Things have changed since the Knight Kit Grid Dip Oscillator days. The Adelaide Hills Amateur Radio Society offers the parts for VK5JST’s Aerial Analyser at about half the price of getting one from MFJ or elsewhere. It is a ‘collection of parts’ and not a kit! The circuit board is nice but not silk screened with parts placement identifications so you have to use the board layout provided in the manual to get the right parts in the right places. There is no surface mount stuff so the soldering isn’t that much of an issue.
The Aerial Analyser is an hf oscillator that feeds an impedance bridge. That outputs voltages for the oscillator, a reference 50 ohm resistance, and the load for analysis by a PICAXE microcontroller. That chip is part of an educational effort for electronic projects such as robots or interactive devices. It is cheap (~$10 for the one in the analyser). There are all sorts of devices, starter kits, and support for it. Programming is simplified as much of the low level stuff is provided in firmware and accessed by a BASIC like interpreter. It appears to be ideally suited to VK5JST’s device.
One indicator of a good design is what people do with it. PA0FRI has a good rundown on his ideas to provide better oscillator buffering. A number of folks have modified the code to add L/C calculations or other things.
This sort of project can be a very good self taught lab course. You can get into the oscillator circuit itself, the calculation of impedance from the bridge measurements, issues of precision and accuracy in analog to digital conversion, natural number arithmetic for complex variables, and all sorts of other fun topics.
more later!
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