Hello John and thank you for the reply.
[email protected] wrote:
Marek, I am not aware of effects like yours being reported from
exposure to much stronger LF fields at LORAN sites and other
transmitting facilities. The magnetic field 2 meters from a loading
coil handling 500 watts might be near or slightly above accepted
limits for human exposure at low frequencies, but not greatly in excess.
That's what I thought about. Polish Radio 225 kHz transmitter had 2 MW
of power and the staff has been working quite close. You probably know
the story about it's 646m-high mast collapse in 1991 due to a human
error during conservation.
However, as you surmise, you are not just being exposed to LF alone.
The two middle items on your list are, far and away, the most likely
sources. In addition to the normal high-frequency components of the
switching waveform, it is possible for there to be surprising amounts
of UHF energy from parasitic oscillations during the on/off
transitions of the FETs. This depends a lot on circuit layout.
I will check waveforms inside the circuit, but there cannot be too much
power generated at high frequencies, because the power balance would be
wrong. But, probably, I am unlucky and there is some kind of resonance
at a few hundreds MHz and most of the oscillations concentrate at that
Your symptoms sound very much like a story I heard in my younger days
of an amateur radio operator whose unshielded high-power HF rig was
emitting parasitic oscillations in the high UHF range. He, too,
experienced a rash and other allergy or flu-like symptoms, and
eventually developed eye problems. I would very much encourage you
shield the rig adequately before further operation!
Yes, that is the general plan, to move the whole TX to a new,
better-designed enclosure. The current arrangement leaves too little
place for the airflow, that's the only reason why the top cover is
I also heard a story about some jerk tuning an open 2m 1kW PA until a
blood started to flow from his nose... Fortunately, no bloody symptoms
here so far ;)
73! Marek SQ5BPM