Meteor Communications Corporation MCC-545C, Эксплуатация и обслуживание, Страница: 24 / 88

DESCRIPTION 2-19
MCC-545C PACKET DATA RADIO
12/2000
Power Line Noise
One of the main sources of external 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 can remove a large amount of this noise. However, as the
number of spikes increase, 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 for an optimum site. Try to set up
the receiver antennas well away from power lines and do not point the antennas directly toward
nearby power lines.
NOTE .
Power companies are required to properly maintain their power lines to reduce noise. Call your
local utility in case of severe noise.
Automobile Ignition Noise
Automobile ignition noise is generated by all gasoline engines and is a result of the high voltage
required to fire the spark plugs. Auto ignition noise is similar to power line noise with the
exception that it does not have the 8-10 ms period which is associated with power line noise. If
the MCC-545C is operated on a vehicle, care must be taken to ensure that the vehicle ignition
system, DC motors, or any other source of electrical noise is isolated through shielding, ferrite
bead, and/or bypass capacitors.
Computer-Generated Interference
All computers and printers contain high-speed circuits that generate spurious signals throughout
the 37-50 MHz band. Interference will result if any of these signals couple into the antenna at
the MCC-545C receive frequency. 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 will generally prevent this type of interference. The noise blanker will not suppress
computer-generated interference.
Signal Interference
This type of interference will occur whenever another transmitter is operating on the receiver
center frequency of the MCC-545C. Antenna nulling and spatial separation can be used to
reduce this type on interference.