Intelpage 5W (POCSAG) Transmitter Installation Manual v1.3
9
6.
Technical Informations
Transmitters
Thick steel and concrete, large magnetic and electric fields, and terrain and weather conditions will affect
transmitter efficiency, so you will need to test the coverage of your local area transmitter at some stage of
installation.
When you perform the test you should pay particular attention to the quality of the messages that you
receive on the test pager. If you receive corrupted messages then it is possible that you will have problems
sending messages to that region.
If you find that you are receiving corrupted messages then you should consider the following methods for
improving transmission quality:
Move the antenna to a position that gives it a clear line of site to all areas you wish to cover.
Reduce the length of the cable connecting the aerial to transmitter.
Use the appropriate coaxial cable to connect the aerial to transmitter which will suit the length of
the cable run. For example use RG213 for runs up to 20 meters and use LDF440 for runs over 20
meters.
Choose another type of antenna for the transmitter.
Position the antenna in a higher location or use an antenna with a higher gain.
Increase the transmitter power. There are a number of objections to this method, such as local restrictions
on aerial power. In addition, doubling the transmitter power to the aerial only gives an increase in range of
a factor of 1:19 (fourth root).
The installation of Multiple Transmitters and Aerials
For buildings in an area with good field strength outside but weak reception within, possibly caused by
shielding due to reinforcement in suspended slabs, metal plating and other building materials:
The supply lead to the aerial can serve as a radiator, effectively providing a 5 meter (yard) range
form the cable.
The supply from open (leaky) coaxial cable as a line radiator lead to a 50 ohm terminator (the
cable is in effect the aerial).
VSWR
WARNING
: VSWR is a measure of impedance mismatch between the transmission line and its load. The
higher the VSWR, the greater the mismatch. A high VSWR means some of the transmitted signal is being
reflected at the antenna, back down the coax line and back into the transmitter itself. If this value is too
high, the amount of power reflected back into the transmitter can damage the transmitter. The minimum
VSWR, i.e., that which corresponds to a perfect impedance match is 1. It is essential that the VSRW of the
antenna and coax connected to the amplifier is set to 1.5 or better using a SWR meter. If this test is
skipped, permanent damage may result to the amplifier. Damage will also occur to the unit if the amplifier is
set to transmit if no antenna is connected to the unit. To transmit without an antenna connected to the unit,
use a dummy load capable of handling at least 5 watts.
