Hi Daniele.
If your RX is successful enough, maybe a simple transformer works well.
Apply a test signal by using a loop, say 20cm diameter, inductively
coupling to the ferrite. Then use a secondary winding which goes
directly to the coax of the RX. Use a 50 Ohm resistor or an
oscilloscope with a 50 Ohm input directly. Adjust the number of turns
to get a maximum signal voltage on the scope. The match also strongly
depends on the position of this secondary winding on the coil. The
impedance becomes lower when you come closer to the center of the rod.
The will affect the Q of the resonated system. So you may build an
arrangement which allows you to move and fix the secondary coil on the
rod. If the signal is strong enough, maybe from a nearby BCD station,
you can reduce the "gain" a bit. I have done it similarly with my
active ferrite antenna, see
https://dl.dropbox.com/u/19882028/LF/DK7FC_LF_p_active_ferrite_antenna.JPG
73, Stefan/DK7FC
Am 28.06.2012 16:14, schrieb Daniele Tincani:
Hello LF,
it seems I managed to build a pretty good ferrite coil (abot 80
turns of Litz wire over a bundle of seven 20cmx1cm rods). Nulling and
peaking seem acceptable for my purposes. With current var cap, tuning
range is about 160-650 kHz and could easily be moved to lower
frequencies by adding a parallel fixed capacitor. Until now I have only
made some quick tests by inductively coupling the coil with the
internal ferrite of a portable radio. I would like now to make the antenna suitable also for
direct connection with a 50 ohm input. What do you suggest: to add for
example a transformer or a buffer amplifier (or both :-))? If a
transformer is recommended, is it advisable to use the main coil as the
primary winding?
73
Daniele IZ5WWB
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