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CoaxialCable

Coax cable is a shielded two-conductor cable with the centre conductor embedded in a di-electricum (an insulator), which is wrapped in foil, a braided shield or even solid copper (usually corrugated); the shield is the second conductor. The whole assembly is covered by an outer jacket, except in the case of rigid or semi-rigid coax. The term coaxial refers to the fact that both conductors share the same axis.


Selection

There are two main types - RG and LMR, another less common type is LDF.

RG-58 coax is old-style thinwire ethernet cable. Don't even think of using that at 2.4GHz ;). RG-58 is also commonly known in the pro A/V industry and pro RF communications industry as "rope substitute"; ie. using it to tie up equipment when rope is not at hand.

Choosing the correct type of cable depends on many things, including the length of cable you require and, of course, your budget. With coaxial cable, you definately get what you pay for, in terms of quality! In all situations, the total attenuation between your radio and your antenna should not exceed approximately 3dB (or, in English, around half the power of the original signal).

More suitable types suggested so far are: LMR-400, LDF-450 LDF-550, RG-213 (although it's about twice as lossy as LMR-400) ...

The LMR series cable is manufactured by External linkTimes Microwave and it consists of both aluminium foil and copper braid as the method of shielding. Connectors for LMR-400 are not too expensive, and even cheap Dick Smith N-Connectors can be adapted for it.

The LDF series cable is manufactured by External linkAndrew. Andrew's range of coaxial cables go by the well known "Heliax" trade mark. The outer shielding consits of solid, contiguous, corrugated copper, but it is NOT spirally wound (Note that a very early version of Heliax was made of spirally wound copper conductor). On the other hand, the FSJ series from Andrew DOES have a spiralled outer shield, but is a contiguous, corrugated copper.
One thing to be very wary of, with Heliax type cables, is connectors... if you don't have a surplus supply of them, they will cost you dearly, N-Connectors to suit LDF4-50 have a RRP of around $80, EACH, when bought new.
There are various competitors' clones of Heliax cable, one such goes by the name of "Cellflex".

CoaxialCable is available in 50Ω and 75Ω impedances, and the cable size (diameter) varies. The standard notation of 50Ω cable is RG-8X, RG-8, RG-58, RG-213 and RG-214. The smallest diameter cable is the RG-58, next up in size is RG-8X. RG-213 is single-shield, RG-214 double-shield.
50Ω is the type of cable you will want for wireless networking @ 2.4GHz, and the great majority of RF comms. installations. 75Ω is generally only used for television (both FTA and pay), and reception of FM radio.

Calculations

Check the External linkTimes Microwave cable calculators to see how much gain each cable loses at 2400mhz

Connectors

Suitable connectors include N-Type and SMA.

References

External linkRG Coaxial & Triaxial Reference Chart External linkadipex diet External link7 for All Mankind

Velocity Factors

Use above link for Belden (RG-xx) cables.

Cable Impedance 150MHz 450MHz 900MHz 2500Mhz Outside Diameter V. Factor
LMR-100A 8.9 15.8 22.8 39.8
LMR-200 4.0 7.0 9.9 16.9
LMR-300 2.4 4.2 6.1 10.4
LMR-400 50Ω1.48 2.66 3.9 6.8
LMR-500 1.2 2.2 3.1 5.5
LMR-600 50Ω0.96 1.72 2.5 4.4
LMR-900 50Ω0.62 1.10 1.6 2.98
LMR-1200 50Ω0.48 0.86 1.26 2.3
LMR-1700 0.35 0.63 0.94 1.7
RG-174 0.1" 0.66
RG-58 0.195"0.66
RG-58 Foam 0.195"0.79
RG-8X Foam 0.242"0.75
RG-213 0.405"0.66

Wavelengths


Here is how to figure out your true 1/2-wave:

Or as an alternative method (in meters):
 V * C
-------    where V = Velocity Factor
 2 * F           C = Speed Of Light (=299792458)
                 F = Freq Of Signal (say 2441000000Hz=2.441GHz)


Version 8 (current) modified Fri, 18 Feb 2011 06:35:29 +1100 by Neytan17
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