Rowland=0Athey are to form a balun, Fergus Kyle will probably know the answ
ers you want,=0Ahe won't be up yet (Ontario)=0AGraham=0A=0A=0A=0A=0A_______
_________________________=0A From: Frans Veldman <frans@privatepilots.nl>
=0ATo: europa-list@matronics.com =0ASent: Friday, 20 September 2013, 10:23
=0ASubject: Re: Europa-List: toroids for vhf comms aerial cable=0A =0A=0A--
=0AOn 09/20/2013 10:34 AM, Rowland Carson wrote:=0A> --> Europa-List messag
e posted by: Rowland Carson <rowlandcarson@gmail.com>=0A=0A> RS list hundre
ds; obviously it needs to have a central hole of a suitable size for RG-58
(or probably RG-400 in my case) to pass through, but what about the other d
imensions, and the magnetic characteristics? It's not clear whether the tor
oids are fitted to act as a filter, as tuning, or as a balun. If, as I susp
ect, the latter, the magnetic characteristics are likely to be more critica
l.=0A=0AThe torroids are there do make it clear to the electrons where the
=0Aborder is between the outer surface of the coax and the antenna leg=0Aco
nnected to it. Without the torroids it is just one long piece of=0Aconducto
r.=0AIt is not that critical though, but without these torroids you will ge
t=0Amore radiation from the cable itself and it will pick up more noise fro
m=0Athe surroundings of the cable, and since this is an airplane packed wit
h=0Alots of electronic stuff you will want to prevent that.=0AThe magnetic
properties of the torroids are critical indeed. I don't=0Ahave a list or ma
nual, part numbers have been disappeared from memory=0Along time ago, but y
ou obviously need to find something suitable for the=0Aintended frequency r
ange (100-150 MHz). Some googling is in order here.=0AOr ask a local radio
amateur club, the popular 2m-band (144 MHz) is=0Aclose to the aircraft freq
uencies and what will work for them will work=0Afor you too. Changes are th
at someone has a box full of these things on=0Ahis bench and is happy to sh
are a few.=0A=0AAs an alternative you can coil up a part of the coax close
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