TM 11-5820-890-20-1
1.11.
TRANSMIT SIGNAL PATH. Continued
MB J4 controls RT-B by passing the ground from pin S to VAA P1, pin S. For AM-7239C and later VAAs
the ground is routed to RT system connector P1, pin S on RT-B. For AM-7239B and earlier, VAA P1, pin
S is connected to the 1 watt audio amplifier in the VAA. The 1 watt audio amplifier places the ground on
pin C of AUD/DATA. The ground is sent through the W4 cable, pin C, then to RT-B AUD/DATA, pin C.
When the LS-671 is installed, the connected handset will provide the necessary ground to transmit.
Either RT-A or RT-B will be controlled depending on whether the LS-671 is connected to MB J3 or J4.
The connection is made by a loudspeaker cable (CX-13292).
b.
Analog Voice Transmit Signals. Audio signals are generated in the handset when the PTT switch is
pressed. These signals are on pin D of the handset and are passed directly to manpack and AM-7239C
and later configuration RTs, or to VAA J2 or J3 for AM-7239B or earlier configurations. For AM-7239B and
earlier configurations, VAA J2 and J3 are wired in parallel to connectors J4 and J5, and connect to the
RT s via W4 cables.
Audio signals are also generated at the LS-671. Cables pass these signals to MB J3 or J4, pin U.
AM-7239B and earlier
J3 audio enters the VAA system connector P1, pin M. The signal is present at the VAA J3, pin D and
J5, pin D. Connector J3 is where the RT-A handset is placed. Connector J5 is connected to the RT-A
AUD/DATA, pin D by a W4 cable. The audio is then processed and transmitted.
J4 audio enters the VAA system connector P1, pin U. The signal is present at the VAA J2, pin D and
J4, pin D. Connector J2 is where the RT-B handset is placed. Connector J4 is connected to the RTB
AUD/DATA, pin D by a W4 cable. The audio is then processed and transmitted.
AM-7239C and later
J3 audio enters the VAA system connector P1, pin M. J4 audio enters the VAA system connector P1,
pin U. The audio is routed through the VAA to RT-A and RT-B system connectors P1, pin E. The audio
is then processed and transmitted.
c.
Whisper (WHSP) Control. The RT whisper mode is selected, by pulling out the RT WHSP control for
RT1523D and earlier, or by the RT menu for RT-1523E. When whisper mode is selected, an internal
audio preamplifier is turned on. The microphone circuit now additionally amplifies the whispered voice.
This allows the use of the radio in situations where the user does not wish to be overheard.
d.
Analog Data Modulation. Data devices are connected in place of the handset on the VAA (AM-72398
or earlier) or RT (AM-7239C or later). The handset is then connected to the RT AUD/FILL. A wide range
of data signals can be transmitted. The data is frequency modulated on the RF carrier and transmitted.
In AD1, all incoming FSK signals are treated the same as voice signals. In TF (TACFIRE) the FSK tones
are changed to a 16 kbps signal.
For RT-1523B and earlier, the RT needs a ground applied to pin F of the AUD/DATA connector for TF
mode. The ground informs the RT to go to the analog data mode. Pin F is grounded by an FSK detector
circuit in the VAA for the vehicular radio. Pin F is grounded by an adapter cable (CX-13308/VRC) for the
manpack radio.
e.
Digital Data Modulation. Data devices are connected to RT AUD/DATA. The handset is then
connected to RT AUD/FILL. A number of data rates are available for selection; 600 bps, 1.2 kbps, 2.4
kbps, 4.8 kbps, and 16 kbps (RT- 1523A/B ). For RT- 1523C/D/E the following data rates are available:
600,1200,2400,4800,16000,1200N, 2400N, 4800N, 9600N, PCKT, and RS-232. When low data rates
are used, the error correction coding allows a greater communication range and increased message
accuracy.
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