Hi Dave,
The puzzle is why the Ropex has problems with a 50 ohm match at 136kHz if
the coil is grounded? The match is the same on an SWR bridge whether the pi
cct is in circuit or not. The Ropex protection cct seems to be some kind of
overcurrent detector in the 50ohm output but I can't remember which side of
the internal LPF it is placed.
Hmmm... Maybe the Ropex protection circuit is TOO fast. 50 ohms is 50 ohms
for a steady state signal, true, but I think the circuit trips on the
key-down transient. With "hard keying" the inrush current into the antenna
can be quite high due to the high Q. An antenna with a Q of 50, or so, is
a very heavy "flywheel"! With 150W of feedline power, 5..10 kW (!) of reactive
power will be circulating in the antenna... It takes quite a big kick to
"spin it up" so to speak.
73
Johan SM6LKM
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