Manufacturers and users identify coaxial cables with the letters "RG" and then a number. Most coaxial cables conform with military specification MIL-C-17, which defines certain parameters the cable must meet. RG8 and RG213 both conform with Mil-spec M17/74 and have the same basic electrical characteristics. They can be interchanged for signals, but not for certain environmental conditions. Most manufacturers strive to meet military specifications for all the cables they produce.
MIL-C-17 also carries sub-categories for environmental considerations for coaxial cables. RG8, an older design of cable, classifies as Type 1 and is labeled "contaminating" because the PVC jacket material breaks down faster with exposure to ultra-violet rays from the sun over time. The PVC jacket material of RG213, however, classifies as Type IIA and labeled "non-contaminating." The PVC jacket on RG213 can last up to two times longer than that of RG8. But other than the material of the outer jacket, the differences between RG8 and RG213 are minimal.
The design of RG8 only allows a maximum of 4,000 volts difference between the center conductor and the shield. RG213 allows 5,000. RG8 can withstand temperatures between -40 and +80 degrees centigrade, while RG213 can only withstand between -40 and +75 degrees. Both use seven strands of wire for the center conductor, but RG213 uses slightly larger strands for an overall diameter of 0.089 inches whereas RG8 is 0.0855 inches. RG213 is slightly heavier at 10.6 lbs. for a 100-foot section whereas RG8 only weighs 10.5 lbs.
RG8 and RG213 commonly carry VHF and UHF radio signals from transmitters to antennas and from antennas to receivers. They also carry high-performance electronic signals for data transmission and computer applications for commercial broadcast, telecommunications, industry and military systems. They are most commonly used in situations that require low signal loss and high operating voltage, particularly to antennas on towers for two-way radio systems. They can also be buried for underground applications.
The military specification requirements for RG8 and RG213 set maximum attenuation or signal loss standards that the cables must meet at certain frequencies. At 100 MHz, RG8 and 213 must not have more than 2.3 dB of loss for a cable length of 100 feet. At 400 MHz, the loss cannot exceed 4.8 dB and at 1,000 MHz it can't exceed 9.0 dB. Both cables must be able to carry a signal with a power of 320 watts. Neither cable must carry signals over 1,000 MHz.