Open Hardware: Radio, Compute Module 4, and More

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Reverse-engineering the Apollo spacecraft's FM radio
Many systems worked together for communication, but I'm focusing on a single module: the voice detector inside the premodulation processor that performed the FM demodulation. The block diagram below shows the operation of the voice detector; I've grayed out the data detector.6 The input contains the voice signal and the data signal at different frequencies; a band-pass filter (green) separates out the voice signal at 30 kilohertz. Next, the blue triangle7 demodulates the FM signal using a "clipper discriminator" circuit. The cyan triangle is an amplifier, producing the "up voice" output signal (red), so-called because it had been transmitted "up" from a ground station. I'll explain this circuitry in detail below.
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PTP and IEEE-1588 hardware timestamping on the Raspberry Pi CM4
PTP is more prevalent in HFT (High Frequency Trading) in finance, scientific research, and distributed databases that need highly accurate timings.
But with a tiny Compute Module 4 able to control hardware timestamps—plus the plethora of available high-quality GPS HATs for the Pi—maybe highly-accurate time could be more democratized!
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Hackaday Podcast 176: Freezing Warm Water, Hacking Lenses, Hearing Data, And Watching YouTube On A PET
It’s podcast time again, and this week Editor-in-Chief Elliot Williams sat down with Staff Writer Dan Maloney to review the best hacks on the planet, and a few from off. We’ll find out how best to capture lightning, debate the merits of freezing water — or ice cream — when it’s warm, and see if we can find out what R2D2 was really talking about with all those bleeps and bloops. Once we decode that, it’ll be time to find out what Tom Nardi was up to while the boss was away with his hidden message in episode 174, and how analog-encoded digital data survives the podcast production and publication chain. But surely you can’t watch a YouTube video on a Commodore PET, can you? As it turns out, that’s not a problem, and neither apparently is 3D printing a new ear.
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