W7ZOI / K7TAU 50KHz ~ 70 MHz SPECTRUM ANALYZER
by Mike Whitco, KC8OAN
This was quite a project, but certainly worth the effort for experience and learning, as well as to provide a valuable piece of test gear. The original articles run in QST magazine, Aug/Sept 98 are available at the ARRL website at http://www.arrl.org/tis/info/pdf/9808035.pdf and http://www.arrl.org/tis/info/pdf/9809037.pdf (requires Adobe Acrobat Reader). Using pc boards from Kanga US, and Hammond cast aluminum boxes from Digi-Key greatly simplified construction. Below is the interior of the analyzer with the front panel removed.
Here is the outside of the analyzer. Bulkhead BNC connectors are used for external connections, although not really necessary.
Response and sensitivity are excellent (Kudos to Wes and Terry on their excellent design: more info at http://www.bright.net/~kanga/kanga/w7zoi_sa.htm). Below is a shot of a 35 MHz signal (center of the screen) from a Leader LSG-17 RF signal generator, with the zero spur on the left, and 70 MHz 2nd harmonic (greatly reduced) on the right (scope is Tektronix 453).
The Tracking Generator (next 2 photos shown below) is an additional section which is while not necessary, a valuable addition for filter response analysis.
The +15 / -15 volt power supply is a homemade garden variety, using a 7815 positive and a 7915 negative three-terminal regulator.
Recently added (21 June, 2003) is an 8th order second IF crystal filter (shown below), switchable from the front panel (in lieu of the default 300KHz bandwidth filter). This filter design is by WB4RNO and W2EKB, and was obtained from chapter 7 of "Experimental Methods In RF Design".
The next page (CLICK HERE) consists of interior views of the individual sections.