181
The Tektronix Type 181 is a time mark generator. There is a benchtop version, the 181, and a rackmount version, the RM181. MOD 110 adds a temperature-stabilized oven for the 1MHZ crystal oscillator, thereby achieving 3 parts per million frequency stability in a 24 hour period, the same stability as the 180A.
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181
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RM181
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Block diagram