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

[Bill Johnson]

From what has been stated, this not a true end fed Half wave using a 9-1 balun.  That is the issue.  The balun needs to be a 49-1 ratio to properly feed an EFHW antenna.  The method you are using requires a different counterpoise than an EFHW.  EFHW are efficient at one frequency and direct harmonics.  So, the balun is likely heating up.  The 53' antenna is a random wire and needs to have a proper counterpoise.  Random end feds are  different birds.

Bill
K9YEQ

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of David Gilbert
Sent: Friday, July 15, 2022 10:42 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Using the K3s Tune button causes a growing SWR on my KPA500


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?
>

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