User's Manual

14221-1510-4440, Rev. B
64
13. If the wattmeter reading is within the range, record the value in the appropriate space on the TEST
PERFORMANCE DATA FORM on page 67, and then advance to the next step in this procedure.
Notes for Troubleshooting Bad VSWR/Reverse Power Readings:
 Make sure the installed antenna element is consistent with the specified frequency range of
the radio by checking the antenna element’s datasheet VSWR spec, etc.
 Verify the NMO antenna base is properly installed and tight on the NMO antenna mount.
 Verify the antenna element is properly installed and tight on the NMO antenna base. Some
elements use a small set screw in the base to secure the element to the base.
 Ensure field-dressed coax cables are properly crimped, including the coax center conductor to
the connector pin, and the coax shield to the connector’s body.
 At the radio’s antenna port connector, verify the antenna coax cable’s RF connector is
tightened in accordance with manufacturer’s guidelines.
 Expect more losses depending on the cable length and RF frequency.
 Expect more reflected power, if measurement is made inside a metallic structure.
 Consider overall measurement accuracy/errors.
 Recheck all antenna connections, and measure the reverse power again. For example: If the
installation employs a ¼-wave unity-gain antenna, observe the NOTE that immediately
follows step 9. If these checks/corrections fail to produce a reading within the range, replace
the antenna and repeat the entire antenna test procedure. Any value exceeding the maximum
allowable reflected power value will result in a diminished RF output signal.
 It is understandable that the user may not have a full control over the test environment. If this
is the case, and after the above recheck the readings are still outside the expected range, use
the following alternative method to ensure the installation is done correctly.
1. Measure the output RF power of the radio directly from the radio.
2. Connect the antenna cable to the radio.
3. Remove the radio installation’s antenna element from the mount (base) and using a
suitable NMO adapter so the antenna mount can be connected to the wattmeter/power
meter.
4. Measure the RF power at the antenna mount.
5. Use the cable loss data in Table 15-4 to calculate the approximate cable losses. After
all losses are accounted for, measurements should be within ±1 dB of the original
output RF power measurement.