Rohde & Schwarz M3SR Series 4100, Service Manual, Page: 68 / 138

R&S M3SR Series 4100 HF Transceivers NMEA Interface (Option) - Function
6124.9007.82.01 1.32
1.3.2.11 NMEA Interface (Option) - Function
This optional module is a standardized NMEA-183 interface (RS422) for connection to an external DSC
controller (Digital Selective Calling). The R&S GS 4102 NMEA Interface has the function of an RS422
controlled audio switch with adjustable control of amplification factors. It allows to connect an audio line
to the radio and to adapt it to the internal radio bus (see Fig. 1.15).
The R&S GS 4102 NMEA Interface provides at the rear of the radio:
¾ RS422 Interface NMEA (TXD, RXD, CTS, RTS) X5011
¾ One transformer-coupled galvanically isolated audio channel X5012
The control logic consists essentially of an FPGA and a FLASH-Memory. To command the FPGA, a
parallel Radio Control Bus (RCB) is connected to the Radio Controller. The FLASH-Memory is used for
configuration data, module parameters and look-up tables. The VCXO (f = 40 MHz) of the control logic
is synchronized with a 100 kHz reference sine wave signal from the synthesizer.
RS422 Interface NMEA
The inputs and outputs of the RS422 Interface X5011 are over-current protected and galvanically iso-
lated via opto-couplers . The RS422/RS232 converter module converts the RS422 Interface levels into
RS232 levels and visa versa. The RS232 receive data (RXD) and transmit data (TXD) are transferred
to and from the Radio Controller. The RS422 Interface works in the asynchronous mode with hand-
shake and a rate of 4800 Baud. The hardware handshake is realized with the FPGA and Radio Control
Bus (RCB).
Audio Channel
The audio channel X5012 can be used as input or output. The direction and amplification are controlled
by the software via the FPGA and the Radio Control Bus (RCB). By means of the variable amplification
it is possible to adapt the different external AF levels to the internal audio bus level of -8 dBm nominal.
The direction of the audio signal (to or from radio) will be given by the push to talk (PTT) signal coming
from the audio connector X5012 (external).
An incoming audio signal of 0 ±10 dB is fed via a transformer to a digitally adjustable amplifier. By using
two analog switches the audio signal can be switched either to the LSB or USB channel of the internal
radio audio bus (Line1_Tx and Line 2_Tx). The internal switch matrix is controlled by the FPGA via the
RCB.
An audio signal received by the radio can be fed via the LSB or USB channel of the internal radio audio
bus. Via the two audio switches inside the R&S GS 4102 NMEA Interface the sideband can be chosen.
The output voltage behind the transformer can be adjusted to 0 ±10 dB.