Fw: Tuning CW Stations in 160 meter contest (correction)

[Don Wilhelm-3]

Lee and folks,

I was all wet with my response this morning about the wide CW filter
settings - I just tried various settings of filter widths, and BFO settings
that are quite skewed from normal.

What I found is that as long as the BFO is positioned so that any part of
the passband contains the sidetone pitch frequency (as observed on
Spectrogram), the transmit frequency will be equal to the frequency of a CW
signal being received AT an audio tone EQUAL to the sidetone pitch.  So wide
filters are OK, and you can position them most anywhere within reason - it
will not change the transmit frequency.

Wayne has done some fancy stuff with frequency control in the firmware!!!
and it works.

I also found with my playing around with different BFO settings, that
changing the BFO frequency setting will NOT alter the pitch change when
switching from filter to filter.  Any change in pitch when switching filters
can be blamed on only 2 things - 1) the signal was not tuned propery to
equal the pitch of the sidetone, and 2) the normal DAC variation found in
the K2 - this should be 30 Hz or less (I typically observe a 10 Hz
difference on Spectrogram).  I do recall that Wayne wrote a long post about
how the K2 maintains pitch on a signal, and I guess I did not digest all of
it at that time.  I must review that post given the revelations I had with
my testing today.

Bottom line - zero beat the signal carefully and the transmit frequency will
be that indicated on the K2 frequency display (or at most 30 Hz away).  The
other operator must be also listening on that frequency, and in a contest,
he may have forgotten to turn RIT off, or perhaps he is working stations a
bit off his frequency intentionally to reduce the QRM???  Who knows what may
be going on at the receiving end, but your K2 is likely to be correct (as
long as YOU don't have RIT or XIT turned on yourself).

73,
Don W3FPR
----- Original Message -----
From: "W3FPR - Don Wilhelm" <[hidden email]>
To: "Lee Buller" <[hidden email]>; "Elecraft Reflector"
<[hidden email]>
Sent: Monday, December 06, 2004 11:09 AM
Subject: Re: [Elecraft] Tuning CW Stations in 160 meter contest

> Lee,
>
> If you are using the default 1.5 kHz CW bandwidth for FL1 and listening
> with a more narrow filter, the answer is 'quite likely'.  Remember that
> the FL1 BFO is always used for transmit.  This results in a filter
> alignment situation that is seldom mentioned - that of transmit frequency
> offset.
>
> This problem happens readily if you center the bandpass during filter/BFO
> alignment and are using a filter wider than twice your sidetone pitch.  If
> you think about it, you should quickly determine that to actually center a
> 1.5 kHz bandpass on a 600 Hz point, the bandpass will be from 1350 Hz down
> to -150 Hz  -- yes, I said that right, the passband will cross over into
> the opposite sideband!  The more likely thing is that you did not set it
> up that way, so the BFO for FL1 is shifted about 500 to 1 kHz from the
> remaining BFOs.  That is the reasoning behind my recommendations that CW
> FL1 be set no wider than 2 times the sidetone pitch.  The 700 Hz width is
> my preferred normal CW receiving filter width, and I personally set my FL1
> to 1.0 or 1.1 kHz to avoid having to shift the FL1 BFO far away from the
> other BFOs.
>
> I do wish that the K2 in CW (and RTTY modes) always used the same BFO for
> transmit as that used for receive, but such is not the case - FL1 is
> always used for transmit in any mode (it is necessary in SSB mode).
> If the FL1 BFO is not close to the same frequency as the BFO currently
> being used for receive, your resulting transmit offset will be quite
> different than your sidetone pitch.  (Note: IMHO, a few tens of Hertz will
> make no noticable difference, but hundreds of Hertz difference in the BFOs
> will be objectionable.)
>
> Wayne - would it be possible to change the firmware to use the same BFO
> for transmitting and receiving for all modes except SSB?  Or is my
> analysis incorrect here?
>
> 73,
> Don W3FPR
>
>
> ----- Original Message -----
>
>> I participated in the 160 Meter CW contest this weekend with my K2/100
>> and noticed something I had never noticed before.  I think that I might
>> have a misadjustment in the filters and I am not sure where.
>>
>> I would tune a station (S&P) to where I thought I was in the bandpass of
>> the RC station.  At least the note sounded good to me.  Invariably, I
>> would have to tune about a tenth of a KC down to actual make the contact.
>> I could call on the higher tone and they would not hear me, but calling
>> on the lower tone they would come back all the time.  I have the filter
>> center set at 700 with filters widths at 1.5 - 700 - 400 - 100.
>>
>> Do I have something set to low or to high with the BFO?  This gets
>> confusing to me.
>>
>

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[Ron D'Eau Claire-2]

Don wrote:
What I found is that as long as the BFO is positioned so that any part of
the passband contains the sidetone pitch frequency (as observed on
Spectrogram), the transmit frequency will be equal to the frequency of a CW
signal being received AT an audio tone EQUAL to the sidetone pitch.  So wide

filters are OK, and you can position them most anywhere within reason - it
will not change the transmit frequency.

Wayne has done some fancy stuff with frequency control in the firmware!!!
and it works.
--------------------------------------

The paper is called "A Detailed Example of the Mechanics Behind Cal FIL"

I think it's still on the Elecraft web site.

The short form is this: When you change the BFO frequency in CAL FIL, the K2
automatically changes the local oscillator frequency to preserve the pitch.

The effect is similar to "passband tuning" in that the passband of the
filter seems to move around a fixed pitch frequency when you change the BFO
frequency.

Ron AC7AC



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[Brian Mury-3]

On Mon, 2004-06-12 at 21:23 -0500, W3FPR - Don Wilhelm wrote:
> What I found is that as long as the BFO is positioned so that any part of
> the passband contains the sidetone pitch frequency (as observed on
> Spectrogram), the transmit frequency will be equal to the frequency of a CW
> signal being received AT an audio tone EQUAL to the sidetone pitch.  So wide
> filters are OK, and you can position them most anywhere within reason - it
> will not change the transmit frequency.
>
> Wayne has done some fancy stuff with frequency control in the firmware!!!
> and it works.

Now if only the sidetone pitch could be changed without having to redo
the filter calibration... I like to change the sidetone pitch
occasionally when I'm on the air for long periods as I find my ears tend
to get less "tired" that way. I can't do that with the K2 without
recalibrating the filters.

--
73, Brian
VE7NGR

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[Don Wilhelm-3]

Brian,

Since the K2 preserves pitch, you CAN freely change the sidetone pitch as
long as both the old and new pitch both fit inside the audio range of the
filter.  The signal being received will not be centered in the passband, but
positioned off to the side of center, but that makes no difference if it
still fits inside the passband (and ideally somewhere within the relatively
flat portion of the passband).

If you want to initially set up the filter (particularly the narrowest) to
operate with a variable sidetone, I suggest that you first decide what the
lowest and highest sidetone pitches will be for you.  Then use Spectogram
and set 2 markers, one at the lowest sidetone and the other at the highest.
Then change the BFO to place the center of your narrow filters between these
markers.  If the flattop portion of the narrowest filter does not fully
cover these frequency extremes, you may widen the filter or simply accept
the fact that you will see some attenuation when using this filter (the tone
you want will be demodulated on the filter slope).

Watch the wider filters too - do not center them - be certain the low
frequency slope of the filter appears to the left (lower frequency) of your
lower sidetone pitch marker and be certain that the filter stopband occurs
before you get to zero frequency (if it does not, you will have signal
detection on the opposite side of zero beat and loose the single signal
tuning capability.

Extra note - anybody now want to resurrect discrete passband tuning?  I
think many of us have gotten hung up on 'setting the BFOs for no frequency
shift between filters', but that is NOT why the shift occurs, any shift is
due to firmware digitizing error.  You can set the BFOs almost anywhere and
there will be little shift between filters.  What I have discovered (after
all this time) that the BFOs shift the passband, but does not change the
pitch - the firmware changes the pitch.  So now I am contemplating using the
CWr filters as a set of discrete passband tuning filters using a fixed
filter width of 400 or 500 Hz and changing the BFOs so the audio range of
each filter is positioned offset a bit from each other (to cut either the
low frequency end or the high frequency end).  Also, I seldom use the
reverse sideband for CW, and there is no reason that the BFOs have to be set
for sideband reversal - I will use the side where the pitch increases with
increasing frequency - that way my brain knows which way I am tuning without
looking at the frequency readout.  This K2 provides more flexibility than I
thought before!!!

73,
Don W3FPR

----- Original Message -----
>
> Now if only the sidetone pitch could be changed without having to redo
> the filter calibration... I like to change the sidetone pitch
> occasionally when I'm on the air for long periods as I find my ears tend
> to get less "tired" that way. I can't do that with the K2 without
> recalibrating the filters.
>


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[Vic K2VCO]

W3FPR - Don Wilhelm wrote:

>   Also, I seldom use the reverse sideband for CW, and
> there is no reason that the BFOs have to be set for sideband reversal -

As someone who has done a lot of playing with the K2's filters, tried discrete
passband tuning, etc., I have to say:

Neat idea!  Why didn't I think of it?  Another passband position for each filter
width!

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

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[Don Wilhelm-3]

Whoops,
Folks, discrete passband tuning will work best by using the same fiilter
width for all the filters - I had a slip of memory and temporarily forgot
that the CW and CWr filters share the same bandwidth.
I guess discrete passband tuning could be something for the RTTY filters -
now how do we get the sidetone offset integrated into the RTTY filters?  And
how do we activate keying and other CW funtions in RTTY mode since that is
really treated as a special case of SSB?  Problems, problems, problems. --  
for CW use it has to be the CW filters.

I am still going to try the discrete passband tuning as well - My current
thoughts - leave FL1 wide but usable (1.0 kHz or 800 Hz). then go to
passband tuning with FL2, 3 and 4 with a 400 Hz filter width; center FL2 at
650 Hz, FL3 at 750 Hz, and FL4 at 550 Hz (assuming a 600 Hz sidetone).  That
should allow a normal 400 Hz filter for crowded band use (FL2) plus the
ability to drop a lower pitched interfering signal out with FL3 and a higher
frequency interfering signal out with FL4.  Turn the centering for FL3 and 4
around if you want to drop off the high end first and the low end with FL4.
I assume most listening would be done with FL1 or FL2   This scheme should
allow better rejection than a narrower filiter and avoid the attenuation
that occurs with very narrow filters.

An extension of the above, one could use CWr to drop off the high frequency
side and CW to drop the low frequency side (or vice-versa) that would still
provide a wide filter for FL1 (but 2 BFOs), and 400 Hz for all the rest,
giving the normal centered filter plus 5 shifted passband positions.  Let
your imagination run wild and try it out.

73,
Don W3FPR

----- Original Message -----

> W3FPR - Don Wilhelm wrote:
>
>>   Also, I seldom use the reverse sideband for CW, and
>> there is no reason that the BFOs have to be set for sideband reversal -
>
> As someone who has done a lot of playing with the K2's filters, tried
> discrete passband tuning, etc., I have to say:
>
> Neat idea!  Why didn't I think of it?  Another passband position for each
> filter width!
>
>

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[Brian Mury-3]

On Tue, 2004-07-12 at 13:40 -0500, W3FPR - Don Wilhelm wrote:
> go to passband tuning with FL2, 3 and 4 with a 400 Hz filter width;
> center FL2 at 650 Hz, FL3 at 750 Hz, and FL4 at 550 Hz (assuming a 600
> Hz sidetone).  That should allow a normal 400 Hz filter for crowded
> band use (FL2) plus the ability to drop a lower pitched interfering
> signal out with FL3 and a higher frequency interfering signal out with
> FL4.  Turn the centering for FL3 and 4 around if you want to drop off
> the high end first and the low end with FL4.

Neat idea.

Couldn't you do the same thing with a single filter by using the RIT?
The pitch of the desired signal would, of course, change, but that's not
a big deal. Then you can still have 4 different filter widths.

--
73, Brian
VE7NGR

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