WB6EYV MicroHunt Foxhunting Transmitter

08/14/2006 - Something that will make for a much more difficult hunt, even in a small area, is to use a very short tone burst every six seconds or so. This is now available as a timing option for the MicroHunt transmitters. With this option, we can program the callsign to be given in multiples of one minute up to a maximum of ten minutes (FCC regulations require the callsign to be given no longer than every ten minutes.) With this option, the transmitter will transmit a tone burst of approximately .25 seconds, and then shut off. I'll be playing around to find out how I can make that burst and still have a working signal. If you are interested in a very challenging advanced hunt, email me and we can work out the desired timing together. This is NOT recommended for beginners since we want to encourage, not discourage, new hunters.

General Information

The Microhunt transmitter is an assembled and tested miniature 50 mW MCW FM transmitter and controller module designed primarily for foxhunting and ARDF (Amateur Radio Direction Finding) on the 2M Amateur Radio ham band. These transmitters are set up to turn on when power is applied and transmission will continue until either the battery dies or the unit is turned off. Powered by a 9V battery, the useful life will range from perhaps 12 hours up to 60+ hours depending on the duty cycle. Because it is used on the ham bands, an amateur radio license is required to operate this transmitter.

Other applications include being used as a beacon for radio controlled aircraft, high altitude balloons, and model rocketry. With the addition of a small speaker, these units have also been used as "sound flags" to allow blind people to use direction finding techniques to get close, and then use their hearing in the same way we use our eyes to find them.

A common question is how far can the 50 mW signal be heard? The answer depends on the antenna and terrain. They have been heard as far as 400 miles (high altitude balloon beacon), 25 miles from the top of a mountain, about 5 miles locally on relatively flat terrain, and maybe 10 feet with a dummy load. For a small venue (several hundred square meters), a rubber ducky will work just fine. A better antenna is needed for longer ranges. For ARDF practice, I use an omni-directional crossed dipole antenna (http://www.west.net/~jay/turnstile.html), and the range on reasonably flat terrain is about five miles. A Yagi or Quad antenna will give more range if it is needed/desired in a specific direction. (The WB2HOL Tape Measure Beam works very well here.)

The MicroHunt transmitter board measures 0.7 x 1.3 inches, and all components (except the PIC crystal) are surface mount. The souce code is not available.

A call sign is required for purchase which is permanently encoded into the module.

Standard Frequencies

Standard frequencies that have been tested include:

The output frequencies are set with a combination of jumpers and the crystal frequency. 146.565 is a standard transmitter hunting frequency here in the US and the crystal is 18.000 MHz. In theory, any frequency can be output ... in practice there are some limitations. It is somewhat important in selecting the combination of jumpers and crystal frequency to minimize jitter to keep the noise in the output at an acceptable level. Please email me if you need another frequency.

Standard timings

Standard available timings are:

Standard Transmitter Identifications

The standard CW transmitter Identifications used are:

The standard transmit sequence is to send the transmitter ID followed by the callsign. After the off time has elapsed, the cycle repeats. The standard identification is sent at approximately 10 WPM followed by your callsign at approximately 20 WPM. Other messages may be available on special request.

Note that I allow 5 seconds for the sending the callsign, so the transmitter ID will transmit for the ontime less the 5 seconds required for sending the callsign.

Special Training/Demonstration Transmitter

Additionally, a special ARDF training mode can be ordered instead of the standard timing and transmitter ID. This special training mode transmits continuously, but will transmit the following sequence:

Ordering information

Single Units - $75.00 each

Set of 5 Units - $325.00 per set ($65.00 each)

Postage - $5.25 USPS Priority Delivery w/Delivery Confirmation

Before I can ship out the module, I will need to know:

Delivery usually runs about one week after receipt of payment to get the unit(s) built, programmed, and tested. Payment can be via check, money order, or PayPal.

Contact me for more information or to order at:

Note: Because an amateur radio license is required to legally use these transmitters, these units will ONLY be sold to licensed hams.

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This page updated on Thursday, February 11, 2010 at 09:30 PDT