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K2 frequency adjustment

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DaveL G3TJP

K2 frequency adjustment

Today I decided to recalibrate my K2 using a very accurate 10MHz source, as well as replacing C31 in the KPA100 (Rev. D) to bring it up to the latest Rev. E.

After leaving both the 10MHz source and the K2 turned on all day to stabilise, I made a start but the first problem encountered was that the filters were just too darned good and wouldn't let me find zero-beat. Plenty 10MHz signal was available and the S-meter lit up with a full line of li'l green apples, but as zero beat was approached, both the S-meter reading and audio dropped out of sight.

To get round this problem, I altered the LSB widest filter (2.4kHz - OP 1) down in frequency and found a healthy S-meter reading could be maintained. The low beat note could both be seen (highest LED flickering in time with the beat) and heard as a slow rise and fall in background noise.

Unfortunately, I was distracted by an artefact that appeared only when an SSB filter was selected with no antenna connected. There was a crackling/crunching sort of noise that was not present on any CW setting or filter. During the hunt for the culprit, I found that if a finger was dabbed on the cathode of D4 (DSB output from BM to xtal filter) the problem cleared up. Also, if a finger was dabbed on T2, the problem went away. Further finger-dabbing along the xtal filter was unhelpful as I was acting as an antenna. Soldering was checked and re-done but the problem remained, so D4 bit the dust and was replaced with a new 1N4148. No improvement.

Ah well, time was passing, so I thought I'd return to the calibration task. No problems were encountered and the task was completed successfully. CAL PLL was followed by a CAL FIL where the adjusted LSB filter was returned to its previous setting and all other filter settings were moved around before restoring them to their original settings. I noted the last digit of the BFO frequency had decremented by 1 in every case.

After this, I was pleased to note that the nasty background noise previously heard when SSB was selected had disappeared, so I'm thinking it was an artefact caused by everything warming up and drifting. Now I shall check tomorrow to see if the artefact has moved and is present when the rig is cold.

Changing C31 in the KPA doesn't appear to have made any difference to its operation, so what was it for? The PA's power output reading still tends to jitter around by +/-10% or so when running into a high quality 50 ohm dummy load.

73 DaveL G3TJP

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Don Wilhelm-3

Re: K2 frequency adjustment

Dave,

That 'artifact' you heard when you had the filter set to hear zero
frequency was most likely some BFO feedthru.

Good that you have put C31 in the KPA100 - it is to avoid a possible
oscillation - it has nothing to do with the power control level.

You can tame the power variation a bit by increasing the value of R98 on
the bottom of the RF board. Increase it until you begin to see a
dropoff in power on 10 meters (check this on low power (power only the
base K2 and not the KPA100). Use the largest value that allows normal
power output on 10 meters. Normally 1k is a maximum value, but if your
base K2 has higher than normal gain, you can go a bit higher.

73,
Don W3FPR

David Lankshear wrote:

> Today I decided to recalibrate my K2 using a very accurate 10MHz source, as well as replacing C31 in the KPA100 (Rev. D) to bring it up to the latest Rev. E.
>
>
>
> After leaving both the 10MHz source and the K2 turned on all day to stabilise, I made a start but the first problem encountered was that the filters were just too darned good and wouldn't let me find zero-beat. Plenty 10MHz signal was available and the S-meter lit up with a full line of li'l green apples, but as zero beat was approached, both the S-meter reading and audio dropped out of sight.
>
>
>
> To get round this problem, I altered the LSB widest filter (2.4kHz - OP 1) down in frequency and found a healthy S-meter reading could be maintained. The low beat note could both be seen (highest LED flickering in time with the beat) and heard as a slow rise and fall in background noise.
>
>
>
> Unfortunately, I was distracted by an artefact that appeared only when an SSB filter was selected with no antenna connected. There was a crackling/crunching sort of noise that was not present on any CW setting or filter. During the hunt for the culprit, I found that if a finger was dabbed on the cathode of D4 (DSB output from BM to xtal filter) the problem cleared up. Also, if a finger was dabbed on T2, the problem went away. Further finger-dabbing along the xtal filter was unhelpful as I was acting as an antenna. Soldering was checked and re-done but the problem remained, so D4 bit the dust and was replaced with a new 1N4148. No improvement.
>
>
>
> Ah well, time was passing, so I thought I'd return to the calibration task. No problems were encountered and the task was completed successfully. CAL PLL was followed by a CAL FIL where the adjusted LSB filter was returned to its previous setting and all other filter settings were moved around before restoring them to their original settings. I noted the last digit of the BFO frequency had decremented by 1 in every case.
>
>
>
> After this, I was pleased to note that the nasty background noise previously heard when SSB was selected had disappeared, so I'm thinking it was an artefact caused by everything warming up and drifting. Now I shall check tomorrow to see if the artefact has moved and is present when the rig is cold.
>
>
>
> Changing C31 in the KPA doesn't appear to have made any difference to its operation, so what was it for? The PA's power output reading still tends to jitter around by +/-10% or so when running into a high quality 50 ohm dummy load.
>
>
>
> 73 DaveL G3TJP

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Brett gazdzinski-2

RE: K2 frequency adjustment

In reply to this post by DaveL G3TJP

Funny, I had today off and decided to do the same thing.
I used the 756 pro as a source, did the adjustment, redid
all the filter bfo settings, and went from 4000 Hz off to about 500,
but I could not tell as I could not zero beat and did not think
of changing the filter.

When both the 756 and the K2 are tuned to the same frequency,
they hear each other, but at maybe 400 or 500 Hz differences.

Close enough for me anyway...

Last time I did my filters, I paid a lot of attention
on getting things to sound the same between filters and
CW normal and reversed.
Tune a signal in spot on the nose (same as sidetone) and
switching between cw normal and reverse does not change the pitch.

That is useful if you have qrm on one side.

Listening on CW or ssb and changing filters does not change the
pitch any, which is nice...

The radio really does work well!
I enjoy listening to cw (at speeds to fast for me to copy)
for hours! ssb sounds good in the headphones, the little speaker
inside the K2 does not really cut it for ssb...

Brett
N2DTS

> Today I decided to recalibrate my K2 using a very accurate
> 10MHz source, as well as replacing C31 in the KPA100 (Rev. D)
> to bring it up to the latest Rev. E.
>
>
>
> After leaving both the 10MHz source and the K2 turned on all
> day to stabilise, I made a start but the first problem
> encountered was that the filters were just too darned good
> and wouldn't let me find zero-beat. Plenty 10MHz signal was
> available and the S-meter lit up with a full line of li'l
> green apples, but as zero beat was approached, both the
> S-meter reading and audio dropped out of sight.
>
>
>
> To get round this problem, I altered the LSB widest filter
> (2.4kHz - OP 1) down in frequency and found a healthy S-meter
> reading could be maintained. The low beat note could both be
> seen (highest LED flickering in time with the beat) and heard
> as a slow rise and fall in background noise.
>
>
>
> Unfortunately, I was distracted by an artefact that appeared
> only when an SSB filter was selected with no antenna
> connected. There was a crackling/crunching sort of noise
> that was not present on any CW setting or filter. During the
> hunt for the culprit, I found that if a finger was dabbed on
> the cathode of D4 (DSB output from BM to xtal filter) the
> problem cleared up. Also, if a finger was dabbed on T2, the
> problem went away. Further finger-dabbing along the xtal
> filter was unhelpful as I was acting as an antenna.
> Soldering was checked and re-done but the problem remained,
> so D4 bit the dust and was replaced with a new 1N4148. No
> improvement.
>
>
>
> Ah well, time was passing, so I thought I'd return to the
> calibration task. No problems were encountered and the task
> was completed successfully. CAL PLL was followed by a CAL
> FIL where the adjusted LSB filter was returned to its
> previous setting and all other filter settings were moved
> around before restoring them to their original settings. I
> noted the last digit of the BFO frequency had decremented by
> 1 in every case.
>
>
>
> After this, I was pleased to note that the nasty background
> noise previously heard when SSB was selected had disappeared,
> so I'm thinking it was an artefact caused by everything
> warming up and drifting. Now I shall check tomorrow to see
> if the artefact has moved and is present when the rig is cold.
>
>
>
> Changing C31 in the KPA doesn't appear to have made any
> difference to its operation, so what was it for? The PA's
> power output reading still tends to jitter around by +/-10%
> or so when running into a high quality 50 ohm dummy load.
>
>
>
> 73 DaveL G3TJP
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

Don Wilhelm-3

Re: K2 frequency adjustment

Brett,

Since you can probably hear 10 MHz WWV at your QTH, why not use that
signal in LSB or USB to set C22 very accurately. The method to do that
is on the Elecraft website on the Builder's Resource page.

I also recommend that one use Spectrogram to tell when WWV is tuned
'just right' - I place markers at 500 and 600 Hz and watch as the
transmitted tones line up with the markers. Once you get it right, you
can expect proper dial calibration within 20 Hz typically. The whole
procedure is in the K2 Dial Calibration article on my website
http://w3fpr.qrpradio.com

When you are done, if the K2 tunes in WWV in LSB or USB mode with
accuracy, all bands will also be accurate. Then if you find yourself
off frequency, you can blame the other radio.

73,
Don W3FPR

Brett gazdzinski wrote:

> Funny, I had today off and decided to do the same thing.
> I used the 756 pro as a source, did the adjustment, redid
> all the filter bfo settings, and went from 4000 Hz off to about 500,
> but I could not tell as I could not zero beat and did not think
> of changing the filter.
>
> When both the 756 and the K2 are tuned to the same frequency,
> they hear each other, but at maybe 400 or 500 Hz differences.
>
> Close enough for me anyway...
>
> Last time I did my filters, I paid a lot of attention
> on getting things to sound the same between filters and
> CW normal and reversed.
> Tune a signal in spot on the nose (same as sidetone) and
> switching between cw normal and reverse does not change the pitch.
>
> That is useful if you have qrm on one side.
>
> Listening on CW or ssb and changing filters does not change the
> pitch any, which is nice...
>
> The radio really does work well!
> I enjoy listening to cw (at speeds to fast for me to copy)
> for hours! ssb sounds good in the headphones, the little speaker
> inside the K2 does not really cut it for ssb...
>
> Brett
> N2DTS

Brett gazdzinski-2

RE: K2 frequency adjustment

Don,
thanks for the great idea of using the spectrogram
and WWV.

That's another thing I did not think of.

I heard some great slow CW on both 80 and 40 meters
tonight!

Brett
N2DTS

> -----Original Message-----
> From: Don Wilhelm [mailto:[hidden email]]
> Sent: Monday, April 16, 2007 7:49 PM
> To: Brett gazdzinski
> Cc: [hidden email]
> Subject: Re: [Elecraft] K2 frequency adjustment
>
> Brett,
>
> Since you can probably hear 10 MHz WWV at your QTH, why not use that
> signal in LSB or USB to set C22 very accurately. The method
> to do that
> is on the Elecraft website on the Builder's Resource page.
>
> I also recommend that one use Spectrogram to tell when WWV is tuned
> 'just right' - I place markers at 500 and 600 Hz and watch as the
> transmitted tones line up with the markers. Once you get it
> right, you
> can expect proper dial calibration within 20 Hz typically. The whole
> procedure is in the K2 Dial Calibration article on my website
> http://w3fpr.qrpradio.com
>
> When you are done, if the K2 tunes in WWV in LSB or USB mode with
> accuracy, all bands will also be accurate. Then if you find yourself
> off frequency, you can blame the other radio.
>
> 73,
> Don W3FPR
>
> Brett gazdzinski wrote:
> > Funny, I had today off and decided to do the same thing.
> > I used the 756 pro as a source, did the adjustment, redid
> > all the filter bfo settings, and went from 4000 Hz off to about 500,
> > but I could not tell as I could not zero beat and did not think
> > of changing the filter.
> >
> > When both the 756 and the K2 are tuned to the same frequency,
> > they hear each other, but at maybe 400 or 500 Hz differences.
> >
> > Close enough for me anyway...
> >
> > Last time I did my filters, I paid a lot of attention
> > on getting things to sound the same between filters and
> > CW normal and reversed.
> > Tune a signal in spot on the nose (same as sidetone) and
> > switching between cw normal and reverse does not change the pitch.
> >
> > That is useful if you have qrm on one side.
> >
> > Listening on CW or ssb and changing filters does not change the
> > pitch any, which is nice...
> >
> > The radio really does work well!
> > I enjoy listening to cw (at speeds to fast for me to copy)
> > for hours! ssb sounds good in the headphones, the little speaker
> > inside the K2 does not really cut it for ssb...
> >
> > Brett
> > N2DTS
>