[Fwd: LF: Ground systems]
Tue, 27 Jul 1999 20:32:12 -0400
> 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