Clifton Laboratories 7236 Clifton Road  Clifton VA 20124 tel: (703) 830 0368 fax: (703) 830 0711

E-mail: Jack.Smith@cliftonlaboratories.com
 

In developing several new kits and examining components, I've made many 2nd and 3rd order intermodulation measurements in June and July (2010). Each measurement takes ten minutes or more, as the intermodulation products are near the instrument noise floor in many cases, thus requiring narrow bandwidth and multiple sweep integration.

After reflection, I decided to automate the measurements so that I can start a complex series of measurements, such as intermodulation performance of an amplifier at various DC supply voltages. Measuring an amplifier at 0.5V intervals between 9 volts and 15 volts supply can easily consume half a day or more. The data then must be transferred from my laboratory notebook to the computer and post-processed in Excel to put it into a form for plotting in Origin.

The figure below is a simplified view of the setup I developed. (Attenuators, filters and some power supplies are omitted from the drawing.)
 

• DC power to the device under test (DUT) is supplied by an HP 6612C power supply which is controlled over the GPIB.
• A sample of the device under test's output signal is provided via a 20 dB directional coupler and is connected to the HP8568B spectrum analyzer's Input 1. The directional coupler output connects to a 20 dB attenuator (not shown) and a band reject filter. The band reject filter extends the spectrum analyzer's dynamic range, permitting accurate measurements of high intercept amplifiers. The band reject filter's output connects to the spectrum analyzer's Input 2.
• To improve the setup's performance floor, the output of each HP8657A signal generator drives a Mini-Circuits ZHL-3A broadband high gain amplifier, with a maximum output of 1 watt. (+30 dBm). Each ZHL-3A connects to a Mini-Circuits 3 dB hybrid combiner through a 12 dB attenuator.
• The power supply voltage, spectrum analyzer and the two signal generators are all controlled by the computer over a GPIB bus with a Prologix USB-GPIB adapter.

I've attempted a program flow chart, but I'm not a professional computer programmer, so I'm sure I've mangled the particular shape to function relationship.