TD 90227GB
2006-09-18/ Ver. C
System Installation
On Site Paging System
9
5.1
UHF Antennas
UHF transmitters in the 900 system use a CXL-70, a broad band half wave coaxial antenna
for 406-470 MHz. The antenna is dc-short-circuited, and has an “N” type connector.
CXL-70 is mounted at the top of an antenna mast or with a supporting boom. The boom
should be at least 0.5 m.
CXL-70 is designed to be insulated from the mast but is delivered with a nut and washer
that are screwed onto the antenna connector if the antenna ground (=coax shield) is to be
dc-connected to the mast.
Note:
The nut and washer are normally not used.
In systems with talk-back, UHF/VHF or UHF/UHF, a common base antenna with duplex
filters can simplify the antenna installation of receiver/transmitter pairs.
5.2
HF Antennas
HF installations can use the following types of antennas:
GP-25L is a 25-175 MHz ground-plane antenna for mounting on a mast. The antenna is
frequency adjusted by cutting the fibre-glass elements to the correct length according to
the diagram that is delivered with the antenna. The antenna has a UHF type connector.
GP 4103 is a 26-47 MHz, dc-grounded ground-plane antenna for mounting on a mast.
The antenna must be ordered for the correct frequency. The antenna has a UHF type
connector.
SAT-1 is a compact helix antenna about 1 metre long for the 27 MHz band that is often
used indoors because of its short length. The antenna has a UHF type connector. The
manufacturer recommends a few different coaxial cable lengths but the same low
standing wave ratio can be achieved by moving the antenna to different possible
mounting locations (standing-wave metre required).
Another alternative is a two-band antenna for HF/UHF plus a duplex filter.
5.3
Tuning Circuits and Power Divider
MFJ-901B
Terminal
Transmitter
Central
Unit
Figure 9. Antenna tuner in HF system.
MFJ-901B, the antenna tuning unit for HF is connected between the transmitter and
antenna.