Re: K3 CW Filter

[Scott Ellington]

Thanks to all for the suggestions.  There does indeed seem  to be something funny about the 400 Hz filter.

73,

Scott  K9MA


On Sep 25, 2010, at 11:17 AM, SCOTT D ELLINGTON wrote:

> I'm just setting up a new K3 (4657), and the 400 Hz 8-pole CW filter (KFL3A-400) seems to have a significant offset.  The 6 dB audio bandwidth (AGC off, internal dBV meter) was 236 Hz, and the center about 100 Hz below the sidetone/CWT.  Setting the offset for that filter to -0.13 put the center frequency within 2 Hz of the sidetone, but only increased the audio bandwidth to 316 Hz.   (ARRL measured 341 for that filter.)   Since the audio bandwidth is still low, I'm guessing the filter bandwidth is less than 400 Hz, in addition to having an offset.
>
> Any comments or suggestions before I bother Elecraft support?
>
> 73,
>
> Scott  K9MA
> ______________________________________________________________
>

Scott Ellington
Madison, Wisconsin
USA



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[Jim Brown-10]

  On 10/6/2010 5:15 PM, Scott Ellington wrote:
> There does indeed seem  to be something funny about the 400 Hz filter.

There are several issues. First, every 8-pole CW filter I've measured
has significant offset, and needs to be compensated, just like the
5-pole filters. 100 Hz is typical.

Second, what you are probably measuring is the CASCADED response of the
400 Hz filter and the DSP IF filters that you have set.  It is entirely
normal for that cascaded bandwidth to be less than 400 Hz.

There are filter measurements on my website. To see the bandwidth of the
400 Hz filter, you must set the IF filter much wider than 400 Hz (like
1kHz) and tell the K3 that the 400 Hz filter is a 1kHz filter. That will
cause the400 Hz filter to be switched in at 1kHz bandwidth.

There are some filter measurements on my website.

http://audiosystemsgroup.com/K3FilterStudy-250HzRoof.pdf

73, Jim K9YC
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