Technical Manual

58 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
Testing the Coax and Antenna
Return Loss (Antenna System)
After confirming that the coax meets specifications, remove the calibrated short
and attach the antenna to the coax. With the instrument connected to the lower end
of the cable, sweep the assembly which now includes the mainline, jumpers, and
antenna. Set markers to frequency range boundaries in use on that line (450-470
MHz).
Test Analysis
Save the results of these tests and name the file.
Pass criteria:
1. The instrument must not have any internal errors or fail calibration.
2. The return loss (coax) test, in which the coax was terminated with a
precision load, must meet the coax manufacturer’s specifications within the
frequency range intended for use on the coax. A cable loss of 2 dB or more
is unacceptable.
3. The Distance To Fault (DTF) test must agree with the estimated length of
the coax +/- 10%.
4. Compute the expected Return Loss for the antenna system. It would be the
antenna manufacturer's specified RL, plus the return loss measured on the
coax in step 2) above. Add one to provide some margin. Consider this the
measured “antenna system return loss”.
5. A measured antenna system return loss less than 14 is unacceptable. Stated
alternatively, a VSWR of 1.5 or higher is unacceptable.
The following table provides Typical VSWR and Return Loss Conversions.
6. Confirm that cable tests pass.
7. Record the results on the DCU maintenance sheet.
Typical VSWR & Return Loss Conversions
VSWR % Reflected Power Return Loss (dB)
1 0 ∞
1.1 0.23 26.4
1.2 0.83 20.8
1.3 1.7 17.7
1.4 2.78 15.6
1.5 4 14
1.6 5.33 12.7
1.7 6.72 11.7
1.8 8.16 10.9
1.9 9.63 10.2
2.0 11.1 9.5