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Field Equipment Setup

The components for field observation of natural VLF radio are:

1. INSPIRE VLF3 receiver with stereo cable
2. Portable cassette tape recorder with headphones
3. Whip antenna
4. Ground stake

The INSPIRE VLF3 receiver was designed by Michael Mideke, one of the founders of INSPIRE, and modified by John Kohus, a long-time supporter of INSPIRE and the provider of the kits. The receiver is designed to receive radio waves in the 0-10 kHz range. The receiver has jacks for plugs from the cassette recorder and a separate microphone. (It also has an audio output jack and volume control that will send the signal directly to headphones without the need for a recorder.) A switch selects between receiver output on both stereo channels and receiver output on one channel and voice (via the microphone) on the other channel.

Portable cassette recorders that work well with the INSPIRE VLF3 receiver have the following features:

• Automatic Gain Control (AGC or ALC) can be disabled (AGC ON/OFF switch)
• Voice operation can be disabled (VOX ON/OFF switch) if voice operation is a feature
• Stereo or mono recorder
• Built-in microphone or separate microphone
• MIC input jack

Minidisc recorders will also work. You need to make sure there is an input into the recorder that you can use from your receiver, a miniplug, for example. Many minidisk recorders have USB input only and that will not work. A "line input" will work for the input from the receiver (a "mic" input is not required).

The simplest antenna for the INSPIRE VLF3 receiver is a whip antenna. A good antenna is a 6-foot telescoping whip antenna available from Radio Shack (Cat. No. 270-1408A).

The ground connection for the receiver can take many forms. The easiest is to connect the ground terminal on the receiver to a piece of metal pipe driven into the ground. At Chaffey, the machine shop made a base plate from 1/4" steel about 30 cm square. This plate has four holes drilled in it so that it can be staked down with spikes for stable support and good ground connection. The receiver is attached to a piece of EMT conduit that fits into a sleeve welded onto the center of the top of the base plate. In the past we have also used a piece of EMT conduit driven directly inot the ground with the receiver mounted to the conduit.

To set up the equipment in the field:

1. Connect the ground stake and antenna to their respective terminals
2. Plug the stereo cable into the "RCVR" jack
3. Plug the other end of the cable into the microphone jack on the recorder
4. Plug the headphones into the headphone jack on the recorder
5. Insert a data tape into the recorder, press "Pause" and "Record"
6. Turn the receiver on
7. At this point you should hear sferics (static) and probably some 60 hertz hum
8. Use the "Pause" switch to control tape movement through the recorder

- Bill Pine
Co-Founder Emeritus, The INSPIRE Project, Inc.