Scalar Network Analyzer
The Minima is my fourth transceiver build. I built three Bitx versions and a few other small receivers and transmitters. I always seem to have problems with my filters, bandpass and crystal filters. Also, I usually discover that in one or more circuits I build I make a mistake and use the wrong component value and the circuit only performs less than it was supposed to. I discovered what instrument I needed to solve all my problem areas, it's called a "Scalar Network Analyzer". With this tool you could draw a plot of your filters, characterize crystals, and analyze circuits for return loss. But they cost a lot of money. But then, after building a W7ZOI wattmeter, a schematic I found in the book "EMRFD", I guy on the EMRFD Yahoo group, told me to check out the PHSNA Yahoo group. The PHSNA stands for the "poor man's scalar network analyzer." This tool can be built for less than $75. including the wattmeter. It uses an Arduino Uno for the brains, an AD9850/51 for the vfo and a small board to connect it all. A brilliant programming guy wrote a Windows based program to control it all and it will do amazing things. You can sweep a filter from 1 hz steps to 1 mhz steps, whatever you wish, and plot it out to an excel graph. It measures SWR, it measures Return loss, and the part I like best, it sweeps a crystal and measures its resonant frequency, its motional capacitance, its motional inductance, its series resistance, and its "Q". With a simple test fixture to hold the crystal, you can measure and characterize a hundred crystals in about thirty minutes and plot them on an excel graph.
I built it in two evenings, and now I'm having a ball redoing all my transceivers to optimize performance.