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K2 PSK offset

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John Wiener

K2 PSK offset

I am noticing a slight drift over several months in my PSK such that my xmit doesn't match my rcv. It is off by about 10 or 20 Hz ... just enough for missed QSO opportunities. Also, there is a slight (10 Hz) shift between FL1 and FL2
I am re-reading the CAL FIL notes.

Should I recalibrate or is there another way to more accurately match freqs? Also, I am guessing I should use the table in the KSV2 manual.

John
AB8O
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Andrew Moore-3

Re: K2 PSK offset

AB8O> I am noticing a slight drift over several months in my PSK such that
my xmit doesn't match my rcv.
AB8O> It is off by about 10 or 20 Hz ... just enough for missed QSO
opportunities.
AB8O> Also, there is a slight (10 Hz) shift between FL1 and FL2

This is normal for the K2 and comes up once in a while on the lists.
Something to do with the resolution of a DAC, if I remember correctly.

I'm not sure if or how it affects PSK operation.

--Andrew, NV1B
..

On Tue, Feb 22, 2011 at 10:49 AM, John Wiener <[hidden email]> wrote:

> I am noticing a slight drift over several months in my PSK such that my
> xmit doesn't match my rcv. It is off by about 10 or 20 Hz ... just
> enough for missed QSO opportunities. Also, there is a slight (10 Hz) shift
> between FL1 and FL2
> I am re-reading the CAL FIL notes.
>
> Should I recalibrate or is there another way to more accurately match
> freqs? Also, I am guessing I should use the table in the KSV2 manual.
>
> John
> AB8O
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Don Wilhelm-4

Re: K2 PSK offset

In reply to this post by John Wiener

John,

The DAC in the K2 limits the BFO accuracy to about 20 Hz., but you can try.
If you are using the K2 for data modes, I would make 2 suggestions. The
first is to turn on the RTTY filter set if you have not already. That
provides you with a separate set of filters that you can customize and
use for data modes, and the compression setting is independent of the
SSB compression setting, so you will not have to remember to turn
compression off when operating data modes.

The second suggestion is that you use Spectrogram and a wideband noise
source (often band noise is sufficient, but try to chose a band segment
where there are no signals, just noise). I have instructions in my
website (www.w3fpr.com) article on K2 Dial Calibration that should prove
useful to you - note, this is refinement of the filter alignment, the
table in the KSB2 manual will get you close, but you can do better than
that.
My recommended filter settings for the RTTY filter set are FL1 = OP1.
FL2 = 1.00, FL3 = 0.70, and FL4 = 0.40. Center the 3 narrow filters at
1000 Hz and set FL1 the same as you would for SSB. RTTYrev is USB while
RTTY is LSB.

If you have the KDSP2 and want to use that with those RTTY filters,
change the DSP center frequency for the RTTY filters to 1.00 too.
To best utilize these filters for data modes, you would normally want to
tune the desired signal close to 1000 Hz on the waterfall (use the VFO
knob), then if you find other strong signals in the filter passband that
are activating the receiver AGC, you can select one of the more narrow
filters to continue the QSO wthout de-sensing the receiver. Note that
the DSP filter will not help with the AGC pumping, only the IF filters
will do that. If you do use the narrow filters, unlock the TX and RX in
the software before switching filters

Your 10 to 20 Hz shift may be the result of using FL1 for transmit and
FL2 for receive. For normal operation, if your FL1 filter is set
properly (the low frequency corner of the passband is set close to 300
Hz, there is no benefit to be derived by having both FL1 and FL2 set to OP1.

Remember that the Elecraft filter crystals are marked only to the
nearest 100 Hz, so there can be +/- 50 Hz different in the optimum
filter settings for your K2 and the nominal settings indicated in the K2
or KSB2 manual. Elecraft does match the crystals to tolerances that are
much less than 100 Hz (10 Hz if I recall), but any one crystal set that
is marked 3.6 can have crystals that have been matched anywhere from
3.55 to 3.65. Thus the manual setting my be up to 50 Hz in error for
your particular crystals set.

73,
Don W3FPR

On 2/22/2011 10:49 AM, John Wiener wrote:

> I am noticing a slight drift over several months in my PSK such that my xmit doesn't match my rcv. It is off by about 10 or 20 Hz ... just enough for missed QSO opportunities. Also, there is a slight (10 Hz) shift between FL1 and FL2
> I am re-reading the CAL FIL notes.
>
> Should I recalibrate or is there another way to more accurately match freqs? Also, I am guessing I should use the table in the KSV2 manual.
>
> John
> AB8O
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>