Technical Manual

Testing the DCU
D C U M a i n t e n a n c e a n d O p e r a t i o n M a n u a l 57
Testing the Coax and Antenna
The coax and antenna will have been tested by the installer. If, over time, the
performance of the DCU has degraded, testing of the coax and antenna may be
warranted. It is quite possible over time that moisture or corrosion has affected the
coax and the system's RF performance. The coax and antenna should be
periodically tested to ensure the system is performing within recommended limits.
Tools Required (in addition to common safety equipment):
• Cable tester capable of measuring Return Loss (a.k.a. VSWR) to 1.0 within
+/- 5% on a 50 Ohm coax
• A 50 Ohm precision coax load
• A zero Ohm coax load
Perform the following procedures to test the coax and antenna.
RF Sweeps
It is important to ensure the cable provides a viable RF path to the antenna.
Imperfect or damaged coax and connectors can be detected electronically.
Furthermore, long cable runs, or runs with questionable turns must be examined
and baselined for RF loss to ensure they will not pose a performance problem for
the equipment.
Calibration
Calibrate the cable tester to ensure it is operating properly for the 250-900 MHz
band.
Return Loss on the Coaxial Cable
Install a precision load at one end of the cable, and at the other end perform a
measurement of return loss (RL) of the entire cable assembly (including all
connectors, jumpers, and mainline.) Set markers at the peak and valley. Measure
and record the values in dB.
Distance to Fault (Coaxial Cable)
Install a calibrated short at one end of the cable and measure the distance to this
fault from the other end. Record the distance.
Coaxial Cable Insertion Loss
With the calibrated short at one end of the cable, determine the actual measured
coax loss from the other end of the cable. (This test will measure the RF energy
that is lost as heat as the signal travels through the coax.) Record the insertion loss.