Dial And Hold - HP 4934A Operating And Calibration Manual

4 Select the transmitter output impedance using the TRIWT key -135,150,600,900
or 1200Q.
Dial and Hold
The HP 4934A can be used with a butt-in to dial up lines or for talking along
a line. The HP 4934A can hold lines which require a DC current to maintain
the connection once the butt-in is disconnected.
The diagram below shows how the hold, dial and reverse functions work.
2-2 Making Measurements