RE: NEC-LIST:MF Ground Constants near High Power Transmitters

Would the soil temperature variations due to MF transmitter currents exceed
those of typical night/day temperature variations?

-----Original Message-----
From: nec-list-admin_at_gweep.ca [mailto:nec-list-admin_at_gweep.ca]On Behalf
Of ghagn_at_erols.com
Sent: Tuesday, February 05, 2002 6:43 PM
To: nec-list_at_gweep.ca
Cc: ghagn_at_erols.com
Subject: NEC-LIST:MF Ground Constants near High Power Transmitters

All:

I had a question from someone on the list asking if the ground constants
measured with low-level signals would be the same as if the measurement
system
used large signals. I unfortunately lost that message. Here is my opinion on
the matter:

1. At MF, the conductivity is the more important quantity.

2. The soil conductivity is a function of temperature, and increases with
increasing temperature. Normally, the change isnt too important over the
ranges of temperature of the soil normally encountered.

3. Large currents in the soil can cause heating, and hence temperature rise.

4. Therefore, the conductivity of soil adjacent to an MF transmitter's
antenna
could go up when the transmitter is energized from the conductivity that
might
be measured when it is off.

5. There might be a change in the input impedance of the MF antenna due to
the
change in conductivity, but if there is a radial ground system the effective
conductivity is already high and an increase in the soil conductivity should
not make any significant difference.

Hope this helps.

George

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