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Tx distortion

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mustang65

Tx distortion

Hi!

I have hade my k2 about 14 years with number 4503 and it been a pleasure to
build and operate it
but now I got problems with distorsion on the TX audio.

It will usully work fine when it been resting over the night but after a
while the distorsion slowly comes.
I t start with the base in the audio are reduced and then the treble are
cracking up. It sounds like you driving a audioamplifier just alittle to
hard.
The problem is the same with thek2/100 or when it removed from the k2.

I have used a 2 tone signalgenerator and loked with a scope att the signal
after the ne602 and after the 10w amplifier
and it looks fine to me but the bandwith of the scope is just 15Mhz so I
might be missing something.

I have replaced u5, Q1, D2and some capacitors on the ksb2 board, tried to
find any bad soldering but no luck.
Can it be a bad capicotor in the ssb filter or in the Tx signal path?

Grateful for any advise.

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mustang65

Re: Tx distortion

I forgott to mention that there is no distortion on Rx only on Tx does that
mean
that the ssb crystel filter is ok or can the filter still cause distortion
only on Tx

Grateful for any help
73 Mike sm3xgm

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Don Wilhelm

Re: Tx distortion

In reply to this post by mustang65

If the filter is OK in receive, it will also be good in transmit. The
only things which differ are diodes D4 and D14 on the KSB2 board.

I would look for one of 2 things - RF Feedback and a bad microphone.

To check for RF Feedback, operate the K2 into a dummy load and listen
with a monitor receiver using a wire for an antenna placed near enough
to the dummy load to obtain an S-9 signal in CW.

To check for a bad microphone, the best way is to substitute another mic
of the same kind.

A question - did you change from an Elecraft microphone to something
else? If that 'new' mic is a dynamic type, did you remove the bias
resistor? If the bias resistor is left in and a dynamic mic is used,
the bias voltage will drive the mic diaphram off center causing it to
"sound funny".

73,
Don W3FPR

On 2/1/2019 11:13 AM, mustang65 wrote:

> Hi!
>
> I have hade my k2 about 14 years with number 4503 and it been a pleasure to
> build and operate it
> but now I got problems with distorsion on the TX audio.
>
> It will usully work fine when it been resting over the night but after a
> while the distorsion slowly comes.
> I t start with the base in the audio are reduced and then the treble are
> cracking up. It sounds like you driving a audioamplifier just alittle to
> hard.
> The problem is the same with thek2/100 or when it removed from the k2.
>
> I have used a 2 tone signalgenerator and loked with a scope att the signal
> after the ne602 and after the 10w amplifier
> and it looks fine to me but the bandwith of the scope is just 15Mhz so I
> might be missing something.
>
> I have replaced u5, Q1, D2and some capacitors on the ksb2 board, tried to
> find any bad soldering but no luck.
> Can it be a bad capicotor in the ssb filter or in the Tx signal path?
>
> Grateful for any advise.

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mustang65

Re: Tx distortion

In reply to this post by mustang65

Many thanks for the answer and good to know that I can rule out the filter
as the problem.

I have not change anything in my setup that I used for severel years and
that is main reasen
I believe something has happend to the k2.

All the tests I done so far has bean made in to a dummyload and a icom 735
as receiver.

I use a shure sm58 microphone that is connected to symetrix 528e micpreamp
, voiceprocessor that
drives the k2. I also have a Icom microphone that I connect directly to
the K2 and it do not make
any difference on the distorsion. Both this setups have worked nice for
many years.

If I use the icom 735 as transmitter and k2 as receiver it still works
fine both with the icom microphone or the symetrix unit and shure
microphone.

The strange thing is when the k2 has been turned of for a couple of hours
and then
start to transmit the tx audio is mutch better then it comes like you
slowly turn upp a pot
the audio gets thinner and the distortion increases.

I monitor the driving signal from the symetrix unit at the same time to
rule out that as a cause.
Looked for cold soldering on the ssb bord.

I have also looked for any components to get varm and so far it is just Q6
on the RF board that gets
araond 122 degrees Fahrenheit that do not seems like a problem.

I have meassured D1 and D14 and looks ok. Can Q2 on the ksb2 board cause
this problem?

73 Mike sm3xgm

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Don Wilhelm

Re: Tx distortion

Mike,

With RF and microphone out of the way, I would look to either coupling
capacitors in the AF path (C20, C32, and C34) or the Speech Compressor
IC for the problem.

Unfortunately, the '2165 speech processor IC is no longer available -
the KSB2 was redesigned to use the '2166 IC instead, but it is not a
drop-in replacement, and if that turns out to be the problem, it means
buying a new KSB2 board.

73,
Don W3FPR

On 2/2/2019 10:07 AM, mustang65 wrote:

>
> Many thanks for the answer and good to know that I can rule out the filter
> as the problem.
>
> I have not change anything in my setup that I used for severel years and
> that is main reasen
> I believe something has happend to the k2.
>
> All the tests I done so far has bean made in to a dummyload and a icom 735
> as receiver.
>
> I use a shure sm58 microphone that is connected to symetrix 528e micpreamp
> , voiceprocessor that
> drives the k2. I also have a Icom microphone that I connect directly to
> the K2 and it do not make
> any difference on the distorsion. Both this setups have worked nice for
> many years.
>
> If I use the icom 735 as transmitter and k2 as receiver it still works
> fine both with the icom microphone or the symetrix unit and shure
> microphone.
>
> The strange thing is when the k2 has been turned of for a couple of hours
> and then
> start to transmit the tx audio is mutch better then it comes like you
> slowly turn upp a pot
> the audio gets thinner and the distortion increases.
>
> I monitor the driving signal from the symetrix unit at the same time to
> rule out that as a cause.
> Looked for cold soldering on the ssb bord.
>
> I have also looked for any components to get varm and so far it is just Q6
> on the RF board that gets
> araond 122 degrees Fahrenheit that do not seems like a problem.
>
>
> I have meassured D1 and D14 and looks ok. Can Q2 on the ksb2 board cause
> this problem?
>
> 73 Mike sm3xgm
>
>
>
>
>
>
>
>
>
>
> --
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mustang65

Re: Tx distortion

In reply to this post by mustang65

Don,

Thanks for the suggestions.
I am thinking of putting the outputsignal from the symetrix 528e microphone
amplifier
to c20 on the ksb2 board so I will bypass U3 and let the signal go direct
to u5 NE602
and that way found out if u2 is bad.
I will come back with the result.

73 Mike sm3xgm

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Jim Brown-10

Re: Tx distortion

The Symetrix unit could be involved. Why are you using it? What mic are
you using?

73, Jim K9YC

On 2/2/2019 10:55 AM, mustang65 wrote:
> I am thinking of putting the outputsignal from the symetrix 528e microphone
> amplifier
> to c20 on the ksb2 board so I will bypass U3 and let the signal go direct
> to u5 NE602

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Don Wilhelm

Re: Tx distortion

In reply to this post by mustang65

Mike,

Notice that U2 also has an output that is involved in PTT and VOX
detection via U4 and the COMP OUT signal.
The signal at the output side of C31 is driving an impedance of about 8k
ohms. I don't know what your Symetrix mic amplifier is capable of driving.

73,
Don W3FPR

On 2/2/2019 1:55 PM, mustang65 wrote:

> Don,
>
> Thanks for the suggestions.
> I am thinking of putting the outputsignal from the symetrix 528e microphone
> amplifier
> to c20 on the ksb2 board so I will bypass U3 and let the signal go direct
> to u5 NE602
> and that way found out if u2 is bad.
> I will come back with the result.
>
> 73 Mike sm3xgm
>
>
>
>
> --
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W2xj

Re: Tx distortion

The symetrix is a pro audio processor. 200 ohms source impedance and is easily capable of over driving any transceiver.

Sent from my iPad

> On Feb 2, 2019, at 2:26 PM, Don Wilhelm <[hidden email]> wrote:
>
> Mike,
>
> Notice that U2 also has an output that is involved in PTT and VOX detection via U4 and the COMP OUT signal.
> The signal at the output side of C31 is driving an impedance of about 8k ohms. I don't know what your Symetrix mic amplifier is capable of driving.
>
> 73,
> Don W3FPR
>
>> On 2/2/2019 1:55 PM, mustang65 wrote:
>> Don,
>> Thanks for the suggestions.
>> I am thinking of putting the outputsignal from the symetrix 528e microphone
>> amplifier
>> to c20 on the ksb2 board so I will bypass U3 and let the signal go direct
>> to u5 NE602
>> and that way found out if u2 is bad.
>> I will come back with the result.
>> 73 Mike sm3xgm
>> --
>> Sent from: http://elecraft.365791.n2.nabble.com/
>> ______________________________________________________________
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mustang65

Re: Tx distortion

In reply to this post by mustang65

Thanks for answers.
The symetrix output impedance is 200 ohm and it is recommended to not load
it
lower then 600 ohms.
I lifted the plus side of c20 and connected a 10k resistor to ground.
I connected the signal from the symetrix output to the plus side of c20.
This way the signal comes direct to ne602 and u3 is not involved.

The distortion is still the same and no difference what signallevel
I put out from the symetrix. from a very low level until a 3 bars of
alc reading. I am still listening to the Lf signal from the symetrix just to
be shure
it is no clipping from the unit.

I know this is not the way to drive the k2 just trying to find a way to see
if U3 is the problem.

The microphone I drive the symetrix is a shure sm58 and I also
use a icom hm12 that i put direct in to the K2.
The first 6 years I used the Icom microphone then the last 8
years I used the symetrix and Shure sm58 that improved the audio.

73 Mike sm3xgm

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Don Wilhelm

Re: Tx distortion

Mike,

It may not be the KSB2 board after all. It could be a problem with the
base K2 PA stage.

With the KPA100 fully removed, what is the maximum power output? Also,
what is the DC voltage during transmit as measured by the K2 meter (tap
DISPLAY to see the voltage), then transmit.
A higher voltage will keep the IMD low. Use no lower than 12 volts for
best results, 13.8 is preferred.

Do a TUNE and measure the DC voltage on the base of either Q7 or Q8. If
it is outside the range of 0.60 to 0.64 volts, there is a problem. Also
note that there is a /CLASS AB signal that also affects bias for SSB.
Go to transmit (not TUNE) in SSB and make certain pin 6 of RF Board U1
goes to zero.

73,
Don W3FPR

On 2/2/2019 3:28 PM, mustang65 wrote:

> Thanks for answers.
> The symetrix output impedance is 200 ohm and it is recommended to not load
> it
> lower then 600 ohms.
> I lifted the plus side of c20 and connected a 10k resistor to ground.
> I connected the signal from the symetrix output to the plus side of c20.
> This way the signal comes direct to ne602 and u3 is not involved.
>
> The distortion is still the same and no difference what signallevel
> I put out from the symetrix. from a very low level until a 3 bars of
> alc reading. I am still listening to the Lf signal from the symetrix just to
> be shure
> it is no clipping from the unit.
>
> I know this is not the way to drive the k2 just trying to find a way to see
> if U3 is the problem.
>
> The microphone I drive the symetrix is a shure sm58 and I also
> use a icom hm12 that i put direct in to the K2.
> The first 6 years I used the Icom microphone then the last 8
> years I used the symetrix and Shure sm58 that improved the audio.
>
> 73 Mike sm3xgm

mustang65

Re: Tx distortion

In reply to this post by mustang65

Don,
Many thanks for the help. I will check the
pa stage tomorrow.

73 Mike sm3xgm

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Jim Brown-10

Re: Tx distortion

In reply to this post by mustang65

On 2/2/2019 12:28 PM, mustang65 wrote:
> The symetrix output impedance is 200 ohm and it is recommended to not load it lower then 600 ohms.

It's been at least 15 years since I looked at a K2 schematic, but Don is
very well equipped to help you there. The photo on the data sheet for
the 528e shows that none of the TRS jacks appear to be properly bonded
to the shielding enclosure, as specified by AES48. This is a classic Pin
One Problem, and a path into the 528e for RF if a cable is connected to
one of them. It isn't clear whether the XLR is properly bonded. If it
isn't, that's another possible path for RF. That could easily be the
cause of audio distortion -- what we commonly call "RF feedback."

This unit is designed to operate at an output level in the range of 2V
RMS, which as W2XJ observed can easily overdrive the K2. The best way to
drive the audio chain of a rig like the K2 is by the addition of simple
voltage divider. I'd start with 26 dB, which is a 20:1 ratio. I'd go
with 1K for the series resistor and 47 ohms for the load. You will, of
course, need a cap in series with your drive to the K2 so that you don't
upset the bias.

The K2 SSB board is low on gain. When I was using one, I worked out a
simple mod to increase the gain by about 6 dB and also roll off the low
end a bit. This allows the mic to hit the peak limiter a bit harder. At
the time, I was using an EV RE11, also a pro mic, but without the
proximity effect bass boost of an SM58. I gave notes on that mod to Don
many years ago. No new parts are needed -- I simply moved two or three
resistors and caps around.

I recall that there were other mods done in the audio chain to increase
gain.

73, Jim K9YC
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Ralph S

Re: Tx distortion

In reply to this post by mustang65

Just a dumb question. Have you checked the DC to the K2 either battery or power suply.

Ralph S. Turk, W7HSG

520-444-6610

> On February 2, 2019 at 1:28 PM mustang65 <[hidden email]> wrote:
>
>
> Thanks for answers.
> The symetrix output impedance is 200 ohm and it is recommended to not load
> it
> lower then 600 ohms.
> I lifted the plus side of c20 and connected a 10k resistor to ground.
> I connected the signal from the symetrix output to the plus side of c20.
> This way the signal comes direct to ne602 and u3 is not involved.
>
> The distortion is still the same and no difference what signallevel
> I put out from the symetrix. from a very low level until a 3 bars of
> alc reading. I am still listening to the Lf signal from the symetrix just to
> be shure
> it is no clipping from the unit.
>
> I know this is not the way to drive the k2 just trying to find a way to see
> if U3 is the problem.
>
> The microphone I drive the symetrix is a shure sm58 and I also
> use a icom hm12 that i put direct in to the K2.
> The first 6 years I used the Icom microphone then the last 8
> years I used the symetrix and Shure sm58 that improved the audio.
>
> 73 Mike sm3xgm
>
>
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
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Jim KO5V

Re: Tx distortion

In reply to this post by mustang65

(Warning: the following is not Elecraft specific!)

It's not a dumb question at all. Years ago, I used an IC-706 on 6M with a small rotatable beam antenna on the roof. I had rearranged the shack, making everything a bit neater. It was all good, until one of the locals came on and told me that he had been monitoring, and my signal had gone from great to garbled. Turns out I had neatly run the new 10' power cord for the rig down the baseboard from the power supply on my workbench, to the desk where the rig was located, about 10' away. The signal coupled into the power cord when the antenna was rotated to a certain direction, so the RF was coupling into the rig and/or PS. That really messed up the transmitted signal.

So, look for some "dumb" change to your overall set-up as well.

Good luck! 73,

Jim KO5V

"Just a dumb question. Have you checked the DC to the K2 either battery or
power suply.

Ralph S. Turk, W7HSG"
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Joe Subich, W4TV-4

Re: Tx distortion

> Turns out I had neatly run the new 10' power cord for the rig down
> the baseboard from the power supply on my workbench, to the desk
> where the rig was located, about 10' away.
10' is almost exactly a half-wave on 6 meters. Your power cord was a
"worst case" for RF feedback on six.

73,

... Joe, W4TV

On 2019-02-02 7:24 PM, Jim KO5V wrote:

> (Warning: the following is not Elecraft specific!)
>
> It's not a dumb question at all. Years ago, I used an IC-706 on 6M with a small rotatable beam antenna on the roof. I had rearranged the shack, making everything a bit neater. It was all good, until one of the locals came on and told me that he had been monitoring, and my signal had gone from great to garbled. Turns out I had neatly run the new 10' power cord for the rig down the baseboard from the power supply on my workbench, to the desk where the rig was located, about 10' away. The signal coupled into the power cord when the antenna was rotated to a certain direction, so the RF was coupling into the rig and/or PS. That really messed up the transmitted signal.
>
> So, look for some "dumb" change to your overall set-up as well.
>
> Good luck! 73,
>
> Jim KO5V
>
>
> "Just a dumb question. Have you checked the DC to the K2 either battery or
> power suply.
>
>
> Ralph S. Turk, W7HSG"

Jim KO5V

Re: Tx distortion

In reply to this post by mustang65

Yeah, that's why I mentioned the length. It was an early "teaching moment" in my ham radio career. Surprisingly, it only took me a few minutes to figure out what I had done, but I had to move the power supply and workbench, and coil up the 706's power cord. I didn't like the new, new shack layout as much as the old new one, though. It also proved to me that some chaos is OK - being too neat has always bitten me somehow!

73, Jim KO5V

"10' is almost exactly a half-wave on 6 meters. Your power cord was a
"worst case" for RF feedback on six.

73,

... Joe, W4TV"
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Bob McGraw - K4TAX

Re: Tx distortion

Don't forget about the length of the ground conductor as well. I've seen
and found more than one instance where the ground conductor was a 1/4
wavelength on the band which caused RFI in the station. That puts the
station at 1/4 wave or a maximum voltage point above ground. It was
acting like a receiving antenna in the presence of the transmitted
RF. For that reason, I do not use an external ground on my station
equipment. It is not needed.

73

Bob, K4TAX

On 2/2/2019 7:32 PM, Jim KO5V wrote:

> Yeah, that's why I mentioned the length. It was an early "teaching moment" in my ham radio career. Surprisingly, it only took me a few minutes to figure out what I had done, but I had to move the power supply and workbench, and coil up the 706's power cord. I didn't like the new, new shack layout as much as the old new one, though. It also proved to me that some chaos is OK - being too neat has always bitten me somehow!
>
> 73, Jim KO5V
>
>
> "10' is almost exactly a half-wave on 6 meters. Your power cord was a
> "worst case" for RF feedback on six.
>
> 73,
>
> ... Joe, W4TV"
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mustang65

Re: Tx distortion

In reply to this post by mustang65

Jim!
Thanks for the information I appreciate it. And thanks Ralph there is no
stupid question
I am grateful for all help I can get cause there can be something I have
missed.

Jim I use a resistordivider to get the right level to the k2 and also
ferritcords on all cabels that
enter the symetrix.
I have the same level of the distortion if I run 500w with amp to an antenna
or only
1w to a dummyload so I hope I am right to rule out rf feedback as the cause.
Also that I have used the same setup for many years without any problems
make me
think that something has happend to the k2 but I can be wrong.

The strange thing that is confusing me is when the k2 been turned of over
the night
there is almost no distorsion when I start to transmitt .
then it slowly arrives in the first couple of minutes.

73 Mike sm3xgm

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mustang65

Re: Tx distortion

In reply to this post by mustang65

Don,

I have done some measuring on the powerstage.
dc voltage during tuning is 14,1 v
Bias Q7 is 0,652v when tuning.
U1 pin6 43mV on ssb transmitting.
I get about 10w max output (do not have a bird)

all measuring was done with a fluke 179.

Q6 gets mutch varmer then Q7,Q8 is this normal?

The strange thing that is confusing me is when the k2 has been turned of
over the night
there is almost no distorsion when I start to transmitt .
then it slowly arrives in the first couple of minutes.

73 Mike sm3xgm

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