Two Way Radio Antenna Cable

RG (Radio Guide) is a military term. The RG series was originally used to specify the types of coax cables for military use. The presence of the letter U supposedly indicated it was for multiple uses. All current RG specifications are based on this obsolete military designation and the current specifications are very loose. You can just about give a coat hanger stuffed in a hot dog an RG designation today.

• Attenuation of Coaxial Transmission Line

Attenuation is the reduction in the strength of a signal. Attenuation of RF cable refers to signal loss. The coaxial cable is used to transfer power between the radio and antenna, in one direction, at any given time. Due to limitations of the cable, some power is lost along the length of the RF cable, known as attenuation.

Attenuation is defined in terms of decibels per unit length, and at a given frequency and 100 ft length is a common reference for comparison since the longer the cable the more attenuation occurs.

Table of data for common coax cable types
Coax Type	Characteristic impedance	Outside diameter	Velocity factor	Atten @ 100 MHz	Atten @ 1000 MHz	Comments
RG5/U	52.5	8.4	0.66	1.0	3.8
RG9/U	51.0	10.7	0.66	0.66	2.4
RG10A/U	50	12.1	0.66	0.66	2.6
RG20A/U	50	30.4	0.66	0.22	1.2
RG58C/U	50	5.0	0.66	1.8	7.6
RG119	50	11.8		0.5	1.8
RG120	50	13.3		0.5	1.8
RG122	50	4.1		1.7	5.5
RG213/U	50	10.3	0.66	0.62	2.6	Polythene dielectric
RG214/U	50	10.8	0.66	0.76	2.9	Double screened, silver plated copper wire
RG223/U	50	5.5	0.66	1.58	5.4
UR43	50	5	0.66	1.3	4.46
UR67	50	10.3	0.66	0.66	2.52	Similar to RG213/U
UR74	51	22.1	0.66	0.33	1.4
UR76	51	5	0.66	1.7	7.3	Similar to RG58C/U
UR79	50	21.7	0.96	0.17	0.6

RG-59

Used for low-power video and RF signal connections. The cable has a characteristic impedance of 75Ω (ohm)s, and a capacitance of around 20pF/ft (60pF/m).

Commonly known as old cable TV coaxial cable or CCTV cable.

Not suitable for most two-way radio application.

RG-6/U

A larger family of cable design not specific to one in particular. RG-6 and RG-6/U are the same. The cable family has a characteristic impedance of 75Ω. It has a smaller conductor and the dielectric insulation is thicker than RG-59. It was made to work better with broadband data and satellite application. Handles frequencies higher than 50Mhz better than RG-59.

Commonly known as small dish satellite TV cable.

Not suitable for most two-way radio application.

RG-58

Used for low power signal and RF connections. The cable has a characteristic impedance of either 50Ω or 52Ω. RG-58 CB coaxial is an affordable choice for basic CB installations. RG-58 (CB cable) has a high loss factor in VHF and UHF frequencies, so it really only is useful in runs less than 50 feet for frequencies above 100 MHz, and 20 feet for frequencies above 400 MHz.

Commonly used for Citizens Band radio.

RG-8/U

This cable is suitable for 50-75 foot runs in the VHF/UHF range. The cable is considered by some to be obsolete. The cable has a characteristic impedance of 50Ω.

RG8x is 50 Ohm cable that is about the same physical size as RG6. It is fairly high loss however and is not that well suited for 70cm except in short runs, however, is suitable for longer runs in the VHF 2m band. RG8 (RG213) is larger 50 Ohm cable that has less loss than RG8X.

RG-213

• thick, 50Ω, low loss

Considered to be a replacement to RG-8 and much better suited for both VHF and UHF operation. The cable has a characteristic impedance of 50Ω. The specifications for RG-213 are tight as compared to RG-8, increasing the consistency from one manufacturer to the next. RG213 is low loss cable with a non-contaminating jacket.

LMR-400

LMR 400 Coax will have .7 dB loss at 30 MHz, with a length of 100 Feet.