This is in regards to W4DES' grounding dilemma. First, both K0IL and
WA1TQG/5 have made excellent comments that bear careful review. I'll
also add: don't drill through the basement floor for a ground rod.
To expand slightly on K0IL's remarks, use 1/2" diameter by 10 foot rods
as a minimum, if you can get them. He is correct about using an array
and spreading them out. There is a Military Handbook on grounding of
facilities that shows such an array, and they also present a chart
showing the reduction of ground coupling resistance vs. number of ground
rods. The curve is steep on the front end, not straight line. Just 3
or 4 rods will reduce the coupling resistance to about 1/5th the value
of a single rod. (Going to more than about 6 or 7 rods gains very
little, and flattens the graph.)
You may wish to see if you can borrow one of those RF clamp-on ammeters
(made by Palomar or MFJ, not certain which) to properly check your
ground leads. It is current flow which radiates, and such an instrument
will give a better idea of the problem than the FS meter.
You did not say if you are using a tuner. I'll guess that you are
because of the mention of home brew wire antennas. If you are end
feeding a wire (and possibly using a tuner for Z match if the wire is
not an odd 1/4 wave multiple), the ground current is understandable.
You then need a shorter, lower impedance path to get that RF into the
earth. If your load is balanced, and fed with open feeder lines via a
tuner, your ground current should be negligible.
You might also want to look into the MFJ Ground Tuners. While I have
not used one, I have reputable reports from engineer/ham friends who do
own them, that they work well for the intended purpose: tuning out
grounding lead reactance. (One of these friends is a retired EE from
UL. He moved from Illinois to a dry area of Arizona, where his entire
RF grounding system is a counterpoise. He MUST tune for the different
bands in order to avoid "hot rig" problems.) Keep in mind that if you
upgrade your ground system OUTSIDE of the house and run a heavy lead
from the rig/shack to that system, your actual ground current may
increase due to lower impedance. That's OK, as long as the ground path
is short. The current may provide the field, but the leads provide the
antenna. The shorter thay are, the less effective radiating area is
available.
Since you are having TVI problems at relatively low power, perhaps
another thing to keep in mind is circulating/radiating ground system
current at the harmonic frquencies. You may wish to view the ground
leads not so much at the operating frequency(ies), but at the
harmonics. Using multiple leads between the rig/shack and the outdoor
ground system, all in parallel but of different (short) lengths, may
help.
You do need to get the shack ground and the tower ground bonded
together. That will reduce the potential difference in the event you
take a lightning hit. Do not unground the rig, as someone suggested.
Best of luck with getting this settled out. (I have no connection
whatever with MFJ or Palomar Engineers.)
73,
Dale Svetanoff, WA9ENA
EMC Engineer at Lindgren RF Enclosures, Inc.
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