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General Radio 1657
Digital RLC meter
Genrad 1657 Digibridge

Available from 1976 to 1978+

Catalog History
 Document Year Page
Catalog78 1978 22
(All manuals in PDF format unless noted otherwise)

The General Radio 1657 Digibridge is a digital RLC meter, introduced in 1976 1.


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The 1657 applies a sine wave to the measured device and a precision resistor in series. The average voltage across each is measured using four different phases relative to the input sine wave, for a total of eight measurements. From these, the resistive and reactive components of the tested device are calculated and displayed.

The 1657 uses a 6503 CPU, which is a 28-pin version of the 6502 with the same instruction set, but fewer address lines. The 1657's firmware is contained in a 2Kx8 ROM, in later versions a 2716 EPROM. A 128-byte SRAM holds scratchpad and the stack.