N2PK VNA is a "....homebrew vector network analyzer (VNA) for transmission and reflection measurements from 0.05 to 60 MHz., with optional narrowband extensions for measurements through 500 MHz. This VNA requires an IBM compatible PC and uses custom software......" , as is described in the web article.
Paul Kiciak, N2PK is the author of this inexpensive, Lab quality tool with a high accuracy and an excellent dynamic range. Many people have built one of its versions. In 2007, I read first articles in established Yahoo group (has more than 1200 members today - 2013). Because of big interest, I started with building, too.
First was original Paul´s version working under DOS (in the middle). Next one was LPT version used ver.4 of VE3IVM board (on the right side). Later I did USB version, too (on the left side).