User's Manual

Doc. No.
Rev.
Date
1.00
2011-12-08
Damm Cellular Systems A/S, Denmark
TETRAFLEX
®
V7.5 MANUAL - TX Combiner for BS41x
TetraFlex® 7.5 Manual 4-9
4.2 TX COMBINER FOR BS41X
4.2.1 Introduction
The BS41x Tetra Radio Base Stations are provided with a TX combiner system to combine
all the installed transmitters to a single antenna.
The combiner system has the following requirements:
 Combine the transmitters to a single feeder with lowest possible insertion loss.
o Give isolation between the TX input ports to avoid the signal from one transmitter to
reach the other transmitters and generate inter-modulation. The isolation
requirement is normally minimum 55dB in order to reach a suppression of the inter-
modulation signals of 70dB relative to the individual carriers.
o Filter the TX antenna output to reduce any unwanted signal in the receiver band of
the Base Station to be less than –106dBm in order to avoid interference in the
receiver with an TX/RX antenna separation of >=30dB.
o Make wide-band filtering of the TX output signal to avoid interference to other radio
equipment installed in the same mast.
Two different methods exist in order to combine several transmitters to a single antenna:
o Cavity Combiner (combining with filters)
o Hybrid Combiner (combining with 3-dB couplers)
The cavity combiner has the advantage that it can combine a high number of transmitters
selectively with almost constant insertion loss independent of the number of transmitters
used. The disadvantage of the Cavity Combiner is that it requires minimum frequency
spacing between each individual transmitter of minimum 175 kHz for the 400MHz band and
250 kHz for the 800MHz band.
The Hybrid Combiner has the advantage that is can combine transmitters with no frequency
spacing restrictions and without any adjustment. For a 2-way Hybrid Combiner the insertion
loss is almost equal to a Cavity Combiner. However to combine more transmitters the
insertion loss increases rapidly. The theoretical insertion loss for a 2-way hybrid is 3dB, for a
4-way hybrid 6dB and for an 8-way hybrid 9dB.
The BS412 2-carrier BS is provided with a hybrid combiner whereas the BS411 and BS414
as standard are provided with cavity combiners. The BS414 can however also be delivered
with a 4-way hybrid combiner.
4.2.2 Cavity combiner system
The Cavity combiner system consists of the TC411 TX Combiner 4-way module and the
TF411 TX Filter. Kits with junction and connection cables connects the units together.