Message-ID: <F0556DC14C0F4C3FB86635A175D9358D@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <005f01cc5c32$66a39ae0$0401a8c0@xphd97xgq27nyf> <182D3176BF9144939EF13D0CBAC4921F@JimPC> <000d01cc5cc3$43001a00$0401a8c0@xphd97xgq27nyf> <3BAE26956D184CBF9E369805BB3AC84E@JimPC>
In-Reply-To: <3BAE26956D184CBF9E369805BB3AC84E@JimPC>
Date: Wed, 17 Aug 2011 22:06:44 +0100
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Subject: Re: LF: Re: ferrite coil - extended range variometer
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Jim

Marconi Marine  used  two  (app)   4 inch  X  1.5 inch   ferrite discs 
bolted
inside the  rotating  inductor  of the  variometer ,
using   machined  tufnol  bolts  and  nuts of course !
in the  Ocean-span Tx , 3 X  807   pa

G..

--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Wednesday, August 17, 2011 9:37 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: Re: ferrite coil - extended range variometer

> Dear Mal, Gary, LF Group,
>
> G3KEV wrote:
>> The Collins equipment used this method in their VFO'S...
>
> ...and in their tunable RF amplifiers, etc., but as far as I am aware they
> did not make permeability tuned ferrite rod antennas... perhaps there is a
> Collins equipment expert who knows different?
>
>> There seems to be some confusion about Variometer. A Variometer consists
>> of
>> two coils in series with one rotated within the other to vary Inductance
>
> This seems a rather restricted definition - I think other devices where 
> you
> achieve variable inductance by altering the mutual inductance between
> different parts of the winding are called a variometers too, for instance 
> a
> smaller diameter coil telescoping inside a larger coil. The "shorted turn"
> tuning method, where you have a movable metal slug, ring, etc, inside a 
> coil
> is a variation on the same principle also. It is also worth pointing out
> that there can be more than two coils, and the coils can be in parallel as
> well as series. This is actually quite useful - if you have a
> series-connected variometer for 136k, you can connect the coils in 
> parallel
> to get roughly 1/4 the maximum inductance for 500k use.
>
> G4WGT's extended range variometer reminded me of the device in the 
> picture -
> it is a rotating coil type of variometer, but the moving coil is actually
> wound on a nearly-spherical iron dust core about 100mm in diameter. By
> utilising the various taps, and changing from series to parallel 
> connection,
> the inductance can be varied in various ranges from a few hundred uH to 
> over
> 3mH.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>
>
>
>
>
>> whereas a ferrite moveable rod inserted inside a coil is referred to as
>> Slug
>> Tuning.
>> mal/g3kev
>>
>> ----- Original Message -----
>> From: "James Moritz" <james.moritz@btopenworld.com>
>> To: <rsgb_lf_group@blacksheep.org>
>> Sent: Tuesday, August 16, 2011 7:17 PM
>> Subject: LF: Re: ferrite coil
>>
>>
>>> Dear Mal, LF Group,
>>>
>>> >Instead of winding a tight coil on to a ferrite rod to get 270 uH and
>>> >tuning with a 250 p variable capacitor...
>>>
>>> The required tuning capacitance would be about 5000pF.
>>>
>>> >...instead wind an air core coil and move the ferrite rod into/out of
>> coil
>>> >for the required inductance necessary for frequency >of interest. This
>>> >would further reduce losses.
>>>
>>> You could tune inductance downwards in this way, but unfortunately any
>>> reduction would be accompanied by reduced magnetic flux due to the
>> received
>>> signal in the antenna winding. So the signal amplitude would be reduced.
>>> Also, I doubt if losses actually would be lower - certainly, the coil
>>> without the ferrite rod will have a much lower Q than with the rod in
>> place,
>>> so a point must come as the rod is withdrawn where Q decreases rapidly.
>>>
>>> Cheers, Jim Moritz
>>> 73 de M0BMU
>>>
>>>
>>>
>>>
>>
>>
>>
>>
>> -----
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>>
>