[Elecraft] K3 DSP shape factor?

[Dave Hachadorian]

So for the DSP:
BW60 = BW6 + 300Hz (approx)

Sounds like good numbers to me. Thanks for the answer!

Dave Hachadorian, K6LL
Yuma, AZ


----- Original Message ----- 
From: "Lyle Johnson" <kk7p at wavecable.com>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Tuesday, April 01, 2008 7:10 PM
Subject: Re: [Elecraft] K3 DSP shape factor?


>> The question I have is "What is the effective shape 
>> factor of the K3 DSP?"
>
> DSP filters usually are so-called Finite Impulse Response 
> (FIR).  FIR filters for a given complexity (length) have a 
> nearly constant transition region width going from the 
> passband to the stopband.  For this reason, "shape factor" 
> varies depending on the width of the filter. ( It also 
> depends on the ultimate attenuation required, and the 
> "windowing function" applied to deal with of the "Gibb's 
> phenomenon" and...)
>
> The following is just an illustration.
>
> Let's say that the transition band for a set of FIR 
> filters from 6 dB to 60 dB is 150 Hz.  [ This number 
> happens to be from a quick check I just did on a dialed-in 
> filter width of 500 Hz, and a center of 600 Hz on my K3. 
> This is using a 2.8 kHz roofing filter, AGC OFF, internal 
> AFV and dBV function, and signal level at the threshold of 
> hardware AGC action. Yes, I tuned to the higher pitch side 
> to make the measurement :-) How to do all of this is left 
> as an exercise for the reader. ]
>
> If the 6 dB width is 500 Hz, then the 60 dB width is 
> (150+500+150 =) 800 Hz and the "shape factor" is 1.6:1.
>
> If the 6 dB width is 2400 Hz, then the 60 dB width is 
> (150+2400+150 =) 2700 Hz and the "shape factor" is 
> 1.125:1.
>
> YMMV, and all is subject to change at the whim of the 
> firmware writers :-)
>
> 73,
>
> Lyle KK7P