There ain't such no thing as a low loss thin cable! not for high
frequencies, anyway! what experience teaches is to put up the thickest
line you can within the closest reach of the antenna, and use the
absolute minimum of thin, flexible cable from there to the antenna
itself. in any case you need good connectors at these frequencies so
the additional price is not a real killer.
there's no way to dodge the physics at these frequencies. try to fish
out reel ends of CATV cables from your local comapny. usually they're
glad to give it away, if you rid them from it. I even got e afew
connectors for my pain. in any case you need to match the antenna to
the cable, so why not at 75 ohms instead of 50?
Saandy 4Z5KS

A SOLID POLYETHELINE COAXIAL LINE :-

Length = 5 metres (15 feet).
Outer conductor diameter = 25 mm (1 inch).
Inner conductor diameter = 7 mm (1/3 inch).
Impedance = 50 ohms.
Velocity factor = 0.665

At 900 MHz, it has an overall matched loss of about 0.8 decibels. With
an SWR of 2:1 loss may increase to 1 dB.

The above figures will give you some idea of the sort of stuff you are
looking for. Halve the diameters and roughly double the loss.

For any other dimensions download program COAXPAIR from website below.
If you have any cable of unknown characteristics lying around doing
nothing, then have a sensible guess at dimensions and just insert data
into the program. It is very easy to use.

The program itself, from audio frequencies up to the GHz range, is
generally at least as accurate as cable dimensions can be measured
using ordinary engineering instruments. It is of professional grade,
usable by cable designers and workers in the field of resonant
transmission lines for impedance-matching purposes. One useful program
output is the input impedance and SWR of any coaxial line, of any
length, for any terminating impedance at any frequency. It is
necessary to know the line's velocity factor which for solid
polyethylene is always 0.66

Other types of line are similarly covered by other programs available
from the website.

But for your particular application, download program COAXPAIR.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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