Specifications

FCS1362 Page 47 of 74 © Nov 2010
For mobile radio covert antennas the limit may be higher – if necessary consult the antenna manufacturer
for guidance.
If the result obtained is outside of these limits then the antenna and its installation should be inspected to
find the cause of the high VSWR, rectified and then re-tested to ensure it meets the relevant limit.
Note that when reviewing the results of a VSWR test consideration should be given to the calibration
accuracy of the meter and the test location. For example sometimes it is possible to obtain erroneous
readings when testing a cellular GSM/3G antenna installation in close proximity to a base station. If the
initial reading is not consistent with expectations it may be worth moving the vehicle to a different location
and carrying out another test.
The final value obtained should be recorded on the installation report.
4.8.3. Testing GPS antennas
As a GPS antenna is an active receive type it must not be connected to any type of transmitter including
an antenna analyser. It is therefore not possible to carry out a VSWR check.
GPS reception requires that the antenna has a clear view of the sky in order to function. This may
require the vehicle to be moved out of the workshop but see section 5.3.6 regarding road testing and
adequate insurance.
The recommended method of checking the GPS antenna is having completed the DC continuity tests
connect it to the GPS receiver and check for satellite acquisition or examine receiver system diagnostics.
Note that it may be necessary to ask the customer to assist with this process as it could require user
authorisation to log on to the network or system to obtain the relevant diagnostic information.
As a further measure the installed GPS antenna could be checked for satellite acquisition against a
reference magnetic mount GPS antenna placed adjacent to the installed antenna. This is then
temporarily connected to the GPS receiver and results compared.
For a GPS Mouse (combined GPS receiver/antenna unit) type a functional check should be carried out.
With the GPS Mouse connected to the terminal equipment check for satellite acquisition or examine
system diagnostics.
4.9. Power up testing
These tests should only be done when the installation and checks in section 4.7 are complete.
Additional checking of transportable equipment may be necessary due to the internal battery supply that
may be fitted. In these cases the power supply lines and fuses should be checked independent of the
portable equipment.
4.9.1. Transmitter output power
This section refers particularly to higher power, as per section 2.3.1.1, and PBR equipment installation.
The power output from the transmitter should be measured using an RF wattmeter connected temporarily
to the transmitter output coaxial socket. The measured power should be checked with the licence
conditions and vehicle manufacturer’s stated power limit.
If the imposed limit stipulates ERP this should be calculated from the transmitter output power and the
known antenna gain and feeder loss.
For example the radio licence conditions may grant 25W, but the vehicle’s manual only stipulates 10W
max for a transmitting device. In this case checking against the licence conditions might actually be
invalid, therefore the vehicle manufacturer’s power limit must take precedence and the installation should
not be commissioned if the power limit is exceeded.
4.9.2. Equipment using ignition sense
Where an ignition sense is used, ensure the mobile equipment turns off when the ignition is switched off.
This test should be carried out with the in-car entertainment unit switched on and repeated again with the
unit switched off.