Re: LF: Re: LF coil tuning

[Peter Dodd <g3ldo@o2.co.uk>]

Many thanks to all those who informed me of the  'shorted turn' methods 
of tuning an inductance.
Regards

Peter, G3LDO
> Many years ago when I did 160m mobile I had a setup in which the mobile
> antenna had a loading coil that used a copper disc approx. 150% of the
> coil dia. placed with a centre boss that could be adjusted and locked
> along the whip with a screw at a point close to the coil. I used to
> puzzle about the difference between capacitive or "shorted-turn" effects
> but in the end just accepted that it "worked" for whatever reasons. From
> memory I think the coil was about 5 inches dia.
> 73
>
> On Sat, 2011-01-29 at 19:15 -0500, John Andrews wrote:
> > Peter,
> >
> > It used to be common MW broadcast practice to use "eddy current disks",
> > which were aluminum rings. In some cases, the ring was put inside the
> > coil, with the ability to rotate it in and out of the plane of the
> > turns. A simpler setup was to have it at one end, mounted on a threaded
> > rod, allowing it to be moved along the axis of the coil. I'm sure there
> > were consequences for "Q", but I don't recall any heating issues.
> >
> > John, W1TAG
> >
> > On 1/29/2011 6:43 PM, Alan Melia wrote:
> > > Hi Peter I think this is analogous to putting an aluminium or brass slug
> > > into a coil as with the VHF Toko range where there is an optional ferrite of
> > > aluminium.core. I have never measured Qs I suspect it is a bit lossy maybe
> > > that is why a single shorted turn is used for a loading coil.
> > >
> > > Alan
> > > G3NYK
> > >
> > > ----- Original Message -----
> > > From: "Peter Dodd"<g3ldo@o2.co.uk>
> > > To:<rsgb_lf_group@blacksheep.org>
> > > Sent: Saturday, January 29, 2011 11:10 PM
> > > 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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