Posted by
Guy, K2AV on
Sep 25, 2010; 10:39pm
URL: http://elecraft.85.s1.nabble.com/K3-CW-Filter-tp5570180p5570923.html
Make sure you're not trying to measure the 400 filter offsets with the DSP
set to 400. To measure the filter offset correctly, first define the filter
"too wide" in the K3 utility. Eg define the 400 filter as if it were 1.4.
Then use a high PITCH setting of 700 to make sure that audio rolloff is not
in play. Make sure that MENU:RX EQ settings are all at zero. Be sure the
AGC is OFF for your measurements and use ATT. Adj SHIFT until the FC value
shows a *0.70. Set WIDTH to 1.20. Now measure your 6 dB points. Average
the two, and offset the filter by that amount. RECHECK and readjust for any
leftover.
In my case, to align the roofer rejection skirts to match DSP skirts and get
max dive on the skirts, I use -30 dB points to set offsets rather than -6 dB
points. For me the roofers are all about the steepest possible skirts for
rejection. The best matching DSP setting is the one (after setting offset)
that when you narrow it up changes the -30 to -60. When I've done that THEN
I measure the -6 dB points and that is my best aligned operating bandwidth
for that filter. Add 50 Hz to that WIDTH setting and use that as the filter
width definition in the K3 utility. This gives me both a "loose" and
"tight" setting for that roofing filter.
73, Guy.
On Sat, Sep 25, 2010 at 1:03 PM, Jim Brown <
[hidden email]>wrote:
> It is quite normal for there to be offset in the 8-pole filters. I
> have three, and they all do. Enter the offsets and be happy.
>
> 73, Jim K9YC
>
> On 9/25/2010 9:17 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?
> >
>
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