Lew,
Excellent observation (and troubleshooting).
Too often a problem can be due to something very simple but
unnoticed. If you build kits (the kind you solder components to a pc
board) you may have noticed many holes place in strategic areas of
the board that have no components installed thru them. They are call
via's and are place to ground the circuit board to avoid sneak paths
for currents that can cause sporadic oscillation in the
circuit. Often there are more screws holding down a board than just
at the corners and they also help proper grounding. A lose screw or
board can lead to very strange operating characteristics. This issue
gets rapidly more complicated designing for VHF and higher
frequencies, but can cause issues even in audio stages.
This "magic" that good RF designers have is what you pay more for.
73, Ed - KL7UW
my first job out of college was as Technician in a small R&D
engineering dept. Our job was to build up design prototypes from the
engineers initial design and test them for proper operation - which
they typically did not do. Then we searched for some of those magic
little "fixes" to the real circuit that did not show in the
schematic. Many rerouting of circuits and bypass capacitors and RF
chokes are placed as result of this type of "fine tuning" of a
design. Your alpha tester do this.
------------------
Date: Wed, 7 Jan 2015 18:50:00 -0800
From: Lewis Phelps <[email protected]>
To: "[email protected] List" <[email protected]>
Subject: [Elecraft] vexing K3 transverter ptoblem solved
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
For what it?s worth, I thought I would pass along my recent
experience with a vexing transverter problem, and the cause of the
problem that I eventually identified.
The issue was that my XV432 would light up its power output
LEDs ever so briefly when the transmitter was keyed, and then shut
down. It was pretty obviously a shorted output situation.
I first assumed it was a faulty coax cable connecting either the K3
to the XV432 or the SV4 32 to the antenna. So I substituted different
cables all the way around, with no benefit.
I even tested the hypothesis that the dummy load had gone bad, and
substituted an older and smaller dummy load. Still no joy.
About the only thing left in the chain between the K3 and the XV432
was the KXV3 transverter I/O board. Upon initial inspection, I saw
that it was wobbling back and forth about 1/4?. Upon closer
inspection (requiring removal of the side panel of the case) it
became clear that a 1/2? long 4-40 machine screw was missing,
allowing the board to flex backward and forward, and apparently
shorting the output.
I replaced the missing machine screw, tightened the other machine
screw on the opposite corner of the I/O board, and the problem was gone.
Moral to the story: mechanical problems can cause electrical problems.
At least I got it fixed in time for the upcoming VHF contest.
73,
Lew
Lew Phelps N6LEW
Pasadena, CA DM04wd
Elecraft K3-10
Yaesu FT-7800
[email protected]
www.n6lew.us
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
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