pa1are wrote:
Hi Cliff,

It is often assumed that imbalance is caused by either sloping or the
proximity of objects to one of the legs of a dipole. In my experience it
is far more likely that imbalance is a result of some imbalance in the
tuner or from a feedline that is not running perpendicular to the
antenna over a big enough length.

I normally use a 2 coil Z-match that works quite well, but I have
experimented with the single coil design and also noticed some imbalance.

Since the output coil is floating you would not expect any imbalance,
but the parasitic capacitance between primary and output coil is the
culprit here. That is why the effect is more pronounced at higher
frequencies and relatively high differential impedances.

In the high frequency part of the two coil Z-match the centre of the
primary circuit is connected to ground, so the parasitic capacitance is
far less likely to cause imbalance.

73, Arend

cliff wright wrote:

Hi!
Anyone had any experience with a G5RV which is NOT symetrical relative
to ground?
Mine is on a sloping section and varies from 3.2 metres AGL at the
western end to 7.5 metres at the Eastern. Although I get a reasonable
match with a single coil Z match tuner I have reason to believe that
there is quite a large electrical imbalance in the system, notably in
the poor rejection of local noise signals.
I came across a Z match circuit on optushome.com.au by VK3YSF which
has a 25 pF variable capacitor from one side of the open wire feeder
to ground. However the article gives no further information about this
component except to call it a "Balance" capacitor.
Has anyone else come across this problem? If so was it a question of
"cut and try" or is there a proper technical approach one can use?
Hoping for some "feedback".
73"s Cliff Wright ZL1BDA
Hi Arend OM.
Thanks for your remarks. I had forgotten that the single coil Z match
could suffer from that problem, but of course you are quite correct.
Perhaps I might go back to the old 2 coil design yet!
All these queries are based on a very bad QRN problem my neigbouring
Ham and I have had from power lines, even though our local lines are
underground! So anything that keeps the sytem balanced is a potential
help in hearing weak signals.
BTW I did try a 50 pF variable from feeder to ground as shown in the
article I mentioned but it had little or no effect.
73"s Cliff Wright ZL1BDA