Some Criteria For Evaluating Antennas
The technician may have chosen not to perform this test because it requires
climbing the tower. This procedure should be done to eliminate jumper cable or
down-lead cable factors. These cables could be either defective and cause the
problem or be fine and absorbing the reflection which masks the problem.
3. Did you perform the measurement directly at the
antenna’s connect or?
Check to see if the antenna was ordered for the correct frequency. The
manufacturer may have mis-marked the antenna or carton. Several methods
can be used to determine an antenna’s frequency. If the technician has swept
the response of the antenna he will know the frequency of best match. That
should be its designed frequency. The technician may also measure the
physical length so that we may compare it to a cut chart.
This is a crude method. If the antenna is of relatively new and the model
number is known, the factory may still have the production test data sheet
which will identify its frequency by Serial Number.
4. What is your operational frequency?
(These devices do not rely upon the site’s transmitter as a signal source.
They can produce more accurate and meaningful results but do not
subject the antenna to full power where arcing or flashover would occur).
b. Network Analyzer/Spectrum Analyzer with Tracking
Generator?
(Occasionally, a technician will use a “TDR”. This is not an industry
recognized instrument for antenna testing, and many manufacturers will
not respond to these measurements because the equipment uses
pulses rather than RF and does not measure beyond band limiting
devices. See Nov/Dec 1996 Microwaves & RF Magazine Article entitled
“Identifying Transmission Line Faults” on page 40 forexplanation of TDR
misapplication).
c . Time Domain Reflectometer?
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FM Antenna User Manual
