Bird Technologies 21-87A-11-xx-T Series-Manual - Manual (Page 10)

TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 4
has been factory tuned in most cases so that no
adjustments are necessary. The specifications for
the 73-90-11-NN family of T-Pass combiners are
listed in Table 1 and the typical T-Pass channel
insertion loss is shown in Table 2. The response
curve shown in Figure 2 shows the typical trans-
mitter noise suppression. Noise suppression
depends on the cavity’s loss setting.
T-Pass Selectivity vs. Cavity Loss
As in the case of bandpass cavity filters, T-Pass fil-
ter selectivity depends on the coefficient of cou-
pling of the cavity loops at resonance. Tighter
coupling decreases insertion loss and selectivity
while loose coupling increases them.
Although 800 - 1000 MHz T-Pass cavity loops can
be set to approximately -0.8 to -3.0 dB insertion
loss at resonance, TX RX Systems Inc. uses two
standard cavity loss settings, -1.25 and -1.80 dB,
that produce adequate selectivity for the majority of
multicoupler applications in this range. The curves
shown in figure 2 represent the lower selectivity
side of the response curve of a typical 6.625 -inch
diameter, 3/4 -wave 860 MHz T-Pass cavity filter.
Bridging loss in a progressive thruline T-Pass
structure varies in the same general manner as
bridging loss in a parallel junction bandpass struc-
ture; it decreases as cavity selectivity increases.
An optimal cavity loss setting exists that minimizes
channel loss under a specified frequency plan and
number of channels. See Tech-Aid No. 92002 (lit.
NO. D3001D93) for a complete set of selectivity
and bridging loss curves for T-Pass cavities from
66 to 960 MHz.
UNPACKING
Most T-Pass transmitter multicouplers are shipped
fully assembled in a cardboard crate. The cavities
are usually mounted in a suitably sized Peg-Rack
which is a patented design of TX RX Systems, Inc.
Other types of mounting may be supplied for cus-
tom tailored systems as specified at the time of
order. In order to reduce shipping costs, some mul-
ticouplers are shipped partially assembled. In this
case, customer assembly of the mounting rack and
installation of the cavity channels may be required.
Accessories or other products ordered with the
multicoupler will usually be found either already
mounted in the rack or packaged separately as cir-
cumstances dictate. It is important to check the
packing slip against the contents to make sure all
parts are accounted for. Any shortages should be
reported to TX RX Systems or its authorized repre-
sentative.
It is important to visually inspect the system com-
ponents for any shipping damage as soon as pos-
sible after taking deliver y. It is the customers
responsibility to file any necessary damage claims
with the carrier.
The transmit combiner is a very rugged device and
is well packaged for damage-free shipping to any
place in the world. However, a high impact during
shipping can have a detrimental affect. A damaged
shipping container is a sure sign of rough handling.
The most easily damaged parts of the combiner
are the tuning rods. These rods are marked where
they exit from the locking nut with a dab of red var-
nish or other color/type of paint. If this seal appears
to be broken it may indicate that the system has
been detuned in transit.
INSTALLATION OVERVIEW
Installation of a TX RX transmitter multicoupler
consists of some or all of the following steps
depending on how completely the unit was assem-
bled at the factory:
1) Determine the exact mounting location for the
multicoupler.
2) Assemble the mounting rack.
3) Install the cavities with isolators then install the
T-Pass Thruline cables and accessories into
the rack.
4) Connect the transmitters and antenna(s) to the
appropriate connectors of the multicoupler.
5) Verify proper operation of each channel by
measuring power output for each individual
channel.
ASSEMBLY
An unassembled multicoupler will usually be bro-
ken down into the following general parts groups:
1) Peg rack assembly.
2) T-Pass cavities with mounting clamps.
3) Isolator & loads on mounting brackets with
mounting clamps.