Last night while transmitting BPSK for 15 minute intervals every half
hour well into the night, I was making use of the opportunity to get on
with the shack rebuilding. My radio room is an upstairs bedroom and the
LF antenna top loading wires pass directly above, attached to the apex
of the roof probably 3-4m above the shack ceiling.
While transmitting, every time I brushed against a piece of earthed
metal I could feel a slight RF burn or shock, not detectable if the
metal was grabbed but unpleasent if touched gently with an arm or
similar. The weather was extremally dry and the antenna load
resistance the lowest it has been for some time, which may be why I have
not seen this before with the new 600 W amplifier. The field is
probably in the region of 2 - 3 kV/m here. Occasionally the
fluorescent tube on the ceiling will light faintly with the RF - this
was much more noticeable and spectacular on an older fitting that was
not on an earthed metal box but left the tube in free space connected to
its starter remotely - on 73kHz that would flash brightly with CW keying
to the extent that I had to leave the light on when beaconing at night
!!
So, if you are sitting in the fields generated by 1kW transmitters be
prepared for a few minor burns / shocks. And don't ever touch the hot
antenna feed, I guess that would give a third degree burn if the arc is
maintained for more than a few seconds To once demonstrate the plasma
arc, I struck one from a (well insulated) screwdriver and managed to
draw it out to 50mm, burning the PTFE wire insulation and marking the
screwdriver tip - and that was only on 150W of 73kHz ! Plasm arc
welders work like this.
Andy G4JNT
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