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TM 11-5820-890-30-5
2-7.
BASlC RT SIGNAL TYPES.
There are five basic signal types used in the RT:
Analog
Digital
Control
Power
RF
Analog signals include the audio and analog data signals.
They can vary greatly in signal level, shape, and
frequency.
Digital signals include the timing clocks and digital data signals. Clock frequencies vary. The clocks are used to
synchronize the serial digital data streams between modules. Within the RT they are typically at logic 0 and logic
1 levels. RT I/O digital signals use the ±5 V logic levels as required by MlL-STD-188-114. Logic 0 is 5 V dc. Logic
1 is -5 V dc. The ECCM fill device uses 0 V for logic 1 and -6.75 V for logic 0. The logic levels in the RT are as
follows:
6.75 V dc Logic: Logic 0 = -0.7 to 2.0 V dc,
Logic 1 = 4.7 to 7.5 V dc
Negative Logic:
Logic 1 = -5.0 to -7.25 V dc
Control signals include the status and control lines. They will be set to logic 1 to indicate or direct a particular
condition. In some cases, a signal name includes a “ –N” to indicate that the logic is reversed. For example, a
logic 1 on the PTT-N line indicates the absence of a PTT; logic 0 indicates a PTT.
Power signals are at constant V dc levels. Most are provided by the power supply as described in paragraph 2-5.
The audio power supply provides the voltages used by the audio/data section.
RF and IF signals are also present in the RT. Coaxial cables are used to pass these signals between modules.
Frequencies range from 12.5 (IF) to 100.5 MHz.
2-8.
RECEIVE RF SIGNAL PATH.
The RF signal received by the RT is processed by four modules to provide the demodulated audio or data signal.
These modules are:
Impedance Matching Network (1A1)
Exciter/Power Amplifier (1A11)
Tuner/Mixer (1A9)
lF/Demodulator (1A8)
See figure FO-1 for the block diagram of this signal path.
The RF signal enters the RT at the ANT connector (J1) and passes through the impedance matching network. The
impedance matching network has four bands. One is a 50-ohm network that is used when a BNC is connected to
the RT. When a manpack antenna is connected to the RT, one of three impedance matching networks is used
depending on the frequency selected.
A logic 1 level is placed on the RF input path by the impedance matching network. If a manpack antenna is
connected to the ANT connector, the switch shown in figure 2-9 stays closed. The logic 1 level is pulled to ground
by the inductor. The impedance matching network detects the change in logic level and selects the appropriate
matching network. If a BNC is connected to the ANT connector, the center part of the connector is pushed in and
opens the switch. The RF signal is fed through the capacitor. The dc level stays at logic 1. The impedance
matching network selects the 50-ohm matching network.
2-12
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