Operations Manual

INSTALLATION 3-2
O&M of the MCC-545B PACKET DATA RADIO
12/2000
Power Line Noise
One of the main sources of external noise are the high voltage power lines common throughout
the country. Noise on these lines is generated by high voltage breakdown occurring on power
line hardware such as transformers, insulators, etc. This noise shows up at the Receiver IF test
point (using a scope) 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 can remove a large amount of this
noise. However, as the number of spikes increases, the effectiveness of the blanker is reduced.
When setting up a site always look at the IF test point with a scope to determine the level of the
power line noise interference. It is mandatory that power line noise be avoided. Try to set up Rx
antennas well away from power lines and try not to point the antennas directly toward nearby
power lines.
NOTE.
Local power companies should maintain power lines to reduce noise. Call your local utility in
case of severe noise.
Auto Ignition Noise
Auto ignition noise is generated by any gasoline engine and is a result of the high voltage
required to fire the spark plugs in automobiles. A basic characteristic of auto ignition noise is
that it is similar to power line noise (i.e., this type of noise generates a DET RF spike visible with
an oscilloscope), but it does not have the 8-10 ms period which is associated with power line
noise. If the unit is operated on a vehicle, care must be taken to ensure that the vehicle ignition
system, any DC motors, and any other source of electrical noise are isolated through shielding,
ferrite beads, and-or bypass capacitors.
Computer-Generated Interference
All computers and printers contain high-speed logic circuits which generate spurious signals
throughout the 37-50 MHz band. If one of these signals occurs at the receive frequency,
interference results when the spurious computer signal is picked up by the receive antenna. To
avoid this type of interference keep the antenna away from buildings that contain computers.
Separating the antennas from the computers by 100 to 300 feet generally prevents this
interference. The noise blanker does not suppress computer-generated interference.
Signal Interference
This type of interference occurs whenever the unit is set up in an area where another transmitter
is operating on the desired receiver center frequency. Antenna nulling and spatial separation can
be used to reduce this type on interference.