SL5067

9

than the picture carrier itself. Thus if the picture carrier level is

reduced by using a resistor on pin 3 (mod index set), the level

of the sound subcarrier will not change. This should be

remembered when setting up a modulator to give the desired

modulation index and vision/sound carrier ratio.

POSITIVE MODULATION

Several references are made in the text to positive video

modulation and AM sound. Whilst it is possible to switch the

device into these modes, it should be noted that the SL5067

will not perform to full SECAM specifications.

Use

of

AM

sound

may

produce

sound–in–vision

interference at higher modulation depths. It should be

possible, however to AC couple in modulated audio. If this is

attempted, the sound tank circuit on pins 15 and 16 would not

be required. The modulated audio signal should be fed into the

Audio input pin (pin 17) via a 470nF capacitor.

The FM/AM select pin can be used as a gain control pin, but

will not switch the device between FM and AM modes.