User manual

105G Wirless Gateway User Manual
Page 151 ©February 2009
two radio transmissions, turning off DO2. Each time the switch is changed should be two
radio messages (two sets of TX/RX flashes) at the mobile unit. Note that when the modules
are within a couple of metres, they may not work well with antennas connected - in this
case, test without antennas.
 Set up the fixed module in one of the test positions - this is normally at a control centre or
repeater site. Fix the antenna in a temporary fashion. You will need to make an initial
assessment on how high the antenna should be mounted.
 Take the mobile module to the other end of the radio path. The antenna at this end can be
either held by the tester, or fixed in a temporary fashion. Note that a person’s body will
affect the radiation pattern of an antenna, so if the antenna is hand-held and the test is not
successful, try again with the antenna fixed to a 1 metre length of plastic pipe or timber. The
tester holds the length of pipe or timber with the antenna above head height.
 Test the radio path by operating the switch. If the radio path is short, and there is a high
level of confidence that the radio path will be reliable, the result can be checked by simply
looking at the TX/RX leds on the mobile unit. If each TX flash is followed immediately by
a RX flash (that is, the TX flash does not flash twice or more times before the RX flashes),
then the radio path is likely to be reliable. Operate the switch several times - do not rely on
one test. If the test is being done outside, the leds will need to be shaded to view the flashes.
 If the radio path is uncertain, then the result should be measured by connecting a laptop
computer, following the procedure outlined in this manual for measuring the radio signal
strength. Before the switch is operated, the background noise level should be measured and
recorded. This measurement is likely to “jump around” or oscillate, to determine an average
measurement. Now operate the switch several times - take the average measurement of the
signal transmitted from the fixed unit.
 The radio path is reliable if the transmitted signal is 10dB above the noise level, or better
than –98dBm. For example, if the noise level is –115dBm, then the minimum level for
reliability is –98dBm. If the noise level is –100dBm, then you need –90dBm for a reliable
path. If the laptop displays a scale measurement instead of a numerical measurement, then
the transmitted signal should be at least 3 divisions, and at least 2 divisions above the noise
level.
 If the weather is poor during the test, then the transmitted signal needs to be 5dB above
noise, or 1 division. It is best not to do radio tests during poor weather.
 Record these measurements for comparison later during commissioning or if the system has
problems later.
If the radio path test is not successful:
1. Increasing the height of the antenna at either module, or at both modules can significantly
improve the result. Sometimes moving the antenna to the side helps, if there is an obvious
obstruction in the radio path.
2. Change one or both antennas to a higher gain if regulations allow.
3. Use a shorter coaxial cable between the antenna and the 105U. (This may involve moving
105U nearer to antenna mounting), or use a different coaxial cable with lower loss.