Can we just swap the crystal to revert our test receiver to its original Apollo frequency? Maybe it's not that simple. And we get unexpected help from yet another generous collector. Apollo Comms Playlist: https://www.youtube.com/watch?v=v49ucdZcx9s Links to doc: https://www.curiousmarc.com/space/apollo-s-band-communications https://virtualagc.github.io/virtualagc/QuestForInfo.html https://www.ibiblio.org/apollo/ Our sponsors - PCBWay: fast turn PCBs, https://www.pcbway.com/ - Keysight: test instruments: https://www.keysight.com/ - Samtec: connectors: https://www.samtec.com/ Support the team on Patreon: https://www.patreon.com/curiousmarc Buy shirts on Teespring: https://teespring.com/stores/curiousmarcs-store Learn more on the companion site: https://www.curiousmarc.com/ Contact info: null 00:00 Our NASA receiver had been modified 01:51 Receiver modules 02:59 Closer look at the VCO 03:58 Receiver principle of operation 05:56 New crystal frequency calculation 06:47 Two types of crystals, which is it? 07:50 Original manual says serial crystal 09:53 Measuring the original crystal 11:29 It's a parallel resonant crystal 12:40 It's a third overtone crystal 14:17 Shout out to Laptech Precision