Found in old American documentation, this circuit can use crystals between 27.5 and 33 MHz operating on the third harmonic. The transistor admits equivalent.
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
Found in Texas Instruments documentation from the 1980s, this circuit applies to digital signal...
We find this circuit in a Popular Electronics of the 90s. The circuit is passive and the coils...