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K2 - Resonate noise on audio

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Jason V

K2 - Resonate noise on audio

I did a lot of testing to try and resolve and isolate the issue. So here are all the details and sorry in advance for being so verbose. Also very green to amateur radio. Got my ticket this year in January and the ink isn't even dry. So please bear with me.

I purchased a QRP K2 (s/n: 00026, not a typo) second hand and was fairly happy with it after performing an alignment and setting the filters. I opted to build and install the KPA100 and KAT100 requiring numerous upgrades to support. Firmware upgrade, VFO, BFO, KPA/KAT100 mods provided with the kits, and replaced the filters with a matched set. I have doubled checked board level mods on the K2 n+1 times and they are done per the manuals.

when doing an alignment and setting the filters after completion there is resonate noise outside the skirts of the filters which wasn't there before. It is present on all bands and modes with the same interval. Stripped the radio back down to a QRP rig and it is still present. Attached a dummy load and tuned to the 7Mhz birdie. When ever the birdie was within the filter the resonance would be present, outside it goes away.
Links to screen shots.
No birdie on cw filter. http://goo.gl/qvMGOq
birdie @ ~633 Hz. http://goo.gl/irDakg
birdie @ ~721 Hz. http://goo.gl/lBEacm

So I brought the Radio to work and put it on the IFR 1900 and it Tx's and Rx's just fine. Probed each of the new crystals and they all appeared fine as well, steep skirts, consistent width, and no spurs. I have screen shots of the IFR if needed.

Comfortable it wasn't going to splatter the bands I put it on the air last night. Logged quite a few DX QSOs via JT65 and listened in on some SSB which sounded great. So the good news is the problem doesn't exist within the filtered audio. But it bugs the bejesus out of me knowing it wasn't there before the mods.

The only options installed during the time of test were the RX160, KAF2, K2NB2, & KSB2. Neither of which have been modified in any way. Except for the new crystals on the KSB2.

Any help or guidance would be greatly appreciated!

Best Regards,
Jason - KV4TY

Phil Wheeler-2

Re: K2 - Resonate noise on audio

I'd check the KSB2. How well are the xtals
grounded (solder joints and such)? Were any
problems introduced while installing the crystals?
etc. KSB2 is a pretty compact board so easy to
introduce solder bridges and such.

If you did mods to the K2 before adding the KPA100
did you use it QRP in that period?

73, Phil w7ox (K2 #380 with KPA100 and KAT100)

On 3/19/14, 10:01 AM, Jason V wrote:

> I did a lot of testing to try and resolve and isolate the issue. So here are
> all the details and sorry in advance for being so verbose. Also very green
> to amateur radio. Got my ticket this year in January and the ink isn't even
> dry. So please bear with me.
>
> I purchased a QRP K2 (s/n: 00026, not a typo) second hand and was fairly
> happy with it after performing an alignment and setting the filters. I
> opted to build and install the KPA100 and KAT100 requiring numerous upgrades
> to support. Firmware upgrade, VFO, BFO, KPA/KAT100 mods provided with the
> kits, and replaced the filters with a matched set. I have doubled checked
> board level mods on the K2 n+1 times and they are done per the manuals.
>
> when doing an alignment and setting the filters after completion there is
> resonate noise outside the skirts of the filters which wasn't there before.
> It is present on all bands and modes with the same interval. Stripped the
> radio back down to a QRP rig and it is still present. Attached a dummy load
> and tuned to the 7Mhz birdie. When ever the birdie was within the filter
> the resonance would be present, outside it goes away.
> Links to screen shots.
> No birdie on cw filter. http://goo.gl/qvMGOq
> birdie @ ~633 Hz. http://goo.gl/irDakg
> birdie @ ~721 Hz. http://goo.gl/lBEacm
>
> So I brought the Radio to work and put it on the IFR 1900 and it Tx's and
> Rx's just fine. Probed each of the new crystals and they all appeared fine
> as well, steep skirts, consistent width, and no spurs. I have screen shots
> of the IFR if needed.
>
> Comfortable it wasn't going to splatter the bands I put it on the air last
> night. Logged quite a few DX QSOs via JT65 and listened in on some SSB
> which sounded great. So the good news is the problem doesn't exist within
> the filtered audio. But it bugs the bejesus out of me knowing it wasn't
> there before the mods.
>
> The only options installed during the time of test were the RX160, KAF2,
> K2NB2, & KSB2. Neither of which have been modified in any way. Except for
> the new crystals on the KSB2.
>
> Any help or guidance would be greatly appreciated!
>
> Best Regards,
> Jason - KV4TY

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Jason V

Re: K2 - Resonate noise on audio

Thanks Phil.

My wife is IPC-7711/7721 and had her inspect my work when it was complete, so pretty confident there. That and I rechecked it several times since the problem began. Removed the old crystals, cleaned up the vias with solderwick, re-installed using insulator pads, and soldered the ground tab to the side of the crystal approce 1/8" above the base. All the cans measured for continuity to the ground plane. Have a metcal soldering station and it makes working in dense layouts easier, not to mention temp controls. No one is perfect though so I could pull the KSB2 and put a few jumpers in it's place. The problem will either follow it or stay.

No. Wish I had stopped to check the K2 mods first. Usually I take an incremental approach to this kind of thing but since I had the radio all apart I did them while I was in there. So I don't know exactly when the problem was introduced.

Don Wilhelm-4

Re: K2 - Resonate noise on audio

In reply to this post by Jason V

John,

Those "resonances" appear to be similar to what I observe when the
soundcard input is overdriven.
See what happens if you reduce the audio into the soundcard.

Did you replace the crystals on the RF board as well? If so, I hope you
re-used the insulators under the crystals. They were needed in the
Field Test boards (serial numbers 100 and below) - boards used after the
Field Test had more complete solder masking and were no longer necessary.

73,
Don W3FPR
On 3/19/2014 1:01 PM, Jason V wrote:

> Attached a dummy load
> and tuned to the 7Mhz birdie. When ever the birdie was within the filter
> the resonance would be present, outside it goes away.
> Links to screen shots.
> No birdie on cw filter. http://goo.gl/qvMGOq
> birdie @ ~633 Hz. http://goo.gl/irDakg
> birdie @ ~721 Hz. http://goo.gl/lBEacm
>
> So I brought the Radio to work and put it on the IFR 1900 and it Tx's and
> Rx's just fine. Probed each of the new crystals and they all appeared fine
> as well, steep skirts, consistent width, and no spurs. I have screen shots
> of the IFR if needed.
>
>

Phil Wheeler-2

Re: K2 - Resonate noise on audio

In reply to this post by Jason V

It sounds like a bear, Jason. But I know you'll
find it eventually, especially with input from Don
W. and Co.

I still think the SSB board is the likely culprit.
But did you do any other mods at that time, like
the A to B mod set? Good to look in those areas
too, if you did. I've done *most* of those
updates, but generally not the post-2002 KPA100
mods and updates: I've had zero issues with mine,
perhaps because the KAT100 gives it a happy
environment. The one recent mod I really
appreciated was the AF gain pot mod. No
components, but traces to cut and jumpers to add
on the three main boards -- a major disassembly.
But well worth doing (likely done on yours, since
I think the mod has been around since 2001); easy
to check for by looking for the long jumper on the
RF board at the front on the underside.

K2 is a great rig. I did a receive compare with my
K3 this morning and it's still one of the best
there is. It is nice, with the new rigs, to not
have the need for disassembly for firmware
updates. Of course, not likely any more for the
K2! Mine was ten years behind in Feb so I did all
the needed F/W updates then.

73, Phil w7ox

On 3/19/14, 11:12 AM, Jason V wrote:

> Thanks Phil.
>
> My wife is IPC-7711/7721 and had her inspect my work when it was complete,
> so pretty confident there. That and I rechecked it several times since the
> problem began. Removed the old crystals, cleaned up the vias with
> solderwick, re-installed using insulator pads, and soldered the ground tab
> to the side of the crystal approce 1/8" above the base. All the cans
> measured for continuity to the ground plane. Have a metcal soldering
> station and it makes working in dense layouts easier, not to mention temp
> controls. No one is perfect though so I could pull the KSB2 and put a few
> jumpers in it's place. The problem will either follow it or stay.
>
> No. Wish I had stopped to check the K2 mods first. Usually I take an
> incremental approach to this kind of thing but since I had the radio all
> apart I did them while I was in there. So I don't know exactly when the
> problem was introduced.
>
>
>

Jason V

Re: K2 - Resonate noise on audio

This post was updated on .

In reply to this post by Don Wilhelm-4

Don,
When the first set of pictures were taken the audio output was in attenuate mode with a minimal AF setting, the signalink Rx gain was set to 25% ish, and the PC mic input gain was set to 25%. The only thing that changed between pictures was the VFO. Last night I had a little time to double check this and had the same results. To rule out the signalink as the culprit I swapped over to the PC's mic input with the same result. Pretty confident it is coming from the radio now.

Tonight I will open her up to double check the crystal insulators are in place and bypass the SSB card.

Thanks for the input guys.

Jason

> Those "resonances" appear to be similar to what I observe when the
> soundcard input is overdriven.
> See what happens if you reduce the audio into the soundcard.

Jason V

Re: K2 - Resonate noise on audio

Quick update.
All the filter crystals on the RF and KSB2 have insulators installed.
The KSB2 was removed (jumpers installed across W2 & W3 and C167 populated) and the noise is still present.

Best Regards,
Jason

Don Wilhelm-4

Re: K2 - Resonate noise on audio

Jason,

Do you have the KDSP2 installed on that K2? If so, make certain the
noise parameters are off - or simply put it into BYPASS. Note that
BYPASS does not survive a power cycle.
If you are power cycling the K2, physically remove the KDSP2 and
complete the audio path with jumpers from J1 pin 1 to J2 pin 1 and from
J1 pin 2 to J2 pin 2 on the control board.

The denoiser algorithm in the KDSP2 can cause "strange stuff" in the
audio spectrum display.

Since you are using a CW filter, it is doubtful that the KSB2 option
could cause what you are seeing (assuming the switching diodes on the
KSB2 are doing their job).

If the situation persists, look at the audio amp, or drive an external
audio amp from the RF Board J5 position to see if it is being produced
in the product detector or the AF amp. I am guessing you may be seeing
mixing products generated by the receiver noise mixing with the signal.

73,
Don W3FPR

On 3/21/2014 10:09 AM, Jason V wrote:
> Quick update.
> All the filter crystals on the RF and KSB2 have insulators installed.
> The KSB2 was removed (jumpers installed across W2 & W3 and C167 populated)
> and the noise is still present.
>
>

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