[Elecraft] 250 Hz and 400 Hz Filter Measurements

[Ed Muns]

VE3KI wrote:
> As someone who mainly operates during CW and RTTY contests, I 
> draw a slightly different conclusion from Craig's and Jim's. 
> In the absence of a true 270 Hz roofing filter, the existing 
> "250 Hz" filter appears to be the best roofing filter option 
> on offer for RTTY contest use. Therefore, while I agree with 
> Ed's conclusion about these two filters, of the two the one 
> that is unnecessary for me is the 400 Hz filter.

Same here.  For the record, I use 8-pole 500 Hz INRADs for CW.  I use the
8-pole 370 Hz (labeled 250 Hz) for RTTY with the DSP Dual-Tone Filter.  The
5-pole 200 Hz works for RTTY, but rolls off the outer edges of the tones
(especially in conjunction with the Dual-Tone Filter) and I prefer the
steeper skirts on the 8-pole 370 Hz filter.  It is enough wider than the DSP
filtering such that little cascade roll-off occurs.

>  From amongst the existing choices, a 500/250 combination 
> seems most effective for my situation. If I were more heavily 
> into 160 CW as compared with RTTY, I might opt for a 400/200 
> combination instead. For a single roofing filter for CW/RTTY 
> use, you might find a 400 to be the best single-filter 
> compromise. Different solutions for different situations.

Exactly.  There isn't a single solution for all scenarios.  That's why there
are filter sockets and a range of alternative filters.  The key is to
understand how the K3 filters work (both DSP and crystal) so that thoughtful
choices can be made by each individual.

73,
Ed
--------------
Ed Muns - W0YK
www.w0yk.com


> Craig AC0DS wrote:
> 
> > I agree with you that there is no need for the 250 Hz 8 pole
> > option.
> 
> Jim Brown K9YC wrote:
> 
> > Indeed, there is no good 
> > reason for the EXISTENCE of this particular 250 Hz filter, 
> > primarily because it is NOT a 250Hz filter by any reasonable 
> > measure.
> 
> and Ed Muns W0YK wrote:
> 
> > Accordingly, in their application as
> > roofing filters for the K3, I see no reason to have both 
> the "250" and the
> > "400" in the same receiver.