Mal is spot on with that one. A well-known Chelmsford firm used the
technique in some of their tx units.
73
On Tue, 2011-08-16 at 13:49 +0100, mal hamilton wrote:
> Sliding ferrite rods in and out of coils has been used since radio
> began to alter inductance. You will find it in radio receiver IF
> transformers as well as aluminium and brass rods.
> I have used this method in PA coils to adjust inductance to that
> required ie a fine tune tool
> It does not have to be rods any shape of ferrite core will do, the
> same applies to brass and other metals depending what you want to do.
> de
> G3KEV
>
>
> ----- Original Message -----
> From: Roger Lapthorn
> To: [email protected]
> Sent: Tuesday, August 16, 2011 12:57 PM
> Subject: Re: LF: Re: Ferrite Loops
>
>
> Hi Jim (et al)
>
> Ferrite rods as 5-20W TX loading coils?
>
> As long as the ferrite doesn't saturate am I right in thinking
> that the use of ferrite rods as coil formers for 137 and
> 500kHz is basically "a good idea"?
>
> From personal experience with 5W this worked well at 500kHz so
> I assume that the idea could be translated to 136kHz if using
> separate rods for each 500uH of inductance so the cores of
> each do not saturate. Am I right in thinking that if you
> bundle x cores together (in parallel) the core will saturate
> at x times the power? Making a ferrite rod based variometer
> would be straightforward - PVC tube with cores sliding
> together lengthwise for example.
>
> Engineering large air-spaced loading coils is quite a feat
> whereas making up, for example, 8-10 separate ferrite coils
> with a range of taps on each is quite easy (and small). Less
> wire would be needed so the losses in the coils would be lower
> compared with the air-spaced equivalent.
>
> Is there mileage in this, say up to 15-20W RF?
>
> 73s
> Roger G3XBM
>
> On 16 August 2011 11:53, James Moritz
> <[email protected]> wrote:
> Dear Tom, LF Group,
>
> what do you think about an array of many
> parallel mounted ferrite rods, each of them
> carrying only a few windigs, all windings
> connected in series (and then perhaps tuned)
> and the rods arraged in such a way that the
> individual apertures dont touch? Or will this
> lead to the dimensions of a comparable air
> loop ;-) ?
>
> I am sure this would work, but I think you have also
> identified the limitation ;-) Fundamentally, if the
> signal has a particular power density at the receive
> site, the antenna must intercept the signal from a
> certain aperture area in order to deliver a certain
> power to the receiver. So there is a limit to how
> small it can practically be, although the actual shape
> can vary to obtain the same aperture - one could make
> a rough comparison between the short, wide loop vs.
> the long, thin ferrite rod, and a long yagi vs. a
> broadside array of dipoles.
>
> I think an array of ferrite rods might be attractive
> in some circumstances - for instance, you could have
> numerous small rods stacked vertically, to produce a
> "ferrite rod vertical" with a small turning circle but
> a relatively large effective area.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>
>
>
> --
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> http://www.youtube.com/user/g3xbm
> https://sites.google.com/site/sub9khz/
>
--
73 es gd dx de pat g4gvw
qth nr felixstowe uk
(east coast, county of suffolk)
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