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 Model radio tracker

The device is really tiny. It weighs just 1.5 grams
This is a 3X magnified size picture showing the locator
(left) and a battery (center) compared to a match (right).
The battery holder is the small tube on the bottom of the locator.

Description:This locator is a tiny radio transmitter designed to help the retrieval of free flight models in windy days, with strong thermal activity and whenever the model is difficult to find after landing. The tracker, installed on the model, will be transmitting its signal for days, being promptly locatable through a hand-held receiver. It is crystal controlled, and works in VHF band emitting an unmodulated impulsive carrier wave (CW). Through this smart technique, the signal is periodically transmitted just for a short time (about 1/20th second every second) and this yields a very long battery duration. Also, the absence of modulation results in a very narrow bandwidth and no spurious frequencies generation.

Receiver requirements: A good VHF receiver, scanner or transceiver is needed. Probably, the cheapest solution is a ham-band (radio-amateur) transceiver. A wide band type is not required but the covered frequency range should be located within 138,..,174 MHz. A 5 KHz tuning step and the 'squelch' function are required too. A slide indicator of the received field strength may be very helpful. A number of very popular models is available from YAESU, CTE, iCOM, KENWOOD and many else. The YAESU FT-23, CTE CT-145/170/180, iCOM iC2E models, can be mentioned just as instance, and all of them will work very well for radio-tracking.

Positioning the tracker: The fuselage should be provided with a small cavity to easily insert and remove the tracker. There are no switches: to turn the tracker on, the battery has to be inserted into the battery-holder, which is located on the bottom of the printed circuit board.
The tracker should be installed carefully with the antenna straight and vertical, coming out of the upper side of the fuselage: this is essential to have a good propagation when the model is placed on the ground. Be aware that a bent, slanting, or horizontal antenna wire, may result in a poor ground range. Avoid positioning the tracker very close to metal parts of the model. Also, the antenna should not be lain into carbon tubes or tail booms, since this material may consistently damp the emitted signal.

Tuning-in the receiver: Tune-in the receiver on the exact frequency of the tracker, then completely turn the receiver 'squelch' knob backwards to its 'off' position: this will temporarily disable the 'squelch' function and only the typical ground noise (no-signal noise) will be heard. Then, adjust the 'volume' knob on the receiver around the middle position and turn the tracker on, by inserting the battery into its holder. If everything is working, short and regular pulses should be heard on the receiver and this is the signal which will be employed to track and retrieve the model. Adjust the 'volume' knob as desired and accurately turn the 'squelch' knob up to the exact point where the ground noise disappears: this way, the signal 'breaks' the squelch and the pulses will sound like short and clear knocks. It should be noticed that, although this method makes it easier to listen to the pulses, the squelch may tend, in some receivers, to cut-off a very weak signal and, for this reason, it should be used carefully in order not to reduce the range of the whole system.

Range: the VHF band propagation takes place mainly in straight line, and this yields excellent directional properties to these wavelengths. In addition, the VHF field strength is considerably affected both by the ground and the shape of its surface, and by the presence of possible obstacles. As in any radio wave point-to-point connection, the maximum reachable distance (range) significantly depends on the receiver sensitivity and on the gain of the receiving antenna. With this tracker and a good hand-held transceiver with the short rubber antenna supplied with it, the signal of a flying model will be received from many Kilometers, and the ground range will be of about  500/700 meters. The range can be increased up to 10/15 Kilometers in flight and 1/1.5 Kilometers on the ground by simply providing the receiver with a good 2 meter band antenna (50 cm. long or more). With a good multi-element directional antenna mounted on a short pole (i.e. HB9E type, 6 dB gain, 2 telescopic and foldable elements), considerably longer distances may be reached.

Battery duration: the micro transmitter mounts a lithium battery (BR435), having a typical duration of more than a week in safety conditions, which ensures a good margin of time to search the model, should the retrieval take time for any reason. These batteries are also used in electronic fish floats and then available in sport fishing shops.

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