Below i will explain how is possible to use a digital oscilloscope in order to replace HP182T cathodic display used by HP8558 spectrum analyzer. Same methode can be used for other old spectrum analyzer with Vertical/Horizontal outputs. I choose Y-T mode because the results in X-Y mode (CH1-Horizontal and CH2-Vertical, internal time base disabled) are poor due slow response of DS2072.

Advantage: measurement results can be exported in digital format, better linearity and precision.

1. Available signal outputs from HP182T/HP8558

Vertical output: low DC amplitude according "dB" strength detected by SA (aprox. 800mV for full scale).
Horizontal output: 10V amplitude (+/-5V), sawtooth waveform, time duration according SA sweep speed. Oscillogram of SA sweeping at 5 msec.
Penlift (blanking) output:
15V amplitude, logic level High during CRT blanking trace. Oscillograme of Penlift vs. Horizontal output.

2. Connection between HP8558 and Rigol DS2072
Aux. A
(vertical out) connected to Y Channel 1 DC input.
Aux. B (Horizontal out) connectd to External Trigger DC input.
Directly BNC-BNC coaxial cables were used.

3. Oscilloscope Settings
Y1 channel: sensitivity 100mV/division.
Trigger input switched to External Trigger.
Time Base - basically internal time base of oscilloscope must to be same with SA. But we have a small problem...DS2072 has 14 horizontal division as against 10 horizontal division of HP182 CRT display.
Let's see what happen with same settings of time base.
In the center is a RF carrier applied to SA input. In the right side is a CRT "blanking" signal. On oscilloscope display is possible to see more than one sweep of SA...

Spectrum analyzer carrier manual shifted at the begin of CRT display. Double sweep can be observed. Exactly 10 divisions can be used on DS2072 display. In this way, MHz/div Scale remain same.

14 division / 10 division = 1,4 times slower.
So, when SA sweeps at 2msec, oscilloscope must be set at 1,430msec (2msec/1,4=1,428msec). Fine adjustments can be done using Horizontal Position.
In this case, MHz/Division Scale is affected! One horizontal division represent SA MHz/div. divided by 1,4.
Example: SA set at 10MHz/division. Oscilloscope indication will be 7.15MHz/division.

Vertical dB indication no need to be corrected. Same 8 divisions are used by HP182T and DS2072.
HP182T CRT example.

RF carrier at the begin and end of 14 division display. Entire display is used, "retrace" effect phenomenon has disappeared.







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