KNB2 - odd behavior

[Ron D'Eau Claire-2]

I can't argue with you on that point Dave, you'd think that they'd drop it
from the exchange.

I find that irritating folks tends act like a feed line with a high SWR. The
energy I had wanted to radiate just comes back to source and produces
overheating and other unwanted side effects.

I do that often enough by accident without doing it on purpose...

Ron AC7AC

-----Original Message-----

I guess I really disagree with this, Ron.  I kind'a think the guy who'd
be confused by that doesn't deserve a big score.  After all, it
indicates he is not capable of doing what is being asked by the contest
rules.  So why should he do well in the contest?

best wishes,

dave belsley, w1euy




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[Leigh L. Klotz Jr WA5ZNU]

Does 0.8W output on 10m/12m sound more like a problem with the lowpass
filters or with T2 being too close to the board?

I re-peaked the 10M inductors at 28.2 and again at 28.4 just for a test,
and still get just under 1W, either directly into a good dummy load with
the KAT2 measuring, or with an external wattmeter.  I haven't tried
twirling the 12m trimmers.

I bought T2 from Mychael so I know it is optimally wound, but I mounted
it tight to the board, which I know is wrong, but it seems that this
gives 5-6W out instead of the <1W I am getting.

I am looking for advice on whether my next step should be to remount T2
(which will require rewinding it as the leads are clipped now), or
taking a deeper look at the filters.

Might an RX sensitivity test tell me something here, as I have the XG1?

73 es TNX,
Leigh WA5ZNU
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[David Zatopek KT5V]

Hi, Vic, thanks for the reply.  I was fairly certainly that the crowd of
large signals had something to do with this, but had never observed this
before.  Probably because my other HF rig's blanker doesn't really "blank"

The K2 blanker has become indispensable in my semi-urban environment.

73 de David

----- Original Message -----
From: "Vic Rosenthal" <[hidden email]>
> The NB can produce spurious signals when there are loud signals on the
band.  In
> the contest, there were so many loud signals that the usual symptom --
sort of a
>   brapp brapp that follows the keying of the strong signal was replaced
with an
> almost continuous noise.  In order for a noise blanker to work it needs to
pick
> up signals over a wide bandwidth.  Turning on the noise blanker has a very
> severe effect on the receiver's dynamic range, which is why it's possible
to
> turn it off!
>

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[Eric Swartz - WA6HHQ]

Check your TX current when set to 10W requested power.

High TX current points to the LPF or output transformer.
Low TX current points to T2 or low drive from the BPF filter.

73, Eric  WA6HHQ


Leigh L Klotz, Jr. wrote:

> Does 0.8W output on 10m/12m sound more like a problem with the lowpass
> filters or with T2 being too close to the board?
>
> I re-peaked the 10M inductors at 28.2 and again at 28.4 just for a
> test, and still get just under 1W, either directly into a good dummy
> load with the KAT2 measuring, or with an external wattmeter.  I
> haven't tried twirling the 12m trimmers.
>
>
>
> I am looking for advice on whether my next step should be to remount
> T2 (which will require rewinding it as the leads are clipped now), or
> taking a deeper look at the filters.
>
> Might an RX sensitivity test tell me something here, as I have the XG1?
>
> 73 es TNX,
> Leigh WA5ZNU
>
>

[Leigh L. Klotz Jr WA5ZNU]

Thank you Eric and Mychael.  Unfortunately, I seem to have mistaken the
problem - I have problems at 20M and up (and a different dip at 4MHz).

My T2 looks fine and was already off the board but I raised it a bit
more with the green tuning tool, and re-peaked the 10M L and 12M C.

I have done a full sweep of W and A vs F and found that I have low
output on 20 meters and higher, and an anomaly at the top of 75 meters.

See http://wa5znu.org/log/2004/11/k2-power.html for a graph and table.

I get 10W out for 2A on 14.0MHz and 5.8W out for 1.68A at 14.35, into a
dummy load right at the BNC, as measured by the KAT2.  17M is about the
same but it goes down from there.

The 75M dip could be something else, as the current is high there for
its low output.

I guess my next step is a full-band re-alignment of the BPF followed by
signal tracing with the RF probe as Don recommended on another post.

Leigh.

On Tue, 9 Nov 2004 7:40 pm, Eric Swartz - WA6HHQ, Elecraft wrote:
> High TX current points to the LPF or output transformer. Low TX current
> points to T2 or low drive from the BPF filter.
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[Leigh L. Klotz Jr WA5ZNU]

Following Eric's directions to measure current draw, I realized that I
had low output on all high bands, not just 10/12m.
Using the TX signal tracing procedure in the manual, I isolated the
problem to the TX mixer buffer amplifier, and found it.
Now I have plenty of output on all bands.
Thanks for all the help Eric and Mychael, and for the great
troubleshooting in the manual!

Details for the record:
U9, the TX mixer output buffer, showed approximately unity gain on all
bands.
I wicked and redid the solder joints of U9, to no avail, so I decided to
check the buffer circuit components.
Sure enough, I had neglected to install C150 on the bottom of the board.
I even found the 330pF capacitor in my bag of "parts left over," hi hi.

C150 provides the RF coupling to ground for voltage divider in the
feedback loop, thus setting the minus input of the op amp roughly equal
to its output, making it roughly unity RF gain instead of 11:1.  I guess
below the middle of 20M or so, the mixer output itself was enough to
drive the output stages.

73,
Leigh.

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