K2 Problem

[walter renner]

I have discovered a problem with my K2 #3511 which has all the latest updates, and has been an excelent radio for the last couple of years.  While using the K2 in the contest this weekend, and operating from 40  meters and up using my center fed dipole that is 250 long fed with 450 ohm ladder line and 4-1 balun on all bands, when I run the power control up on the K2 so that the radio switches to high power I get intermod at the point of transintion form low to high.  I do have the KAT100 tuner in line and it tunes well on all bands. I realize that the KAP100 is using diode switching in the ant changeover circuit. Is it possible that rectifaction is happening with local broadcast stations, and why should this start up at this time? is it possible that the switching diodes have failed? The intermod is enough to take out all but the strongest stations. I can eliminate the intermod with an external T- match home brew tuner.  Any ideas?
K0ARO
Kurt
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[Don Wilhelm-3]

Kurt,

You could be correct that rectification in the TR switch in the KPA100 is at
fault, BUT that should not take place under normal conditions.

Check the bias voltage to the TR switch (junction of R11 and R12) if it is
lower than 90 volts, that is your problem - trace it back to the origin.  A
non-functioning Q6 or Q7 could also cause similar problems.

The diodes themselves are likely OK unless they have suffered abuse
resulting from some other problem.

73,
Don W3FPR

> -----Original Message-----
>
> I have discovered a problem with my K2 #3511 which has all the
> latest updates, and has been an excelent radio for the last
> couple of years.  While using the K2 in the contest this weekend,
> and operating from 40  meters and up using my center fed dipole
> that is 250 long fed with 450 ohm ladder line and 4-1 balun on
> all bands, when I run the power control up on the K2 so that the
> radio switches to high power I get intermod at the point of
> transintion form low to high.  I do have the KAT100 tuner in line
> and it tunes well on all bands. I realize that the KAP100 is
> using diode switching in the ant changeover circuit. Is it
> possible that rectifaction is happening with local broadcast
> stations, and why should this start up at this time? is it
> possible that the switching diodes have failed? The intermod is
> enough to take out all but the strongest stations. I can
> eliminate the intermod with an external T- match home brew tuner.
>  Any ideas?
> K0ARO
> Kurt
>

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[VR2BrettGraham]

W3FPR replied to K0ARO, who noticed nasties on transmit when
K2 switches to KPA100:

>You could be correct that rectification in the TR switch in the KPA100 is at
>fault, BUT that should not take place under normal conditions.
>
>Check the bias voltage to the TR switch (junction of R11 and R12) if it is
>lower than 90 volts, that is your problem - trace it back to the origin.  A
>non-functioning Q6 or Q7 could also cause similar problems.
>
>The diodes themselves are likely OK unless they have suffered abuse
>resulting from some other problem.

What perfect timing - I put my K2 into service after about a year
& it does same thing, as well as now making other undesirable
noises when I plug in SO2R mic switching system that is same
as when K2 was last used - right down to the cable that plugs
into the radio itself or the radio the K2 was to replace.

Hopefully some similarities here - cheers!

73, VR2BrettGraham

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[Don Wilhelm-3]

Brett,

Rather than looking for similarities, you may want to look for potential
ground loop sources.  Those ground loops are really 'sneaky' and can cause
strange effects.  Locating the real source can be a grand problem in itself
because there are so many possible 'sneak' paths.  I wish you luck and good
troubleshooting.

One 'help' I can offer -- see what happens when transmitting into a dummy
load -- that will eliminate the possibility that RF-in-the-shack could be
the root of your problems.

Sorry, but there are no 'simple' answers.

73,
Don W3FPR

> -----Original Message-----
>
> W3FPR replied to K0ARO, who noticed nasties on transmit when
> K2 switches to KPA100:
>
> >You could be correct that rectification in the TR switch in the
> KPA100 is at
> >fault, BUT that should not take place under normal conditions.
> >
> >Check the bias voltage to the TR switch (junction of R11 and
> R12) if it is
> >lower than 90 volts, that is your problem - trace it back to the
> origin.  A
> >non-functioning Q6 or Q7 could also cause similar problems.
> >
> >The diodes themselves are likely OK unless they have suffered abuse
> >resulting from some other problem.
>
> What perfect timing - I put my K2 into service after about a year
> & it does same thing, as well as now making other undesirable
> noises when I plug in SO2R mic switching system that is same
> as when K2 was last used - right down to the cable that plugs
> into the radio itself or the radio the K2 was to replace.
>
> Hopefully some similarities here - cheers!
>
> 73, VR2BrettGraham
>

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[VR2BrettGraham]

W3FPR continued:

>Rather than looking for similarities, you may want to look for potential
>ground loop sources.  Those ground loops are really 'sneaky' and can cause
>strange effects.  Locating the real source can be a grand problem in itself
>because there are so many possible 'sneak' paths.  I wish you luck and good
>troubleshooting.
>
>One 'help' I can offer -- see what happens when transmitting into a dummy
>load -- that will eliminate the possibility that RF-in-the-shack could be
>the root of your problems.
>
>Sorry, but there are no 'simple' answers.

Yes, not simple - change nothing but the radio & problems
start.  Not the thing one wants to experience in the heat of
doing something important.

Difference between K2 at max & KPA100 at minimum
should not result in significant difference in RF environment.
Two radio contest station in apartment is pretty extreme, but
K2 with no special precautions has been fine - could never
do SSB with OMNI-6 without an isolation transformer &
serious work on rear panel spigot EMC improvements.

I still believe the rig has developed a fault whilst in storage &
perhaps it's all related.

BTW, I have posted to the list before my observations of
noise as result of computer control of the radio.  In listening
to myself on second rig when frantically trying to find some
new cabling-related fault, it was clear there is a significant
amount of noise being transmitted by K2 that is the direct
result of KIO activity.  Mine, after small 400 watt amp, puts
out what looks to be several watts whenever K2 is polled for
frequency info.  Now I know I can't use computer control when
on SSB until I find the root cause of that.

Transmit audio also sounds lousy in general as compared to
after I changed compression ratios a bit - all combined, if not
so busy trying to keep run going whilst troubleshooting,
probably would have chucked K2 out third floor window.

But last time when in use, same K2 in same side of console
with same cables, same this, same that & same the other,
didn't do any of this (except transmitted KIO noises).  Bit
busy with other things & need good CW rig for CQ WW CW,
so fingers crossed part of problem here is like that at K0ARO
& therefore may help get to the bottom of it all in time.

73, VR2BrettGraham

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