User's Manual

MHX-920 Operating Manual:Glossary 7
WARNING:
Direct human contact with the
antenna is potentially unhealthy
when the L400 is generating RF
energy. Always ensure that the
L400 equipment is powered down
during installation.
WARNING:
Never work on an antenna
system when there is lightning in
the area.
3.2.2 Installing External Cables, Antennas and Lightning
Arrestors
Qualified and experienced personnel must carry out the installation,
removal or maintenance of all antenna components. Never work on an
antenna system when there is lightning in the area.
Direct human contact with the antenna is potentially unhealthy when the
L400 is generating RF energy. Always ensure that the L400 equipment is
powered down during installation. At all times a distance of shown below
should be maintained between the antenna and any person when the device
is in operation.
Antenna
Impedance
(ohms)
Antenna
Gain (dBi)
Minimum
Separation
Distance (cm)
Min Gain
50
0
39
Max Gain
50 18 305
Surge Arrestors
The most effective protection against lightning is to install two lightning
(surge) arrestors, one at the antenna, the other one at the interface with the
equipment. The surge arrestor grounding system should be fully
interconnected with the transmission tower and power grounding systems to
form a single, fully integrated ground circuit. Typically, both ports on surge
arrestors are N-female.
External Filter
Although the L400 is capable of filtering out RF noise in most
environments, there are circumstances that require external filtering.
Paging towers and cellular base stations in close proximity to the L400
antenna can desensitize the receiver. Microhard Systems’ external cavity
filter eliminates this problem. The filter has two N-female ports and should
be connected in line at the interface to the RF equipment.
Cabling
The following coax cables are recommended:
Table 3 Cable Loss
Cable Loss (dB/100ft)
LMR 195 10.7
LMR 400 3.9
LMR 600 2.5