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Time mark generators put out pulses at user-selectable intervals. | Time mark generators put out pulses at user-selectable intervals. | ||
They are primarily used for calibrating the time-base of oscilloscopes. | They are primarily used for calibrating the time-base of oscilloscopes. | ||
The 180A | |||
The signal path of the 180A starts with the OCXO, which produces 1 MHz. | |||
That waveform is divided down using synchronized monostable multivibrators. | |||
Switches on the front panel select which of the divided-down pulse signals | |||
will be added together to form the output waveform. | |||
This scheme does not require precision in the time constant of the monostable multivibrators. | This scheme does not require precision in the time constant of the monostable multivibrators. | ||
The only precision component in the 180A is the OCXO (part number [[158-007]]). | The only precision component in the 180A is the OCXO (part number [[158-007]]). | ||
The manual suggests an interesting procedure for calibrating the OCXO, | |||
In addition to the time mark generator functionality, the 180A also produces | |||
sine waveforms at 5 MHz, 10 MHz, and 50 MHz. | |||
These frequencies are produced by feeding the 1 MHz OCXO output to a series of three frequency multipliers. | |||
First the 1 MHz is quintupled to get the 5 MHz signal. | |||
Then the 5 MHz signal is doubled to the the 10 MHz signal. | |||
Then the 10 MHz signal is quintupled, yielding the 50 MHz signal. | |||
Each of the three frequency multipliers is composed of a [[6DK6]] pentode | |||
driving an LC resonator tuned to 5 MHZ, 10 MHZ, and 50 MHz. | |||
The 180A manual suggests an interesting procedure for calibrating the OCXO, | |||
by attaching a small antenna to deliberately interfere with the national time standard broadcast, | by attaching a small antenna to deliberately interfere with the national time standard broadcast, | ||
and observing the interference with a communication receiver. | and observing the interference with a communication receiver. | ||