Spectrum Analyzer

This is a spectrum analyzer I built. This test instrument is based on the "Poor Man's Spectrum Analyzer" originally designed by Murray Barlowe, WA2PZO, and presented in the September 1986 issue of HAM RADIO magazine. I purchased the VHF "cable ready" tuner and the VHF/UHF tuner (the VHF section is not used) from Science Workshop (WA2PZO) and placed them in a single enclosure shown in the photo. I added a sawtooth generator for the frequency sweep described by Joe Carr in the September 1987 issue of HAM Radio magazine. The spectrum analyzer uses an oscilloscope for the display and can display the spectrum from 1 to 900 MHz in two ranges. The resolution is selectable to be 250, 56 or 15 kHz. A spectrum trace of the commercial FM band here in Huntsville from the oscilloscope is shown in the figure below.

I added an AFC so I could use this instrument as an FM radio. There is an AFC on/off switch at the top center of the front and a volume control on the right. I wanted to add other features such as a calibrated display (amplitude and frequency), programmable start and stop frequencies, and the capability to plot the spectrum display. To do this, I developed an interface to my personal computer. When I completed this design, I published it in the premier issue of Communications Quarterly magazine shown below. The title of the article is "Interface Your Computer to the 'Poor Man's Spectrum Analyzer'." The first page of the article is also shown below. I have received much interest in the article, some from overseas including New Zealand and Brazil.

When the article was published, there was an error introduced into Figure 4. One person who called me found the error. The corrected schematic is shown below. The error involves pins 8 and 12 on U4C and U4D, respectively. Those pins go to the B side of the edge connector, pin 13.

Since then, WA2PZO has republished my article in his own publication, " Build Your Own Spectrum Analyzer", shown below.

If you would like to order the book, tuners, and other parts to build a spectrum analyzer like mine, click on the link below to visit the website of Science Workshop.

Science Workshop