hi Miguel,
really interesting, but first I have to recover the 52.5 MHz crystal to convert the TR503 to TR502.
Among other things, the TR503 does not have the logic interface (the one connected to the SA via the cable with LEMO connectors).
As I understand it, the logic interface allows you to make a brighter dot appear on the CRT of the SA and to control the frequency meter DC508 or similar.
--Cheers
Attilio
Attilio