Coaxial Cable Characteristics and Data Used in Amateur Radio
Stations
It is of
importance when making decisions about getting the right coax for your Ham
Station to understand that there are trade-offs that have to be considered
between transmitter power, antenna gain, coax loss, and your total Ham
Station system performance. Your bank account may also enter into the
equation like most Hams.
The db differences in gains or losses on transmit and receive
between the choices available to you are the important
issue.
A difference of 3 db either way will not be
apparent to the stations that you are communicating with on the other
end; around the block or around the world. They won't hear or see (on the
S meter) any difference if you run your transmitter at 50 watts instead of
its maximum 100 watt output power as an example. This is a difference
of about 3db! The same ratio holds true comparing 500 watts with 1000
watts! Now take this same analogy and apply it to coax. Here is an
example: Your present coax is 100 feet long and has a loss of 3db per
100 feet.You change it to the
same length, 100 feet, using a more expensive coax that has only about
.1db loss per 100 feet. (Very Expensive Stuff!) This is about a
3db increase in signal strength to the antenna that you were loosing in
the old coax. The station on the other end still won't know the
difference, neither will your receiver! A difference of 3 db or less
between two antennas, two types of coax, or two station configurations is
usually not sufficient to justify the higher costs of the more expensive,
lower loss, coaxial cable unless you are a perfectionist with lots of
money.
However, a difference of 6 db may well justify the
more expensive approach with the higher quality coax or antenna
setup. Remember, if you can't increase your transmit or receive signal
by at least 5 or 6 db or more, if may not be worth the effort and
expense.
The tables below should help you decide what if any coax
changes you need to make. Color Key: Green shade 50 - 52
ohm
Coax dB Loss per 100 Feet using common coax
types:
dB
Loss / 100 feet Frequency Mhz Cable Type
1.0
10
50
100
200
400
900
1000
3000
5000
6A, 212
.26
.83
1.9
2.7
4.1
5.9
6.5
9.8
23.0
32.0
8 MINI, 8X
1.1
2.5
3.8
5.4
7.9
8.8
13.0
26.0
LMR -240
.24
.76
1.7
2.4
3.4
4.9
7.5
7.9
14.2
18.7
8, 8A, 10A, 213
.15
.55
1.3
1.9
2.7
4.1
7.5
8.0
16.0
27.0
9913, 9086, 9096
0.9
1.4
1.8
2.6
4.2
4.5
13.0
4XL8IIA, FLEXI 4XL
0.9
1.4
1.8
2.6
4.2
4.5
13.0
LMR-400
.9
1.2
2.5
4.1
4.3
LMR-500
.7
1.0
2.0
3.2
3.4
LMR-600
.6
.8
1.4
2.5
2.7
8214
.60
1.2
1.7
2.7
4.2
7.8
14.2
22.0
9095
1.0
1.8
2.6
3.8
6.0
7.5
9, 9A, 9B, 214
.21
.66
1.5
2.3
3.3
5.0
7.8
8.8
18.0
27.0
11,11A,12,12A,13,13A, 216
.19
.66
1.6
2.3
3.3
4.8
7.8
16.5
26.5
14, 14A, 217
.12
.41
1.0
1.4
2.0
3.1
5.5
12.4
19.0
17,17A,18,18A, 218, 219
.06
.24
.62
.95
1.5
2.4
4.4
9.5
15.3
55B, 223
.30
1.2
3.2
4.8
7.0
10.0
14.3
16.5
30.5
46.0
58
.33
1.2
3.1
4.6
6.9
10.5
14.5
17.5
37.5
60.0
58A, 58C
.44
1.4
3.3
4.9
7.4
12.0
20.0
24.0
54.0
83.0
59, 59B
.33
1.1
2.4
3.4
4.9
7.0
11.0
12.0
26.5
42.0
62, 62A, 71A, 71B
.25
.85
1.9
2.7
3.8
5.3
8.3
8.7
18.5
30.0
62B
.31
.90
2.0
2.9
4.2
6.2
11.0
24.0
38.0
141,141A, 400, 142, 142A
.30
.90
2.1
3.3
4.7
6.9
13.0
26.0
40.0
174
2.3
3.9
6.6
8.9
12.0
17.5
28.2
30.0
64.0
99.0
178B,196A
2.6
5.6
10.5
14.0
19.0
28.0
46.0
85.0
100
188A, 316
3.1
6.0
9.6
11.4
14.2
16.7
31.0
60.0
82.0
179B
3.0
5.3
8.5
10.0
12.5
16.0
24.0
44.0
64.0
393, 235
.6
1.4
2.1
3.1
4.5
7.5
14.0
21.0
402
1.2
2.7
3.9
5.5
8.0
13.0
26.0
26.0
405
22.0
LDF4-50A
.06
.21
.47
.68
.98
1.4
2.2
2.3
4.3
5.9
LDF5-50A
.03
.11
.25
.36
.53
.78
1.2
1.4
2.5
3.5
Note: These tables are
typical specifications for comparison only. Values may not be
exactly as quoted by a specific
mfg.
Example: Using 100 watts output from transmitter with no
changes to antenna system except replacing your old coax with 3db
less loss coax, the ERP of the antenna system would increase to 210
watts. This is a 3db gain achieved by the new coax. Remember,
you have to achieve about 6db gain or loss to to make much
difference
Using this table, you should see
that with every 3db increase, your effectively doubling the
ERP.
Velocity Factor of Propagation Through Coaxial
Cable The velocity factor is the speed at which an RF signal
travels through a material compared to the speed the same signal travels
through a vacuum. The velocity of propagation is inversely proportional to
the dielectric constant. Lowering the constant increases the
velocity. Generally, the higher the velocity factor, the lower the loss
through a coaxial cable.
"Typical"
Velocity Factor of Coaxial Cable by type
VF%
Transmission line type
95
ladder line
82
twin-lead
79
coaxial cable / foam dielectric
75
RG-6 and RG-8 coax (thick)
66
RG-58 and RG-59 coax
(thin)
General
Rules for Coaxial Cable D = diameter of
insulation under the shield d = diameter of inner
conductor.
Velocity Factor, Velocity of Propagation,
Vp The higher the velocity factor, the lower the loss through the
cable. Raising the D/d has no effect on Vp Raising the dielectric
constant lowers Vp
Capacitance
Raising the D/d ratio lowers capacitance Raising the dielectric
constant raises capacitance Impedance Raising the D/d radio raises
impedance Raising the dielectric constant lowers
impedance
Attenuation or Loss
Raising the D/d ratio lowers attenuation Raising the dielectric
constant raises attenuation
