PULSE COUNTERS ARE usually used just for measuring pulses. When combined with a microwave frequency counter's inhibit input and a pulse generator, however, time-varying signals can be accurately characterized. Such characterization is the focus of a four-page white paper from Phase Matrix, Inc. (San Jose, CA) titled, "Measuring Time Varying Microwave Signals."
This paper focuses on the company's 1230A/1231A VXI microwave pulse/CW counters. The inhibit input can be used to define the time interval in which a frequency measurement is to be made. The frequency versus time characteristics of the repetitive time-varying signals can then be measured. Examples include the output of voltage-controlled oscillators (VCOs), chirped radars, or the pulling of microwave signals due to pulse modulation.
In addition to detailing the setup for making the profile measurement, the note provides a setup diagram. Though simple, this setup vows to fully characterize time-varying microwave frequencies both quickly and accurately. The application note also offers tips. When setting the pulse width to the desired sample width, for example, as wide a window as possible should be used.
The pulse generator should be set to trigger externally. It is best to set the delay to the minimum value. To move the measurement window to the next desired position, the delay setting of the 1911A is increased after the measurement at minimum delay is taken. The measurement window is actually generated by the 1911A pulse generator. To measure frequency versus time, it can be moved through the signal under test.
Phase Matrix, Inc., 109 Bonaventura Dr., San Jose, CA 95134; (408) 428-1000, FAX: (408) 428-1500, Internet: www.phasematrix.com