Telephone Line Tester (CB21266E)

We found this circuit in a Radio Electronics from the 90s. The circuit is for conventional analog lines. All components are common nowadays.

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We found this circuit in an English publication from the 1980s. The circuit uses current...
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The circuit shown in the figure can be useful in cases where a common telephone extension is used....
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We found this circuit in an American documentation from 1977. The circuit must not be powered by a...