DB
ELETTRONICA TELECOMUNICAZIONI S.p.A.
KCL 30 SY
- FM broadcasting exciter/transmitter - U
SER
’
S
M
ANUAL
27 /37
7.
SINTEL 96 MODULATION BOARD
7.1
GENERAL DESCRIPTION
The modulation board SINTEL 96 allows a high quality direct carrier modulation accepting a
composite stereo (MPX) or a mono input signal with up to 3 SCA subcarriers (for example
RDS, ARI, ...).
The mono input signal is filtered by a 7
th
order elliptic filter with a very flat response (20Hz
÷
15kHz
with
±
0.25 dB) and an optimum out of band attenuation (>50 dB for frequencies greater than
19 kHz), then the signal is amplified (or attenuated) and passed to the VCO oscillator for the FM
carrier modulation. The VCO is controlled by a digital PLL circuit with an high stability quartz
reference to obtain a synthesized oscillation very stable: the frequency setting is very agile using on
board dip-switches (the minimum step is 10 KHz).
The composite stereo signal and the SCA sub carriers are just amplified or attenuated for correct
modulation depth adjustment before the VCO: the stereo performances of SINTEL 96 are
excellent (stereo separation >60 dB from 20Hz to 15 kHz, S/N>80 dB)
Before the VCO, an adjustable and bypass able deviation limiter prevents the FM carrier from
excessive modulation depth and adjacent channel interference according to all the international
standards (CCIR, FCC, ....): furthermore an automatic locking circuit enable the output modulated
signal of SINTEL 96, only when the internal PLL is locked correctly avoiding all the unwanted
emissions.
