Exalt Communications Inc.
EX-2.4i Installation and Maintenance Manual
Page 36
MAN-002400, Revision 001
2005-12-01
In this test, it is highly desirable to RF cables that are pre-tested, known good and known loss at
the operating frequency. If the cables are short (in the range of 6 feet or less), you can estimate
the loss, including connectors, to be less than 1dB each. The estimate of cable loss is critical to
the overall confidence of the measurements made in this test.
There are two critical specifications that can be tested in this configuration:
-
RF output power
-
Radio receiver threshold
To measure output power, simply insert any value of attenuation between the radios between 60
and 90dB. Make sure that both of the radio’s RF output power settings are at maximum. Using
the voltmeter, measure RSL in both directions. The RSL measured value should match the
appropriate value in accordance to the inserted attenuation. Such as:
RSL = RF Output Power – cabling losses – total attenuation
You can further verify output power by adjusting output power using your computer (in
administration mode) and evaluate the corresponding change to the RSL measurement.
For threshold testing, the key is to insert a measured amount of loss that is close to, but not
exceeding the radio’s specified system gain. System gain is the difference between RF output
power and receiver threshold. At your selected modulation and bandwidth settings, determine the
specified threshold performance, and choose a value of attenuation (including cable losses) that
adds to roughly 5 to 15dB less than the system gain.
For example, if the threshold for your measurement is -85dBm, the output power is +27dBm, so
the System Gain is 112dB. Choose a value of total attenuation in the range of roughly 100-
105dB. Once this attenuation is inserted, verify RSL readings as in the first step, and then, using
your computer, adjust radio output power attenuation in 1dB steps until the receiving radio (the
one whose output power you are not adjusting) Link LED turns from green to yellow. This
would indicate that threshold has been reached. At this point, verify the equation for system gain
using the new output power level setting and verify that the threshold performance is meeting the
published specification.
Due to the variables involved in this test, you may read a measurement that is 1 to
as much as 2dB off of the expected value. It should be of no concern unless the
value is more than 3dB worse than expected.
Once threshold is verified in this direction, you may repeat the process in the opposite direction
by adjusting RF output power of the other radio.
You may wish to perform threshold measurement tests for all combinations of bandwidth and
modulation that you are using – especially if testing for the purposes of troubleshooting. It
should not be necessary to vary center frequency, as this does not typically have any impact on
