Space Weather Monitors- Stanford SOLAR Center







SID Monitors
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Why a new antenna design?

The original AAVSO antenna design accompaning their Gyrator II circuit was fussy and tended to oscillate. It was also frustratingly difficult to tune. To avoid the problems, we switched to the MAX 275 as a bandpass filter tuned to the desired frequency we wanted to mintor. with a simple antenna design.. With a handful of metal film resistors, it has a very steady frequency response and a nice high-Q, about 100 hz from the centre frequency. All of the tuning is on a daughter card that plugs into the main board. The frequency board has only two 10K pots that we pre-set the frequency before shipping the unit to the school (or radio club, or person, etc.). If an area proves difficult to monitor at one particular frequency then we can ship other frequency boards tuned to other frequencies to try. These modules are simple to install by the user and do not require any external equipment such as an oscilloscope or DMM.

There was some initial concern about the small wire low-Q loop. But we did some tests and noticed a huge difference in the 14 AWG tuned-loop vs. the 26 AWG non-tuned loop. When the 14 AWG wire loop was not tuned, the number of turns of the wire made the difference in how well we picked up the VLF signal.

With our 14 AWG tuned antenna and the SID monitor with the 26 AWG untuned antenna, our performance is quite good.

We expect our students receiving SID monitors to contruct their own antenna, and we provide information on building several inexpensive models. Given the wide variation in materials used, we needed the SID monitor to work regardless how the students assembled their antenna. So we came up with our basic design. However, other designs are certainly possible and we welcome suggestions for improved low-cost antennae.

©2015 by Stanford SOLAR Center