TMA2Q/LPC2Q Quadrature Tower Mounted Amplifier Instruction Manual
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pointed down and to the left. Similarly, the CW (Green reference) connector is pointed down and to the right. Also shown
for reference are the polarities of the most forward (shortest) dipole elements. The antenna configuration shown applies to
the CLP5130-1X antenna but the concepts apply to any cross-polarized antenna.
The two polarities should be marked with a color scheme for reference and this scheme should be carried
through the TMA2Q to the LPC2Q. In the supplied system, the colors Red and Green are used for reference,
where Red indicates a CCW rotation and Green indicates a CW rotation of the incoming radio waves as viewed
from the rear of the antenna; refer to figure 2.
If the reference connections shown in figures 1 and 2 are followed, the right-hand and left-hand circular
polarizations theoretically are output on the LPC2Q ports, marked respectively RHP and LHP on the end panel.
These connections and resulting polarizations require field verification. If they are found to be wrong, it is only
necessary to swap the connections to ports 3 and 4 of the quadrature coupler inside the LPC2Q.
B.
Protection and Transmission Considerations and Pre-Installation Tests
Caution
: Never work on the antenna system, coaxial cable systems, TMA2Q or LPC2Q if a lightning storm is in
the area. If a lightning storm is approaching, turn off the LPC2Q and disconnect the transmission lines and power
supply from the LPC2Q before it arrives. If lightning already is striking nearby do not touch any part of the
system including the PC that is used to collect data from the system.
Detailed transmission design and pre-installation tests are beyond the scope of this document. Only basic
recommendations are given here. To verify proper operation, it is suggested that all components used in the
installation be tested together before installation according to local practices. This includes the TMA2Q and
LPC2Q assemblies as well as the user-provided coaxial cables, power supplies and receivers. The quadrature
coupler in the LPC2Q depends on proper 50 ohm termination impedances on all ports. It is very important that
both transmission circuits are fully connected and terminated before any tests.
All coaxial cables and connectors should be high (commercial) quality, obtained from reputable suppliers and as
short as possible to minimize transmission losses. To minimize phase and attenuation differences in each circuit
section, the manufacturer and model of coaxial cables and connectors should be the same. To minimize phase
differences the cable section length differences should be as small as possible. Table 1 shows cable section
length differences that will produce 1° and 5° phase differences at various frequencies for typical 10 mm coaxial
cable. If possible, cable lengths and attenuation characteristics should be verified before installation with a
Cable and Antenna Tester (CAT) or Vector Network Analyzer (VNA). Both reflection (return loss or VSWR) and
transmission measurements should be included in these tests and compared with expected results.
Table 1 ~ Phase differences for LMR-400 coaxial cable (0.85 velocity factor)
Frequency
(MHz)
Length
to produce
1° phase
(mm)
Length
to produce
5° phase
(mm)
50
14.2
70.8
100
7.1
35.4
250
2.8
14.2
500
1.4
7.1
