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<p>Dick Rollema wrote:
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<b>To All from PA0SE</b> <b>To
measure the total resistance of my aerial system I can use a Wayne Kerr
admittance bridge type B.601. To do that the bridge must be connected to
a generator and detector.</b><b>A method involving less work is using my
homemade impedance bridge with built-in noise source and battery and using
the 137kHz receiver as detector. This gadget measures R up to 270 ohms
and X as a capacitance between -150pF and +150pF in parallel with the R-control.
On 137kHz the X-control range is too small and I leave it at the zero position.
The null is found by varying the R-control of the bridge and the vacuum
capacitor tuning the aerial system. The null is very sharp when the receiver
is switched to a narrow passband.</b><b>The calibration marks on the R-control
are at multiples of 10 ohm. But the R-value can be read with much better
accuracy by afterwards measuring the resistance of the R-control pot with
a digital multimeter. There is no need to open the box of the bridge for
this; the resistance can be measured at the port for the unknown.</b> <b>After
subtracting the loss resistance of the loading coil I find for the earth
resistance:</b> <b>July 1999
: 28 ohm</b><b>February 2000: 33 ohm</b><b>February 2001: 32
ohm</b> <b>Summer 2000 I have measured even lower values but I did
not put them on paper.</b> <b>It amazes me that the resistance is
lower in summer than in winter. I had expected the opposite.</b><b>There
are no trees near the aerial.</b> <b>When it rains or in fog the resistance
rises considirable, as indicates by the aerial current dropping by up to
25%.</b> <b>Could that be due to water particles being heated in the
field around the aerial? Or is it only caused by increased leakage via
the aerial insulators and the feed-in?</b> <b>73, Dick, PA0SE</b></blockquote>
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