Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

the cable and that replacement is in order.
Signs of a poor coaxial connection or degraded
cabling will be poor radio reception or low
transmission range.
You can check the state of the cable by
monitoring its VOP with a TDR (Chapter 3).
You can identify cable breakdown or failure,
or confirm that the cable is stable and within
known specifications.

Choosing Coax for Marine Applications

In choosing coax cable, we’ll look at three spec-
ifications: type, attenuation, and impedance.

Type

Coax is identified by various RG types,
including RG-8, RG-213, RG-8X, RG-58,
RG-59, and RG-6U, as well as LMR, such as
LMR-400. These designators can be a bit con-
fusing, but the letters and numbers do have
meaning. We’ll use RG-8/U as an example:

Rstands for radio frequency

Gstands for government

8 represents a government approval number

Urepresents a universal specification

If the letter A, B, or C appears before the

slash (for example, RG-8A/U), it indicates a

specification modification. The only way to be

crystal clear on these subtle specification dif-

ferences and letter designators is to check out

the website for one of the major coaxial sup-

pliers (e.g., Belden, http://www.belden.com) and

compare the specifications closely.

Table 16-1 lists the characteristics of five

types of coaxial cable found on boats:

• RG-58/U is very thin and typically used
  only for interconnecting electronics
  where lengths are short and signal attenu-
  ation is not a problem.


• RG-59/U is used to connect television
  antennas and cable service.


• RG-8X is typically used to connect VHF
  and HF antennas up to lengths where
  attenuation becomes excessive.


• RG-8/U and RG-213 are both used to
  conduct maximum power to VHF and
  HF antennas.
  Some letter designators don’t fall under
  this set of government rating numbers. A good
  example is the LMR-400 coaxial mentioned
  above. In this case, “LMR” is simply a registered

coaxial cable and antennas 167

Specification RG-58/U RG-59/U RG-8X RG-8/U RG-213

Nominal O.D.^3 / 16 ''^1 / 4 ''^1 / 4 ''^13 / 32 ''^13 / 32 ''

Conductor AWG #20 #23 #16 #13 #13

Impedance, ohms 50 75 50 52 50

Attenuation/100', dB

@50 MHz 3.3 2.4 2.5 1.3 1.3

@110 MHz 4.9 3.4 3.7 1.9 1.9

@1,000 MHz 21.5 12.0 13.5 8.0 8.0

Reprinted with permission from Boatowner’s Electrical Handbook, second edition, by Charlie Wing

Coaxial Cables

TABLE

16-1