Message-ID: <4D4E8B96.7040207@o2.co.uk>
Date: Sun, 06 Feb 2011 11:52:54 +0000
From: Peter Dodd <g3ldo@o2.co.uk>
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To: rsgb_lf_group@blacksheep.org
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In-Reply-To: <1296346941.31303.8.camel@pat-compaq-evo>
Subject: Re: LF: Re: LF coil tuning
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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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