AN646 Datasheet, PDF (14/46 Pages) Silicon Laboratories – Si477X EVALUATION BOARD TEST PROCEDURE

AN646
2.4.9. Stereo Pilot Rejection
A pilot tone is transmitted at 19 kHz to identify stereo broadcast transmissions. In order not to disturb instruments
such as amplifiers and recorders connected to the tuner, the pilot tone and its subcarriers must be sufficiently
suppressed in the tuner. Stereo pilot rejection is the quality criterion of a tuner that is measured as the ratio of
wanted audio frequency voltage to pilot frequency voltage according to the equation:
Pilot Rejection = 1 kHz + 20 x log ( pilot/ f) – V19 kHz)
Where f is FM frequency deviation and pilot is pilot frequency deviation.
1. Configure the audio analyzer:
a. Set Function = RMS Select.
b. Set Bandwidth = BP 3%.
c. Set Units = dBV.
d. Set Frequency Mode = FIX: 1 kHz.
e. Set Filter = OFF
2. Configure generator #1:
a. Set carrier frequency = 98.0 MHz.
b. Set RF level = 60 dBµV.
c. Select Stereo Modulation
d. Set FM Deviation = 67.5 kHz.
e. Set Mode L = R.
f. Set Source = LFGEN (internal). Set LFGEN frequency = 1 kHz.
g. Set Pre-emphasis = 75 µs.
h. Set Pilot = ON.
i. Set Pilot Deviation = 6.75 kHz.
j. Enable modulation. Enable carrier.
3. Audio 1 kHz level (dBV) = V1 kHz.
4. Configure audio analyzer frequency mode = FIX: 19 kHz.
5. Audio 19 kHz level (dBV) = V19kHz.
6. Pilot Rejection (relative to pilot) (dB) = V1 kHz – V19kHz + 20 x log10 (pilot/ f) = V1kHz – V19kHz – 20.
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