"Jim" wrote in message
...
thanks guys for your input! ok, forget about thin and supple. i need 50
ohm impedance coax at 900mhz into a uniden scanner(bnc connector) with a
15 foot run. what coax of any size is commonly available that would be
suitable?

If you insist on 50 Ohm skinny cable, get the LMR240. Loss for 15 feet will
be 1.15 db. I believe HRO sells it. About the same diameter as RG59. There
is also an LMR240UF, which is very flexible. The UF has slightly more loss,
but at 15 feet you won't see it. $10 should get you 15 feet. We used this
stuff at 2 GHz. The regular 240 has a solid center conductor, the UF is
stranded. You might have trouble getting a BNC connector on the non-UF.

Tam/WB2TT

"Jim" bravely wrote to "All" (13 Nov 05 13:51:06)
--- on the heady topic of " coax for 900mhz?"

Ji From: (Jim)
Ji Xref: core-easynews rec.radio.amateur.antenna:220026

Ji thanks guys for your input! ok, forget about thin and supple. i need
Ji 50 ohm impedance coax at 900mhz into a uniden scanner(bnc connector)
Ji with a 15 foot run. what coax of any size is commonly available that
Ji would be suitable?

Listen, these nice guys are all BS'ing you. Remember that cable is
rated in dB/1,000ft, so that with only 15 of cable -- ANY -- will be
about the same. You will probably have more loss in the connectors!

A*s*i*m*o*v

.... Everyone hates me because I'm paranoid.

Huh? All my charts list loss per one hundred feet...however, unless he
needs every last bit of signal, 15 feet of RG-58 would be OK...see:
http://bwcecom.belden.com/Catalog/Te...cteristics.pdf

Scott

Asimov wrote:
"Jim" bravely wrote to "All" (13 Nov 05 13:51:06)
--- on the heady topic of " coax for 900mhz?"

Ji From: (Jim)
Ji Xref: core-easynews rec.radio.amateur.antenna:220026

Ji thanks guys for your input! ok, forget about thin and supple. i need
Ji 50 ohm impedance coax at 900mhz into a uniden scanner(bnc connector)
Ji with a 15 foot run. what coax of any size is commonly available that
Ji would be suitable?

Listen, these nice guys are all BS'ing you. Remember that cable is
rated in dB/1,000ft, so that with only 15 of cable -- ANY -- will be
about the same. You will probably have more loss in the connectors!

A*s*i*m*o*v

... Everyone hates me because I'm paranoid.

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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