Message text written by J D Bean
>Please could anyone give me some guidance on the preferred co-axial cable
to use when wiring to Bob Archer comm. & transponder aerials?
I would like to lay them in place before fitting the top to the fuselage.
I will be purchasing in the UK and on looking at the catalogues (RS,
Farnell & Maplin) there are now quite a few differing ratings (75, 63, 50
ohm etc), choices of conductor type and size along with a whole plethora
of
insulation and screening 'systems'.<
You definitely require 50 ohm cable. The better quality products will
minimise losses and reduce interference. The Bob Nuckolls AeroElectric
Connection refers to RG-58 as the standard specification and the RG-223
which is the double -shielded equivalent. In the Maplin catalogue this
equates to order codes XS51F & XS61R respectively. I see from his reply to
you he now recommends RG-400 which doesn't appear to be available yet in
the UK catalogues. I would have thought that you should get satisfactory
results from RG-58 or RG-223 otherwise they wouldn't have been recommended
in the first place. It just depends on how much searching you are prepared
to do.If you don't have a Maplin Catalogue they can be contacted on 01702
554000.
The amount you require very much depends on where you put your aerials.
This cable is suitable for all 3 common applications (Comm, GPS and
transponder).
I have not seen the Archer transponder aerial but if it is similar to most
other transponder aerials (ie 1/4 wavelength) it will require a groundplane
in a composite aircraft. This needs to be a minimum of about 140mm diameter
(for transponder freqs). I made mine using a layer of tinfoil within a flat
layup of 'bid'. It was cut to a D shape providing a straight edge so that
it can be bracket mounted to the fuselage side. When doing the layup leave
a little of the foil exposed in the centre to provide good electrical
connection after drilling for the connector on the base of the aerial.
Regards
Nigel Charles
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