K2 - Problems on 40m

[Zac Brown-2]

Fellow K2 builders,

Well my K2 has been up and running now for about 2 weeks.  I finished
building the KAT2 last week and finally put up an antenna that should be
able to work 80 - 20m this weekend.  My previous antenna was a 20m attic
mounted horizontal loop fed with coax.  The new one is a 135 ft outdoor
flat-top fed with ladder line.  So far, I've been very pleased with the
K2 and with the new antenna setup.

All bands seem to be working fine except 40m.  When I attempt to
transmit (or tune) on 40m, I'm hearing some strange "chirping" noises in
the headphones, then the display shows "low p", regardless of which
antenna I plug into it.  It does the same thing when I plug in a dummy load.

When I key, I hear the chirping sounds as well.  It almost sounds like
very small birds chirping under water.  Also, when I key, the s-meter is
showing some strange behavior.  It looks like 4 or 5 different bars are
all lighting up at once, and they're not even sequential bars.  For
example, the left-most bar, a few in the middle, and the right most bar
might light up.  Some appear to be flickering.  I'm only getting these
problems on 40m - all other bands appear to work fine.

The really strange thing is that 40m receive and transmit appeared to be
working fine last week.  The KAT2 was able to find a match even with my
undersized loop.  But, when I transmitted, I did notice the chirp and
the s-meter was behaving as I described above.  I tried it a few times,
then went back to 20m.  Nothing much has changed here except for the new
antenna, but as I said, it's doing the same thing even when I plug it
into a dummy load.

Any ideas?

Thanks,

Zac
KD5IEF
K2# 4907
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[Zac Brown-2]

Fellow K2'ers,

After exchanging a few emails with Don, I did a close inspection of the
components related to the 40m low pass filter.  L25 and L26 have
continuity and the correct # of turns.  Capacitors C225-C229 have
continuity and are the correct values.  VFO at 7000 kHz shows 11914.29,
so that looks fine too.

I went ahead and reheated the solder joints for L25, L26, and C225-C229
for good measure, although I didn't see or measure any problems with
those components.

I removed the KAT2 and found that I don't seem to have any problems with
the base K2 with the KAT2 removed.  With my DL1 attached and the KAT2
removed, if I set the K2 to 7100 kHz or so, and dial in 2.0 watts of
power, that's about what is displayed when the "tune" button is pressed,
and also what I measure at the test points on the DL1.  So, I'm thinking
that the problem may be in the KAT2.

I went thru the process of performing the bridge null adjustment (C55)
and the power calibration (R1 and R2) on the KAT2 again, just to be sure
that everything was calibrated properly.

After making the adjustments on 40m, everything appeared to be working
correctly.  However, after setting R2, when I put the ATU into CALS and
started cycling thru the bands, I noticed some strange behavior.

40m showed 1:1 at first, but after cycling thru all the other bands,
when I got back to 40m, it now shows 9.9:1, and I hear a faint whining
sound coming from the tuner.  This is the same sound that I was hearing
in the headphones earlier, but now I actually hear it coming from the
tuner, with no headphones or speaker plugged in.  Maybe one of the
relays is making this noise.

When I tune on 20m and 17m, the display is showing the power (e.g. P
2.5) even when I have the ATU set to CALS.  On all other bands, the
display shows the SWR, as it should.  But for some reason, on 20m and
17m, it's showing me power instead of SWR.

I'm stumped.  After carefully reviewing all my solder work, everything
looks fine to me.  And as soon as I finished the C55 adjustment and
R1,R2 adjustment, things seemed to be fine.  But once I cycled thru the
bands once, the problems started cropping up.  I did all of these tests
while plugged into the DL1.

Since I don't get any strange behavior when the KAT2 is removed, I'm
inclined to think that the problem lies somewhere in the KAT2.  However,
all of the tests in the manual check out.  That is, until I cycle thru
the bands after the power calibration.

Any ideas?

Thanks,

Zac
KD5IEF
K2 4907


Zac Brown wrote:

> Fellow K2 builders,
>
> Well my K2 has been up and running now for about 2 weeks.  I finished
> building the KAT2 last week and finally put up an antenna that should be
> able to work 80 - 20m this weekend.  My previous antenna was a 20m attic
> mounted horizontal loop fed with coax.  The new one is a 135 ft outdoor
> flat-top fed with ladder line.  So far, I've been very pleased with the
> K2 and with the new antenna setup.
>
> All bands seem to be working fine except 40m.  When I attempt to
> transmit (or tune) on 40m, I'm hearing some strange "chirping" noises in
> the headphones, then the display shows "low p", regardless of which
> antenna I plug into it.  It does the same thing when I plug in a dummy
> load.
>
> When I key, I hear the chirping sounds as well.  It almost sounds like
> very small birds chirping under water.  Also, when I key, the s-meter is
> showing some strange behavior.  It looks like 4 or 5 different bars are
> all lighting up at once, and they're not even sequential bars.  For
> example, the left-most bar, a few in the middle, and the right most bar
> might light up.  Some appear to be flickering.  I'm only getting these
> problems on 40m - all other bands appear to work fine.
>
> The really strange thing is that 40m receive and transmit appeared to be
> working fine last week.  The KAT2 was able to find a match even with my
> undersized loop.  But, when I transmitted, I did notice the chirp and
> the s-meter was behaving as I described above.  I tried it a few times,
> then went back to 20m.  Nothing much has changed here except for the new
> antenna, but as I said, it's doing the same thing even when I plug it
> into a dummy load.
>
> Any ideas?
>
> Thanks,
>
> Zac
> KD5IEF
> K2# 4907
>

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