Cutdown Method via remote signals

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Permalink Reply by Howard Brooks on March 8, 2010 at 4:04pm

Dear Kenneth,

Most active cutdowns utilize amateur radio frequencies requiring a licensed radio operator to control the radios. Here is a link to a simple cutdown device developed by the Edge of Space Sciences group in eastern Colorado:

http://www.eoss.org/hardware/w5vsi_beacon.htm

Hope this helps,
Howard

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Permalink Reply by Kenneth Schnautz on March 8, 2010 at 4:29pm

Thanks, Howard.

I found this site as well a few weeks ago and was hoping to find out how it works (a non-technical description). I assume the signal is sent from a device on the ground, and the orange box (containing the Alinco DJ-C1) somehow receives the signal and actuates a cutdown procedure?

Are the products used available from a retailer? I'd like to attempt this method, but I'd like to know the basics of what is going on before I go any further into this method.

Thanks again.
Ken

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Permalink Reply by Howard Brooks on March 9, 2010 at 3:30pm

Dear Ken,

You might want to contact Jason Krueger and see if StratoStar is planning to build an off-the-shelf command controllable cutdown device. I know they have worked on timed cutdown devices to terminate flights that go on for too long.

The EOSS device is a homebuilt system. Some of the details are on the webpage in the schematic and basic program code.

The Alinco DJ-C1 is a very small radio transceiver that operates on the 2-meter band (144 - 148 MHz). The cutdown process is accomplished with a custom made electronics board (see the schematic on the EOSS page) that listens to the output from the Alinco for the proper DTMF(Dual Tone Multi-Frequency) command sequence. The DTMF tones are two sinusoidal tones of differing frequencies that are transmitted simultaneously (used in most telephone communication).

Looking at the schematic, you can see that the audio output from the radio is connected to a chip CD22203 that is a DTMF converter. The output of the CD22203 is fed into a Basic Stamp I that uses the basic code, also on the website, to process all incoming traffic until it hears the proper cut-off command sequence. The output on pins 12 and 13 of the Basic Stamp I is fed into a simple transistor amplifier circuit that sends the power signal to the relays that will allow a current to flow through a wire and burn through the payload string cutting the balloon away. Please keep in mind that there are extra elements in the circuit and the software to allow the radio to also serve as a beacon for direction finding purposes.

In addition to what is shown, you will need a transmit radio on the ground that can broadcast at the proper frequency the required cutdown command. Depending on the transmitter, you may need a special DTMF tone producer. Of course, you will also need to have some sort of cutting device, typically a high resistance wire wrapped around the payload string that draws a large current from a set of batteries that are dedicated to the cutdown mechanism.

One major problem could be locating the decoder chip described by the EOSS team. You may have to use a different decoder unit and there are many on the market. Some are offered for Radio Controlled aircraft purposes.

To summarize, a command based cutdown system needs a licensed amateur radio operator, two radios, a code converter, and a payload string cutting device. When the time comes to cutdown, the radio operator must send the proper code sequence to the receiver that flies between the balloon and the parachute. The receiver must be connected to decoding electronics that "hear" the proper command and activate the cutdown device.

Hope this helps a little.

Howard

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Permalink Reply by Kenneth Schnautz on March 9, 2010 at 3:37pm

Thanks for this. It helps a lot and I look towards incorporating this method into our High Altitude Ballooning projects.
Ken

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