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| Coaxial cable |
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Idiot's guide to coaxial cable
Coaxial cable is an electrical cable consisting of a round, insulated conducting
wire surrounded by a round, conducting sheath, usually surrounded by a final insulating layer.
The cable is designed to carry a high-frequency or broadband signal, usually at radio frequencies. Coaxial Cabling
is a two conductor closed transmission medium that is often used for the transmission of RF energy. It yields excellent performance
at high frequencies and superior EMI control/shielding when compared to other types of copper cabling. Coaxial cabling is commonly found
in broadcast and networking systems. Listed below are some common terms and definitions that are related to coaxial
cabling:
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Usual
terms, used in conjunction with coaxial cable:
Attenuation
(Insertion Loss): Loss of power. Attenuation is usually
measured in dB loss per length of cable (ex. 31.0 dB/100Ft.).
Attenuation increases as frequency increases.
BALUN: An acronym for BALanced/UNbalanced. A device
commonly used to change one cabling media to another (ex.
coaxial to twisted pair balun).
Center Conductor: The solid or stranded wire in the
middle of the coaxial cable. The conductor diameter is measured
by the American Wire Gauge (AWG).
Coaxial Adaptor: A device used to change one connector
type to another or one gender to another (ex. BNC to SMA Adaptor).
Coaxial Cable: A two conductor cylindrical transmission
line typically comprised of a center conductor, an insulating
dielectric material and an outer conductor (shielding). Coaxial
cable can be flexible (typical to the assemblies found in
this catalog), semi-rigid or rigid in nature.
Coaxial Connector: The interconnection device found
at each end of a coaxial cable assembly. There are many common
types of coaxial connectors such as: BNC, SMA, SMB, F, etc.
Dielectric: The insulating material that separates
the center conductor and the shielding.
Electromagnetic Interference (EMI): Electrical or electro-magnetic
energy that disrupts electrical signals.
Frequency: The number of times a periodic action occurs
in one second. Measured in Hertz.
Impedance: The opposition to the flow of alternating
or varying current. Measured in Ohms.
Jack: The female connector usually containing a center
socket.
Plug: The male connector usually containing a center
pin.
RG/U: Symbols used to represent coaxial cable that
is built to U.S. government specifications (R=Radio Frequency,
G=Government, U=Universal Specification)
Shielding: Conductive envelope made of wires or metal
foil that covers the dielectric and the center conductor
Twinaxial: An offshoot from coaxial cabling. Two center
conductors with one dielectric and braided shielding.
VSWR (Voltage Standing Wave Ratio): Amount of reflected
power expressed as a ratio (Ex. 1.25:1) VSWR increases as
frequency increases.
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STANDARD CABLE TYPES
Most coaxial cables have a characteristic impedance of either 50
or 75 ohms. The RF industry uses standard type-names for coaxial
cables. The U.S military uses the RG-# or RG-#/U format (probably
for "radio grade, universal", but other interpretations
exist). For example:
Detailed comparison of typical coaxial cables
| Type |
RG-316 |
RG-174 |
RG-58/U |
RG-59 |
RG-213/UBX
|
RG-213
FOAM |
AIRCELL
7 |
BELDEN
H-155 |
BELDEN
H-500 |
__ |
| Impedance |
50 |
50 |
50 |
75 |
50 |
50 |
50 |
50 |
50 |
Ohm |
| Outer
diameter |
2,6 |
2,6 |
5,8 |
6,2 |
10,3 |
10,3 |
7,3 |
5,4 |
9,8 |
mm |
| Loss
at |
30
MHz |
18 |
20 |
9,0 |
6,0 |
1,97 |
3,7 |
__ |
3,4 |
1,95 |
dB/100m |
| 144
MHz |
32 |
34 |
19 |
13,5 |
8,5 |
4,94 |
7,9 |
11,2 |
4,9 |
dB/100m |
| 432
MHz |
60 |
70 |
33 |
23 |
15,8 |
9,3 |
14,1 |
19,8 |
9,3 |
dB/100m |
| 1296
MHz |
100 |
110 |
64,5 |
__ |
28 |
18,77 |
26,1 |
34,9 |
16,8 |
dB/100m |
| 2320
MHz |
140 |
175 |
__ |
__ |
__ |
23,7 |
39 |
|
24,5 |
dB/100m |
| Velocity
factor |
0,7 |
0,66 |
0,66 |
__ |
0,66 |
0,8 |
0,83 |
0,79 |
0,81 |
__ |
| Max.
load at |
10
MHz |
900 |
200 |
__ |
__ |
__ |
2000 |
2960 |
550 |
6450 |
W |
| 145
MHz |
280 |
9 |
__ |
__ |
__ |
1000 |
1000 |
240 |
1000 |
W |
| 1000
MHz |
120 |
30 |
__ |
__ |
__ |
120 |
190 |
49 |
560 |
W |
Additional types of coaxial cable
| Type |
Diam. |
Bending
radius |
Imp. |
Vel. |
Kg/100m |
pF/m |
10 |
14 |
28 |
50 |
100 |
144 |
435 |
1296 |
2400 |
| Aircell
7 |
7.3
|
25
|
50
|
0.83
|
7.2
|
74
|
|
3.4
|
3.7
|
4.8
|
6.6
|
7.9
|
14.0
|
26.1
|
38.0
|
| Aircom
Plus |
10.8
|
55
|
50
|
0.85
|
15.0
|
84
|
0.9
|
__
|
__
|
|
3.3
|
4.5
|
8.2
|
14.5
|
23.0
|
| H-2000
Flex |
10.3
|
50
|
50
|
0.83
|
14.0
|
80
|
|
1.4
|
2.0
|
2.7
|
3.9
|
4.8
|
8.5
|
15.7
|
23.0
|
| H-1000 |
10.3
|
75
|
50
|
0.83
|
14.0
|
80
|
|
1.4
|
2.0
|
2.7
|
3.9
|
4.8
|
8.5
|
15.7
|
23.0
|
| H-500 |
9.8
|
75
|
50
|
0.81
|
13.5
|
82
|
1.3
|
__
|
__
|
2.9
|
4.1
|
__
|
9.3
|
16.8
|
24.5
|
| H-100 |
9.8
|
__
|
50
|
0.84
|
__
|
80
|
|
__
|
__
|
__
|
4.5
|
__
|
__
|
__
|
__
|
| H-43 |
9.8
|
100
|
75
|
0.85
|
9.1
|
52
|
1.2
|
__
|
__
|
2.5
|
3.7
|
__
|
8.0
|
14.3
|
23.7
|
| LCF
12-50 |
16.2
|
70
|
50
|
?
|
22
|
?
|
0.67
|
__
|
<
1.17
|
__
|
2.16
|
<
3
|
<
4.7
|
<
9
|
<
13
|
| LCF
58-50 |
21.4
|
90
|
50
|
?
|
37
|
?
|
0.5
|
__
|
<
0.88
|
__
|
1.64
|
<
2.2
|
<
3.5
|
<
7
|
<
10
|
| LCF
78-50 |
28
|
120
|
50
|
?
|
53
|
?
|
0.35
|
|
<
0.62
|
__
|
1.15
|
<
1.6
|
<
2.5
|
<
5
|
<
7
|
| RG-223 |
5.4
|
25
|
50
|
0.66
|
6.0
|
101
|
|
6.1
|
7.9
|
11.0
|
15.0
|
17.6
|
__
|
__
|
__
|
| RG-213U |
10.3
|
110
|
50
|
0.66
|
15.5
|
101
|
2.2
|
|
3.1
|
4.4
|
6.2
|
7.9
|
15.0
|
27.5
|
47.0
|
| RG-174U |
2.8
|
15
|
50
|
0.66
|
__
|
101
|
__
|
__
|
|
|
30.9
|
__
|
__
|
__
|
__
|
| RG-59 |
6.15
|
30
|
75
|
0.66
|
5.7
|
67
|
__
|
__
|
|
|
12.0
|
__
|
25.0
|
33.6
|
__
|
| RG-58CU |
5.0
|
30
|
50
|
0.66
|
4.0
|
101
|
__
|
6.2
|
8.0
|
11.0
|
15.6
|
17.8
|
33.0
|
65.0
|
100.0
|
| RG-58
others |
4.9
|
32
|
50
|
0.78
|
3.2
|
82
|
__
|
__
|
__
|
8.3
|
11.0
|
__
|
23.0
|
44.8
|
__
|
| RG-11 |
10.3
|
50
|
75
|
0.66
|
13.9
|
67
|
__
|
__
|
__
|
4.6
|
6.9
|
__
|
18.0
|
30.0
|
__
|
As you can see, the common RG-58 from Radio Shack is NOT the best you can do and will lower your effective power out! Use it only for short runs.
So where does all this lost power go? Its dissipated as heat inside the cable. With a 100W transmitter you'll already notice your RG58 heating up
after several minutes of operation which is definitely not what your want.
BELDEN makes terrific coax in various qualities and with low loss (measured in dB’s…decibels per 100m). 3dB loss = 1/4 of your signal strength
- either lost or gained. Watch out for the correct impedance…RG-8 and RG-58 have 50 Ohms. RG-59 and RG-6 (Low Loss Version of RG-59)
have 75 Ohms. Most antennas are 50 ohm and so are most transmitters.
Don't buy more than you need to make the long run to your antenna and don't make up a few "jumpers" to go between your exciter, VSWR meter and your antenna as all you'll
do is create higher SWR and more line losses. Finally, don't use cheap TV cable!
Check our shops for good coax.
SO WHAT IS THIS SWR (VSWR) EVERYONE TALKS ABOUT?
VSWR is a measure of how well two devices are impedance matched to each other. Typical radio equipment is designed for 50 ohm load impedance,
so we usually use 50 ohm cables and build or buy antennas that are specified for 50 ohm. While most cables have a flat impedance over
frequency (they measure 50 ohm at all frequencies you are likely to use), the same is not true of the antennas. A 1.0:1 VSWR is a perfect match.
That means the load impedance is exactly 50 ohms. A 2.0:1 VSWR is obtained when the load impedance is either 25 ohms or 100 ohms.
Because most transmitters will deliver full power with a load VSWR of up to 2.0:1, this value is usually considered the limit for acceptable
operation. Many prefer to keep their VSWR below that however, but for all practical purposes, it is unnecessary to spend time or money
trying to get much below a VSWR of 1.5:1. The benefits will be hard to measure and even harder to notice. On the other hand, coaxial cable losses increase rapidly, for a given frequency of operation, when the antenna VSWR exceeds 2.0:1. This
can even, in some extreme cases, result in the coaxial cable burning, even when running 100 W. Using a higher grade of cable will definitely
improve things, but even high quality coaxial cable becomes very lossy when VSWR exceeds 3.0:1 at higher HF frequencies (or VHF and
higher).
COMMON CONNECTOR TYPES
"UHF" connector: The "UHF" connector is the old industry
standby for frequencies above 50 MHz (during World War II, 100 MHz
was considered UHF). The UHF connector is primarily an inexpensive
all purpose screw on type that is not truly 50 Ohms. Therefore,
it's primarily used below 300 MHz. Power handling of this connector
is 500 Watts through 300 MHz. The frequency range is 0-300 MHz.
"N" connectors: "N" connectors were developed
at Bell Labs soon after World War II so it is one of the oldest
high performance coax connectors. It has good VSWR and low loss
through 11 GHz. Power handling of this connector is 300 Watts through
1 GHz. The frequency range is 0-11 GHz.
"BNC" connctor: "BNC" connectors have
a bayonet-lock interface which is suitable for uses where where
numerous quick connect/disconnect insertions are required. BNC connector
are for exampel used in various laboratory instruments and radio
equipment. BNC connector has much lower cutoff frequency and higher
loss than the N connector. BNC connectors are commonly available
at 50 ohms and 75 ohms versions. Power handling of this connector
is 80 Watts at 1 GHz. The frequency range is 0-4 GHz.
"TNC" connectors are an improved version of the
BNC with a threaded interface. Power handling of this connector
is 100 Watts at 1 GHz. The frequency range is 0-11 GHz.
"SMA" connector: "SMA" or miniature connectors
became available in the mid 1960's. They are primarily designed
for semi-rigid small diameter (0.141" OD and less) metal jacketed
cable. Power handling of this connector is 100 Watts at 1 GHz. The
frequency range is 0-18 GHz.
"7-16 DIN" connector: "7-16 DIN" connectors
are recently developed in Europe. The part number represents the
size in metric millimeters and DIN specifications. This quite expensive
connector series was primarily designed for high power applications
where many devices are co-located (like cellular poles). Power handling
of this connector is 2500 Watts at 1 GHz. The frequency range is
0-7.5 GHz.
"F" connector: "F" connectors were primarily
designed for very low cost high volume 75 Ohm applications much
as TV and CATV. In this connector the center wire of the coax becomes
the center conductor.
"IEC antenna connector": This is a very low-cost
high volume 75 ohm connector used for TV and radio antenna connections
around Europe.
Additional reading here.
Check our shops for good coax.
Discuss this article in our Forum!
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