[Lf] [Fwd: LF: Measuring resistance of aerial system]

[Andre' Kesteloot]

Dick Rollema wrote:

> To All from PA0SE 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.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.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. After subtracting the loss resistance of the
> loading coil I find for the earth resistance: July 1999          : 28
> ohmFebruary 2000:  33 ohmFebruary 2001:  32 ohm Summer 2000 I have
> measured even lower values but I did not put them on paper. It amazes
> me that the resistance is lower in summer than in winter. I had
> expected the opposite.There are no trees near the aerial. When it
> rains or in fog the resistance rises considirable, as indicates by the
> aerial current dropping by up to 25%. 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? 73, Dick, PA0SE
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