User's Manual

Document Number: 0100SM1401 Issue: 10-14

RF Feeders and Protection

Lightning Arrestor

A lightning arrestor is used to help minimize lightning damage to radio devices. Lightning arrestors are made to bleed off

electrostatic build-up to help prevent a direct lightning strike from hitting the antenna system. Also, if a lightning strike

happens nearby, the arrestor helps to route the energy to ground.

The lightning arrestor is typically installed on the inside of a radio hut, between a coaxial tail lead the antenna feeder cable.

The lightning arrestor comes with an N-Type female socket on each end.

RF Coaxial Cable

There are many types of RF coaxial cables available, but it is sometimes difficult to

know which type of cable to use.

There are two main aspects of a cable to consider when selecting the right cable for

the job.

Bend Radius:

The bend radius of a cable is a specification given to a cable to define how flexible

the cable is. Exceeding the bend radius specification can change characteristics

within the cable and lead to reduced RF performance. The thicker the cable is, the

wider its bend radius will be, however, the thicker the cable, the lower its electrical

resistance will be, providing less impact on the radio system gain.

The cable connected from the radio to the lightning arrestor is typically quite short. This allows a thin, flexible cable to be

used. Thin flexible cables have a higher electrical resistance characteristic than thick rigid cables, but as there is only a short

length being used, the impact on radio system gain is negligible. The thick rigid cable is typically connected from the hut to

the top of an antenna mast connected to an antenna.

Cable Loss:

Each cable has its own specified cable loss characteristics. These characteristics can vary depending on what frequency is

being carried through the cable. See the table below for typical cable loss values.

Loss (dB) Relative to Distance (m) - at 450MHz

Cable Type 1 dB 3 dB 6 dB 9 dB

RG58 2.3 m (7ft 6in) 7 m (23ft) 14 m (46ft) 20 m (65ft 6in)

RG223 3.1 m (10ft) 8 m (26ft) 18 m (59ft) 28 m (92ft)

RG213 6.1 m (20ft) 18 m (59ft) 37 m (121ft 6in) 55 m (180ft 6in)

LDF 4-50 19 m (62ft) 57 m (187ft) 114 m (374ft) 171 m (561f)

LDF 5-50 38 m (124ft) 114 m (374ft) 229 m (751ft) 343 m (1125ft)

Part E – Radio Planning and Design