Operations Manual

INSTALLATION 3-3
O&M of the MCC-545B PACKET DATA RADIO
12/2000
3.1.2 Horizon Angle
The second consideration in site selection is the horizon angle in the direction of the Master
Station. To achieve optimum performance at ranges of up to 1600 km (1000 miles), the horizon
or look angle must be free from obstructions, buildings, bridges, etc., and must be within 2 or 3
degrees of horizontal. Trees and other shrubbery do not present a problem if they are not within
6.1 m (20 ft) of any element of the antenna. At shorter ranges the horizon angle can be higher.
3.1.3 Power Source
The 545B requires a 12 VDC power source. An automobile battery provides an excellent power
source. Care must be taken to ensure that proper wiring is used to support the 545B high in-rush
current during transmission. Typical transmit current is 25 to 30 amps for a period of about .10
seconds. A #14 wire (or two #16 wires) should be used for both +12 VDC and ground. Keep the
wire length shorter than 10 feet. Remember that this is 20 feet counting the ground return. The
545B contains a 20 amp internal fuse and a special circuit that protects the unit from a power line
reversal. The fuse will have to be replaced if the power lines are reversed.
3.1.4 Site Dimensions
In order to obtain the maximum performance from a Meteor Burst Communications System, the
Station must be set up on level flat ground. The terrain in front of the antenna must be flat and be
free of buildings and other structures for a distance of at least 30 times the height of the antenna.
Operation in an area that does not have a ground plane to support ground reflection can reduce
meteor performance by a factor of two.
3.1.5 Antenna Considerations
The final consideration in setting up a site is selecting the antenna and co-ax cable. Any antenna
that provides a 50 ohm load will work. This impedance must be maintained at both Tx and Rx
frequency. In a single frequency system, a very narrow bandwidth antenna can be used. The
information bandwidth of the system is less than 15 KHz.
The higher the antenna gain the better the performance. Yagi antennas work better than dipoles
(2 to 4 times improvement). Always maintain the same polarization as the Master Station
antenna. For example, if you use a whip antenna with the 545B, the Master Station antenna must
be vertically polarized.
In a Meteor Burst System, the height of the antenna should be optimized as a function of the
distance between the Master Station and the Remote Station. A plot of best antenna height vs.
range is given in Figure 3.1-1 below.