FM Transmitter
Sistemas Electrónicos S.A EM 100 DIG
Technical Manual - v1.2 - November 2005
20
2.4.5 Operation with a RDS or SCA Encoder.
1) Connect the BNC-type <AUX> connector to the output of the RDS or SCA Encoder. If the internal
optional stereo coder is used, connect the <LF MONITOR> BNC output to the pilot tone
synchronization input of the RDS coder, if present.
2) Select the <AUX> command menu screen and push <OK> to vary the channel sensitivity.
Adjust both transmitter sensitivity and/or the level of the external generator for the deviation required,
as explained in the previous Manual sections. Consider that 0dB modulation reading (not the input
level) in this field means 10% total modulation or 7.5kHz deviation, i.e.the standard setting for a SCA
auxiliary channel. In the case of RDS,a reading of -11.5 dB or 2kHz is the correct value of modulation.
3) Total modulation and deviation may be read in the <MPX> display screen, with the addition of
any other composite signal simultaneously present. If only the final modulation due to the auxiliary
signal requires to be measured, momentarily disconnect every other baseband signals present on
the inputs and change mode to <MONO> or <MPX EXT> mode, for the measuring operation only.
This is not required when you display only the auxiliary signal.
4) If you have changed transmission mode selection or removed any input signal for check purpose,
reverse to the original setting and reconnect any previously disconnected signal.
2.4.6 Modulation Adjustment with Broadcast SignaL.
Check the overall modulation level for adequacy, as follows:
1) Select the display menu screen <MPX>: The total modulation will be displayed, both in dB and as
deviation in kHz. An analog moving bar and a digital peak reading are shown at the same time.
2) Send a sufficiently constant-level music signal to modulator input, and check that the measure
hovers around 0dBm and moves into the upper range during signal peak only and by no more than
1 or 2dB. For any other reading,adjust the mixer console’s "MASTER" or output attenuator until the
above conditions are obtained. The red <LIMITER> alarm LED should never or rarely light up, as this
would indicate distortion.
If the limiter is set just above 75kHz, the red LED will light up above 0dB and the modulation measured
will never show a much greater value. Factory pre-set is 100kHz (+2.5dB).
2.4.7 Check of Pilot Tone on Stereophonic Broadcast.
In case of internal stereo coder, no allowance is externally provided to change the pilot tone level,
which is usually internally pre-set for 9-10 %of modulation, i.e. -21 ~ -20dB or 7 ~ 7.5kHz deviation.
In case it is externally provided by a separate stereo coder, it must be measured in absence of
audio modulationand any other auxiliary signal as below described:
1) Disconnect any signal from the external stereo-encoder input and any RDS or SCA signal.
2) Select the display menu screen <MPX> and check the pilot tone, which must be now the only
signal present. The standard level is that previously stated ,i.e.: 9~10% or -21 ~ -20dB, and may be
adjusted accordingly on the external stereo encoder to suit the request.
3) Connect again any previously disconnected signals as done.
