An OCF is an unbalanced antenna and it must have a choke to keep RF off
the feed line into the shack. I use about ten turns of coax on a 4 inch
PVC pipe right outside the wall where the feed comes into the house. It
might be more or less, I am not at home to look. You can research it.
Other choke baluns would help, if they present a high enough impedance.
That seems to have cured RFI problems for me but I have occasionally
felt like I needed more isolation. Many people have advised me to get
rid of the OCF and go with something balanced but it suits my multi-band
needs for now.
I am pretty sure RF on the feed line would cause the tuning circuits in
the KAT to act crazy. I'll leave that one for the Elecraft gurus to
answer.
Buck
k4ia
On 1/8/2014 5:57 AM, Ray Coles 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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