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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 -----
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
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