Microhard Systems IP-921, Operating Manual

Page: 156 / 173

© Microhard Systems Inc. CONFIDENTIAL 156
IP9xx Series
7.0 Installation
Transmit Power
Having read thus far through the factors to be considered, it should
be clear that they are all interrelated. Transmit power should be set
for the minimum required to establish a reliable communications path
with adequate fade margin. Required transmit power is dictated pri-
marily by distance, antenna type (specifically the ‗gain‘ of the anten-
nas being used), and the receive sensitivity of the distant IP Series.
Cable and connector losses (the physical path from the modem‘s
‗antenna connector‘ to the antenna‘s connector) must also be taken
into account.
Receive Sensitivity
The IP Series has exceptional receive sensitivity, which can produce
a number of benefits, such as: added fade margin for a given link,
being able to use less expensive coaxial cable or antenna types, be-
ing able to operate at greater distances for a given distant transmitter
power (perhaps negating the requirement for a Repeater site!). Dis-
tance, antenna gain, transmit power, and receive sensitivity are criti-
cal ‗numbers‘ for radio path calculations. Fortunately, the IP Series
features the maximum available transmit power combined with ex-
ceptional receive sensitivity -
two ‗numbers‘ which will produce the
most favorable path calculation results.
Fade Margin
When all radio path numbers are being considered and hardware
assumptions are being made, another factor to consider is the ‗fade
margin‘ of the overall system. the fade margin is the difference be-
tween the anticipated receive signal level and the minimum accept-
able receive level (receive sensitivity). Being that the Spectra 920A
performs to exacting specifications, the overall deployment should be
such that the modems may be utilized to their full potential to provide
a reliable and robust communications link. A typical desired fade
margin is in the order of 20dB, however oftentimes a 10dB fade mar-
gin is acceptable.