frequencies correspond to different addressing step lengths. The accumulated method sequentially
outputs sinusoidal data at a sampling clock rate.
Figure 6.5 CTCSS Transmit Block Diagram –
OMISSIS
At the moment the PTT button is released, the audio signal transmission ends, and the subsonic
signal phase reversals and continues to remain in the air for approximately 155ms to ensure
sufficient voice path closure processing time at the receiving end. Among them, the inversion of the
subsonic phase is realized by the above-mentioned sinusoidal table addressing phase jump.
The subsonic signal is weighted by the modulation coefficient (which can be configured by
software) and superimposed with the audio signal, and then modulated by FM.
The detailed usage is detailed in Appendix A2.2.1.
6.1.2 CDCSS send
The transmitter first transmits the original data 12-bit via the golay coding cycle to the 23-bit DCS
code, then the DCS code is NRZ(1) mapped, and the two-stage interpolated and filtered data is
input to the FM modulator to obtain the modulation phase value and the baseband modulation to
form the CDCSS. Baseband signal output.
Figure 6.6 Transmitter system block diagram
Detailed usage is detailed in Appendix A2.2.2.
6.1.3 DTMF sending
The DTMF signal is generated by a combination of four sets of high frequency signals and four sets
of low frequency signals. The low frequency signal is 2.5 dB lower than the amplitude of the high
frequency signal. The DTMF signal is sent before the start of the audio signal, after the PTT is
valid, and under normal circumstances, from the PTT press to the transmission of the DTMF signal,
there is an idle state of about 600ms in the middle, in order to allow the receiver to have enough
time to enter Detection mode.
Flow Description:
Like CTCSS, DTMF signals are also generated by querying a sine table. The high frequency signal
is superimposed with the low frequency signal and weighted by the modulation frequency offset
coefficient, which is modulated by FM and output. Each DTMF code corresponds to a signal length
of 50ms, followed by an IDLE state of 50ms. The length of the code that DTMF can support is
determined by the user.
OMISSIS
Figure 6.7 DTMF Transmit Block Diagram
