Paul,
I suspect you have an antenna system problem rather than a KX2 problem.
Operate the KX2 into a dummy load as David Shoaf has suggested to verify
that it is working as expected.
The fact that your doublet is fed with "450 ohm" parallel transmission
line does not mean that you will be feeding 450 ohms.
The characteristic impedance of the feedline and the impedance to be
matched at the shack end depends NOT on the feedline characteristic
impedance, but the length of the feedline and the impedance presented at
the antenna. That will change from band to band. It can range from a
very low impedance to a high impedance. There are a lot of variables
such as the length of your doublet, the length of the feedline, and the
frequency.
As has been said, most 9:1 transformers are Ununs (autotransformers) and
not a balun at all.
A proper balun would better be termed a common mode choke which will
minimize the common mode RF on the coax. Place it at the junction of
the parallel feedline and the coax coming into the shack. I would
suggest the Elecraft BL2 which is switchable between a 1:1 and a 4:1
configuration. Use whichever setting gives the least "tuning activity"
to the ATU.
73,
Don W3FPR
On 8/15/2017 6:53 PM, Paul Smith wrote:
I have and love my KX2 serial number 855. Lately the ATU seems to be "turning loose
of the setting" I usually can hit the tune button again and get it to tune. I use a
doublet at 50 ft fed with 450 ohm line and a home brew balun/ Unun. I question the balun
as when I ordered, the wrong cores came and I wound the balun which was supposed to be a
9:1.
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