Ground Conductivity Meter JUMA GCM1 Ground conductivity plays a fundamental role in antenna performance. This is especially important for HF low band verticals to get low radiation angle and to avoid ground losses. To get good antenna performance the ground conductivity should be good in wide area ie several wave lengths from an antenna.

Constructed with 30mm fiberglass tubes, W=1m, H=0.5m

Indicator is mounted with a 5mm plastic panel

Hot galvanized nail soil terminal

This meter is measuring the absolute value of ground conductivity at 500kHz. The meter feeds RF between the two 150mm long soil terminals spaced 1 meter and measures the RF current which is indicated in mS/m conductivity. 500kHz is used to minimize stray capacitance and inductance effects in the measuring wires. Good ground conductivity starts from 10mS/m (0.01S/m) and up. Medium conductivity is around 5mS/n (0.005S/m). Poor conductivity is as low as 1mS/m (0.001S/m).

Fiberglass angle, hand screw for quick disassembly

GCM1 PCB layout

Internal view

Extra holes for adj trimmers

Block diagram

Measurement method Features Conductivity ranges,100mS/m (0.10S/m) and 10mS/m (0.01S/m) Width 1m, height 0.5m, weight less than 2 kg Battery 9V. Endurance 20h with alkaline and 42h with Lithium battery Low battery indicator at 6V Adjustment Adjust zero indication for both ranges with the trimmer resistor Z100mS and Z10mS Connect a resistor between soil terminals and adjust indication to full scale with the gain trimmers G100mS and G10mS. 150 ohm for 100mS and 1500 ohms for 10mS scale. Note that the calibration resistor values are preliminary based on calculation and early experiments. They will be updated later if needed. Downloads - Schematics (PDF) - BOM indicator (Excel) - Layout top (PDF) - Layout bottom (PDF) - BOM other parts (Excel) - Drawing (PDF) - Printable front panel text (PDF) - PCB Gerber files (ZIP) Update 2023-08-15 OH7SV Back to OH7SV projects