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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 [1]
* Calculations [2]
* Connectors [3]
* References [4]
* Velocity Factors [5]
* Wavelengths [6]
-------------------------
SELECTION
There are two main types - RG [7] and LMR [8], another less common
type is LDF [9].
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 [10], LDF-450 [11]
LDF-550 [12], RG-213 [13] (although it's about twice as lossy as
LMR-400 [14]) ...
The LMR series cable is manufactured by Times Microwave [15] 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 Andrew [16]. 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 [17] is available in 50 and 75 impedances, and the cable
size (diameter) varies. The standard notation of 50 cable is RG-8X
[18], RG-8 [19], RG-58 [20], RG-213 [21] and RG-214 [22]. The smallest
diameter cable is the RG-58 [23], next up in size is RG-8X [24].
RG-213 [25] is single-shield, RG-214 [26] double-shield.
50 is the type of cable you will want for wireless networking @
2.4GHz, and the great majority of RF comms. installations. 75 is
generally only used for television (both FTA and pay), and reception
of FM radio.
CALCULATIONS
Check the Times Microwave cable calculators [27] to see how much gain
each cable loses at 2400mhz
CONNECTORS
Suitable connectors include N-Type [28] and SMA [29].
REFERENCES
RG Coaxial & Triaxial Reference Chart [30] adipex diet [31] 7 for All
Mankind [32]
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
50
1.48
2.66
3.9
6.8
LMR-500
1.2
2.2
3.1
5.5
LMR-600
50
0.96
1.72
2.5
4.4
LMR-900
50
0.62
1.10
1.6
2.98
LMR-1200
50
0.48
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:
* In feet: 492 x (Velocity Factor) / Frequency (MHz)
* In inches: 5904 x (Velocity Factor) / Frequency (MHz)
* In mm: 150 x (Velocity Factor) / Frequency (GHz!!)
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)
Links:
------
[1] http://melbournewireless.org.au/#selection
[2] http://melbournewireless.org.au/#calculations
[3] http://melbournewireless.org.au/#connectors
[4] http://melbournewireless.org.au/#references
[5] http://melbournewireless.org.au/#velocity_factors
[6] http://melbournewireless.org.au/#wavelengths
[7] http://melbournewireless.org.au/?RG
[8] http://melbournewireless.org.au/?LMR
[9] http://melbournewireless.org.au/?LDF
[10] http://melbournewireless.org.au/?LMR-400
[11] http://melbournewireless.org.au/?LDF-450
[12] http://melbournewireless.org.au/?LDF-550
[13] http://melbournewireless.org.au/?RG-213
[14] http://melbournewireless.org.au/?LMR-400
[15] http://www.timesmicrowave.com/
[16] http://www.andrew.com/
[17] http://melbournewireless.org.au/?CoaxialCable
[18] http://melbournewireless.org.au/?RG-8X
[19] http://melbournewireless.org.au/?RG-8
[20] http://melbournewireless.org.au/?RG-58
[21] http://melbournewireless.org.au/?RG-213
[22] http://melbournewireless.org.au/?RG-214
[23] http://melbournewireless.org.au/?RG-58
[24] http://melbournewireless.org.au/?RG-8X
[25] http://melbournewireless.org.au/?RG-213
[26] http://melbournewireless.org.au/?RG-214
[27] http://www.timesmicrowave.com/cgi-bin/calculate.pl
[28] http://melbournewireless.org.au/?N-Type
[29] http://melbournewireless.org.au/?SMA
[30] http://bwcecom.belden.com/college/Cable101/coaxrefc.pdf
[31] http://www.shoppharmacycounter.com/t-Adipex-Medicine.aspx
[32] http://www.styledibs.com/m-581-7-for-all-mankind.aspx
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