User's Manual

8 MHX-920 Operating Manual: Glossary
WARNING:
The L400 can only be used with
any antennas listed in Appendix
A and this the antenna
separations shown in Appendix
A.
WARNING:
Be careful with dBi vs dBd gains
on antenna specifications.
Antenna manufactures may not
clearly indicate the gain on the
antenna if it is dBd or dBi. Note
1dBd = 2.15dBi.
Factors to take into consideration when choosing a cable are:
• price;
• bend radius limitations (the lower performance cables generally can
bend more sharply)
• performance requirements; and,
• distance between the equipment and the antenna.
When installing the cable, always begin fastening at the top near the
antenna connector/surge arrestor. The cable must be supported at the top
with a hose clamp or wrap lock, and at 5 ft intervals down the length of the
tower. Over-tightening the fasteners will dent the cable and reduce
performance. If properly grounded surge arrestors are not installed at both
the top and the bottom of the cable, then the cable should be grounded to
the tower at these locations using a cable grounding kit. If the tower is non-
conductive, then a separate conductor, physically separate from the cable,
should be run down the tower.
Antenna
Before choosing an antenna, you should have some knowledge of the path
loss and the topology of the equipment. If the equipment is in a fixed
location and is to communicate with only one other unit also in a fixed
location, then a Yagi antenna is suitable. Choose a Yagi with enough gain
to ensure adequate gain margin. When deploying the Yagi, point the
antenna towards the intended target, ensuring the antenna elements are
perpendicular to the ground for vertical polarization.
In applications where there are multiple units that you must communicate
with or units, which are in motion, you may select an Omni-directional
antenna with appropriate gain.
See appendix A for a list of approved antennas types that can be used
with the L400 radio modem. If you require another type of antenna
please contact Microhard Systems Inc.
Microhard Systems Inc. can provide you with approved antennas to ensure
FCC and Industry Canada compliance.
ERP is calculated as follows:
ERP = Tx Power(dBm) - Cable/Connector Loss(dB) + Ant Gain(dBi)
Antenna Gains must be in dBi when calculating the 36dBm ERP limit.
1dBd = 2.15dBi
Use the guidelines in the previous section for calculating cable and
connector losses. If cabling and connector losses are 2 dB, then the
maximum allowable gain of the antenna will be 8 dB.