User's Manual

Doc. No.
Rev.
Date
1.00
2011-12-08
Damm Cellular Systems A/S, Denmark
TETRAFLEX
®
V7.5 MANUAL - Antenna System for BS41x
TetraFlex® 7.5 Manual 4-5
antenna of >30dB to ensure proper operation. The TX separation is normally achieved
without much effort.
Three identical low-cost feeders are required for the RX antenna system. As the main RX
filters are located in the TMA, cables with good screening are needed to avoid radiation into
the cables. Cables should either be double shielded or with solid screen. For most
applications ¼ inch corrugated cables is the optimum choice. Cables of type RG58/U and
RG213/U should not be used.
The TMA has a nominal gain of 15 dB and the system is designed to have a nominal total
gain from TMA input to BS RX connector input of +6dB. With some margins this allows a
maximum feeder loss of 8dB. Attenuators are provided in the BS to adjust the total gain. Note
that use of lower-loss cables will not improve system performance, just increase the cost.
The following table indicates the maximum allowed length of different possible cable types:
Cable with 8dB loss
450MHz
850MHz
RG223/U
28m
19m
RG214/U
50m
35m
1/4 inch (RFS CF14-50)
85m
60m
3/8 inch (RFS LC38F-50)
105m
75m
1/2 inch (RFS LCF12-50)
170m
120m
5/8 inch (RFS LCF58-50)
220m
155m
If very thick cables are used, jumper feeders in both ends may be needed.
Cables and connectors between antenna and TMA412/TMD412 shall be resistance to water
ingress and migration.
4.1.2.3 TX antenna
The BS uses a TX antenna for all the installed TETRA carrier units, which may optionally also
be used for receiving. All components used in the TX antenna system need to be high quality
components with low inter-modulation to avoid distortion product to jam the receiver inputs.
The requirements include the TX antenna itself and also the feeders and connectors.
The TX antenna feeder should be provided with connectors of type 7/16. Other connector
types should be avoided, including connectors of type N. For 2-carrier only base stations
without Duplexer N-type connectors can be used at antenna and BS.
The feeder cables shall have as low as possible insertion loss and have a solid screen.
Cables with woven shields of thin wires should never be used.
The TX cable loss can be compensated, by increasing the TX output power to balance the
system requirements. For a low-power Base Station this can be an acceptable solution but
for a high-power BS this can give an unacceptable increase in the mains power consumption
or may not be possible at all.
As guideline, the TX antenna feeder loss for a high-power BS should not exceed 2dB. This
can be achieved when not exceeding the following cable lengths: