Elecraft

K3 Tx Spurious on Specific Frequencies on 160/80/40

Classic

List

Threaded

12 messages Options

Elecraft mailing list

K3 Tx Spurious on Specific Frequencies on 160/80/40

In general I've found the spurious performance of the K3 to be pretty good,
but I've noticed something today that I thought it would be worth asking
more widely if anyone else has seen and fixed.

I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
also reported me weakly on c. 600 Hz either side of this frequency.
Sometimes skimmers have bad spurious responses, but seeing this on more than
one skimmer caused me to look more closely at my transmit spectrum. I
discovered that - particularly on 40m - there were specific frequency ranges
where a pair of sidebands appeared that move at 150% of the change in
carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
kHz. They cross over with the carrier just below 7013 kHz.

Similar patterns recur in other parts of 40m, but they are strongest near
the bottom of the band. There are dramatic step changes in the level of the
spuria at the boundaries between synthesiser segments - So I see spurii from
7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
strength when they are about +/- 500 Hz from the carrier, but drop
significantly in level as you get further from the carrier.

The level of these spurii is what was concerning - at their worst they were
less than 30dB down on the transmit signal. They grow somewhat non-linearly
with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
-35dBc and at 100W they are a little less than -30dBc. I can see the same
style of spuria in some segments on 80m and 160m - but at lower levels.

I assumed this was a fault with that specific radio - and in some ways it is
- but the same spurii are present on both K3s that I have here - but on the
second radio they are no worse than -45dBc.

I've disconnected everything connected externally from the radio, tried
different power supplies, and recalibrated the synthesiser and Tx gain with
no significant change.

Both radios have the original synthesisers - not the KSYN3A.

Any leads from anyone on this one?

73,

Andy, G4PIQ

______________________________________________________________
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
Message delivered to [hidden email]

Rick Bates, NK7I

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

I don't have an answer, I have no test gear that would even allow a look
(other than another radio). But I'm curious how you're measuring and
observing (not doubting) these results.

Except for the reports seen on the air to validate your observations; if
the radio change barely affects the results and the condition does not,
it's either a failure of both radios or the testing environment (i.e.
transmitting into the same antenna).

What happens with changes in power output, different (dummy) loads?
Then the eternal question; since this hasn't been noted before at your
station; what else is different or has changed? Have you tightened your
antenna connectors lately?

HNY,
Rick NK7I

On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote:

> In general I've found the spurious performance of the K3 to be pretty good,
> but I've noticed something today that I thought it would be worth asking
> more widely if anyone else has seen and fixed.
>
>
>
> I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
> also reported me weakly on c. 600 Hz either side of this frequency.
> Sometimes skimmers have bad spurious responses, but seeing this on more than
> one skimmer caused me to look more closely at my transmit spectrum. I
> discovered that - particularly on 40m - there were specific frequency ranges
> where a pair of sidebands appeared that move at 150% of the change in
> carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
> kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
> kHz. They cross over with the carrier just below 7013 kHz.
>
>
>
> Similar patterns recur in other parts of 40m, but they are strongest near
> the bottom of the band. There are dramatic step changes in the level of the
> spuria at the boundaries between synthesiser segments - So I see spurii from
> 7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
> strength when they are about +/- 500 Hz from the carrier, but drop
> significantly in level as you get further from the carrier.
>
>
>
> The level of these spurii is what was concerning - at their worst they were
> less than 30dB down on the transmit signal. They grow somewhat non-linearly
> with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
> -35dBc and at 100W they are a little less than -30dBc. I can see the same
> style of spuria in some segments on 80m and 160m - but at lower levels.
>
>
>
> I assumed this was a fault with that specific radio - and in some ways it is
> - but the same spurii are present on both K3s that I have here - but on the
> second radio they are no worse than -45dBc.
>
>
>
> I've disconnected everything connected externally from the radio, tried
> different power supplies, and recalibrated the synthesiser and Tx gain with
> no significant change.
>
>
>
> Both radios have the original synthesisers - not the KSYN3A.
>
>
>
> Any leads from anyone on this one?
>
>
>
> 73,
>
>
>
> Andy, G4PIQ
>
>
>
>
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

______________________________________________________________
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
Message delivered to [hidden email]

Elecraft mailing list

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Thanks Rick. To answer those questions.

I'm measuring this with the radio into a power attenuator and then with
additional attenuation into a Perseus SDR operating as a spectrum analyser -
well below its overload threshold and with plenty good enough phase noise
and dynamic range to see this. I've also confirmed the signals are there on
the second K3.

I ripped out all the normal station cabling as part of the testing - so -
yes everything is tight.

I suspect I haven't noticed this before for two reasons. Firstly - the level
of the spurii are very variable by specific frequency in the band - so you
have to be a bit unlucky - and unless you're listening for it yourself on
site - most times it would be too weak for people to comment / skimmers to
pick it up. Also - the times I have run this radio with a second receive in
band while transmitting it's normally been with the run radio above 7025
where the spurii are at a much lower / no existent level.

Secondly - I wonder if something is degrading in that radio. The fact that
the spurious level changes significantly with drive levels suggests this is
being generated by a non-linearity in the PA chain, and I wonder if I'm
short of gain somewhere in the driver strip so the ALC is forcing the low
levels in the strip to be driven harder.

It is present on both radios, but is 15dB worse on one radio than the other.

Andy, G4PIQ

-------------------------

NK7O wrote :-

I don't have an answer, I have no test gear that would even allow a look

(other than another radio). But I'm curious how you're measuring and

observing (not doubting) these results.

Except for the reports seen on the air to validate your observations; if

the radio change barely affects the results and the condition does not,

it's either a failure of both radios or the testing environment (i.e.

transmitting into the same antenna).

What happens with changes in power output, different (dummy) loads?

Then the eternal question; since this hasn't been noted before at your

station; what else is different or has changed? Have you tightened your

antenna connectors lately?

HNY,

Rick NK7I

On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote

In general I've found the spurious performance of the K3 to be pretty good,
but I've noticed something today that I thought it would be worth asking
more widely if anyone else has seen and fixed.

I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
also reported me weakly on c. 600 Hz either side of this frequency.
Sometimes skimmers have bad spurious responses, but seeing this on more than
one skimmer caused me to look more closely at my transmit spectrum. I
discovered that - particularly on 40m - there were specific frequency ranges
where a pair of sidebands appeared that move at 150% of the change in
carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
kHz. They cross over with the carrier just below 7013 kHz.

Similar patterns recur in other parts of 40m, but they are strongest near
the bottom of the band. There are dramatic step changes in the level of the
spuria at the boundaries between synthesiser segments - So I see spurii from
7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
strength when they are about +/- 500 Hz from the carrier, but drop
significantly in level as you get further from the carrier.

The level of these spurii is what was concerning - at their worst they were
less than 30dB down on the transmit signal. They grow somewhat non-linearly
with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
-35dBc and at 100W they are a little less than -30dBc. I can see the same
style of spuria in some segments on 80m and 160m - but at lower levels.

I assumed this was a fault with that specific radio - and in some ways it is
- but the same spurii are present on both K3s that I have here - but on the
second radio they are no worse than -45dBc.

I've disconnected everything connected externally from the radio, tried
different power supplies, and recalibrated the synthesiser and Tx gain with
no significant change.

Both radios have the original synthesisers - not the KSYN3A.

Any leads from anyone on this one?

73,

Andy, G4PIQ

______________________________________________________________
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
Message delivered to [hidden email]

Elecraft mailing list

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

I think I have worked it out.

Taking the lid off and poking about showed that if I touched the crystals at
the DDS end of the filter on the synthesiser board, the spurious levels
rose. Upon taking the lid off the other (newer) radio, I realised that the
KSYN3 in the new radio (SN 8529) had a shield installed that neither of the
KSYN3s in the older radio (SN 4198). Looking at both construction manuals -
somewhere between 2010 an 2013 a shield was added to the KSYN3, so this
looks like leakage from the DDS pre-filtering, and some aluminium is the
pragmatic answer to get the issue down to acceptable levels.

As an experiment, I have just grounded the 4 crystal cases (recognising this
may change the characteristics of the passband a little) - and it has
improved the performance by 15dB - putting the two radios in line with each
other.

73,

Andy, G4PIQ

From: [hidden email] <[hidden email]>
Sent: 01 January 2021 18:31
To: '[hidden email]' <[hidden email]>
Subject: RE: K3 Tx Spurious on Specific Frequencies on 160/80/40

Thanks Rick. To answer those questions.

I'm measuring this with the radio into a power attenuator and then with
additional attenuation into a Perseus SDR operating as a spectrum analyser -
well below its overload threshold and with plenty good enough phase noise
and dynamic range to see this. I've also confirmed the signals are there on
the second K3.

I ripped out all the normal station cabling as part of the testing - so -
yes everything is tight.

I suspect I haven't noticed this before for two reasons. Firstly - the level
of the spurii are very variable by specific frequency in the band - so you
have to be a bit unlucky - and unless you're listening for it yourself on
site - most times it would be too weak for people to comment / skimmers to
pick it up. Also - the times I have run this radio with a second receive in
band while transmitting it's normally been with the run radio above 7025
where the spurii are at a much lower / no existent level.

Secondly - I wonder if something is degrading in that radio. The fact that
the spurious level changes significantly with drive levels suggests this is
being generated by a non-linearity in the PA chain, and I wonder if I'm
short of gain somewhere in the driver strip so the ALC is forcing the low
levels in the strip to be driven harder.

It is present on both radios, but is 15dB worse on one radio than the other.

Andy, G4PIQ

-------------------------

NK7O wrote :-

I don't have an answer, I have no test gear that would even allow a look

(other than another radio). But I'm curious how you're measuring and

observing (not doubting) these results.

Except for the reports seen on the air to validate your observations; if

the radio change barely affects the results and the condition does not,

it's either a failure of both radios or the testing environment (i.e.

transmitting into the same antenna).

What happens with changes in power output, different (dummy) loads?

Then the eternal question; since this hasn't been noted before at your

station; what else is different or has changed? Have you tightened your

antenna connectors lately?

HNY,

Rick NK7I

On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote

In general I've found the spurious performance of the K3 to be pretty good,
but I've noticed something today that I thought it would be worth asking
more widely if anyone else has seen and fixed.

I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
also reported me weakly on c. 600 Hz either side of this frequency.
Sometimes skimmers have bad spurious responses, but seeing this on more than
one skimmer caused me to look more closely at my transmit spectrum. I
discovered that - particularly on 40m - there were specific frequency ranges
where a pair of sidebands appeared that move at 150% of the change in
carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
kHz. They cross over with the carrier just below 7013 kHz.

Similar patterns recur in other parts of 40m, but they are strongest near
the bottom of the band. There are dramatic step changes in the level of the
spuria at the boundaries between synthesiser segments - So I see spurii from
7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
strength when they are about +/- 500 Hz from the carrier, but drop
significantly in level as you get further from the carrier.

The level of these spurii is what was concerning - at their worst they were
less than 30dB down on the transmit signal. They grow somewhat non-linearly
with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
-35dBc and at 100W they are a little less than -30dBc. I can see the same
style of spuria in some segments on 80m and 160m - but at lower levels.

I assumed this was a fault with that specific radio - and in some ways it is
- but the same spurii are present on both K3s that I have here - but on the
second radio they are no worse than -45dBc.

I've disconnected everything connected externally from the radio, tried
different power supplies, and recalibrated the synthesiser and Tx gain with
no significant change.

Both radios have the original synthesisers - not the KSYN3A.

Any leads from anyone on this one?

73,

Andy, G4PIQ

______________________________________________________________
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
Message delivered to [hidden email]

Elecraft mailing list

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

And a small correction to this in case anyone else gets inspired to do
anything. Grounding just one of the crystals improved the performance by
about 8dB - but did not get as good as the KSYN3 with a shield. It clearly
needs the full treatment.

73,

Andy, G4PIQ

From: [hidden email] <[hidden email]>
Sent: 01 January 2021 20:57
To: '[hidden email]' <[hidden email]>
Subject: RE: K3 Tx Spurious on Specific Frequencies on 160/80/40

I think I have worked it out.

Taking the lid off and poking about showed that if I touched the crystals at
the DDS end of the filter on the synthesiser board, the spurious levels
rose. Upon taking the lid off the other (newer) radio, I realised that the
KSYN3 in the new radio (SN 8529) had a shield installed that neither of the
KSYN3s in the older radio (SN 4198). Looking at both construction manuals -
somewhere between 2010 an 2013 a shield was added to the KSYN3, so this
looks like leakage from the DDS pre-filtering, and some aluminium is the
pragmatic answer to get the issue down to acceptable levels.

As an experiment, I have just grounded the 4 crystal cases (recognising this
may change the characteristics of the passband a little) - and it has
improved the performance by 15dB - putting the two radios in line with each
other.

73,

Andy, G4PIQ

From: [hidden email] <mailto:[hidden email]>
<[hidden email] <mailto:[hidden email]> >
Sent: 01 January 2021 18:31
To: '[hidden email]' <[hidden email]
<mailto:[hidden email]> >
Subject: RE: K3 Tx Spurious on Specific Frequencies on 160/80/40

Thanks Rick. To answer those questions.

I'm measuring this with the radio into a power attenuator and then with
additional attenuation into a Perseus SDR operating as a spectrum analyser -
well below its overload threshold and with plenty good enough phase noise
and dynamic range to see this. I've also confirmed the signals are there on
the second K3.

I ripped out all the normal station cabling as part of the testing - so -
yes everything is tight.

I suspect I haven't noticed this before for two reasons. Firstly - the level
of the spurii are very variable by specific frequency in the band - so you
have to be a bit unlucky - and unless you're listening for it yourself on
site - most times it would be too weak for people to comment / skimmers to
pick it up. Also - the times I have run this radio with a second receive in
band while transmitting it's normally been with the run radio above 7025
where the spurii are at a much lower / no existent level.

Secondly - I wonder if something is degrading in that radio. The fact that
the spurious level changes significantly with drive levels suggests this is
being generated by a non-linearity in the PA chain, and I wonder if I'm
short of gain somewhere in the driver strip so the ALC is forcing the low
levels in the strip to be driven harder.

It is present on both radios, but is 15dB worse on one radio than the other.

Andy, G4PIQ

-------------------------

NK7O wrote :-

I don't have an answer, I have no test gear that would even allow a look

(other than another radio). But I'm curious how you're measuring and

observing (not doubting) these results.

Except for the reports seen on the air to validate your observations; if

the radio change barely affects the results and the condition does not,

it's either a failure of both radios or the testing environment (i.e.

transmitting into the same antenna).

What happens with changes in power output, different (dummy) loads?

Then the eternal question; since this hasn't been noted before at your

station; what else is different or has changed? Have you tightened your

antenna connectors lately?

HNY,

Rick NK7I

On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote

In general I've found the spurious performance of the K3 to be pretty good,
but I've noticed something today that I thought it would be worth asking
more widely if anyone else has seen and fixed.

I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
also reported me weakly on c. 600 Hz either side of this frequency.
Sometimes skimmers have bad spurious responses, but seeing this on more than
one skimmer caused me to look more closely at my transmit spectrum. I
discovered that - particularly on 40m - there were specific frequency ranges
where a pair of sidebands appeared that move at 150% of the change in
carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
kHz. They cross over with the carrier just below 7013 kHz.

Similar patterns recur in other parts of 40m, but they are strongest near
the bottom of the band. There are dramatic step changes in the level of the
spuria at the boundaries between synthesiser segments - So I see spurii from
7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
strength when they are about +/- 500 Hz from the carrier, but drop
significantly in level as you get further from the carrier.

The level of these spurii is what was concerning - at their worst they were
less than 30dB down on the transmit signal. They grow somewhat non-linearly
with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
-35dBc and at 100W they are a little less than -30dBc. I can see the same
style of spuria in some segments on 80m and 160m - but at lower levels.

I assumed this was a fault with that specific radio - and in some ways it is
- but the same spurii are present on both K3s that I have here - but on the
second radio they are no worse than -45dBc.

I've disconnected everything connected externally from the radio, tried
different power supplies, and recalibrated the synthesiser and Tx gain with
no significant change.

Both radios have the original synthesisers - not the KSYN3A.

Any leads from anyone on this one?

73,

Andy, G4PIQ

______________________________________________________________
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
Message delivered to [hidden email]

Elecraft mailing list

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

I believe the rather thick "shield" was actually a stiffener to prevent
microphony at high audio levels using the internal speaker.

Regards,

Mike VP8NO

On 01/01/2021 18:22, g4piq--- via Elecraft wrote:

> And a small correction to this in case anyone else gets inspired to do
> anything. Grounding just one of the crystals improved the performance by
> about 8dB - but did not get as good as the KSYN3 with a shield. It clearly
> needs the full treatment.
>
>
>
> 73,
>
>
>
> Andy, G4PIQ

w4sc-2

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Andy,

I would be interested as to what the shield looks like. I have a 73xx s/n that does not have the shield. At some point near the end of the their production, K3 was built with KSYN3A.

How did you ‘ground’ the crystal cases? My radio came with the stiffener installed on the synthesizer.

Ben W4SC

Sent from Mail for Windows 10

______________________________________________________________
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
Message delivered to [hidden email]

w4sc-2

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Mike,

That’s a good point. Is Andy referring to the stiffener or an additional shield around the crystals?

Ben W4SC

Sent from Mail for Windows 10

______________________________________________________________
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
Message delivered to [hidden email]

Wes Stewart-2

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Correct. My K3 was the first one to have the stiffener. I discovered the
microphonic synthesizer early on (2008 IIRC) and demonstrated it to an Elecraft
engineer in my shack. His radio had the same problem. It didn't take high
levels, noises in the shack would modulate it; they were more random and harder
to see than single frequencies, but they were there.

Of course the new upgraded boards are free of this.

Considering the lightweight construction, the almost total lack of shielding and
the questionable TMP connectors, the K3(S) is remarkably free of birdies and
spurious garbage. It's there just usually not objectionable.

Wes N7WS

On 1/1/2021 3:36 PM, Mike Harris via Elecraft wrote:

> I believe the rather thick "shield" was actually a stiffener to prevent
> microphony at high audio levels using the internal speaker.
>
> Regards,
>
> Mike VP8NO
>
> On 01/01/2021 18:22, g4piq--- via Elecraft wrote:
>> And a small correction to this in case anyone else gets inspired to do
>> anything. Grounding just one of the crystals improved the performance by
>> about 8dB - but did not get as good as the KSYN3 with a shield. It clearly
>> needs the full treatment.
>>
>>
>> 73,
>>
>>
>> Andy, G4PIQ

Elecraft mailing list

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Thanks Wes, Mike and Ben,

Ah - I hadn't realised the shield was there as a mechanical stiffener - I
did think it was very thick. I did notice the microphonics while I was
testing - of course a good solid thump to the radio is an important part of
any debugging process to find dodgy connections - and I could see the effect
of microphony on the stability of the carrier.

I was only talking about that stifferer - which I assume also works as a
shield - not anything additions.

To ground the crystal, I just used a short wire from a ground via to the
nearest crystal can - and to test grounding all 4 I stuffed a piece of
aluminium foil in between all 4 xtals.

When I measured it properly - the single ground improved the worst case
performance at 100W from -28dBc to -35dBc, but the addition of the foil to
ground them all made it a bit worse (back to about -30 dBc). Swapping in the
shielded KSYN3 from the other radio gives about -45dBc worst case at 100W -
much the same on both radios.

The best answer might be to buy some KSYN3As - but of course they're not
readily available right now - though I am aware of the pre-order interest
form. And they could have similar issues of course. I haven't bothered to
this point since even with the KSYN3s performance is good enough to operate
SO2R in-band within 1-2 kHz with less than 100m of antenna separation here.

73,

Andy, G4PIQ

From: [hidden email] <[hidden email]>
Sent: 01 January 2021 21:22
To: '[hidden email]' <[hidden email]>
Subject: RE: K3 Tx Spurious on Specific Frequencies on 160/80/40

And a small correction to this in case anyone else gets inspired to do
anything. Grounding just one of the crystals improved the performance by
about 8dB - but did not get as good as the KSYN3 with a shield. It clearly
needs the full treatment.

73,

Andy, G4PIQ

From: [hidden email] <mailto:[hidden email]>
<[hidden email] <mailto:[hidden email]> >
Sent: 01 January 2021 20:57
To: '[hidden email]' <[hidden email]
<mailto:[hidden email]> >
Subject: RE: K3 Tx Spurious on Specific Frequencies on 160/80/40

I think I have worked it out.

Taking the lid off and poking about showed that if I touched the crystals at
the DDS end of the filter on the synthesiser board, the spurious levels
rose. Upon taking the lid off the other (newer) radio, I realised that the
KSYN3 in the new radio (SN 8529) had a shield installed that neither of the
KSYN3s in the older radio (SN 4198). Looking at both construction manuals -
somewhere between 2010 an 2013 a shield was added to the KSYN3, so this
looks like leakage from the DDS pre-filtering, and some aluminium is the
pragmatic answer to get the issue down to acceptable levels.

As an experiment, I have just grounded the 4 crystal cases (recognising this
may change the characteristics of the passband a little) - and it has
improved the performance by 15dB - putting the two radios in line with each
other.

73,

Andy, G4PIQ

From: [hidden email] <mailto:[hidden email]>
<[hidden email] <mailto:[hidden email]> >
Sent: 01 January 2021 18:31
To: '[hidden email]' <[hidden email]
<mailto:[hidden email]> >
Subject: RE: K3 Tx Spurious on Specific Frequencies on 160/80/40

Thanks Rick. To answer those questions.

I'm measuring this with the radio into a power attenuator and then with
additional attenuation into a Perseus SDR operating as a spectrum analyser -
well below its overload threshold and with plenty good enough phase noise
and dynamic range to see this. I've also confirmed the signals are there on
the second K3.

I ripped out all the normal station cabling as part of the testing - so -
yes everything is tight.

I suspect I haven't noticed this before for two reasons. Firstly - the level
of the spurii are very variable by specific frequency in the band - so you
have to be a bit unlucky - and unless you're listening for it yourself on
site - most times it would be too weak for people to comment / skimmers to
pick it up. Also - the times I have run this radio with a second receive in
band while transmitting it's normally been with the run radio above 7025
where the spurii are at a much lower / no existent level.

Secondly - I wonder if something is degrading in that radio. The fact that
the spurious level changes significantly with drive levels suggests this is
being generated by a non-linearity in the PA chain, and I wonder if I'm
short of gain somewhere in the driver strip so the ALC is forcing the low
levels in the strip to be driven harder.

It is present on both radios, but is 15dB worse on one radio than the other.

Andy, G4PIQ

-------------------------

NK7O wrote :-

I don't have an answer, I have no test gear that would even allow a look

(other than another radio). But I'm curious how you're measuring and

observing (not doubting) these results.

Except for the reports seen on the air to validate your observations; if

the radio change barely affects the results and the condition does not,

it's either a failure of both radios or the testing environment (i.e.

transmitting into the same antenna).

What happens with changes in power output, different (dummy) loads?

Then the eternal question; since this hasn't been noted before at your

station; what else is different or has changed? Have you tightened your

antenna connectors lately?

HNY,

Rick NK7I

On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote

In general I've found the spurious performance of the K3 to be pretty good,
but I've noticed something today that I thought it would be worth asking
more widely if anyone else has seen and fixed.

I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
also reported me weakly on c. 600 Hz either side of this frequency.
Sometimes skimmers have bad spurious responses, but seeing this on more than
one skimmer caused me to look more closely at my transmit spectrum. I
discovered that - particularly on 40m - there were specific frequency ranges
where a pair of sidebands appeared that move at 150% of the change in
carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
kHz. They cross over with the carrier just below 7013 kHz.

Similar patterns recur in other parts of 40m, but they are strongest near
the bottom of the band. There are dramatic step changes in the level of the
spuria at the boundaries between synthesiser segments - So I see spurii from
7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
strength when they are about +/- 500 Hz from the carrier, but drop
significantly in level as you get further from the carrier.

The level of these spurii is what was concerning - at their worst they were
less than 30dB down on the transmit signal. They grow somewhat non-linearly
with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
-35dBc and at 100W they are a little less than -30dBc. I can see the same
style of spuria in some segments on 80m and 160m - but at lower levels.

I assumed this was a fault with that specific radio - and in some ways it is
- but the same spurii are present on both K3s that I have here - but on the
second radio they are no worse than -45dBc.

I've disconnected everything connected externally from the radio, tried
different power supplies, and recalibrated the synthesiser and Tx gain with
no significant change.

Both radios have the original synthesisers - not the KSYN3A.

Any leads from anyone on this one?

73,

Andy, G4PIQ

______________________________________________________________
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
Message delivered to [hidden email]

w4sc-2

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Andy

You may have a solution in hand for the spurious…

The stiffener plate mod kit is still showing as available. I am wondering if there would be any improvement gained by grounding the crystal cans in a K3 with the plate, or even necessary.

K3STFNR_K3 Synthesizer Stiffener Plate Kit – Elecraft

Ben W4SC

Sent from Mail for Windows 10

______________________________________________________________
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
Message delivered to [hidden email]

Rick Bates, NK7I

Re: K3 Tx Spurious on Specific Frequencies on 160/80/40

In reply to this post by Elecraft mailing list

Andy,

My suggestion is rather basic (I've learned that sometimes the most
obvious is often missed, don't ask how I know). Take the time to open
the case and tighten every bolt, nut, screw and reseat the connectors
(wiggle everything). Then retest. Over time, some radios self-loosen
bolts etc. in particular those that bond boards to mounts (thermal
flexing). ;-) However Elecraft is not just 'some radio', but it's
worth a peek.

I would also suggest a redo of the power calibration sequence, to have
those values at the ready for Elecraft (save the config file to send to
them). I say this because recent reports of LPA failure of a few K3's
have appeared on this list (one may be carrying more load if another has
failed). If that has happened, non-linearity could be increased (as the
radio strives to make the power level as set), amplified through each stage.

By then the support staff at Elecraft should be back on duty for further
comments and testing.

It's curious (disturbing) that both of yours exhibit the same issues
(though one is 'better').

Good luck, please report back any useful comments or fixes.

HNY,
Rick NK7I

On 1/1/2021 10:34 AM, g4piq--- via Elecraft wrote:

> Thanks Rick. To answer those questions.
>
>
>
> I'm measuring this with the radio into a power attenuator and then with
> additional attenuation into a Perseus SDR operating as a spectrum analyser -
> well below its overload threshold and with plenty good enough phase noise
> and dynamic range to see this. I've also confirmed the signals are there on
> the second K3.
>
>
>
> I ripped out all the normal station cabling as part of the testing - so -
> yes everything is tight.
>
>
>
> I suspect I haven't noticed this before for two reasons. Firstly - the level
> of the spurii are very variable by specific frequency in the band - so you
> have to be a bit unlucky - and unless you're listening for it yourself on
> site - most times it would be too weak for people to comment / skimmers to
> pick it up. Also - the times I have run this radio with a second receive in
> band while transmitting it's normally been with the run radio above 7025
> where the spurii are at a much lower / no existent level.
>
>
>
> Secondly - I wonder if something is degrading in that radio. The fact that
> the spurious level changes significantly with drive levels suggests this is
> being generated by a non-linearity in the PA chain, and I wonder if I'm
> short of gain somewhere in the driver strip so the ALC is forcing the low
> levels in the strip to be driven harder.
>
>
>
> It is present on both radios, but is 15dB worse on one radio than the other.
>
>
>
> Andy, G4PIQ
>
> -------------------------
>
> NK7O wrote :-
>
> I don't have an answer, I have no test gear that would even allow a look
>
> (other than another radio). But I'm curious how you're measuring and
>
> observing (not doubting) these results.
>
>
>
> Except for the reports seen on the air to validate your observations; if
>
> the radio change barely affects the results and the condition does not,
>
> it's either a failure of both radios or the testing environment (i.e.
>
> transmitting into the same antenna).
>
>
>
> What happens with changes in power output, different (dummy) loads?
>
> Then the eternal question; since this hasn't been noted before at your
>
> station; what else is different or has changed? Have you tightened your
>
> antenna connectors lately?
>
>
>
> HNY,
>
> Rick NK7I
>
>
>
> On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote
>
>
>
> In general I've found the spurious performance of the K3 to be pretty good,
> but I've noticed something today that I thought it would be worth asking
> more widely if anyone else has seen and fixed.
>
>
>
> I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
> also reported me weakly on c. 600 Hz either side of this frequency.
> Sometimes skimmers have bad spurious responses, but seeing this on more than
> one skimmer caused me to look more closely at my transmit spectrum. I
> discovered that - particularly on 40m - there were specific frequency ranges
> where a pair of sidebands appeared that move at 150% of the change in
> carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
> kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
> kHz. They cross over with the carrier just below 7013 kHz.
>
>
>
> Similar patterns recur in other parts of 40m, but they are strongest near
> the bottom of the band. There are dramatic step changes in the level of the
> spuria at the boundaries between synthesiser segments - So I see spurii from
> 7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
> strength when they are about +/- 500 Hz from the carrier, but drop
> significantly in level as you get further from the carrier.
>
>
>
> The level of these spurii is what was concerning - at their worst they were
> less than 30dB down on the transmit signal. They grow somewhat non-linearly
> with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
> -35dBc and at 100W they are a little less than -30dBc. I can see the same
> style of spuria in some segments on 80m and 160m - but at lower levels.
>
>
>
> I assumed this was a fault with that specific radio - and in some ways it is
> - but the same spurii are present on both K3s that I have here - but on the
> second radio they are no worse than -45dBc.
>
>
>
> I've disconnected everything connected externally from the radio, tried
> different power supplies, and recalibrated the synthesiser and Tx gain with
> no significant change.
>
>
>
> Both radios have the original synthesisers - not the KSYN3A.
>
>
>
> Any leads from anyone on this one?
>
>
>
> 73,
>
>
>
> Andy, G4PIQ
>
>
>
>
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]