[Elecraft] [K3] Elecraft roofing filters

[ni0c]

W4TV wrote: 


> My source is Elecraft: www.elecraft.com/K3/K3_8_pole_plots.htm
> 
> Look specifically at the last two plots which show: 
> 
>            KFL3A-400      KFL3A-250 
>   -6 dB      435 Hz         370 Hz 
>  -60 dB      935 Hz         785 Hz 
>    SF        2.15:1         2.12:1  
> 
> INRAD do not publish the curves for the Elecraft (or Yaesu 
> 8215 KHz) 250 Hz filter.  However, they do show the curve 
> for the 8830 KHz (Kenwood) version of the same filter and 
> it shows a similar percentage bandwidth (367.5/845 Hz at 
> -6/60dB). 
> 

NI0C responds:

I'm still wondering what the tolerance is on such published curves.  

 
> Did you run those tests in a Data mode or with the CW pitch 
> set to 800 Hz?  If not, the low frequency skirts will be 
> sharpened significantly and the measured bandwidth will 
> less than the roofing filter.  With a CW pitch of 560 Hz 
> I measure 10% less bandwidth than in DATA (CF = 1500 Hz or 
> 2210 Hz).  If I reduce the pitch to 300 Hz, the measured 
> bandwidth is further reduced (due to the DSP filter's low 
> frequency cut-off). 
> 
> 73, 
> 
>    ... Joe, W4TV 

NI0C responds:

My testing was done in CW mode with the pitch in the 
low 300's (320 Hz, as I recall).  So, when I repeat the tests,
I'll vary the pitch and see what happens, say 300 Hz, 600 hz, 
and 800 Hz.  

73 & Thanks, Joe,  for your info!

Chuck Guenther NI0C