From: g4gvw <g4gvw@aol.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <4D44ADB7.50108@charter.net>
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	 <000c01cbc00e$4a122790$4001a8c0@lark>  <4D44ADB7.50108@charter.net>
Date: Sun, 30 Jan 2011 00:22:21 +0000
Message-Id: <1296346941.31303.8.camel@pat-compaq-evo>
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Subject: Re: LF: Re: LF coil tuning
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Peter,

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
> >>
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com
> > Version: 8.5.449 / Virus Database: 271.1.1/3411 - Release Date: 01/29/11 19:34:00
> >
> 
-- 
73 es gd dx de pat g4gvw
 qth nr felixstowe uk
(east coast, county of suffolk)