[Elecraft] K3/KPA500/KAT500 SWR problem UPDATE

[Stephen Prior]

Ray,

Very interesting stuff, thanks.  As the user of an off-center fed doublet
myself, I was initially very nervous of running more than my usual 100W.
As it happened, I need not have worried, as I have never experienced the
problems you describe with the arrival of the KPA/KAT500.  The reason may
well be the choking I use on the doublet, and I suspect that you are on the
right track here.  I took a belt and braces approach to this a year or so
ago.  I have a drop of about 20 feet of 300 ohm 'balanced' feeder whereupon
a conversion to heavy duty coax is made via a choke balun based upon
GM3SEK's work - using the recommended ferrites, combining three different
chokes in series to cover the whole of the HF range.  It's very heavy and
physically quite large so I have it mounted in a box on a flat roof about
20 feet above the operating position.  The coax (short run) goes down to
the shack and through another 3 section choke balun on the back of the
amplifier.

GM3SEK's article is well worth a careful read.  Miscellaneous bits of
ferrite are likely to do nothing, and the combination of coaxial coils and
ferrite in Ian's design works extremely well in my experience.  An added
bonus was that it also reduced my local noise floor considerably.

http://www.ifwtech.co.uk/g3sek/in-prac/index.htm#1005

...is all you need.  In the UK you can get the ferrites from  Farnell in a
couple of days although they are quite expensive.  Accept no imitations!

73 Stephen G4SJP




On 8 January 2014 10:57, Ray Coles <raycoles96 at gmail.com> wrote:

> As the original poster under this heading I figured you might be interested
> to know what I have achieved so far, even though I am not yet ready to send
> the white smoke up the chimney.  Briefly, my problem was that my KAT500
> would go into uncommanded tunes during a QSO, usually on digital modes.The
> practical result was that I had to restrict TX power to less than 40Watts
> on
> most bands to avoid a burst from the Chicago Piano in the KAT. I had
> assumed
> an antenna/feeder problem and had changed every last connector, wire, balun
> and insulator in my system before asking for help from the Reflector Brains
> Trust. All of the other people who subsequently reported a similar problem
> made me feel a little better, and I also received a lot of diagnoses and
> practical advice which I have followed or will follow soon. One of the
> simplest was from Ron WB4OOA: Carry out a K3 Gain Calibration via the K3
> Utility (I had to download the latest Utility version to make this work
> properly) then Install the KAT500 V1.42 Beta (Not quite as easy as it
> sounds). After this things were better, and my power setting on the K3
> always appeared on the KPA500 wattmeter. I could now operate at higher
> power
> on some bands but had to stay below 40W on 40m. I had also adjusted the per
> band retune trigger SWRs upwards via the KAT500 Utility which also helped a
> little.
>
> I remain convinced though, that the basic trigger problem lies with the
> antenna system (an OCF multiband dipole) and I am continuing to work on
> this
> aspect using my analyser. Why it should have suddenly kicked off after many
> months of solid performance, and why changing everything hasn't yet cured
> it
> remains a mystery. My next steps are to try a choke balun on the feeder
> (parts now to hand) and to prune the antenna to get a better resonance on
> the bands of interest. Now if only this darn rain would stop! (I still
> think
> some tweaking of the KAT500 software might also help!)
>
>
>
> Ray Coles, C.Eng. M0XDL
>
> 10 Littlemoor Road,
>
> Weymouth DT3 6AA
>
> Tel: +44 (0) 1305 833699
>
> Mob: 07831 516517
>
>
>
>
>
>
>
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