VS1 Operations and Maintenance Manual Operating the transmitter
Issue 3.1 2013-10-01 Page 2-59
SCA tab: (see Figure 2.41)
• MPX SCA: Connector (J7:A for SCA1, J7:B for SCA2) for use with an externally generated
SCA; select Enabled or Disabled. When enabled, all the selections listed below are active.
– Input Level: signal level that represents 10% modulation. Enter a value between 1 and
5 V p-p (typically 3.50 Vpp).
• SCA Reduction: Attenuation applied to the SCA input; set between 0 and 20% (used to
reduce the modulation level of the main audio when SCAs are enabled; typically, for every
2% of SCA modulation, the main audio modulation must be reduced by 1%).
• Internal SCA1/2: Enable or disable the appropriate internal SCA (SCA1 or SCA2). When
enabled, the settings listed below are active for the associated SCA signal (1 or 2).
– SCA1 or SCA2 Injection Level: enter value between 0 and 20% (typically 10%); this level
is added to the composite baseband signal.
– SCA1 or SCA2 Frequency: enter value between 20 and 100 kHz (typically set to 67 kHz
or 92 kHz).
– SCA1 or SCA 2 Input Level: enter value between -12 and +12 dBu, which represents
the input voltage level that yields 10% modulation (typically 0.0 dBu).
– SCA1 or SCA2 Lowpass Filter: select Enabled (applies 7.5 kHz low-pass filter to audio
input) or Disabled.
– SCA1 or SCA2 Preemphasis: select 0 us, 50 us, 75 us or 150 us.
– SCA1 or SCA2 Mode: select FM (frequency modulated sub-carrier, typical) or DSB-SC
(double side band suppressed carrier).
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