User Manual Part 2

Lynx.GX Installation and Management
Narrow Beam Antennas (High Gain)
This is the next most effective countermeasure. Narrow-beam antennas ensure that the transmitted power is
sent in a single direction; this minimizes the possibility of causing interference inadvertently to other users.
Narrow beam antennas also reject off-azimuth signals being received from potential sources of interference and
have high gain, which boosts desired receive levels and improves the carrier-to-interference signal level.
When selecting narrow beam antennas, it is helpful to know that larger antennas generally out-perform smaller
antennas. Another important antenna specification is the front-to-back ratio, which ensures rejection of
unwanted signals from azimuth angles behind the antenna. High performance antennas with improved sidelobe
attenuation are also available.
Frequency Selection
You often can overcome interference by exchanging frequencies of both ends of the radio link (for example,
change your A1 terminal to an A2 and change the other end from an A2 to an A1). For the GX series, this
requires swapping of the RF Unit from end to end. Also, changing channel plans (for example, from A to B) can
be very effective, provided multiple channel plans are available.
See “Channel Plans” on page 70 for frequency selections. The near-end radio and the far-end radio must be
corresponding (such as A1 / A2).
Antenna Polarization
Cross-polarized antennas can provide approximately 20 to 30 dB discrimination of unwanted signals. The actual
discrimination depends upon the antenna design and any rotation of polarization along the path (for example,
due to reflections). Substantial discrimination only exists between two orthogonal polarizations:
▪ Vertical versus horizontal
▪ Left-hand circular versus right-hand circular
There is only 3 dB discrimination between circular and linear (vertical or horizontal) polarization.
If changing polarization to minimize interference, the antenna polarization must be changed at both ends of the
link.
Transmit Power
The maximum level into the receiver is -20 dBm. Errors can occur in the receive data stream above this level.
You should reduce transmit output power on very short paths to avoid overload.
Equipment/Antenna Location
Interference is occasionally caused by the radio equipment or the antenna being too close to another similar
transmitter. Moving the radio equipment, 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. Before turning up a new link, use a spectrum analyzer (either built-in or external) to monitor the
spectrum at each end to check for possible interfering signals. For more details, see the section that follows.
Appendix G. Troubleshooting 94