[600MRG] Sampling Oscilloscope

[Frank Lotito]

Some time ago on various bulletin boards I posted an inquiry on "how to properly use a sampling oscilloscope to view the rise and fall times of a CW keyed transmitter, or to monitor the envelope waveform of an amplitude modulated signal, e.g., PSK-31 or SSB." I was experiencing aliasing problems and did not know how to correct it. I lamented that my last "analog scope" had a CRT on its last leg. I never did get an answer to my problem. I found my answer, as simple as reading "the whole instruction manual!" The following applies to both my Tektronix TDS-120, and my B&K 2530 sampling scopes, and speculating other "modern sampling type" oscilloscopes. On the front panel, find and press the button that is titled ACQUIRE. Then find and select the options PEAK DETECT, and if available on your sampling scope, REAL TIME mode. Set up the scope for EXTERNAL TRIGGER and use the keying device or audio tone to key the transmitter. Voila! No more aliasing! Both my scope's manuals contain a chart on the relationship between sweep speed and the maximum input frequency to avoid aliasing in the normal sampling mode (non-Peak Detect mode.) No doubt the significance of this chart did not ring a bell when I first obtained these scopes. Shame on me.  73 Frank Lotito  K3DZ / WH2XHA