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Superposing a Fullerphone
The Fullerphone may be used over a single line and earth return or a double wire.
Since a Fullerphone operates on DC, it is possible to work with a telephone or switchboard on the same line, a method known as superposing.
This feature provides speech communication between the two telephones and Morse communication between the two Fullerphones.
The speech is not heard in the Fullerphones, since speech currents can pass through a Fullerphone, but are kept out of the chopper by the Fullerphone filter.
The Fullerphone signals, being DC, are not heard in the telephones because the capacitors in the telephone circuit and they are bypassed through the magneto bell.
There is, therefore, no mutual interference. The extra insertion loss is neglectable.
Apart from the simple series superposed method,
there are also circuits known as superposed series and superposed phantom.
The latter two circuits were normally used on lines connecting two exchanges, requiring a Superposing Unit (One Transformer) on each side.
Connection of two Fullerphones on a single line with earth return or double wire line.
Simple series superposed circuit, a Fullerphone and a telephone or switchboard connected in series to the line at each station.
The line may either be a double wire or single line with earth return.
Superposed Series
circuit using a single line with earth return or double wire and a Superposing Unit on each side.
Superposed Phantom
circuit using a double wire and a Superposing Unit on each side. This method is the best to use when a double wire is available.
The Fullerphone current splits in the winding, half flowing through each line.
At the distant station the currents re-combine and return through the earth.
Superposing Units (One Transformer) in opened position, previously known as "Experimental Transformer, Compositing", is a 1:1 ratio transformer having the primary and secondary windings split at a central point. (left)
The transformer is toroidal wound on a special dust ring core. The inductance of each winding is 7H at 300Hz, insertion loss is about 1dB.
Superposing Unit closed (right).
On the lid is a tongue for clipping the unit to Switchboards UC 10-line, 6-line or Frames D and P (Distribution and Protection).
Wireless for the Warrior
