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 end-fed 1/2 wave lengt
antenna offers an impedance of 1500 ohms, but center-fed dipoles offer
an impedance of 72-75 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.
Mag-mount 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 center-connected 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 floating-metal 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 free-floating 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 open-end 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 end-fed 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 re-creating a coaxial dipole, with the
counterpoise radiator that is forced to source ground, becoming a
high-impedance 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 high-impedance 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, non-radiating 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 11-meter 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 1/2-wavelength of the radiated signal. One half wave for the 11-meter 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:

RG-59 .66
RG-59/U (foam) .79
RG-8 .66
RG-8/U (foam) .80

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

492 x (Velocity Factor) / Frequency (MHz)

For example, I want to figure out the true half wave coax length for RG-59/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 1/2-wave multiple

28.44 feet 1-wave multiple

42.66 feet 1/2-wave multiple

56.88 feet 1-wave multiple

71.10 feet 1/2-wave multiple

85.32 feet 1-wave multiple

and so on . . . .

Use only the lengths that fall on the 1/2-wave multiples and you will be all set.

Now in order to get the true SWR of the system, you have to throw away that 3-foot jumper cable for now. The SWR meter has to fall on a 1/2-wave 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 1/2-wave 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 trade-offs 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....

• V=(IR), I=(V/R), R=(V/I)

• P=(IxV) or P=(I²R)

  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=R₁+R₂+R₃+... etc.
    Parallel circuit R_T=(R₁xR₂)/(R₁+R₂) or 1/[(1/R₁)+(1/R₂)+(1/R₃)+(...)]

    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/C₁)+(1/C₂)+(1/C₃)+(...)] or (C₁xC₂)/(C₁+C₂)
  Parallel circuit capacitance = C₁+C₂+C₃+... 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 magnetic-field 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) = L₁+L₂+L₃+... etc.
  Parallel circuit inductance = 1 /[(1/L₁)+{1/L₂)+(1/L₃)] or (L₁xL₂)/(L₁+L₂)

  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)

• T_P = Primary Turns
  T_S = Secondary Turns
  V_P = Primary Voltage
  V_S = Secondary Voltage
  I_P = Primary Current
  I_S = Secondary Current

  Transformer Efficiency as a percent = (P_O/P_I)x100
  P_O = Power output
  P_I = Power input
  (T_P/T_S)=(V_P/V_S)=(I_S/I_P)=sqRt[Z_P/Z_S]
  Z= Impedance as measured in ohms

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 T-38 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 T-38 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 (3x10⁸)/(1.08x10⁶) 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 log₁₀(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 log₁₀(P2/P1)

  Z=138 log₁₀(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 7-Megahertz 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 transformer-no 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=SWR-1/(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)