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Tx distortion

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Jim Brown-10

Re: Tx distortion

On 2/2/2019 7:54 PM, Bob McGraw K4TAX wrote:
> 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.

There are so many things wrong in this short paragraph that I hardly
know where to start. I strongly suggest that you buy and study N0AX's
recent ARRL book on Grounding and Bonding. What you seem to be
describing is also a violation of the National Electric Code. And while
you're at it, buy and study the ARRL Antenna Book.

73, Jim K9YC

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Jim KO5V

Re: Tx distortion

In reply to this post by mustang65

Mike,

That sounds like some old component failing as it warms up. Have you checked all electrolytic capacitors in the circuit(s)? I have a couple of radios from the '90s that I've had to re-cap, and my 1993 Ford truck has three electrolytics in its main engine control computer that were bad. I'm sure that there are other active components that could fail, but lately, my experience has been that electronics from the '90s and early 2000s seem to have bad capacitors fairly often.

73, Jim KO5V

"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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hdv

Re: Tx distortion

In reply to this post by Jim Brown-10

RVerzonden vanaf mijn Samsung Galaxy-smartphone.
------4e-- Oorspronkelijk bericht --------Van: Jim Brown <[hidden email]> Datum: 03-02-19 14:30 (GMT+08:00) Aan: [hidden email] Onderwerp: Re: [Elecraft] Tx distortion On 2/2/2019 7:54 PM, Bob McGraw K4TAX wrote:> 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.There are so many things wrong in this short paragraph that I hardly know where to start. I strongly suggest that you buy and study N0AX's recent ARRL book on Grounding and Bonding. What you seem to be describing is also a violation of the National Electric Code. And while you're at it, buy and study the ARRL Antenna Book.73, Jim K9YC______________________________________________________________Elecraft mailing listHome: http://mailman.qth.net/mailman/listinfo/elecraftHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:[hidden email] list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.htmlMessage delivered to [hidden email]
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George Winship, NC5G

Re: Tx distortion

In reply to this post by mustang65

Maybe something in this thread will help.

http://elecraft.365791.n2.nabble.com/K2-SSB-Performance-Improvement-td7596200.html

73,
George NC5G

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Don Wilhelm

Re: Tx distortion

In reply to this post by mustang65

Mike,

Is there any chance you have the K60XV option in that K2?
If so, you can set split the transmit path into 2 pieces because the
Transverter output takes its output from just after the bandpass filters
- i.e. - it does not use the Q5, Q6, Q7 and Q8 stages.

Set up for a transverter band operation with the output in the range of
1 mV - It should not matter which is the IF band.

Monitor the output at the Transverter output to check for distortion.
If present, the problem is in the RF Chain before it reaches the
amplifier stages.
If it is clean there, look at the RF Chain after the bandpass filters.

73,
Don W3FPR

On 2/3/2019 1:26 AM, mustang65 wrote:

> 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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Don Wilhelm

Re: Tx distortion

In reply to this post by mustang65

Mike,

Of some concern is the heating of Q6 - but I don't think it is
unreasonable if you can still hold your finger on it.

Hint for troubleshooting. *IF* the problem is in the RF amplification
chain (Q5 thru Q8) then it should appear in TUNE as well as in SSB.
I would suggest that you measure the DC voltages for Q5 thru Q8 after
the K2 has been idle for some time, and then after some period of
operation after which the distortion could be expected to begin.

One thing you might want to try is to measure the resistance from the Q6
emitter to ground before distortion begins and after it starts. It
should be 1.5 ohms (so use a low resistance scale). If it changes,
consider replacing R50, but also be aware that there may be something
causing the voltage on the base of Q6 to change as well.

If your Q6 is a 2sc5739 instead of a 2SC2166 (the 2SC5739 has a plastic
tab instead of the metal tab on the 2SC2166), then change RF Board R46
to 330 ohms.

73,
Don W3FPR

On 2/3/2019 1:26 AM, mustang65 wrote:

mustang65

Re: Tx distortion

In reply to this post by Jim Brown-10

Don,
Thanks for all help.
I have measured on q5,q6,q7 when it been resting over night and when it is
warm
and the difference is smal.

q5 base cold )7,9 varm 7,9
q6 base 1,04 emitter 0,28 varm base 1,03 emitter 031 caculeted gives Ic
200mA Pdissipation 2,8W

q7 cold bas 0,658 varm 0,647
All in ssb with no modulation.

I looked with he scope on the base of q5,q6,q7 on the3.8 MHz signal in
tuning
and on q5 I have a nice sinuswave but on q6 it lookslike a sampled digital
sinuswave
a sinus stairway. On q7 base the positiv side hase roud sinuswave form but
the negativ
side is like a saw vawe sharp edge.
Maybe the scope loads the signal down I do not no the cap. of the probe but
guess it is
about 16pF.

The strange thing is way there is almost no distotion when it been resting
over the night
but comes in after a couple of minutes transmitting.
I put it out in the cold for a while but the distortion was still there even
if it was cold
so it do not looks like it is the temp more like a old care battery that
almost empty but will
get back a little power resting a night even if you do not charge it.

I have replaced the electrolytic caps on
the ksb2 board but can there be bad caps on the controlboard
that effects transmitt but maybe receive just a little?

I been thinking if there is a problem with the bfo or vco it should effect
Rx as mutch as Tx.

73 Mike sm3xgm

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mustang65

Re: Tx distortion

In reply to this post by Jim KO5V

Jim,
Thanks for the advice. It is also my experiece that electrolytic caps are
the main reasen for mailfunction
specially in a bit older electronic euqvipment. I have replaced all el.caps
in the ksb2 board but not any
on the other boards mostly because I beleive they are commen with receiving.
On the other hand can there be any circuit that draws more current in Tx
then Rx and start rippel on the
dc voltage ?

73 Mike sm3xgm

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mustang65

Re: Tx distortion

In reply to this post by Jim KO5V

Don,

I forgott to mention that I do not have the k60xv option but that hade been
a nice way
to rule out the powerstage.

I wonder can there be any circuit that draws more current in Tx then Rx
and causing rippel on the
dc voltage during tx but not rx due to a cap that has lost capacitans?

Have replaced all el. caps. on the ksb2 board but not any on the other
boards.

73 Mike sm3xgm

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Don Wilhelm

Re: Tx distortion

Mike,

There is very little change in current for the low level stages between
receive and transmit, but the RF amplifier stages Q5 thru Q8 draw more
current in transmit.

Have you checked your power supply to make sure it is not producing
ripple or low voltage during transmit. A low power supply voltage will
increase the IMD significantly.
Check the power supply connections as well. Monitor the voltage the K2
sees during transmit by using the K2 display function rather than
measuring the power supply voltage directly.

73,
Don W3FPR

On 2/5/2019 6:26 AM, mustang65 wrote:

> Don,
>
> I forgott to mention that I do not have the k60xv option but that hade been
> a nice way
> to rule out the powerstage.
>
> I wonder can there be any circuit that draws more current in Tx then Rx
> and causing rippel on the
> dc voltage during tx but not rx due to a cap that has lost capacitans?
>
> Have replaced all el. caps. on the ksb2 board but not any on the other
> boards.
>

mustang65

Re: Tx distortion

In reply to this post by mustang65

Don,

I missed that the collector q6 must be the most ineresting pin to look at
and when tuning on 80 meters there is a nice 3.8 Mhz sinuswave.

73 Mike sm3xgm

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mustang65

Re: Tx distortion

Don,

Thanks for advice.
Have checked with to different powersupplies one is a icom ps15 with new
caps. and the other is a
homemade unit both is linear with transformer.

The voltage looks stable on k2 display with 13,8 from Icom and 14,2 from the
other.

Looking with the scope I see 120mv ripple with Icom and 80 mv with the
other
on voicepeaks and ssb tx.

I have replaced c16 and c13 on the controlboard with no inprovment.

73 Mike sm3xgm

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