Rainbow Antenna Analyzer
A Low-Cost, Automated and Graphical Way to Determine Antenna Performance
George Heron, N2APB n2apb@amsat.org
Joe Everhart, N2CX n2cx@voicenet.com
Clark Fishman, WA2UNN wa2unn@nac.net
The Rainbow Antenna Analyzer is a small and inexpensive measurement device designed to determine antenna performance across the amateur bands through use of automatically collected SWR readings.
A very low power transmitter is swept across selected frequencies by a microcontroller, and the transmitter's signal is routed through an absorptive SWR bridge to an antenna system (feedline and radiator). These match indications are input to the microcontroller which retains the corresponding frequency and SWR readings throughout the measurement period.
During this measurement period, the microcontroller rapidly displays the individual frequency and SWR values by means of colorful LEDs and bar graph array. When all SWR readings are made, the microcontroller displays the relative frequencies of minimum SWR, thus indicating antenna resonances.
Frequency and SWR data may be downloaded to a PC optionally attached to the Rainbow Analyzer via an RS-232 serial cable. A special software program for the PC collects the data pairs and displays a graphic representation of the antenna performance. The resulting plot clearly shows the resonant frequencies of the antenna system under test. The PC may also be used to remotely control the Analyzer for manual selection of frequencies of interest.
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