STE sas Milano - ITALY
Pag. 9 of 14
DATA/VOICE input ( D/V - J1 pin n.18 )
The transceiver has two main operating modes, depending on D/V input :
1) D/V = Low ( 0 V )
“Voice” (analogue) signals can be transmitted with narrow band frequency modulation
(NBFM).
Depending on the selectors S2 and S4 (“A” or “B” position), PM (phase modulation
with 6 dB/oct emphasis) or FM (frequency modulation with flat frequency deviation) can
be selected.
Note : During “Voice” operating mode the Tx data input (TXD) is disabled .
2)
D/V = High ( 5 V ).
Digital Data can be transmitted ( max data rate = 9600 Baud ) and the modulation
system is changed to “GMSK”.
The transceiver employs a Two Point Modulation system (VCO plus PLL Reference
Oscillator – see block diagram Fig. 2 ) to provide a flat response from 4.8 KHz down to
DC.
Note : In “DATA” operating mode the TX “VOICE” analog input “ATX” (J1- pin n.9) is not disabled.
Signal on “ATX” input must be avoided.
PM , with an optimum audio response from 300 Hz to 3KHz, is best suited for voice or telephone grade
signals (DTMF, AFSK slow speed Modems, selective call, etc.) and has the best “S/N” ratio with an Rx
sensitivity of - 120 dBm ( 12 dB SINAD ).
FM with 3 KHz fixed deviation can be the best choice for audio signals ranging from 50 Hz to 5 KHz
(Fast Modems, V/F converters, etc.).
Receiver sensitivity is –110 dBm ( 12 dB S/N ).
During “DATA” operating mode the TX has only two discrete transmitted frequencies :
Bit “0” (“TXD” input= 5V) corresponds to a transmitted frequency F
L
= Fc – 3KHz
Bit “1”(“TXD” input = 0V) corresponds to a transmitted frequency F
H
= Fc +3KHz
(Fc is the nominal RF channel center frequency).