Rik Strobbe wrote:
At 09:51 24/07/99 +1200, ZL2CA wrote:
>Connecting the mains earth to the RF earth INCREASED THE RF RESISTANCE
>OF THE ANTENNA.
I (and others) experienced the same. I think that this increase could be
explained by the fact that the 'returning' current coming from the
'radial-earth' and from the 'mains-earth' have different phase, so simple
'resistor-wise' paralleling of both earthsystems is not valid. If the
phase-difference between both currents is large enough the resulting total
current will be less than the current from 1 system only. Or said otherwise
the total resistance will increase instead of decrease.
Would be interesting if not only the currents in both earthsystems but also
their phasedifference could be measured.
The measurements by Kevin ZL4MD and myself did not include checking for
a phase difference in current going to each ground system. However, if
there is a "reactive difference" it could easily be tuned out by
adjusting the variometer, and there WAS NO CHANGE NEEDED IN TUNING for
the test we conducted. The net resistance did increase (as already
reported). So my conclusion is that even if there is a reactance shift,
that could be "tuned out", but any increase in resistance necessarily
lowers efficiency.
As I commented earlier, this type of observation is likely only for an
RF earth system that is already working very well (enough to show up
what happens with non-ideal layout of what was hoped to be "radials").
In my case, with a suburban-sized property, even though I have an
extensive ground radial system, with earth stakes at most outer ends, I
notice a small increase in LF antenna current when I jumper the mains
earth to the RF earth. This shows that in my case the connection of an
additional earth lowers the net resistance of the antenna. Also I have
not noticed that retuning the antenna is needed ie the change is
resistive only. Note that I run all of my shack via a 5 kVA isolation
transformer, including a multisection low pass filter on the mains side,
in an attempt to keep mains noise out of my VLF/LF receiving gear, and I
usually leave it that way during transmit. I will try to find time to
do some phase checks on respective earth currents, when jumpering the
isolation, but my expectation is that they would be in phase, or very
close to in phase.
Bob ZL2CA
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