Analog Demodulation
FPC1000
128
User Manual 1178.4130.02 ─ 02
Selecting the FM broadcast time
The FM broadcast time parameter selects the time constant of the deemphasis filter.
This deemphasis filter is commonly used in FM broadcasting to improve the S/N ratio.
In that case, a modulated signal is extorted by a pre-emphasis filter before transmis-
sion, for example to eliminate frequencies that are more prone to interferences.
The deemphasis filter reverses the emphasis function after demodulation.
The deemphasis filter is available for 200
kHz and 300
kHz demodulation bandwidths.
1. Press the "BW" key to open the bandwidth menu.
2. Select the "FM Broadcast" menu item.
3. Select the time constant you need.
● "Off": Applies no deemphasis filter.
● "50 µs": 50 µs time constant (used, for example, in European FM broadcast-
ing).
● "75 µs": 75 µs time constant (used, for example, in North American FM broad-
casting).
Table 11-1: Measurement times for the demodulation bandwidths
Demodulation bandwidth [Hz]
Measurement time [ms]
2000000
1
989000
3
650000
4
500000
6
300000
10
200000
16
100000
32
50000
65
30000
112
20000
163
10000
327
Table 11-2: Measurement time calculation for audio lowpass filters
Audio lowpass
Measurement time
DBW/1
x 1
DBW/10
x 10
DBW/30
x 30
DBW/100
x 100
Bandwidth Configuration
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