K2 filter bandwidth versus real bandwidth...

[Steve Kallal]

I've set up my K2 with the following bandwidths for the RTTY mode:
 
FL1    OP1
FL2    1000 Hz
FL3    500 Hz
FL4    250 Hz

I am listening to an Olivia signal (a digital mode) with a 500 Hz bandwidth.
I would expect FL3 at 500 Hz to pass the whole signal. Instead I have to
select FL2 at 1000 Hz bandwidth. Looking at the waterfall for the Olivia
signal, I get about 750 Hz passed rather than 1000 Hz.

If I want to pass a 500 Hz signal, what bandwidth should I select in the
filter calibration? I guess the selected bandwidth isn't measured at 6 db
down, or is it?

73,

Steve N6VL

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[David Woolley (E.L)]

Steve Kallal wrote:
>
> If I want to pass a 500 Hz signal, what bandwidth should I select in the
> filter calibration? I guess the selected bandwidth isn't measured at 6 db
> down, or is it?

As this is done by open loop control of a varicap control voltage, I'd
expect the relationship to vary considerably between units.  If you need
  finely tuned settings, you should probably set the filter using a
spectrum display, with white noise input, e.g. using the spectrogram
method.  You can probably use your digital mode terminal program instead
of spectrogram.

I think it is probably safer to treat the displayed bandwidth as an
(approximately) monotonic function of true bandwidth, rather than
measuring the actual bandwidth.

--
David Woolley
Emails are not formal business letters, whatever businesses may want.
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[Don Wilhelm-4]

Steve,

The numbers displayed for the filter width are not necessarily the
actual width of the filter.  The actual bandwidth depends on the
particular combination of crystals and varactors in your K2.

Use Spectrogram to measure the actual width of your filter if you wish
to have a precise bandwidth.

73,
Don W3FPR

Steve Kallal wrote:

> I've set up my K2 with the following bandwidths for the RTTY mode:
>  
> FL1    OP1
> FL2    1000 Hz
> FL3    500 Hz
> FL4    250 Hz
>
> I am listening to an Olivia signal (a digital mode) with a 500 Hz bandwidth.
> I would expect FL3 at 500 Hz to pass the whole signal. Instead I have to
> select FL2 at 1000 Hz bandwidth. Looking at the waterfall for the Olivia
> signal, I get about 750 Hz passed rather than 1000 Hz.
>
> If I want to pass a 500 Hz signal, what bandwidth should I select in the
> filter calibration? I guess the selected bandwidth isn't measured at 6 db
> down, or is it?
>
>  

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