Re: LF: Re: Ferrite Loops

[Roger Lapthorn <rogerlapthorn@gmail.com>]

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 <james.moritz@btopenworld.com> 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

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