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Yes it works well, also VLF. The nice thing is
that you don't need the flexible connections for the rotating part, wheras the
downsides may be less tuning range (only "up" in frequency), and a slight
increase of losses. The wire loop can be replaced by a metal plate, but (at
least for LF), a shorted multiturn coil made from RF litz would
minimize induced losses.
For 9 kHz I have considered rotating
a ferrite plate, sandwitched between two copper sheets. In an
orientation parallel to the magnetic field, the ferrite enhances
inductance, whereas in the orthogonal position the eddy currents decrease
it. In my case I ended up without the copper as I got sufficient
tuning range with the ferrite alone. The 90° turning
range (compared to 180° for a traditional variometer) feels a bit unusual, but
allows simple mechanical operation by pulling a string attached to one side of
the plate.
Best 73,
Markus (DF6NM)
Sent: Sunday, January 30, 2011 12:10 AM
Subject: LF: LF coil tuning
The
traditional method of tuning an LF loading coil is to use a variometer.
I
have been investigating methods of tuning coils for mobile use and one
method that appeared briefly in one of the ARRL Handbooks of the 50s
was the shorted turn method of tuning.
I tried a home made coil of
136uH on a 5cm diameter former and using a
shorted turn of 2mm insulated
wire and obtained a tuning range of 32uH.
(136 - 102uH).
Has anyone
out there tried this?
Regards
Peter
G3LDO
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