SWR Changes while in QSO with Tuner

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  • Updated 3 months ago
I don't understand why I am seeing the SWR change while in a QSO. I am using a Buddi-Pole antenna set up as a dipole. In either SSB or CW portions, I can tune to a 1.5 or less. Howerver as I'm sending CW or chatting with SSB, all of a sudden, I see the SWR shoot up to max in red. I have to hit the tune button again to get it back down.
Any ideas ?
Thanks.
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Ken Golubski

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Posted 3 months ago

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AH0U

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Not familiar with that antenna but is it possible it is heating up as you use it and shorting out or changing its match???
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Ken Golubski

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No, not changing the match. Running barefoot at 100W.
Thanks.
(Edited)
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Ross Lambert

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Ken, how much power are you using?
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Tim N9PUZ

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I believe the Buddipole antenna is rated for 250W.
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Ronald / W4RJF

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I would also suspect feedline, connectors or antenna...
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Ken Golubski

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I will take a closer look at connection when daylight returns.
Thanks
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John W9KXQ

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Ken, I have been experiencing the same situation on my SteppIR Vertical.  It currently won't move the tape and thus I was blaming it.  I have about 3:1 SWR on the SteppIR right now, so the Flex 6500 Tuner will adjust to almost no SWR as indicated on the Flex.  During 15 second FT8 transmissions the SWR will shoot up to the max or near max in red, causing me to hit the tune button again.  When I do, the SWR will tune back to min again and he may stay there for several QSOs or maybe shoot back up with next transmission.  I am perplexed too,  I rather doubt it is the feedline and it is outdoors so I don't believe it is heating up.  I hope you get a solution.
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Bill W2PKY

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Something in the FLEX Tuner is heating up. This happens to me on 160M. A lot depends on the load characteristics. If very low impedance can cause parts to heat up in the tuner. Changing the feed line length may help. 
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John - AI4FR

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No doubt a bad connection some place.
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Ross Lambert

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I have the same problem with my end fed.  It's rated for 3000 watts but the swr changes as the QSO progresses. I think it's in the tuner. I do not have the problem when the tuner is not needed on the TA33,  Flex dudes ........ any ideas?

Ross 
W2TT
(Edited)
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Bill W2PKY

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Add some more coax to the transmission line so the tuner is looking into a better [lower] SWR. 
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Ross Lambert

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Tried that. No difference
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Bill W2PKY

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What band are you on and how much coax did you add?
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Ross Lambert

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it doesnt matter what band.but mosty happens on 80, 40, 30 mostly
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Neil D Friedman N3DF

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Ken, what is the SWR typically into your Buddipole with the Flex tuner off?
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Ken Golubski

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When I first put the antenna up (it's very portable) I had a 1 to 1 at 7.150.
However, I did move the antenna on it's tripood a tad, so that probably changed it a bit.
Right now, it's over 2.5 on 7.191 and will tune to 1.1 to 1
Thanks
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N8AUM

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Has it worked ok before or is it a new setup ?  
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Ken Golubski

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This is a new radio and setup.
Thanks
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Michael Walker, Technologist

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I have seen this happen on my HF mobile station.

After lots of work, it was determined that RF was coming back in on the surface of the coax.  When this happens, it looks like an increase in reflected SWR as the reflected voltage rises.  When this happens, the tuner sees the increase, and therefore the atu wants to tune.

The fix for this is to add some Mix 31 or Mix 43 chokes on the feedline at both ends of the coax (antenna and radio).  This will provide a high impedance for the common mode currents.  

This document does talk about common mode currents and how to fix them.  http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf

I hope that helps.  Mike 
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Ken Golubski

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Sounds like a good idea. I will try that.
Thanks, Michael !
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Mike Smoot

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The plug-and-play feedline that Buddipole supplied with my antenna kit has a substantial RF choke built into the antenna end of the line, just prior to the mini-banana plugs. Adding more ferrites at both ends further improved my setup.
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Mike Smoot

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I've had similar sounding occurrences with my Buddipole.  Turned out the problem was in how I attached the coil taps to the loading coils.  The taps grab onto the chosen coil turn from underneath with a small hook which pulls slightly upward on the coil wire to make a tap connection. I was tightening the tap thumbscrew too much - which caused the selected coil turn to be pulled slightly out of alignment with the adjacent turns - which in turn allows the tap's "hook" to bridge two adjacent turns, effectively shorting two coil turns.  The fix in my case is to only slightly tighten the coil taps when installing them.  As your coil is probably warming up somewhat with 100W,  then I suspect expansion is also a factor.
 
73 - Mike, KB1MH

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Ken Golubski

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Interesting. I do make it tight. I will loosen it tomorrow because today is kind of busy.
Thank you !
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Mark - WS7M

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I suspect heating of some kind.  It doesn't really matter what the antenna is rated at.  I had a cubical quad years ago that was supposed to handle 1KW.   I was using an SB-200 amp which at best maybe put out 700w.   I came out one day to find the little coils at the end of the quad dripping their plastic coating.  Something had heated them up pretty good.

I run a loop right now with a center balun that is rated at 5kw.  With the antenna wire not well matched that balun heats pretty bad and I see the SWR rise very quickly.  So I trim it carefully and keep it well tuned.  I don't op out of my SWR range much and if I do it is short QSO.  

Even 100w will heat stuff up.
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Mike - VE3CKO, Elmer

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If it's possible try another piece of feedline. Could have water in coax, frozen now but still will give symptoms your experiencing.