In this episode, I review two frequency meters from the 1950s/1960s: the Rohde & Schwarz type WAM (BN 4312/2; 30-500 MHz) and type WAL (BN 4321/2; 470-2500MHz). With errors margins down to ± 0.08%, these were very high precision instruments in their days.
Both instruments work on the resonance principle, but the resonation circuits are completely different, and especially the WAL has fascinating aspects to it with its tuneable λ/4 line (tuned cavity). Another interesting part is the use of now-forgotten Dezifix-B connectors.
In the video, I do teardowns and a repair attempt and see whether any precision can still be achieved…
https://youtu.be/EuDcRPdHJE0