At 12:10 p.m. 30/01/2011, you wrote:
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
Hello Peter and the LF fraternity,
I use a large ex-NDB loading coil that can be tapped on any single
turn. For fine tuning there is a single rotary shorted turn.To
minimise losses the cross-section of the shorted turn is large [about
40mm X 10mm] and the whole thing is silver-plated on brass. Although
I have never bothered to measure the inductance variation it works
well for transmitting on 180 and 500 kHz. I intend to try it on 136
kHz over our coming southern hemisphere winter.
Cheers,
Kevin ZL4MD
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