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To All from PA0SE

Spurred on by Steve, GW4ALG, I also measured the current above and below my aerial loading/tuning coil.

The aerial is my multiband one for 10 - 160 m; consisting of a 2 x 20 m dipole, centre fed by 11m open line feeder. For 136 kHz the feeder wires are strapped together in the attic shack . There the loading coil is located; its bottom end is connected to a radiator of the central heating system. The current from the bottom end of the coil flows from that radiator to the boiler, which is adjacent to the shack, and from there via its gas pipe to the gas main which is the only earth connection. So the gas pipe actually forms part of the radiating system, the vertical part of which is about 18 m in total (7 m gas pipe + 11 m strapped feeder line). The earth resistance varies a bit with the season but usually is around 30 ohms.

The coil is 56 cm high of which the upper 12 cm is shortcircuited. I have found out earlier that it makes no difference in aerial current whether the upper unused turns are left open or shortcircuited. Fine tuning is by a vacuum capacitor in parallel with the coil. Because this causes an extra current in the coil, increasing its loss, I take care to make the coil so large that only a small capacitance is required for resonance.

I adjusted the transmitter for 2A aerial current flowing into the strapped feeder wires.

Current in the connection from the coil to the central heating radiator was then 2.1A.

I used the same thermo couple instrument for both measurements.

73, Dick, PA0SE