[Amps] al-1500 parasitic?? or some other problem?

[carl seyersdahl]

David, when you made the comment that you used another amp and had the same
problem, I begin to suspect something External to your amps, as in something
that may be acting as  diode and generating spurious signals!! things like
corroded connections anywhere, in the antenna , coax, towers, downspouts,
There are a gazillion things like that which could upset the applecart!!! If
you aren't using a dummy load I'd suggest you beg, borrow , or steal or
otherwise find one to eliminate some of the external possibilities!!! Just
my $.02 worth!!!!
   carl / kz5ca
----- Original Message -----
From: "David Robbins" <k1ttt@arrl.net>
To: "'Amps'" <amps@contesting.com>
Sent: Tuesday, May 14, 2002 6:30 PM
Subject: RE: [Amps] al-1500 parasitic?? or some other problem?


> 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
> > >
> > >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
>
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