I've gotten tired of searching flying fields for my rockets. This summer I decided to get a radio beacon to help me locate them. I've written this up because it is a frequently asked question on rec.models.rockets. I searched the internet for ideas, and what I found fell into these categories:
    Low power, FM broadcast band
    These transmitters use very low power on the FM broadcast band. Typical reception distances of 1/4 - 1/2 mile are claimed.

    Wildlife Locators
    Specialized devices with ranges of 5 to 10 miles. I haven't purchased one yet, however

    Amateur Radio
    Most handheld ham radios are larger and heavier than most of my rockets will handle. However, I've found a number of much smaller devices intended for unlicensed radio uses, and I'm using those.

FM Broadcast

The device pictured to the right is a Radio Shack FM Wireless Mike module kit, Cat. No. 28-4030. These can be be found on sale for around $10. I got a few hundred feet out of it, when listening on a Sony Walkman. Greater distances can be covered when using a better receiver and antenna.

Wildlife Locators

One of the fliers at the local Tripoli launches has used falconry locators to keep an eye on his 7,000' flights. He has two: one from L.L. Electronics that will handle high shock loads, and the other from Merlin Systems. Some of these claimed to be trackable from 5 - 10 miles! This is what I wanted, but the recievers are expensive ($400 - $600). I was successful at picking up beacons from Walston on 218.180 mhz and the Merlin on 216.045 mhz using my amateur radio handheld transceiver! So there may be cheaper alternatives. There are quite a few companies selling the wildlife locators; most don't have prices on the net. I also haven't figured out which FCC rules cover them (possibly Part 15 - unlicensed devices which have power output limitations).

Here are the companies I found selling wildlife locators:

More Radio Telemetry Equipment Suppliers.

Ham Radio

I decided to pursue the amateur radio path, and obtained a amateur radio technician license. My call sign is KC0IYT. The ham radio community does a lot of fox hunting for sport, and to track down defective personalities who have nothing better to do than make a nuisance of themselves on the band. The book Homing In is a good starting place for information about fox hunting. It's author runs the HOMING IN -- Radio Direction Finding web site and has a RDF FAQ.

I've obtained modules or kits for three different beacons:

  1. Radio Shack
  2. Linx
  3. Ramsey
In my searches I discovered the Programmin' By Pete Free Projects Page. His pages are worth reading (whever they are now, his pages appear to be gone) - he's got some great projects! His locator becons page talks about two transmitters: Radio Shack and Radiometrics. Both of my locators and receiver antenna are based on Pete's designs.

The Radiometrics transmitter is about $20. Unfortunately, it's sole US dealer, Lemos International, has a large 'small order' charge for orders under $250. I decided to keep looking.

Radio Shack 433.92 transmitter.
This is the same device that you can see over on the Programmin' By Pete Free Projects Page. It was Radio Shack part #900-6896 and cost $10. Radio Shack appears to have discontinued this product. It's power output is listed as 8mw and has an operating voltage range from about 3v to 15v. I'm driving it with a 12-volt "N" cell and a 555 timer that runs it at about 1hz.

I am able to receive from this device with my Yaesu VX-1 amateur radio HT in "FM-Wide" mode.

You can also purchase this module mounted on a circuit board for about $50 from Oliver's Rocket Stuff.


Linx Technologies

I discovered Linx Technologies using AltaVista; I believe I was searching on the "TX-1" part number. Oddly enough, I just noticed that the PbP page does refer to a 'Linx FM transmitter'. They sell three series of transmitters:

    HC
    A 900mhz module
    LC
    A tiny surface mount device, available in 315mhz, 418mhz and 433mhz varieties.
    RM
    Appears to be similar to the HC, and is also available in 315mhz, 418mhz and 433mhz varieties.

All of these devices can be purchased in small quantities from RF Digital and Digi-Key with only the usual mail order shipping and handling charge. I wanted the RM series devices, but they were unavailable, so instead I purchased the 433mhz LC series transmitter. I picked that frequency because it is in the 70cm amateur radio band (420-450mhz).

The Linx LC's data sheet specifies the output to be +8dbm (6.4mW) into 50 ohms when powered at it's maximum rated voltage of +5v. The datasheet describes them as being capable of complying with FCC Part 15 (unlicensed low-power devices) but suggests allowing space to attenuate the signal. Well, I have a ham license and I'd like the power to get distance.

There are now two amplifiers available for this device. I purchased a BBA-519-A power amplifier that is supposed to amplify this device to 50mw.

The LC is a SMD device. It's surface mount, with pads on the bottom and a small channel up the side to make soldering easier for prototyping and hobbiests like me. I etched a small circuit board (using the Radio Shack board etching kit) and was able, with some difficulty, to solder the device to it. I built the PbP morse code IDer from a Microchip PIC 16F84 and Yagi.

I've done a little bit of experimentation with each of these; with the Linx transmitter and antenna in the open air (on my apartment balcony) I get at several thousand feet out of it. I set my radio to FM-Wide mode and tuned around a bit until I got the best signal at 433.865MHZ. I was then able to take a quarter to a half mile walk and still pick up the transmitter. This was with the transmitter on it's side the the grass of one of the sod farms I fly from.

I find the biggest problem with the beacon is physical destruction. On most of the flights, the radio has gotten dammaged one way or another and has stopped transmitting. Even on landings that didn't hurt the rocket at all, the battery was ripped away. Since the above picture was taken, I've replaced the Micochip IDer with an Atmel AVR IDer and built a solid mounting case for it out of 29mm tubing and a 29mm coupler.

I have a second beacon built on a 3/4-inch wide circuit board (it fits in a BT-20 tube). This beacon includes the BA-519 power amplifier and has a PIC (16F84) mounted on one board. I planned to power it with a small 12v battery, however I discovered that it only lasted a few minutes! Changing some resistor values and using a fresh battery might help; however, I've been powering it with a 9V battery.


Ramsey Electronics Model Rocket TRacking and Telemetry Transmitter Kit
The Ramsey MR6 is a simple 144mhz transmitter with fairly limited range. It is an all-surface mount kit, which can be challenging to assemble. The carrier can be modulated, but I haven't tried that yet.


Homebrew
There are a number of amateur radio books that describe how to build radios for the Amateur band. The ARRL Handbook discusses theory and provides some examples. However, I've found Experimental Methods in RF Design (ISBN: 0-87259-879-9) to have a wealth of information.

I've found these sites to have interesting information on homebrew radios:



Amateur TV
Why stop at a simple beep? Why not transmit video?!


Finally, here are some other links that might be useful:


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Last updated: [ July 9, 2003 ] Revision # [ 3 ]
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