7T11

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The Tektronix 7T11 is a time base plug-in for the 7000-series scopes. It was specially designed to build a sampling oscilloscope configuration together with the 7S11 sampler and one of the sampling head plug-ins.

Because the 7T11 and 7S11 have direct interconnections side by side, they work also in slow mainframes. The 7T11 supports up to two 7S11 for dual channel or X–Y operation.

Key Specifications

Sweep rate	50 μs/Div to 10 ps/div, variable speed-up ×2.5 on all ranges (i.e. down to 4 ps/Div)
Trigger bandwidth	500 MHz internal, 1 GHz from external trigger sources, 14 GHz in HF Sync mode
Trigger sensitivity	×1 internal: 125 mV to 1 V_p-p, 5 kHz to 500 MHz ×10 internal: 12.5 mV to 1 V_p-p, 5 kHz to 50 MHz ×1 external 50 Ω: 12.5 mV to 2 V_p-p, DC to 1 GHz ×10 external 50 Ω: 1.25 mV to 2 V_p-p, 1 kHz to 50 MHz ×1 external 1 MΩ: 12.5 mV to 2 V_p-p, DC to 100 MHz ×10 external 1 MΩ: 1.25 mV to 2 V_p-p, 1 kHz to 50 MHz HF Sync mode: 10 mV to 500 mV_p-p @ 1 GHz, 200 mV to 500 mV_p-p @ 12.4 GHz
Input impedance (Trig Input)	selectable, 1 MΩ / 50 Ω
Max. input	1 MΩ: 100 V DC or P-P to 1 kHz, above 1 KHz derate at -6 dB/octave down to 5 V_p-p 50 Ω: 2 V (DC + peak AC)
Jitter	Sequential mode:< 10 ps at fastest sweep, < 0.4 Div otherwise Random mode: < 30 ps at fastest sweep, 1 Div otherwise HF Sync mode: < 20 ps with 12.4 GHz, 200 mV_p-p signal

Operation

Due its sampling principle (so called undersampling), the 7T11 can only be used on repetitive signals and samples are always taken from signal portions delayed from the trigger event. This delay is adjustable on the front panel to select the portion of interest. At the three lowest sweep ranges, the 7T11 changes from undersampling to real-time sampling.

Due the high bandwidth of the sampling heads, there is no Y-delay-line in the heads, so the 7T11 needs an external pre-trigger if there are random, high-jitter signals or if the original signal triggered onto needs to be observed. In the special case of a periodic signal with low jitter, a random sampling mode can be used so that the signal triggered on can be observed. In this case, an internal PLL locks to the signal and generates an internal pre-trigger.

To display the triggering event without slowing the sweep rate enough to see the next pulse, the input signal can be delayed by using the 7M11 analog delay line plug-in.

X-Y operation is possible up to 14 GHz if one 7S11 resides in the A-horizontal slot of a 4-slot mainframe.

Manual or external sweep is possible to connect a slow pen plotter.

Additionally, there is an internal 200 MHz tunnel diode oscillator, which can be synchronized from external signals up to 14 GHz. This oscillator in turn drives a 10 MHz tunnel diode oscillator that provides the internal trigger signal.

The 7T11 uses a BSM connector for pulse output on the front panel.

Note the 7T11 does not work in a 7854 mixed-mode scope while the updated 7T11A does. A 7T11 can be field upgraded to 7T11A.

Links

Tekscope Vol. 2 No. 1, Feb 1970: Basic Sampling - Introduction of 7T11, 7S11 and 7M11
Tekscope Vol. 5 No. 2, Mar-Apr 1973: Servicing the 7T11 Trigger Circuit
Tekscope Vol. 5 No. 3, May-Jun 1973: Servicing the 7T11 Sweep Circuit

Pictures

7T11 front
7T11 side connection
7T11A and 7S11 with S-4 in a 7613 mainframe displaying a 1 GHz sine
7T11A front
Right view
Left view
Trigger board in a 7T11
Back side of trigger board
Timing board in a 7T11
Tunnel Diode CR28 in a 7T11
Tunnel Diode CR28 in a 7T11A
Arming circuit detail (tunnel diodes CR142, CR152)

Measurements

noisy 8 GHz taken with 7T11 and 7S11 + S-6 in a 7904
7S11, 7T11, S-4 displaying a 1 GHz sine (normal mode)
7S11, 7T11, S-4 displaying a 1 GHz sine (smooth mode)
7S11, 7T11, S-4 displaying a 1 GHz sine (smooth mode, variable-persistence storage display of a 7613 mainframe)
Rackmount 7633 with two 7S11 and a 7T11 displaying a 2 GHz sinewave