Dealing with Cable Loss

If an antenna is mounted on a mast remotely from the equipment hut, then feeder loss
needs to be taken into account in the link budget. The fatter the feeder, the lower the
loss but the more expensive the feeder. Also, the higher the frequency, the higher the
loss. In PMR installations at VHF and UHF frequencies, you often see 3⁄8- or 1⁄2-inch
feeder used (good imperial measurements here). As frequency increases (for example,
1800 MHz/1900 MHz) either 7⁄8- or often 1 1⁄2-inch feeder has to be used. Not only is this
expensive in material terms, it is also hard to handle because of the bending radius of
the copper waveguide inside the corrugated outer plastic jacket (1 1⁄2-inch feeder comes
in very large rolls).
Even with fat feeder, a loss of 1 or 2 dB between the antenna and the equipment hut
is quite common. This is why there has been an increasing use of mast-mounted lownoise
amplifiers in cellular applications. Putting at least the first stage of the Low-
Noise Amplifier (LNA) ahead of the feeder loss improves receive sensitivity. Similarly,
it is quite common to find High-Power Amplifiers (HPAs) installed at the mast head to
maximize transmitted power.
An additional consideration is lightning protection. Earth bonding may be needed
to protect people in the hut. Earthing often does not protect equipment, which may
well be damaged by a direct strike on the tower. Mast-mounted HPAs and LNAs are
intrinsically quite vulnerable to lightning damage.