[Elecraft] Using the K3s Tune button causes a growing SWR on my KPA500

[David Gilbert]

No.  Over time the current does not "back up".

Something in your system is heating up.  My bet would be that your 
toroids used as common mode chokes are heating up due to the very high 
voltages that exist at the end of an end fed half wave antenna.  It's 
not likely to be a current problem since there isn't much current at all 
at the end of a half wave antenna ... unless yours isn't actually a half 
wave at whatever frequency your feeding it.

It is also possible that something in the Palstar tuner is heating up, 
but it uses decent looking inductors wound on ceramic forms so I really 
doubt it.

I'm guessing that you aren't using any sort of counterpoise with your 
EFHW.  If you did, it would have the effect of making your EFHW look a 
bit more like just a severely off-center fed dipole with the result that 
the voltage (and possibly the mismatch) would be less.

In any case, don't go key down any longer than you need to if you don't 
want to fry the toroids before you get a chance to fix the problem.

73,
Dave AB7E



On 7/15/2022 7:53 PM, Peder Kittelson wrote:
> When on 80 meters, the longer I hold the tune button down the higher the
> SWR goes to the point the KPA500 folds back with warnings.  I don't usually
> hold down the tune button longer than about 5-6 seconds.
>
> I use a Manual Palstar BT1500A tuner which does a good job of tuning my
> EFHW wire antenna.  So the initial tune is very good. I sometimes will hold
> down the Tune button on the K3s for maybe 5-6 seconds with the initial tune
> at 1-1 SWR.
>
> The KP500 first shows a 1-1 SWR.  Then 1.2-1, 1.3-1 and so on.  I stop when
> it reaches 1.5-1.
>
> I suppose that initially the transmitting wire sends out the signal and
> over time the current backs up.  I have torroids in place to prevent RFI
> coming back down the antenna transmission line.
>
> I only use the system for CW.  So when I send, the problem does not
> escalate to the point of a dangerous SWR.
>
> I wonder if this is a normal problem when holding the tuning button
> longer?  And since I do not hold down the key for a long period of time it
> doesn't develop.
>
> Still, I am looking at solutions. And I am concerned.
>
> Your thoughts?
>