K2-CW-Filter-Response: is that ok?

[Karsten Eppert (DK4AS)]

I have set the wide CW-Filter (Fil1) to 1,5 and aligned the BFO to a
pitch of 700 Hz. I applied HF of constant frequency to the
receiver-input with a signal strength that generated S9+10 db max. and
plotted the S-meter versus variation of the VFO from high pitch to low
pitch in 100 hz-steps. So I could determine a filter-curve. What strikes
me is, that even at very low pitch-frequencies there is hardly
attenuation and even at zero beat the S-meter still shows approx. S3.
Turning the VFO "behind" zero-beat lets the S-meter decrease but it
takes another 300 Hz until S0 is reached. The tone of the "wrong"
sideband remains audible at even higher frequencies.

In real amateur life this means, that strong near-by stations close to
zero-beat still affect the AGC considerably.

 

My question is: is that typical for the cw-filter-design of the k2 or is
something wrong with my device? Do I have any method to check, if
something is dead or badly installed?

By the way: I did the same kind of plot with the Filter of the
SSB-Adapter (OP1). Result: perfect.

 

Karsten

DK4AS

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[Vic K2VCO]

Karsten Eppert(DK4AS) wrote:

> I have set the wide CW-Filter (Fil1) to 1,5 and aligned the BFO to a
> pitch of 700 Hz. I applied HF of constant frequency to the
> receiver-input with a signal strength that generated S9+10 db max. and
> plotted the S-meter versus variation of the VFO from high pitch to low
> pitch in 100 hz-steps. So I could determine a filter-curve. What strikes
> me is, that even at very low pitch-frequencies there is hardly
> attenuation and even at zero beat the S-meter still shows approx. S3.
> Turning the VFO "behind" zero-beat lets the S-meter decrease but it
> takes another 300 Hz until S0 is reached. The tone of the "wrong"
> sideband remains audible at even higher frequencies.

There's probably nothing wrong with your filter.  If you wish to have a wide CW
filter setting, you should locate the BFO during the CAL FIL adjustment so that
the filter passband is higher with respect to zero beat.  If you use Spectrogram
-- see <http://www.n0ss.net/index.html#Spectrogram> -- you can see this graphically.

With correct adjustment, you should not hear any signal on the 'wrong' side of
zero beat.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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[Ron D'Eau Claire-2]

Look at it this way. You're using a 700 Hz pitch with a 1.5 kHz wide filter.
If you center the 700 Hz in the filter bandpass, the bandpass will extend
750 Hz above and 750 Hz below the 700 Hz beat frequency. That puts your
carrier zero beat 50 Hz inside the bandpass so you can hear a beat note on
the "wrong" side of the carrier. The skirts of the filter response will let
you hear beat notes well beyond the 750 Hz edge of the bandpass.

Vic's suggestion to move the bandpass "up" away from the carrier frequency
is exactly the thing to do. Make sure the lower-frequency cutoff point is
above the carrier frequency to ensure you still get "single-signal" (or
"single sideband") reception.

Ron AC7AC


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