id: apollo_fm_voice_subcarrier_mod
label: Apollo FM Voice Subcarrier Mod
category: '[Apollo USB]'
flags: [python]

parameters:
- id: sample_rate
  label: Sample Rate (Hz)
  dtype: real
  default: '5120000'
- id: subcarrier_freq
  label: Subcarrier Frequency (Hz)
  dtype: real
  default: '1250000'
- id: fm_deviation
  label: FM Deviation (Hz)
  dtype: real
  default: '29000'
- id: tone_freq
  label: Test Tone Frequency (Hz)
  dtype: real
  default: '1000'

outputs:
- label: out
  domain: stream
  dtype: float

templates:
  imports: from apollo.fm_voice_subcarrier_mod import fm_voice_subcarrier_mod
  make: >-
    apollo.fm_voice_subcarrier_mod.fm_voice_subcarrier_mod(
      sample_rate=${sample_rate},
      subcarrier_freq=${subcarrier_freq},
      fm_deviation=${fm_deviation},
      tone_freq=${tone_freq})

documentation: |-
  Apollo FM Voice Subcarrier Modulator

  Source block that generates a 1.25 MHz FM subcarrier with a sinusoidal test
  tone. Transmit-side counterpart to the voice subcarrier demodulator.

  The signal chain is: test tone -> FM modulator -> upconvert to 1.25 MHz
  -> real-valued output. With default parameters this produces a signal
  matching the Apollo USB downlink voice subcarrier (+/-29 kHz deviation).

  On the real spacecraft, voice audio (300-3000 Hz) drives an FM VCO at
  113 kHz, which is mixed with the 512 kHz master clock and doubled to
  produce the 1.25 MHz FM subcarrier.

  Parameters:
    sample_rate: Output sample rate in Hz (default 5.12 MHz)
    subcarrier_freq: FM subcarrier center frequency in Hz (default 1.25 MHz)
    fm_deviation: FM deviation in Hz (default +/-29 kHz)
    tone_freq: Internal test tone frequency in Hz (default 1 kHz)

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