We found this balanced modulator circuit for DSB and possibly SSB transmissions in US 1980s telecommunications documentation. The diodes can be replaced with equivalents.
The integrated circuit used in this project is not common today, but it can be implemented with more...
Found in an American publication from 1969, this circuit can be adapted to be used as a shield....
This current meter with many scales was found in a 80s American documentation. The operational amplifier...