SI4721 datasheet(29/68 Pages) SILABS

29 / 68 page

AN388

Rev. 0.2

2.3.16. 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 = Vaudio0 (1 kHz) + 20*log (pilot/f) – Vaudio0 (19 kHz)

where

f is FM frequency deviation and pilot is pilot frequency deviation.

1. Connect test equipment as shown in Figures 1, 2, or 3.

2. Configure the tuner in standard configuration, except for setting in mono operation. Set the tuner in stereo

mode.

3. Configure the audio analyzer:

a. Select Analyze.

b. Set Function = RMS Select.

Set Bandwidth = BP 3%.

ii. Set Units = dBV.

iii. Set Frequency Mode = FIX: 1 kHz.

4. Configure generator #1:

a. Set carrier frequency = 98.1 MHz.

b. Set RF level = 60 dBµV.

c. Select Stereo Modulation.

Set FM Deviation = 67.5 kHz.

ii. Set L = R.

iii. Set Source = LFGEN.

iv. Set LFGEN frequency = 1 kHz.

v. Set Pre-emphasis = 75 µs.

vi. Set Pilot = ON.

vii. Set Pilot Deviation = 6.75 kHz.

d. Enable modulation.

e. Enable carrier.

5. Audio 1 kHz level (dBV) = V1kHz.

6. Configure audio analyzer frequency mode = FIX: 19 kHz.

7. Audio 19 kHz level (dBV) = V19kHz.

8. Pilot Rejection (relative to pilot) (dB) = V1kHz – V19kHz + 20*log10 (

pilot/f) = V1kHz – V19kHz – 20.

9. Pilot Rejection (relative to 75 kHz) (dB) = V1kHz – V19kHz + 20*log10 (75 kHz/

f) = V1kHz – V19kHz + 0.91.

SI4721 Datasheet(PDF) 29 Page - Silicon Laboratories