User's Manual

INSTALLATION AND MAINTENANCE MANUAL
LYNX.sc E1 FAMILY
SPREAD SPECTRUM RADIOS
SEPTEMBER 1999
PAGE 4-20 SECTION 4: TROUBLESHOOTING
4. Antenna Polarization
Cross-polarized antennas can provide approximately 20 to 30 dB discrimination of unwanted
signals. The actual discrimination will depend upon the antenna design and any rotation of
polarization along the path, for example, due to reflections. Discrimination only exists between two
orthogonal polarizations:
- vertical vs. horizontal or
- left-hand circular vs. right-hand circular
There is only 3 dB discrimination between circular and linear (vertical or horizontal) polarization.
Interference can sometimes be overcome by changing antenna polarization at both ends of the link.
5. Spreading Code Selection
There are 4 selectable spreading codes provided for the LYNX.sc radio (See Section 3.12.3). These
codes are selected by DIP switches and provide some discrimination against interference from other
LYNX.sc transmitters. The discrimination is limited to approximately 3 to 6 dB for radios using the
same channel plan. This is the difference between the co-channel C/I when using different codes for
the wanted and unwanted signals. When combined with a different frequency channel, the code
discrimination improves significantly beyond 3 to 6 dB. See Section 3.12.3 for code selection
details.
6. Transmit Power
The maximum level into the receiver is 0 dBm. Above this level, errors may occur in the receive data
stream. Transmit output power should be reduced on very short paths to avoid overload.
7. Equipment/Antenna Location
Occasionally, interference is caused by the radio or the antenna being too close to another similar
transmitter. For example, at 2.4 GHz, microwave ovens can exhibit interference if mounted near the
radio or antenna. Other high powered transmitters may also cause interference. Moving the radio,
the antennas, or the interfering equipment can reduce or eliminate interference.
Interference countermeasures rely to some extent on the
measurement of the received interference level and frequency.
Prior to turning up a new hop, a spectrum analyzer can be used to
monitor the spectrum at each end to check for possible interfering
signals. See Section 4.8.1 for more details.