Where's the under-$1k spectrum analyzer?

Contrary to readers' fantasies, instrument manufacturers don't routinely send product samples to editors. Thus, like many engineers, I collect and refurbish older test equipment, some of which eventually works.

I purchased a Systron-Donner model 712/809-1 spectrum analyzer at a surplus store's chip-and-dent sale. According to its crumbling calibration stickers, this 1960's vintage instrument once served at a Federal Aviation Administration site. My analyzer came with a nonfunctional marker generator, intermittent switches, and poorly written service documentation. I'm ready for a replacement.

Secondhand Hewlett-Packard and Tektronix spectrum analyzers of mid-1970's vintage sell for $2000 or more, while analyzer plug-ins for older oscilloscopes languish in the under-$100 range. Most inexpensive heavily used analyzers I've examined work as well as—or as poorly as—my Systron-Donner dinosaur.

I can purchase a brand-new, decently performing dual-trace 100-MHz oscilloscope for under $1000, so where's the under-$1000 spectrum analyzer?

In an effort to find one, I investigated the "Poor Man's Spectrum Analyzer" (PMSA) designed in 1978 by Murray Barlowe (WA2PZO) and sold in modular kit form by Science Workshop (www.science-workshop.com). Barlowe's design replaces the analyzer's display with an oscilloscope and uses a voltage-tuned TV tuner as a frequency-selective "front end."

Although Science Workshop's PMSA kits require assembly, packaging, and calibration, its modules cost under $100 each. The analyzer's ultimate performance, however, depends on the user's construction skills and access to calibration instruments.

When he designed the PMSA, Barlowe didn't enjoy access to many components we take for granted today—logarithmic detector ICs, receivers-on-a-chip, and surface acoustic wave (SAW) filters. Today, a single-chip microcontroller could provide the command, control, and interface functions in an updated PMSA design.

By using firmware control instead of front-panel controls, a designer could substitute electronic devices for expensive switches and pots and replace conventional wires with PCB traces that shorten signal paths. As controls "disappear," holes in a chassis also go away, thus reducing RF leakage and packaging costs.

So, where's the latest under-$1k spectrum analyzer? I'll bet a couple of laid-off engineers are working on it in a garage in Silicon Valley or in a lab over a noodle shop in Taipei. They're tapping the cornucopia of surplus RF components spilling out of defunct telecom companies and are using cheap PCs to test and control their prototype, to capture schematics and lay out PCBs, and to write an all-inclusive, comprehensive user's manual in readable English.

What am I saying? There'll be no manual—if there were, I'd be writing this column as fantasy.