[Elecraft] Re: K2 - 2nd Xtal Filter

[wayne burdick]

On Mar 5, 2005, at 3:27 AM, Stewart Baker wrote:

> Anyone any experience of, or thoughts about adding another 3 crystals 
> to the K2
> 2nd crystal filter ?

Hi Stewart,

The present 2-crystal filter (as on newer units, or older units with 
the 2nd XFIL mod) is very carefully designed to provide different 
bandwidths on CW and SSB. Equally important, this filter must be 
centered at the same frequency as the main filter over the full 
controllable bandwidth range. L34 and related circuitry, along with the 
varactor diode, accomplish these tasks.

If you wanted to add more crystals here for the purpose of improving 
ultimate attenuation, two crystal filters switched by pin diodes would 
be needed, along with a complete re-design of all associated circuitry 
(I.F. amp output, product detector input, CW/SSB control, bandwidth 
control in the CW case). This would be very difficult and 
time-consuming, and the resulting circuit would not fit in the present 
location. That would require the use of coax cables to a separate 
module, along with other potential issues such as RF pickup. Chances 
are the result would not be much of an improvement.

If your goal is to improve ultimate attenuation, the KDSP2 is a much 
saner route.

73,
Wayne
N6KR


---

http://www.elecraft.com