d. Auxiliary IF, Frequency Standard, and
switches in the waveguide run to the antenna, but the off-
Telephone Circuits. The IF, frequency standard, and
line PA can be inhibited only by the switch at its
waveguide coupling. Likewise, a break at the off-line PA
telephone entry panel contains the external connections
waveguide coupling will not inhibit the on-line unit.
for the auxiliary 70or 700-MHz signals, the frequency
Auxiliary contacts in the waveguide transfer switch sense
standard, and the external telephone circuits. The
which PA is the online unit and configure the high voltage
auxiliary IF signal lines are terminated at the IF patch
disabling circuits accordingly. One power amplifier is
panel. The frequency standard is routed directly to the
coupled through to the antenna while the other is
frequency standard distribution amplifier in the RSS.
coupled to the dummy load by the transmit waveguide
The dummy load is capable of
dissipating the full power output of the off-line PA for
troubleshooting, testing, and adjustment.
a. Waveguide Components and 8-Foot Antenna.
The transmission path from the power amplifier to the
antenna feed. The antenna feed is composed of three
antenna consists of solid and flexible waveguide
components, an orthogonal mode transducer (OMT), a
sections, a transmit waveguide switch, dummy load, and
circular polarizer and a feed tube assembly. The
proximity switches that are part of a safety interlock
antenna feed passes through the center of an eight-foot
An orthogonal mode transducer, circular
parabolic reflector with the front end of the feed tube at
polarizer, feed tube assembly, and reflector make up the
the focal point of the reflector. The orthogonal mode
antenna portion of the transmission and reception path.
transducer is a three-port device consisting of a transmit
(1) Proximity switches are used at four
port, a receive port, and a common port. Energy can
locations in the waveguide system, to sense an
pass into the transmit port through the OMT and out of
uncoupled or loose coupling at the waveguide quick-
the common port. Energy can also pass into the
disconnect joints. These switches are wired into the
common port through the OMT to the receive port. The
transmit port is isolated from the receive port; that is,
supplies so that if a faulty connection exists at the quick
energy going into one will not pass on to the other.
disconnects, the high voltage to the klystron in the PA will
Signals at these ports will not mix with each other
be disabled and RF power cannot be generated. These
because the transmit and receive ports are orthogonal
switches are located just above each PA, at the antenna
(at 90 degrees) to each other. Isolation, between the
entry panel, and at the waveguide connection at the 8-
transmit and receive ports is in excess of 40 dB.
foot antenna input. The proximity switches at the top of
each PA operate independently. The on-line PA will be
inhibited by its associated proximity switch and the two
Figure 6-14. Antenna Feed Cross Section.