Main program signal characteristicsMain program signal characteristics

Main program signal characteristics

Monophonic transmission

11. The baseband signal shall comprise audio frequency components of the program signal within the band 30 Hz to 15 kHz. Pre‑emphasis of the audio signal shall be in accordance with the admittance/frequency characteristic of a parallel resistance‑capacitance circuit having a time constant of 50 microseconds (see figure A2.4).

12. For monophonic transmission, without pilot sub‑carrier, the deviation of the main carrier by the M signal shall not exceed 75 kHz.

Stereophonic transmission

13. The pilot‑tone system shall be employed for the transmission of stereophonic signals. In this system the baseband signal consists of:

(a) a compatible signal, M, which shall produce a deviation of the main carrier of not more than 67.5 kHz; and

(b) a double sideband, amplitude modulated, suppressed sub‑carrier signal generated by the modulating signal S. This signal shall produce a frequency deviation of the main carrier not exceeding 67.5 kHz when L and R signals are equal and of opposite phase; and

(c) a pilot signal which shall have a frequency equal to one half of that of the sub‑carrier, and shall produce a frequency deviation of the main carrier of not less than 6 kHz and no more than 7.5 kHz.

For stereophonic transmission, under all conditions of modulation by the composite baseband signal, the maximum instantaneous carrier frequency deviation shall not exceed 75 kHz.

Sub‑carrier frequency

14. The frequency of the (suppressed) sub‑carrier shall be 38,000 4 Hz.

Sub‑carrier suppression

15. The residual sub‑carrier shall not produce a deviation of the main carrier of more than 750 Hz.

Audio frequency response

16. The M and S channels shall substantially pass audio frequency components in the band 30 Hz to 15 kHz.

Pre‑emphasis

17. Pre‑emphasis of the signal S shall be identical with that of the compatible signal M and shall be the same as that for monophonic transmission. The pre‑emphasis characteristic of the audio signal shall be in accordance with the admittance/frequency characteristic of a parallel resistance‑capacitance circuit having a time constant of 50 microseconds (see figure A2.4).

Modulation polarity

18. The relative phase of the pilot signal and the sub‑carrier is such that, when the transmitter is modulated by a multiplex signal for which L is positive and R = L, this signal crosses the time axis with a positive slope each time the pilot signal has an instantaneous value of zero. The phase of the pilot signal should not differ by more than 3 degrees from the above state. Moreover, a positive value of the multiplex signal corresponds to a positive frequency deviation of the main carrier.