Hello everyone,
Am 07.07.2013 00:45, schrieb edgar:
Hi Roelof,
For a test, to isolate the Minwhip, could the signal be re-transmitted
by a small transmitter, battery powered, at a higher frequency to a
local receiver?
Regards, Edgar
Moonah, Tasmania.
My thought, too. An 'isolation' of the feedline would have to be a
significantly larger impedance than the input into the amplifier itself
(the 50 ohm output into the coax doesn't matter at all). Even most RF
transformers won't do because of their capacitance (which is generally
larger than the input of a FET, unless one uses an 'Austin
transformer'-like design). And a coax choke is useless... even if you
could build one with enough inductivity, the stray capacitance will
bypass it.
The problem with the flea-powered 'FM transistors' (single-transistor
design) is their very limited dynamic range; you'd need to filter out
the frequency band of interest before the modulator. This makes it a bit
complex for a quick test... Miniwhip, filter, demodulator, tiny FM
transmitter, all built inside a small case.
So you may end up at another solution: A 'Active Differential E-field
Antenna' as described at www.vlf.it, which is basically two E-field
probes, back-to-back, connected to a differential amplifier with
excellent common-mode rejection:
http://www.vlf.it/cr/differential_ant.htm
All the best,
Wolf DL4YHF .
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