Some Criteria For Evaluating Antennas
Side mounting too close to the tower can detune an antenna. The required
spacing distance between the antenna and any other metal object decreases
as the operational frequency increases. Some good numbers per our factory
test procedure for omnidirectional antennas are from 100 ft. at 30 Mhz to 5 ft.
at 900 Mhz.
5. Did you measure the antenna erect , free and clear of
metal objects?
Some antennas have direct ground lightning protection. These normally
measure as a DC short between the connector’s inner and outer conductor but
will be the proper 50 Ohm impedance at RF. See lightning notes in the catalog
specs to determine if this antenna model should measure as an open or a
short.
6. What is t he DC continuity measurement using an
ohmmeter?
If the second antenna measures OK under the same mounting conditions, the
technician’s first antenna is probably defective. If the second one yields the
same bad result, the problem is unlikely to be the antenna. Perhaps the
transmitter is not operating on the expected frequency. Substitution of a
dummy load is an option if a second antenna is not available but the test is
less meaningful because it is actually testing only the cable.
7. Did you have the opportunity to substitute an identical
antenna?
It could either be new and defective or had performed nominally for some time
before failing. It is a good practice for technicians to test products on receipt
before transporting them to the job site. Manufacturer's warranties cover only
manufacturing defects, not damage from an improper installation. An example
would be mounting a standard antenna upside-down. This would put the drain
hole at the top where it could collect water and cause the product to fail over
time. Factory options given to an inverted antenna include reconfiguring both
the drain hole location and any electrical beam tilt.
8. When was the antenna installed?
Website
www.305broadcast.com
Whatsapp
+1 305-200-3322
FM Antenna User Manual
