[Lowfer] re: GROUND RESISTANCE

[Ed Phillips]

Hi Rick ground resistance is frequency sensitive so needs to be measured at
the operating frequency at LF, using either a commercial RF bridge or you
can construct a simple but effective unit....see
http://www.alan.melia.btinternet.co.uk/aelossbr.htm
There are also several articles on aerials for 136kHz that we used the
bridge to measure."

	The simple method I've used here [very dry location sitting on an alluvial fan from the San Gabriel mountains] is to tune up the transmitter, note antenna current and power supply current, and then replace the antenna with a series combination of a high-voltage variable capacitor and carbon resistors.  I keep the circuit tuned with the capacitor and adjust the resistors until I get the same antenna current at the same input current from the PS.  I believe this gives me the equivalent series circuit for the antenna and ground system alone and may include the effects of some losses in tree limbs near the antenna.

	The antenna is a modified 50 foot Hygain "HiTower" and the effective capacitance at the feed point is hughe - almost 450 uufd.  The ground system is four 8' rods inserted into the dry soil with great effort [ended up drilling a hole with a pipe and hose] and 6 feet apart.  Measured with a DC ohmmeter the resistance between any pair is never less than about 500 ohms, even after one of our rare rains.  The rest of the ground system is a strap to a 2" copper water line from the street to the house - total length about 135 feet.  With this combination the effective antenna circuit resistance [loading coil loss isn't part of the circuit] varies from 30 to 60 ohms!!!!!  Very discouraging considering the infinitesimal radiation resistance at 180 kHz. 

Ed