R&S M3SR Series 4100 HF Transceivers Motherboard - Function
6124.9007.82.01 1.28
On the external audio connector there are 4 isolated differential audio lines. Two lines (LINE_RX_1,
LINE_RX_2) are outputs used for RF receive direction. The other two lines (LINE_TX_1, LINE_TX_2)
are inputs used for RF transmit direction. The nominal external audio level can be in the range -10 to
+10
dBm into 600 Ω. The input/output circuitry are adjusted by the FPGA to translate a level in this
range to the nominal Audio Bus level of -8
dBm.
Where necessary, operational amplifiers are used to achieve appropriate audio signal levels.
Microphone level
The microphone input is located on the Front Panel. The dynamic microphone provides a level range
of 0.3 to 10
mV, the elektret microphone covers 3 to 100 mV. This 30 dB range is compressed to 20 dB
by a compressor on the Front Panel. A level control is used to adjust the microphone signal to the level
of the Audio Bus.
Audio level relations and control
The HEADSET potentiometer is mapped to the headset volume control of the audio amplifier. The
HEADPHONE/SPEAKER potentiometer is mapped to the volume control of the other 3 audio
amplifiers. Reason: If "jack output" is in use, both speakers are off, otherwise only one of the speakers
is on, depending on INT/EXT signal, derived from user input INT/EXT button.
Speakers
The internal speaker works at approximately 0.5 W, the external speaker (rear connector) at max. 3 W
/ 4 Ω, filtered by a 5 kHz lowpass filter. Power-on clicking is eliminated.
Sidetone
Sidetone is a property of Transmit mode only. The sidetone is switched on and off via a bit in the control
register. Its level is controlled to the volume determined by the volume control. The sidetone
attenuation is adjustable between 0 and 25.5
dBm in steps of 0.1 dB.
ERASE
Crypto keys and configuration data stored on Radio Controller shall be erased by unauthorized
handling of the device and by user request. For this, the Radio Controller has an H-active ERASE input
signal which must be pulled to GND for normal operation. In order to activate ERASE, the signal must
be disconnected from GND. There are 2 possibilties to activate ERASE mode. The ERASE input is fed
to X26.6 (backplane connector) where it can be connected to X26.44 (ground). The external connection
at X26 is intended to be of short wire length only. A jumper placed on X304 deactives any ERASE
function on X26. The ERASE mode can also be activated by pressing the ERASE button on the Front
Panel.
Ethernet
On the Motherboard there is a quad port HUB for 10 MBit/s Ethernet communication. Via this HUB the
Radio Controller, R&S
GB 4000C and an external remote device like a PC are connected together.
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