Hello all,
A few weeks ago I asked for advice on the use of the KAT2 feeding a length
of coax, followed by a balun connected to the balanced feeder of my doublet.
In my case 15 metre of coax is needed between the K2 and the balun/open wire
feeders.
Quite a few people seem to have a similar situation and are happy with the
KAT2 and balun.
I used the program dipole3.exe from the late G4FGQ to run a simulation on
several bands. From 80 to 10 m the efficiency was about 50 - 60 procent,
which is not really bad.
However it is not very good either and I decided to try a balanced tuner,
before installing a KAT2 (which I will eventually). I purchased a MFJ 974HB
and though I did not have very high expectations of it, I was pleasantly
surprised. It matches the doublet fine, but that is not the point. The
balance seems to be excellent as most of my local noise is now gone,
compared to using a 1:4 balun. Even the LAN crud on 14.030 MHz is almost
gone.
This complies with earlier findings that at my location the better part of
local noise is contained inside the houses.
The centre of the antenna is mounted on a 5 metre long fibre glass pole,
dropping to 1.5 metre at the ends. It runs above the semi-flat roof of a
block of 5 houses. I live in the middle one.
When the balance is less than perfect common mode noise is introduced in the
system.
The difference is amazing; on 80 I can listen again to the band noise going
up and down as waves on the seashore.
Though this works for me at the moment, it should be nice if someone
(Elecraft?) could come up with a stand alone truely balanced automatic
antenna tuner.
73,
Roelof Bakker, pa0rdt
Middelburg, Netherlands
JO11tm
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