User Manual

Analog Demodulation
R&S
®
FPC
146User Manual 1178.4130.02 ─ 05
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 14-1: 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 14-2: 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