[AMRadio] Odd tuning on 160M


John King k5pgw at yahoo.com
Sat Jul 18 14:24:22 EDT 2009


Mike, I suspect that stray RF is getting to the auto tune circuits if it is indeed an autotune tuner. Sounds like RF peaks in the Amp might be upsetting the applecart. Grounding can be a PROBLEM if you have ground loops. However, I would suspect "stray" RF since it seems to happen when QSOing as opposed to during tune. The RF level is probably mostly constant in tune as opposed to higher peaks when pulsing with modulation peaks or CW peaks.

I have also had more problems with stray RF using solid state exciters than tube finals with pi network or Pi L network. I once had a solid state exciter driving a SB 220 and at times a Collins 30S1 and the feed back from the amp to the exciter would sometimes cause the whole thing to go into oscillation during tune up.

Since you do not have the problem with the AMP out of the line, I suspect high RF fields caused by the high power Amp GUMMING up the works. You might try changing the lengths of feedline on 160 and 80 to see if placing the voltage and current nodes at different spots might help the problem. Another feeble suggestion might be a balun in the feedline. you might be saturating the balun inside the tuner. 

I think I would try a different exciter, if possible, and maybe one with tube tube finals. Harmonic suppression may be better as well as stray RF  with tube finals and a different output circuit. If that doesn't help, then you might try a different type amplifier. may have to borrow one.

Checking the interconnecting Coax cables would not be a bad idea either. Mike, the answer is, I JUST DON'T KNOW!! I am just "thinking outloud" and hoping I hit on an idea for you. Good luck and 73, John, K5PGW  
--- On Sat, 7/18/09, M. K. Hess <mkhess at kias.org> wrote:

> From: M. K. Hess <mkhess at kias.org>
> Subject: [AMRadio] Odd tuning on 160M
> To: amradio at mailman.qth.net
> Date: Saturday, July 18, 2009, 9:16 AM
> Hi Folks,
> 
> Here's a question that may need to get filed under "dumb",
> or maybe not, but
> here goes!
> 
> I have a V-Beam, a Vertical, and a Dipole, all capable of
> 160M operation. I
> use a K3 as my exciter, an Alpha 91B as an Amp, and
> a Palstar AT-Auto for the tuner. The following happens with
> any of these
> antennas, including my dummy load (Heath CanTenna)...
> 
> I have the Alpha in Stby, and key up the K3 w/ 10w through
> the Palstar to
> "whatever" load.... If finds a 1:1 match and all is well.
> If I advance the K3 to 120W all remains well... Can Xmit
> all day and night,
> without issue. NOW....
> 
> I fire up the Alpha 91B, and begin to tune it.... after a
> couple of seconds,
> the Palstar starts to "re-tune" the load. I wait until it
> settles, and 
> start the Alpha load again, same thing... this happens a
> few times until
> finally the Palstar thinks it's got a match, AND the Alpha
> thinks it's
> happily loaded...
> 
> Finally, I hear someone calling.... I call back... as I'm
> talking, the
> Palstar starts re-tuning again and the Alpha usually goes
> into Hi-SWR
> shutdown...
> I fiddle with them for a bit, and try the call again....
> Sometimes it stays
> stable, most times it goes haywire several times during the
> QSO...
> 
> WTF is going on!?!?!?!
> 
> I have grounding out the ying-yang, and no RF back to the
> station, I have
> heavy duty parts from the shack to the antennas.. (See my
> web www.n3eaq.net
> for details)
> This mostly seems to happen on 160 and 80 and DEFINITELY on
> 1885 when I'm
> trying to do AM!
> 
> Any ideas!?!?!?! All help is appreciated!
> 
> Mike - N3EAQ
> 
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