Peter Chadwick wrote:
>
>At one time (some 30 years ago) there was a company in the UK called Codar, who
>made coil stock like B & W. they did move to a higher temperature material than
>polystyrene - from memory, I think it was ABS, but I'm not totally sure
>of that.
>
>At the kW level, I'm a bit dubious about the old polystyrene rod supported coil
>stock: there's a lot of amps involved, and even if you follow Rich's advice and
>provide cooling air, I think you could be pushing it.
There was once an article in Ham Radio which described how to make
B&W-like coil stock using two or four flat strips of fibreglass, glued
on with epoxy. It should give better high-temperature performance than
the kind where the wire is melted in.
Another trick is to support the wire on a cross-shaped former made from
two sheets of fibreglass, with either notches or four rows of holes
along the outer edges. That one needs hardly any epoxy on the wires,
only to hold the former together.
>You need something like 12
>AWG anyway at LF and thicker at HF. Antenna Tuner coils can run with quite high
>working Q's, depending on the circuit configuration, and that can push the
>heating. I use 2.5 inch diameter ceramic formers, although fibreglas
>works well.
>Alternatively, a self supporting coil for the higher bands, wound with
>1/8 inch
>diameter tube. Even with ceramic coil forms, I think it's worthwhile proving
>cooling for the tank circuit with a small fan.
>
>Provided you can drill mounting holes, glass jars shouldn't be too bad for a
>heat resistant low loss form. You are supposed to be able to cut glass under
>water with scissors and drill it under water with a masonry drill - neither of
>which I have ever tried!
>
>73
>
>Peter G3RZP
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
>
--
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
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