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Tektronix TG501
time-mark generator
Tektronix TG501

Produced from 1974 to 1995

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix TG501 is a time-mark generator plug-in for the TM500 system.

There is also a TG501A.

Note the output must be terminated into 50 Ω or there may be no signal at all.

Key Specifications

Interval 1 ns to 5 s in 1−2−5 sequence
Timing accuracy Stability 1×10-5, long-term drift 1×10-5 per month (with Option 1, 5×10-7 / 1×10-7 per month)
Error Readout Accuracy 1 digit (±0.1% points), Range to ±7.5%
Amplitude ≥1 V peak on 5 s through 10 ns; ≥750 mVp-p on 5 ns and 2 ns; ≥200 mVp-p on 1 ns (separate output) (all into 50 Ω)
Trigger Output Slaved to marker output from 5 s through 100 ns. Remains at 100 ns for all faster markers
External Reference Input 1 MHz, 5 MHz or 10 MHz; TTL compatible (internally hard wired so output frequencies counted down to 1 MHz)

Rear Interface Signals

Connector Pin Description
Signal Return
28A 27A Marker Out (requires front BNC disconnection)
27B 28B Trigger Out (requires front BNC disconnection)
25A 26A Internal 1 MHz Clock Out (TTL)
24B 25B External Clock Input
26B 22B Data Good (High when BCD data valid)
17A..20A 22B bit 4..1 BCD Display data, MSD
21A..24A 22B bit 4..1 BCD Display data, LSD
16A 22B Fast=Low, Slow=High


The TG501 internally produces a 1 MHz reference clock, either from an internal crystal oscillator, or from an externally supplied frequency.

A 100 MHz VCO is phase-locked to this reference frequency (in fixed-frequency mode) or to the output of a variable 1 MHz astable multivibrator (in variable frequency mode). When the variable oscillator is in use, its frequency is digitally compared to the fixed 1 MHz reference and displayed as a deviation in percent with a pair of LEDs indicating the sign (fast or slow).

A chain of dividers running off the 100 MHz clock provide the selectable output markers.