Exalt Communications, Inc.
r-series
Installation and Management Manual
5000007 (ETSI)
72
2007-02-12 (draft)
Multipath Propagation
Multipath propagation is a term that encompasses changes to the RF path, such as reflections
and/or refraction, causing partial or complete destruction of the radio signal, and thus excessive
bit errors and/or system outages.
Rapid changes in temperature, inversion layers, humidity, air pressure, water evaporation, as
well as standing water or moisture on objects along the path are all examples of changes that can
cause multipath propagation. New building construction near either end of the path or along the
path can cause new reflection characteristics.
If your system has been operating without issue and is suddenly experiencing issues that are
symptomatic of a certain time of day or related to change in climatic events or some of the
external factors listed above, this is likely the cause. Consult a professional RF path engineer in
these cases. Often, minor repositioning of the antennas at either or both ends can reduce or
eliminate these problems.
RF Interference
RF interference is usually indicative of another radio system nearby either end of your radio
system or aimed towards one or both ends of your radio system – usually at or near the same
frequency and usually with a similar signal level.
Other forms of RF interference also exist, such as electronic equipment placed close to the radio
chassis or transmitters that couple onto the cabling or grounding system of the radio. Microwave
ovens and wireless communication devices used near the equipment or cabling are examples of
electronic equipment interference.
The Exalt EX-5 series Digital Microwave Radios operate in license-exempt
bands. Microwave ovens, wireless Internet devices and cordless phone technology
may also use this frequency band. It may be necessary to separate the radio
chassis, cabling system and antenna from these devices.
RF interference, like most other causes of problems, is indicated by significant bit errors and/or
system outages.
One means to determine presence of interference is the use of a spectrum analyzer that covers the
same range as the radio system. A professional RF engineer can use a spectrum analyzer to
locate sources of interference, measure these sources, and determine potential remedies to take to
operate in the presence of interference.
If a spectrum analyzer is not available, the radio’s RSL port can help determine RSL levels of
interfering signals. By turning the far-end radio off, the residual RSL measured by the radio
indicates the level of interference seen by the radio. It is possible that interference levels below
that which can be measured still have an impact on the radio system – especially if the radio
system has low fade margin or is using a high order modulation.
Exalt Digital Microwave Radios provides considerable flexibility to tune to different frequencies
across the bands within which they operate. This is the easiest method to use to try to avoid