At this point nothing is a stupid question, I am definitely confused.
I am using other radios in the shack to measure it. It was first
noticed for the bad clicks on 15m. The 15m station has an ft-1000mp
with antennas on a separate tower about 300' away from the 20m tower.
To eliminate the rx as a problem I also hear it on a ts-680 that is
connected to a 6m antenna on yet another tower.
Add another twist or two...
There is also a sub-harmonic being generated at exactly 1/2 the tx
frequency. It comes and goes exactly in sync with the 1.5x 'harmonic'.
Now the real kicker! I swapped the al-1500 out for an hf-2500, and the
'harmonics' are still there. And they respond to the tune control on
the hf-2500 exactly the same as on the al-1500.... so now I am down to
the 'some other problem'... still related to amps, but apparently not
specifically the al-1500. This makes the problem much more important to
find and fix as the last resort plan was to move the al-1500 to 10m, but
obviously this is not going to fix the problem now.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: Steve Katz [mailto:stevek@jmr.com]
> Sent: Tuesday, May 14, 2002 21:42
> To: 'David Robbins'; 'Amps'
> Subject: RE: [Amps] al-1500 parasitic?? or some other problem?
>
> Okay, I'll ask the seemingly stupid but logical question: What are you
> using
> to measure this spur? Have you tried using something else? (That is,
if
> you're using a receiver, have you tried a different receiver? A
spectrum
> analyzer? Anything different from what you originally used?)
>
> WB2WIK/6
>
>
> > Ok, thanks for all the testing suggestions and comments. Below I
will
> > try to answer all the questions and suggestions so far. I also find
it
> > hard to believe it is produced by the amp, but am running out of
other
> > causes.
> >
> > I have tracked the spur from 21000 to 21450 (tx from 14000 to 14300)
it
> > is always exactly 1.5 times the tx frequency, the frequency of it is
not
> > affected by the amp tuning controls. The onset point does vary with
> > load, near 14000 the swr is about 2:1 and the spur doesn't start
till
> > about 1kw output, at 14300 the swr is 1.2:1 and the spur is there at
> > about 200w output from the amp but is much more sensitive to the amp
> > tune control.
> >
> > I have generated it with and without the input bandpass filter and
the
> > output stubs in all possible combinations with 2 different radios.
> >
> > I unfortunately don't have an adequate dummy load right now, but
even at
> > almost 1:1 swr at the best frequency for the stack the spur is still
> > there as loud and predictable as ever. (note the stack is 300' from
the
> > shack, with the shack off the side of the beams, and there is no
other
> > sign of rf feedback in any equipment, all grounds have been checked)
> >
> > I have swapped the ft-1000mp for a ts-870, there was no change in
the
> > spur at all.
> >
> > The amp does not have a qsk board.
> >
> > There is nothing in the rx antenna jack on the ft-1000mp or the
ts-870.
> >
> > I can't believe it is a design flaw as the amp functioned normally
for
> > several years with no problems. And this is so repeatable now that
I
> > can't believe we didn't notice it or that someone else hasn't also
seen
> > it in multi station contest operations.
> >
> >
> > David Robbins K1TTT
> > e-mail: mailto:k1ttt@arrl.net
> > web: http://www.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >
> >
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