Ryan Malloy
493c21c511
Implement the transmit/generate side as streaming GNU Radio blocks, complementing the existing receive chain. Each block maps to a physical instrument on CuriousMarc's Keysight bench: pcm_frame_source - PCM bit stream generator (sync_block + FrameSourceEngine) nrz_encoder - bits to NRZ waveform (+1/-1) with upsampling bpsk_subcarrier_mod - NRZ x cos(1.024 MHz) BPSK modulator fm_voice_subcarrier_mod - 1.25 MHz FM test tone source pm_mod - phase modulator: exp(j * deviation * input) usb_signal_source - convenience wrapper wiring all blocks together Includes GRC YAML definitions for all blocks under [Apollo USB] category, 49 new tests (271 total, all passing), and a loopback test that validates the full TX->RX round trip including frame recovery with 30 dB AWGN.
60 lines
1.9 KiB
Python
60 lines
1.9 KiB
Python
"""
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Apollo BPSK Subcarrier Modulator -- NRZ data onto 1.024 MHz subcarrier.
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The transmit-side counterpart to bpsk_subcarrier_demod. Takes an NRZ baseband
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waveform (+1/-1) and modulates it onto a 1.024 MHz cosine subcarrier via
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simple multiplication: output(t) = nrz(t) * cos(2*pi*f_sc*t).
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This is Bi-Phase Shift Keying (BPSK): the cosine phase flips 180 degrees
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when the NRZ data changes sign.
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On the real spacecraft, a 33522B AWG (or equivalent) generates this
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BPSK-modulated subcarrier before summing with the voice subcarrier.
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Reference: IMPLEMENTATION_SPEC.md section 4.2
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"""
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from gnuradio import analog, blocks, gr
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from apollo.constants import PCM_SUBCARRIER_HZ, SAMPLE_RATE_BASEBAND
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class bpsk_subcarrier_mod(gr.hier_block2):
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"""BPSK modulator: NRZ float input -> BPSK subcarrier float output."""
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def __init__(
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self,
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subcarrier_freq: float = PCM_SUBCARRIER_HZ,
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sample_rate: float = SAMPLE_RATE_BASEBAND,
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):
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gr.hier_block2.__init__(
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self,
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"apollo_bpsk_subcarrier_mod",
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gr.io_signature(1, 1, gr.sizeof_float),
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gr.io_signature(1, 1, gr.sizeof_float),
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)
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self._subcarrier_freq = subcarrier_freq
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self._sample_rate = sample_rate
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# 1.024 MHz cosine subcarrier (continuous phase, maintained by sig_source)
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self.carrier = analog.sig_source_f(
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sample_rate, analog.GR_COS_WAVE, subcarrier_freq, 1.0, 0,
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)
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# Multiply NRZ data by subcarrier
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self.mixer = blocks.multiply_ff(1)
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# Connect: input (NRZ) -> mixer port 0, carrier -> mixer port 1 -> output
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self.connect(self, (self.mixer, 0))
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self.connect(self.carrier, (self.mixer, 1))
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self.connect(self.mixer, self)
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@property
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def subcarrier_freq(self) -> float:
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return self._subcarrier_freq
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@property
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def sample_rate(self) -> float:
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return self._sample_rate
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