Phantom circuit

Phantom working increased the number of circuits on long-distance routes in the early 20th century without putting up more wires.

Since the mid- to late 1960s most balanced, professional condenser microphones for recording and broadcast have used phantom powering.

By far the most common circuit uses +48 V DC fed through a matched pair of 6.8 kΩ resistors for each input channel.

Simple DC signalling can be achieved on a telecommunications line in a similar way to phantom powering of microphones.

The multiplexed FDM telecommunications carrier system usually did not use the baseband of the cable because it was inconvenient to separate low frequencies with filters.

On the other hand, a one-way audio phantom could be formed from the two pairs (go and return signals) making up the star-quad cable.

Ideally, the loading would be removed or reduced for a permanent connection, but this is not feasible for temporary arrangements such as a requirement for outside broadcast.

By contrast, when the circuit is in the phantom configuration the currents in the two wires of each pair are in the same direction and the magnetic flux is being cancelled.

However, "bunched pairs" can also refer to the straightforward connection of two lines in parallel which is not a phantom circuit and will not reduce the loading.