 SWR
Facts
swr, ohms, RESISTANCE, CAPACITANCE,
INDUCTANCE, REACTANCE, RESONANCE, Coaxial Cable Attenuation Ratings,
THERE IS
MORE TO IT THAN YOU MAY THINK.
What you are
changing, is the impedance of the coax, that is working
against an impedance
that is different than that of the coax
As you use specific
lengths, the impedance of the antenna is no longer
present, the antenna's own impedance combines in a series
and parallel
combination where you see the coaxial line become part of
the antenna
system. At these points, it is possible to tune this as
an entire
unit.
The inefficiency of the unit as a whole does suffer. Due
to the
impedance the antenna induces to the system, that the
coax becomes an
active part of the antennas own radiating field.
Depending on how the coax is placed, the coax can
actually help
improve the efficiency of the unit by offering extra
surface area via
the use of it's outer shield, and it's overall length 
to work like a
coaxial dipole. Or a basic coaxial antenna with a tuning
stub.
Because most antenna systems for CB radio, use open ended
systems that
have a center fed radiator, thats insulated from the
shield. This
presents problems in trying to determine true SWR.
1. the coax at specific key points offers impedance that
can vary from
infinite, to a dead short  even though the coax is
insulated from
making contact with both the center or the shield at any
point along
the line. This is a factor of length in free space,
versus length of
propagation through a conductor, or velocity factor as
determined by
the conductors ability to transfer energy from one source
to another.
The speed of light is finite, so is electron flow, and
the distance
magnetic and electrical waves travels. The type of
conductor is a key
point in how long these specific lengths should be.
However, when an antenna is connected, the extremes of
the
impedances the coax can present, are lessened. To the
values
of the antenna itself, the sources' own output impedance,
and the coax itself.
2. Spacing of the conductors in a coaxial line. The
impedance is
determined by spacing of the conductors thru the use of a
dielectric
material. A different dielectrical material  with the
same spacing of
the conductors, can offer a different impedance. Although
in most
cases, the dielectrical material and conductors own
physical distance
from each other, determines the overall impedance into a
balanced
system. 450 ohm Ladder line, 300 ohm twin lead, are
different forms of
spaced conductors, however, they should not be confused
with coaxial
antenna feed systems. Coaxial systems, due to the nature
of their use,
are unbalanced, the outer shield is considered to be at
earth
potential, or at least used in this fashion, to gain the
benefit of
actually having the antenna work to form it's own
impedance and offer
a means to receive or transfer energy as a balanced load
thru the use
of an unbalanced conductor.
3. Counterpoise, or earth ground potentials. Many
problems arise from
coaxial systems that have little means to attach
themselves to earth
grounds except for attachment to either a rod to earth
[recommended
for protection] or a floating ground that is not
connected to earth
but does connect the coaxial shield to an artifical
ground, or plate.
This offers a means to generate a mirror image, or the
secondary
conductor to return energy back to the source to make the
circuit
complete.
Secondary effects, or events, can use impedance matching
circuits to
always present a balanced load, even though the feed
point impedance
of the antenna itself is vastly different. An endfed 1/2
wave lengt
antenna offers an impedance of 1500 ohms, but centerfed
dipoles offer
an impedance of 7275 ohms, while a ground plane antenna
offers an
impedance of 36 ohms. All of the above can be directly
fed, but will
require the use of matching circuits to meet the expected
coaxial
impedance for it to be considered balanced.
Problems? Artifical, or floating grounds that have no
true ground
connections to offer the coax a means to return energy to
the source.
Artifical grounds not connected to the shield of the
antenna at the
antennas own location, the impedance of the antenna is
affected.
Magmount antenna systems fit this catagory. If you think
back to the
above coaxial dipole, remember that the antenna
"sees" two types of
impedances  one of the counterpoise present, but not
connected, and
the coax presenting an unbalanced complex impedance.
The antenna presents its' own impedance to both of these
working
elements. Two types of counterpoise are present working
against the
radiator, or centerconnected antenna. In a fashion, a
metal plate
which is the mounting location of the antenna, can be
considered a
free floating metal shield that can develop an opposite
charge as a
wave, generated by the antenna, passes over this surface.
The coax
does not care what this shield can do, if the antennas
own impedance
is affected by the impedance at the point of mounting.
The floatingmetal shield, presents it's own impedance to
the antennas
radiating field, and attempts to mirror it. Our effort is
to provide a
balanced impedance that is close to the coaxial lines own
impedance at
both the feed point and source point. Then the coaxial
line terminate
to a balanced system with energy that is still present in
the
conductors, both the center and shield returns to the
source in
exactly the opposite phase, minus the energy expended to
generate the
waves at the antenna as the floating counterpoise. The
waves, as they
travel along the antenna and this freefloating metal
shield, are
considered equal and opposite to each other in this
balanced system.
If the antenna cannot present an impedance that meets the
expected
impedance of the source, the coaxial line then offers a
series of
points along the line where the impedance varies from the
antennas own
impedance, to the impedance of the coax, which can be
found at certian
key lengths.
Since we are using an antenna connected to one end of the
coax, and
the shield is not connected, the shield attempts to force
itself to
the potentials present at the source.
The counterpoise, is the coax, as far as the source is
concerned at this point. However, what affects the
antennas
impedance to the coax, is determined by the aspect of the
counterpoise, with respect to the coax, and the metal
that
should be the counterpoise at the antennas location that
is
not connected to the coax.
To make a coax based antenna system work in this
situation, the
length of coax, does depend on the length, or distance of
length, the
coax is from the source, and the impedance of the antenna
and the
counterpoise present at the antenna mounting location.
The openend system, with the antenna acting as a tuning
stub over an
isolated ground plane system, or counterpoise, the
connection point
presents it's own impedance to the unbalanced coax. This,
along with
the length of coax used, the shield of the coax is forced
to be used
as the sources own counterpoise, with the coax feedpoint
of the
antenna and it's mirror image presenting it's own
impedance. In
essence, an endfed coaxial dipole with a tuning stub
with a matching
radiator presenting a capacitive and inductive reactance
to compliment
the antennas own reactance in both a series, and
parallel, impedance.
Forcing the source ground or counterpoise, to the same
potential as
the isolated counterpoise of the antenna, the coax then
becomes less
of a counterpoise, and can offer a means to transfer
energy thru it's
own unbalanced feedline. As if you were to connect the
radio to the
metal plate, with no concern to length of coax.
There is still a problem though, and that is with the
impedance the
counterpoise the source ground is now connected to.
Location of the
radiator [antenna] above this surface, and the ability of
this surface
to provide the proper impedance, can once again force the
coax to
become a means in which it will present a complex
impedance that is
length dependent.
e.g  An antenna, rated for 50 ohms impedance with 18
feet of coax,
over a counterpoise that forces the antenna to become a
radiator that
is now presenting 120 ohms of impedance.
Throw out the coax length, and use an abritrary length 
say 14 feet.
The antenna will present a series impedance of 170 ohms,
with
paralled impedance of 35 ohms. The SWR, in a rough guess,
should be
about 2.2:1  pretty poor, but not extremely dangerous.
An energy loss
is occuring here.
If we change the length of coax, to say 18 feet. The coax
then becomes
a means to balance out an unbalanced system.
This is where Voltage [E] and Current [M] waves come into
play.
In a balanced system  with both the antenna,
counterpoise, and coax
are all the same impedance. Then using unbalanced coax,
the system\
sees the proper impedance at any point along the line.
When the antenna itself is not the right impedance, the
coax then
takes on the role of attempting to balance itself to both
the source
and the antenna radiator. Even though the coax itself is
inherently
unbalanced, the extremes that it plays in this system [no
shorts
please] are at the two extreme ends of the impedances,
which are; the
antenna, source, and counterpoise, presenting themselves
to the coax.
The three basic elements, source, antenna, and
counterpoise
impedances, affect how the E and M waves propagate thru
the coax, and
the antenna itself.
In an poorly matched system, the impedances are
different.
By changing coax lengths, you are affecting the source
length of
counterpoise, even though the coax is bonded and forced
to the same
potential as the source ground. The coax becomes active,
and the metal
the antenna is floating upon to radiate, is also
affected. The
counterpoise metal the antenna is above will attempt to
raise it's own
impedance because of the influence the coax has on the
unbalanced
feedpoint. Changing coax length, in this type of system
[shield left
floating at antenna] you are recreating a coaxial
dipole, with the
counterpoise radiator that is forced to source ground,
becoming a
highimpedance path for return energy, and the coaxial
shield now has
a high voltage peak appearing at 1/2 wave length from the
source, and
a reflected voltage peak appearing at 1/2 wave from the
antenna.
The above might help explain some events...
1. Audio Squeal  excessive RF energy that the coax now
must radiate
due to out of phase relationships from forward waves
interacting with
reflected waves, inside a highimpedance shell [vehicle],
is now
forced to return to the source at any point that will
accept this
energy  including the microphone.
2. Unstable SWR  energy values that are equal [low SWR]
when the
antenna is left stationary in one spot. SWR becomes poor
during
attempts to move it to another location, or simple
vehicle motion
causing the whip to move, is changing the relationship of
antenna
impedance over a fixed impedance due to location.
3. Trimming coax lowers VSWR. This technique is the key
in realizing
that the antenna, and the counterpoise it's supposed to
work with, are
not equal. This means that the coax is forced to become a
part of the
antenna system and unless the antenna is either tuned or
relocated to
a better position, you MUST use a specific length of coax
in order to
keep the system stable and not to create situations like
1 and 2 above
 let alone
transmitter damage.
The
antenna subsystem is the most important part of your CB
system. It's tuning can make you or break
you. When checking SWR or Standing Wave Ratio, you
will be hooking up a simple form of a directional watt
meter. The meter measures Forward power in the system and
then compares it to the reverse or reflected power in the
system. Instead of showing you power, the
meter is calibrated to show the RATIO of coupling from
radio to antenna system. If there is all
forward power and no reflected power the antenna system
has a one to one (1:1) ratio with the transmitter.
By checking the SWR at channels 1 and 40 on your CB, you
will know if the antenna is too "long" or too
"short" for the center of the desired
band. You will also be able to evaluate your
system performance and troubleshoot problems. For
instance a SWR too high (over 3:1) all over the band can
be an indication of a bad part or junction, poor ground
or poor location. An SWR too low over the whole
band (1:1 for all 40 channels) can indicate a low
efficiency antenna or lossy component. Safe
operation of your CB should be with an SWR of 2:1 or
less. Most people would prefer to be 1.5:1 or
less. A good quality antenna and proper
installation (location very important) should easily
result in an SWR of less than 1.5:1
The coax cable is a means for
transferring your RF signal to the radiating portion of
the radio system. The cable, in theory, is meant to be a
contained, nonradiating link. Because it does not
radiate and serves only to transfer RF between two
components of the transmitter system, it's performance in
terms of efficiency is affected by length, but only in
terms of overall resistance. In other words, using a long
run of coax will reduce the total amount of signal at the
antenna, but only because of loss due to resistance and
NOT because of standing waves.
Ideally, you want to check the SWR
of your antenna at the antenna feedpoint. In a perfect
world, this is the best way. However, we all know that
this is ludicrous to expect in a standard base antenna
installation. Unless a remote SWR meter head is
incorporated, we usually use the standard SWR meter
located at the radio. The drawback is that resistance and
slight impedance mismatch of the coax affects the overall
SWR reading.
Because radio waves are tuned
wavelengths of energy, we have to take into account the
coax cable length. A typical 11meter signal has a basic
wavelength of 36 feet/wave. "Tuning" the coax
for the exact full wavelength tends to throw off the SWR
meter by not allowing any standing waves to return to the
meter. Excess RF on the coax has been given an ideal
medium by which to "hide" electrically from
your SWR meter. That is not to say that the excess RF is
not returning to the radio, you just can't see it on your
meter.
What we want to do is create an
environment where any excess RF (standing waves) are
rendered as visible as possible to the meter. This is
effectively done by using multiples of the 1/2wavelength
of the radiated signal. One half wave for the 11meter
band is 18 feet. However, this is not the length that you
will cut your coax. There is another factor that affects
the length. This is Velocity Factor. The velocity factor
is basically a term for how fast the signal moves through
the coax. This factor affects the overall electrical
performance of the coax and thus needs to be accounted
for when determining the true half wave length
Here are the velocity factors of
the various Belden coaxial cables:
RG59 .66
RG59/U (foam) .79
RG8 .66
RG8/U (foam) .80
Here is how to figure out your true
1/2wave:
492 x (Velocity Factor) / Frequency
(MHz)
For example, I want to figure out
the true half wave coax length for RG59/U (foam) on my
home channel (ch. 33  27.335):
492 x .79 / 27.335 = 14.22 feet
Now add 14.22 to itself to
determine your 1/2 wave multiples. Remember to use every
other number. See the example below:
14.22 feet 1/2wave multiple
28.44 feet 1wave multiple
42.66 feet 1/2wave multiple
56.88 feet 1wave multiple
71.10 feet 1/2wave multiple
85.32 feet 1wave multiple
and so on . . . .
Use only the
lengths that fall on the 1/2wave multiples and you will
be all set.
Now in order to get the true SWR of
the system, you have to throw away that 3foot jumper
cable for now. The SWR meter has to fall on a 1/2wave
point on the coax run. Using the example above, you need
a 14.22 foot jumper from the radio to the SWR meter, and
a 1/2wave multiple length from the SWR meter to the
antenna. If my antenna is 65 feet away from my radio, I
need a 14.22 foot jumper from the radio to the antenna,
and a 71.10 foot length between the SWR meter and the
antenna.
Further Considerations
Now that we've said all this, we
should discuss the tradeoffs between having the perfect
lengths of coax vs. having the shortest possible run for
efficiency purposes. If it is possible to test the SWR
while the antenna is installed, by all means do so. After
you have your match as flat as possible, reduce the coax
length to the shortest possible run. Your SWR will remain
the same as far as the antenna is concerned and you may
reduce the overall length of your coax enough to add more
efficiency to the overall system. Experiment with this
and have fun!
'
OHMS LAW  A potential
difference of 1 volt will force a current of 1
ampere through a resistance of 1 ohm. OR....
 P=(IxV) or
P=(I^{2}R)
Potential
Difference (V) = The difference in
voltage between the two ends of a conductor
through which a current flows. Also known as a
voltage drop.
CURRENT (I)
The quantity of electrons passing a given
point (Unit of measure: AMPERE)
VOLTAGE (V)
Electrical Pressure or Force. (Unit of measure:
VOLT)
RESISTANCE (R)
Resistance to the flow of current (Unit of
measure: OHM)
POWER (P)
The work performed by current (Unit of measure:
WATT)
RESISTANCE
 The opposition to flow of charge through a
material, expressed in ohms. Resistance is
similar in many respects to mechanical friction.
The resistance of a wire depends on its material,
length, thickness and temperature.
 R_{T} = Total
Resistance
Series circuit R_{T}=R_{1}+R_{2}+R_{3}+...
etc.
Parallel circuit R_{T}=(R_{1}xR_{2})/(R_{1}+R_{2})
or 1/[(1/R_{1})+(1/R_{2})+(1/R_{3})+(...)]
Resistivity
of
various materials 
(higher =
more resistance) 
Silver 
9.9 
Copper 
10.37 
Gold 
14.7 
Aluminum 
17.0 
Tungsten 
33.0 
Nickel 
47.0 
Iron 
74.0 
Carbon 
21,000 
CAPACITANCE  Measured
in farads, sometimes referred to as a condenser.
May be defined as the property of a circuit to oppose any
change in voltage.
 Series circuit capacitance = 1/[(1/C_{1})+(1/C_{2})+(1/C_{3})+(...)]
or (C_{1}xC_{2})/(C_{1}+C_{2})
Parallel circuit capacitance = C_{1}+C_{2}+C_{3}+...
etc.
Top
INDUCTANCE
 Measured in henries, sometimes referred to as a choke.
May be defined as the property of a circuit to oppose any
change in current. Inductance can be in phase or out of
phase. As the current increases through an inductor, the
magnetic field increases, exactly in step. At the instant
the current reaches it's maximum positive value, it's
rate of change is zero. This means maximum field strength
but zero magneticfield movement and therefore zero
counter electro magnetic force due to moving magnetic
fields. Thus maximum current and zero counter emf occur
at the same instant with an alternating current applied.
 I=(V/X), V=(IX),
X=(V/I)
I = Current, in A (usually rms)
V = emf, in V (usually rms)
X = Reactance, in ohms (or w) Series circuit inductance (Field of
inductors uncoupled) = L_{1}+L_{2}+L_{3}+...
etc.
Parallel circuit inductance = 1 /[(1/L_{1})+{1/L_{2})+(1/L_{3})]
or (L_{1}xL_{2})/(L_{1}+L_{2})
REACTANCE
 The opposition to a flow of charge due to
inductance and capacitance, similar to
resistance.
 Capacitive Reactance X_{C}=2µfC
Inductive Reactance X_{L}=2µfL
µ= 3.141592654 or 3.14 rounded
RESONANCE
 Resonance is the basis of all transmitter,
receiver, and antenna operation. Without resonant
circuits there would be no radio communication.
Resonance is the condition when XL=XC
or (2µfL)=(1/2µfC) or wL=1/wC
 X_{L} =
inductive reactance in ohms
X_{C} = Capacitive reactance in
ohms
f = Frequency
L = Inductance in Henries
C = Capacitance in farads
w = 2fµ
The
"Q" of a circuit is a measure of
quality when inductance and capacitance are
involved. Q=(X_{L}/R)=(2µfL/R),
Q=(X_{C}/R),
Q=(R/X).
Frequency of a
Tuned Circuit  f=(1/2µ)x sqRt[LC], BW=(F_{O}/Q)
 BW = Bandwidth
F_{O} = Frequency of resonance
Transformers
 Voltage ratio: (T_{P}/T_{S})=(V_{P}/V_{S}),
Current ratio: (T_{P}/T_{S})=(I_{S}/I_{P})
Audio
Speed of Sound in air (27^{o} C) = 1,139.67
ft./sec.
Intensity measured in decibels (dB). Frequency
measured in hertz (Hz).
Range of human hearing is approximately 20 Hzto 20 KHz.
 120 dB = Pain
120 dB = Aircraft engine at 20 ft.
110 dB = Amplified rock music
110 dB = Thunder
108 dB = Piezoelectric buzzer at 12 in.
90 dB = Air Force T38 2,500 ft. overhead
90 dB = C02 pellet gun at 12 in.
85 dB = Digital alarm clock at 12 in.
80 dB = Electric typewriter at 18 in.
70 dB = Air Force T38 at 1 mile
65 dB = Typical conversation
62 dB = Paper clip dropped on desk from 12 in.
61 dB = Computer keyboard at 18 in.
56 dB = Telephone dialtone
54 dB = Pencil eraser tapped on desk at 12 in.
45 dB = Average residence
30 dB = Soft background music
20 dB = Quiet whisper
0 dB = Threshold of hearing
Frequency (f)
vs. Wavelength (#) # =(c/f),
F=c/ #where c=speed of light. Example:
The wavelength of a 108 MHz signal is (3x10^{8})/(1.08x10^{6})
or 2.78 meters.
Antennas 
Adding inductance to an antenna lengthens the antenna.
Adding capacitance shortens it. Adding inductance and
capacitance allows tuning over a broad range.
 Z=276 log_{10}(d/r)
for two parallel wires or flatlead, 300 ohm line
Z = impedance in ohms
d = center to center separation
(inches,feet,millimeters,whatever)
r = conductor radius (same unit as in d)
dB = 10 log_{10}(P2/P1) Z=138 log_{10}(di/d)
for round lead or coaxial, 75 ohm line
Z = Surge impedance in ohms
di = inside diameter of hollow tubing
d = diameter of center conductor
in other words a coaxial line can be measured to
determine impedance.
# =(V / f )
or (300,000,000 / f ) = (300,000 / f
in KHz) = (300 / f in MHz)
# = Wavelength (Meters)
c = Speed of light
f = Frequency (Hertz)
V = velocity of radio waves, meters/second =
300,000,000
The length of a 7Megahertz
antenna is: (#/2) feet = (468/ f )
#/2 feet = (468 / f )= (468 / 7) =
66.9 Feet
Antenna wavelength in
inches # =11,811/f
For wavelength in coaxial cable
multiply by velocity of propagation.
Approximate length for a quarter wave whip
antenna in inches = lambda/4 or 2775/F in MHZ
Length of a quarter wave
line (matching transformerno end effect)
L = 246(vf) / f
L = Length in feet
vf = velocity factor of transmission line (see
below)
Velocity Factor
Air insulated parallel line  0.975
Air insulated coaxial cable  0.85
Polyethylene parallel line (twin lead)  0.82
Polyethylene coaxial cable  0.66
Voltage Standing Wave
Ratio (VSWR)  VSWR=(V_{max}/V_{min})
or SWR=(I_{max}/I_{min})
The ratio of current or voltage
delivered to an antenna to that reflected back
down the line is the reflection coefficient,
p. It is equivalent to p=SWR1/(SWR+1).
Power reflected back to the source is a mismatch
meaning not all power is being absorbed by the
load as wanted
all this
was copied off a news article,so dont qoute me as the
maker just passing all this along
Coax Data
Attenuation  db/100 feet
Belden # Impedance 100 MHz 400 MHz 1000 MHz OD V Factor
9880 50 1.3 2.8 4.5 .390 .82
This is Thicknet Ethernet cable. Most is marked "Style 1478" and
has a #12 solid center conductor and 4 shields (2 braid/2 foil).
Attenuation  db/100 feet
Belden # Impedance 100 MHz 400 MHz 1000 MHz OD V Factor
8240 50 4.9 11.5 20 .195 .66
8267 50 2.2 4.7 8 .405 .66
8208 50 9 .405 .66
9258 50 3.7 8 12.8 .242 .78
9913 50 1.3 2.8 4.5 .405 .82
9914 50 9 .403 .66
Attenuation  db/100 feet
Hardline Impedance 100 MHz 400 MHz 1000 MHz OD V Factor
1/2 50 0.8 1.8 3.0 .500 .66
1/2 75 0.93 2.2 3.6 .500 .66
3/4 50 0.66 1.49 2.4 .750 .66
3/4 75 0.7 1.55 2.6 .750 .66
7/8 50 0.55 1.3 2.3 .875 .66
7/8 75 0.5 1.35 2.25 .875 .66
Attenuation  db/100 feet
RG # Impedance 100 MHz 400 MHz 1000 MHz OD V Factor
4 /U 50
5 B/U 50 .332 .66
6 /U 75 2.1 5 6.9 .27 .78
6 A/U 75 11 .332 .78
7 /U 95
8 /U 50 1.8 4.7 6.9 .405 .66
8 A/U 50 9 .405 .66
8 /X 50 3.7 8 12.8 .242 .78
9 /U 51 2.2 4.7 8.9 .42 .66
10 A/U 50 .475 .66
11 /U 75 2 4.2 6.8 .405 .66
11 A/U 75 9 .405 .66
12 A/U 75 2.15 4.7 8.2 .475 .66
13 A/U 75 2.2 4.6 8 .425 .66
14 A/U 52 1.4 3.1 5.8 .545 .66
15 /U 76
16 /U 52
17 A/U 52 .81 1.9 3.8 .87 .66
18 /U 52 .81 1.9 3.8 .87 .66
19 /U 52 .7 1.5 3.5 1.12 .66
20 /U 52 .7 1.5 3.5 1.195 .66
21 /U 53 .332 .66
22 B/U 95 3 9.5  .42 .66
23 /U 125
24 /U 125
25 /U 48
26 /U 48
27 /U 48
28 /U 48
28 A/U 50
29 /U 53.5 .184 .66
30 /U 58
31 /U 51
32 /U 51
33 /U 51
34 /U 71 .63 .66
35 /U 71 1 2.5 4.5 .94 .66
36 /U 69
37 /U 52.5
38 /U 52.5
39 /U 72.5
40 /U 72.5
41 /U 67.5
42 /U 78
43 /U 95
44 /U 50
45 /U 50
46 /U 50
47 /U 50
48 /U 53
54 A/U 58 4 8 12 .25 .66
55 B/U 53.5 4.3 8.8 16.5 .206 .66
56 /U 53.5
57 /U 95 .625 .66
58 A/U 50 4.9 11.5 20 .195 .66
58 C/U 50 4.9 11.5 20 .195 .66
59 B/U 75 3.4 7 11.1 .242 .66
60 /U 50
62 A/U 93 2.7 5.4 8.3 .242 .84
63 /U 125 .405 .84
64 /U 48
65 /U 950 20 50  .405 
66 /U 69
71 B/U 93 1.9 3.2 8.5 .25 .84
72 /U 150
73 /U 25
74 /U 50 .615
76 /U 50
77 /U 48
78 /U 48
79 B/U 125 .475 .84
80 /U 51
81 /U 52
82 /U 52
83 /U 35
84 /U 71 1 2.5 4.5 1 .66
85 /U 71 1 2.5 4.5 1.565 .66
86 /U 205
87 A/U 50 .425
88 /U 50
89 /U 125
90 /U 50
91 /U 50
92 /U 50
93 /U 50
94 /U 50 .5
95 /U 50
96 /U 50
97 /U 50
98 /U 50
99 /U 50
100 /U 35 .242 .66
101 /U 70
102 /U 140
108 A/U 78 26.2 .235
109 /U 76
111 /U 95
114 /U 185 .405 .66
115 /U 50 .375
116 /U 50 .49
117 /U 185
118 /U 50 .78
119 /U 50 .465
120 /U 50
121 /U 50
122 /U 50 7 15.2 25 .16 .66
124 /U 73
125 /U 150
126 /U 50 .28
128 /U 50
130 /U 95 .625 .66
131 /U 95
140 /U 75 13 .233
141 /U 50 3.2 6.9 13 .19
142 /U 50 3.9 8.2 13.5 .206
143 /U 50 .325
144 /U 75 .41
156 /U 50 .54
157 /U 50 .725
158 /U 25 .725
161 /U 70 .09
164 A/U 75 .87 .66
165 /U 50 .41
174 /U 50 8.9 17.5 28.2 .101 .66
178 B/U 75 10.5 28 46 .075
179 B/U 75 10 16 24 .105
180 B/U 95 5.7 10.7 17 .145 .66
181 /U 125 .64
187 A/U 75 9.8 15.8 25 .11 .66
188 A/U 50 9.8 15.8 25 .11 .66
190 /U 50 .7
191 /U 25 1.46
195 /U 95 9.8 15.8 25 .155 .66
196 A/U 50 9.8 15.8 25 .08 .66
209 /U 50 .75
210 /U 93 3.1 .242
211 /U 50 .73
212 /U 50 1.6 3.6 8.8 .336 .66
213 /U 50 2.2 4.7 8 .405 .66
214 /U 50 2.2 4.7 8 .425 .66
215 /U 50 2.2 4.6 9 .475 .66
216 /U 75 .425 .66
217 /U 50 1.4 3.1 5.8 .545 .66
218 /U 50 .81 1.9 3.8 .87 .66
219 /U 50 .81 1.9 3.8 .87 .66
220 /U 50 .7 1.5 3.5 1.12 .66
221 /U 50 .7 1.5 3.5 1.195 .66
223 /U 50 4.5 9.2 14.3 .212 .66
224 /U 50 1.5 3 6 .615
225 /U 50 7.5 .43
226 /U 50 .5
227 /U 50 .49
228 /U 50 .795
279 /U 75 .145
280 /U 50 .48
281 /U 50 .75
301 /U 50 .245
302 /U 75 3.9 8 12.8 .206
303 /U 50 9.8 15.8 25 .17 .66
304 /U 50 .28
307 /U 75 .27
316 /U 50 10.4 16.5 31 .102 .66
393 /U 50 2.1 4.4 7.5 .36
400 /U 50 3.1 8.1 13 .171
403 /U 50 13.6 26.5 45 .116
404 /U 50 16.3 32.4 68 .116
405 /U 50 22 .085
Coaxial Cable
Attenuation Ratings
Nominal attenuation db/100 feet at (MHz)

RG/U CABLE 
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

LMR400 


.9

1.2


2.5

4.1

4.3



LMR500 


.7

1.0


2.0

3.2

3.4



LMR600 


.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



LDF450A 
.06

.21

.47

.68

.98

1.4

2.2

2.3

4.3

5.9

LDF550A 
.03

.11

.25

.36

.53

.78

1.2

1.4

2.5

3.5

RG/U CABLE 
1.0 
10 
50 
100 
200 
400 
900 
1000 
3000 
5000 
55,6A,212

4000

1500

800

550

360

250


150

65

50

8 MINI,8X 
4000

1500

800

550

360

250


150

65

50

8,8A,10A,213 
11000

3500

1500

975

685

450


230

115

70

9913,9086,9096 

3500

1500

975

685

450


230

115

70

4XL8IIA,FLEXI 4XL 

3500

1500

975

685

450


230

115

70

9095 
11000

3500

1500

975

685

450


230

115

70

9,9A,9B,214 
9000

2700

1120

780

550

360


200

100

60

11,11A,12,12A,
13,13A,216 
8000

2500

1000

690

490

340


200

100

60

14,14A,217 
20000

6000

2400

1600

1000

680


380

170

110

17,17A,18,18A,
218,219 
50000

14000

5400

3600

2300

1400


780

360

230

55B,223 
5600

1700

700

480

320

215


120

60

40

58 
3500

1000

450

300

200

135


80

40

20

58A,58C 
3200

1000

425

290

190

105


60

25

20

59,59B 
3900

1200

540

270

270

185


110

50

30

62,62A,71A,71B 
4500

1400

630

440

320

230


140

65

40

62B

3800

1350

600

410

285

195


110

50

31

141,141A,400
142,142A 
19000

9000

3500

2400

1600

1100


650

350

245

174 
1000

350

160

80

80

60


35

15

10

178B,196A

1300

640

330

240

180

120


75

40



188A,316 
1500

770

480

400

325

275


150

80

53

179B

3000

1400

750

480

420

320


190

100

73

393,235 

25000

9500

6300

4300

2800


1700

880

620

402 

9000

3500

2400

1600

1100


650

350

245

405 







130



LDF450A 
19000

6100

2600

1880

1310

906

563

551

294

217

LDF550A 
44000

7700

7740

5380

3720

2550

1620

1520

785

568










