Bird Technologies 21-87A-11-xx-T Series-Manual - Manual (Page 14)

TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 8
It is advised that the center pin on all mating N
male connectors be checked for proper alignment
before connection to the multicoupler. A cocked
center pin in the male connector can permanently
damage the mating female connector. In many
cases, simple field replacement of the damaged
connector is not possible and replacement of an
entire subassembly may be required to make the
unit operational.
This system is designed for use with separate
transmit and receive antennas. For best operation,
the transmit and receive antennas should be sepa-
rated vertically by 20 feet with little or no horizontal
offset between antennas. Lesser separations can
be used but with an increased risk of harmful inter-
ference between radio systems. In most cases, it
will be desirable to mount the receive antenna
higher than the transmit antenna to maximize the
talk-back range of low power portable radios.
Intermodulation Considerations
Following the previously mentioned antenna spac-
ing recommendations will go a long way toward
minimizing or eliminating intermodulation (IM)
interference. IM is the result of a frequency mixing
process that occurs when two or more RF signals
are present simultaneously in the same circuitry
where nonlinearity occurs. Product frequencies
generated have frequencies that are determined by
relatively simple mathematical relationships such
as F(im) = 2F1-F2 and are normally determined by
doing a computer intermodulation analysis for the
antenna site. These products can be generated in
UG27 Elbow Connector
& UG57 Male-Male
Adaptor
UG57
Male-Male
Transmitter
Transmitter
Transmitter
Single
or Dual
Section
Isolators
Single
or Dual
Section
Isolators
Single
or Dual
Section
Isolators
T-Pass
Cavity Filter
Channel 3
Channel 2
Channel 1
Wattmeter 2
50 Ohm
Load
Wattmeter 1
This T-Pass Loop
requires a 3-1268
short circuit
connector
Figure 6: Equipment hookup for measuring T-Pass channel performance.