
>
>The KX1's filter passband is a compromise to allow varactor tuning over a wide
>range. Since some ripple is unavoidable in this case, adjustment of the FILTER
>control may occasionaly be desireable to optimize for a particular signal pitch.
>Of course the effect is lessened by the KX1's AGC when signals and noise are at
>high levels.

hi Wayne - I understand that a filter can have passband ripple, but in this 
case I seem to be experiencing 10-15dB of "ripple", and the main "trough" is 
right in the middle of recommended 600Hz tone.

I'm sorry, that just doesn't seem right. 

I realize this filter is not as capable as the K2 filter, but I don't have 
anything like this kind of ripple on my K2s.

I guess I am really not understanding what you wrote above - normally, I 
would vary the FILTER control to narrow the IF BW to focus on the signal I 
am receiving and eliminate QRM and QRN around it. I would zero beat with the 
other station at 600Hz since that is the BFO offset. If I understand the 
above statement, after zero-beating I will need to use the RIT while 
changing the FILTER to put the received tone into the filter passband...? (I 
am not able to run the test now, since I spent most of today recovering from 
a Windows crash, but I recall the filter was many dB down at 600Hz at narrow 
settings.)


>If you weren't interested in wider bandwidths at all, you could select a
>different termination impedance, although I haven't experimented with this. I
>wouldn't recommend doing this without fully re-testing the passband at all
>settings of the FILTER control.

It would be fair to say that I could live with poorer performance at wider 
BWs, and focus on sub-1000Hz for CW - I could even imagine adding a little 
switch for the two BW ranges if I was interested enough.

Would I be changing R19? Could you suggest some ranges to try?

thanks! - jeff wk6i




--
Jeff Stai               jds@twistedoak.com
Twisted Oak Winery      http://www.twistedoak.com/
Rocketry Org. of CA     http://www.rocstock.org/
Amateur Radio           WK6I