Specifications

Table Of Contents
APPENDIX D: INSTALLATION DETAILS
Page 206 MRC-565 Packet Data Radio Operations & Maintenance
APPENDIX D: INSTALLATION DETAILS
Site selection and general installation guidelines are provided in this section, including
instructions for cabling, antenna and power source connections. Power up procedures,
initialization and functional test procedures are described that should be performed prior to
placing the MRC-565 on-line within the network.
Site Selection
There are 5 important factors to consider in selecting an optimum site:
1. External noise/interference
2. DC power source
3. Horizon angle
4. Antenna type
5. Antenna height
External Noise/Interference
Noise and signal interference can reduce the performance of the MRC-565. The most common
sources of noise and interference are as follows:
Cosmic Noise
Power Line Noise
Auto Ignition Noise
Computer-Generated Interference
External Signal Interference
Cosmic Noise
Cosmic noise is the limiting noise factor in a meteor burst system. This noise is generated by star
systems in the galaxy and is frequency dependent. The noise is approximately 15 dB above
thermal at 40 MHz and 13 dB above thermal at 50 MHz. This noise is diurnal in nature. It is the
highest when the antennas are pointed directly at the center of the galaxy and lowest when they
are pointed at right angles to it. Daily variations of 3 to 4 dB can be expected. An optimal
meteor burst site is one that is limited only by cosmic noise.
Power Line Noise
One of the main sources of manmade noise are high voltage power lines. Noise on these lines is
generated by high voltage breakdown occurring on power line hardware such as transformers
and insulators. This noise can be seen with an oscilloscope at the Receiver IF test point as a
series of spikes that occur every 8 ms (1/60 Hz) or every 10 ms (1/50 Hz). The level of the spikes
will be much higher than the normal background noise floor. The number of spikes can vary,
depending upon the level of interference, from one or two every 8-10 ms to several dozen every
8-10 ms. The impulse noise blanker in the MRC-565 will remove a large amount of this noise.