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

[Steve Katz]

> 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.
	  

	//Seems obvious this is NOT a parasitic, it's a product created
elsewhere.  I've seen this kind of thing many times in densely populated
contest stations, and it's often quite surprising what's caused it...things
like oxidized guy cabling, all sorts of stuff.  Using a ferrite circulator
between the amp and the feedline can help a lot, but an "HF - kilowatt"
version of such an item is very costly. -WB2WIK/6 


> 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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