Motorola GR300 TPL Encoding, DPL Encoding, Beep Tone Encoding, Squelch/Repeater Audio, CSQ Input

Section 4

Theory of Operation

TPL Encoding

Two signals are used for TPL generation:

•Clock frequency at the exact TPL rate from the microprocessor

•Clock frequency at 64 times the TPL rate from the timer module

These signals are fed into a switched capacitor low pass filer U17, then sent to the transmitter.

DPL Encoding

For generating DPL signals, the microprocessor sends the digital code out its pin 9. Data inversion is done inside the microprocessor if required. The timer module produces a high frequency clock signal that is fed into the low pass filter U17. Operation is very similar to TPL encoding described above.

Beep Tone Encoding

Timer U15 generates progress tones (Morse ID, warning beeps, etc). Square wave output is filtered and summed at the transmit audio junction U11D, then it passes through the output buffer amp to the transmitter audio input at P2-2.

Squelch/Repeater Audio

The repeat audio is passed through input unity gain stage U18B, the audio hi-pass filter U11 and U11A to remove the TPL/Digital encode, de-emphasized by the R29/R30/C34 network and finally to squelch gate.

U12B and U12C. The microprocessor controls the squelch gate. The repeat audio is summed at the transmit audio junction U11D, then passes through the output buffer amp to the transmitter audio input at P2-2

CSQ Input

From the 8 or 16 channel GM300 radio, U4B and U4F are used to select the CSQ input connection and polarity. The COR logic signal is presented to the microprocessor input port pin 20.

March, 1993 6880902Z68-O Section 4-1