Picture of 433 MHz UHF lost model radio beacon

Here's a simple 433.92 MHz short range radio beacon that may be handy for locating downed R/C planes, lost ballons, model rockets - or perhaps hidden transmitter "fox hunts"! 433.92 MHz is internationally a free band slot, and although only low power transmitters (10-25 mW) are legal, UHF signal punch thru' light vegetation etc is superior to 2.4 GHz microwaves.

It's based around a cheap (~US$5-10) low power (a few mW) Keymark/Spirit-On TXC1 data transmitter, fooled into transmitting audio tones generated by a cheap PICAXE-08M microcontroller. Ranges are up to a km line of sight, dropping to 100-200 metres thru' light vegetation and wooden buildings etc. Compared with flashing lights & beepers, the beauty of a wireless locator relates to all hours convenience & simple direction finding even thru' light vegetation etc. A cheap "sniffer" receiver ( based around a companion RXB1 Keymark receiver module) is shown at => http://www.picaxe.orconhosting.net.nz/433rx.htm

NOTE- keep this simple locator beacon approach in perspective! Do not expect it to locate the likes of your $$$$ FPV (First Person View) model plane downed miles from anywhere in deep woods. For serious locator use, more powerful transmitters & GPS encoding should be considered. These of course can be costly, have higher battery drain and may be tedious to configure .

UPDATE - early 2012: Chinese firm Dorji have recently released some cheap (< US$10 a matched TX/RX pair) ASK 433 MHz data modules that significantly improve this beacon! Their transmitter is particularly appealing, as it's power is boosted to a (legal) 25 mW, giving ranges some 4-5 times greater than the KeyMark/SpiritOn equivalent ! A sensitive UHF scanner can still detect it thru' light vegetation etc to ~500 metres, and LOS (line of sight) several km ! The Dorji receiver, which usefully can also be persuaded as a band monitor, is somewhat more sensitive than the Keymark as well.

Since these Dorji ASK modules have shown themselves clearly superior, more versatile, smaller and far cheaper they're now recommended instead of the Keymark! As circuitry & layout will need to be slightly changed however (see => www.picaxe.orconhosting.net.nz/dorjiask.htm & a Dorji based 433 MHz "sniffer" receiver => www.picaxe.orconhosting.net.nz/dorji-tonerx.jpg ), the Instructable is presently still Keymark module based.

Update -Nov. 2012 : A superior Dorji based tape measure antenna Instructable is now available => www.instructables.com/id/433-MHz-tape-measure-antenna-suits-UHF-transmitte/

Update -Sept 2014: An improved PT4302 engined SpiritOn RXN3-B module is now stocked as Jaycar's ZW3102 receiver. Performance has been found very pleasing, & the versatile supply voltage ( 2.4V-5.5V) is especially welcome. Refer RSSI wiring details under comments at this Instructable end. RECOMMENDED!

manuka (author) 4 months ago

Recently released LoRa™ devices are showing amazing range boosts (~ x10 ) that of regular 433 MHz setups. Yes - even in built up areas &/or vegetation, signal coverage may be 100s of metres rather than 10s !

Although somewhat more costly (US$20 range), for more demanding beacon needs these SX127x based modules are looking a wiser approach. They're easy to drive with a simple PICAXE micro too.

See => http://www.instructables.com/id/Introducing-LoRa-...

manuka (author) 11 months ago

"Sniffer" details for the new ZW3102 ( SpiritOn RXN3-B) module.

manuka (author) 11 months ago

Jaycar's classic ZW-3102 receiver module has recently been upgraded with a new PT-4302 RF IC. The module is still pin for pin compatible with the orginal Keymark one, & performance may even be superior. It pleasingly accepts a supply between 2.4 -5.5V, but the RSSI tap seems not as straight forward. ( Refer picture)

manuka (author) 2 years ago
A Dorji ASK module based Instructable, featuring a 3 element Yagi tape measure antenna, is now available => www.instructables.com/id/433-MHz-tape-measure-antenna-suits-UHF-transmitte/
MichaelR11 year ago

I just found out about the concept of transmitter hunting last week and I am attempting to absorb a lot of information. I was hoping to get a little help from this group. I like the idea of the "fox" hunt but would like to scale it down for kids. I am looking to have the hunt limited to a medium size field and have it for teams of 9-13 year olds. Range 100-200 Ft and fairly robust equipment. No licenses for ham radio. I am looking at WiFi finders, Bluetooth, etc. Any suggestions?


patang971 year ago


I'm on lookout for a simple RF beacon transmitter and receiver. I want to track a device that will be require 0.5km to 1km tracking on ground. It should be small to fit on 0.5-2inch plate (both sides) and weight should be less than 15gram. Any suggestions or help is much appreciated.

manuka (author) 1 year ago
Phew-this sounds a big ask. What is this robot intended to DO? Do you have pictures & schematics available? Where are you living? Any help available locally? Budget? Resources? Who is the robot for ? Whees or "walking" type?

Realistically it may take you ages just to get to grips with the nature of microcontrollers (& their programming). Linking them to devices which will control the motors (stepper types are considered better) may be even more of a challenge. The robotic rover at => http://www.picaxe.orconhosting.net.nz/rover.jpg took 6 months & US$1000 to construct.

Best you start with micros REALLY SIMPLY! There are numerous types (Arduino etc), but I usually find the PICAXE family the best starters - refer to the UK makers site => www.picaxe.com
gsandhu21 year ago

I’m working on a project which is about making a rescue
robot . I have struggling with it for 4 months and now all the mechanical works
had been done . but I’m facing difficulty in make the robot to work with rf
module can u plzz help me…

I want make transmitter and receiver that can control the
motion…I mean that receiver should have control 8 dc gear motor and each dc
motor should have a forward and backward botton to control the motion ……can u
kindly help me with this project ….if u can make the circuit board diagram for
the PCB ….or any other suggestion plz reply……mail me at “sunny1995gagan@gmail.com”

manuka (author)  gsandhu21 year ago
A "rescue robot"! Sounds useful but just how big ? Actions ? Power supply? Range ? Budget? Time frame? End use ? Your wireless data experience ? Best tell me more!

Reliable wireless control of such devices may be quite a challenge I'm afraid...
The rescue robot is about 80 cm in length and 55 cm in breadth. it is powered by 12 Volt dc gear motor. Till now I have invested $120 for this project and all the work has been completed but the wireless part is still incomplete.

I want all the 8 motor to work separately., and each motor should have a forward as well as backward button.
Truly speaking I'm new to these microcontroller so can u tell me the easiest way to control these 8 motors. rf module will be best... As it's cheap and simple to use..

Plz help tell me the easiest way u can
Thnx for ur active participation. To this problem
Gizmobot2 years ago
Thanks for the recent update . . . this is an awsome instructable . . .
I am thinking this would work perfect for a "hide and seek" sort of game for my kids - we are working on some map reading and orientation skills - before a big backpacking trip.
Would this be a good fit for a game where I used 6 or 9 of the transmitters as hidden "treasures" (say in a waterproof box or pvc pipe) then gave the kids a map with the locations marked and let them have a receiver where a LED light or group of lights would come on as they got closer???
I have seen some references (including one in the link below) to these being used in "fox hunts" or geocaching - but hadn't seen anything specific so as a relative newbie I thought I maybe should confirm. :-)
Thanks again for all the great information!!
manuka (author)  Gizmobot2 years ago
Gizmobot: Happy to help- combining electronics with the outdoors makes for an appealing activity for high energy youngsters!

Further sleuthing with the Dorji module has revealed a valuable signal strength tap that suits enhanced work- refer attached pix. In conjunction with a 433 MHz tape measure Yagi antenna absolutely remarkable performance has resulted.

I'm still organizing this as a brand new Instructable, but have uploaded pix to =>https://picasaweb.google.com/113235065280579741262/Dorji_DF

manuka (author) 2 years ago
Oct. 2012 updateYes ! Dorji's DRA886RX  receiver module readily converts to general 433 MHz band monitoring. Check the quick "proof of concept" breadboard layout below -diverse circuitry alterations naturally can be made. Refer Dorji ASK module insights => www.picaxe.orconhosting.net.nz/dorjiask.htm

Although of course NOT as sensitive as a dedicated $$($) UHF scanner, such a 433 MHz data module hack is dirt cheap,educational,dead easy to use & is particularly handy for diagnostic checks on all manner of 433 MHz devices. Investigate (by HEARING/SEEING band activity) the likes of wireless door chimes, backyard weather stations, car remotes.garage door openers, wireless data devices,local 433 MHz band interference,pickup antenna and device siting benefits etc etc. HIGHLY RECOMMENDED!
Very cool idea. I saw these modules on Sparkfun the other day and thought they might be used for robot navigation (distance and bearing).
manuka (author) 4 years ago
Happy to help ! Perhaps initially check my crusty old PICAXE resource site http://www.picaxe.orcon.net.nz for ideas. However the best PICAXE resource is at the makers http://www.picaxe.com  This Hellscreiber circuitry is really an engine - it can modulate almost any transmitter. I simply used the 433 MHz one for simplicity. Stan
thanks, again -
great resource & helpful script which allows to create different types of rf sending/receiving devices !
manuka (author) 4 years ago
Marc: Where are you ? Have you referred to the SMT resource page => http://www.picaxe.orconhosting.net.nz/smthell.htmThe PICAXE-08M SMT code is here =>http://www.picaxe.orconhosting.net.nz/VKZLHELL.BAS
please accept my apologies for my late reply-
and, much more important:

thanks so much for posting the links!
will have a look at it asap - (late over here - 4.20 AM)

(did some research meanwhile and found another really helpful example on instructables
http://www.instructables.com/id/Wireless-temperature-sensor/ )

orcon has plenty of sources too, thanks a lot, again!

Best Regards
am a total newbee to picaxe (not to mention microcontroller coding)
hence commands such as HIGH, LOW, SLEEP and GOTO are not easy enough to master for me yet :

- would you mind to hint me towards how to code this
probably post a link for similar examples ?

apologies for being that helpless - i did my googling
and did not find one example for a newbee-easy-to-understand-
picaxe rf transmitter-receiver example
including code and schematics example yet
(not to mention a "breadboarded" or "circuited" image coming with it)
and was happy to find your instructable!

however: thanks for posting all this!
i would love to build this -
may i ask which code you are refering to ?

- Multi-tone (SMT) Hellschreiber

which -amongst other links- links to ...

which links to ...
sdtacoma4 years ago
This looks awesome. I am interested in building one to track down a balloon. Do you have a list of parts used? I see them here-and-there in the Instructable but a list would be very helpful.
The range of this project will be too small to locate a Balloon that may have landed miles and miles away from you.
manuka (author)  looking4ideas4 years ago
looking4ideas: Splutter- I DID say limited range at the intro ! A simple RDF antenna (such as a "cotanga" Yagi) can give a few hundred metres range thru' light vegetation & a good 500m- 1km line of sight (LOS). Elevating yourself on a low hill, rooftop or even a ladder can allow scanning over a field etc for beaming insights. Many lost models & balloons etc are of course snagged in the tree tops, and may otherwise be invisibly almost above you when searching at ground level!
Yes, the range is not good enough to find it from miles away. I am just hoping that this can narrow down it's direction/location when close to it. Plus it is small and light.

manuka (author) 4 years ago
go_junior8: Bravo on the keen observation! The cap. can go to either pin of the PICAXE, but I'd moved it to it's own output ( "Pin2") on this Instructable for flexibility. This way the LED can be controlled on it's own. On the older layout I had it in parallel with the LED of course at "Pin1". The PICAXE will indeed have to be programmed with something first. For insights see resources such as http://www.picaxe.orcon.net.nz 
manuka (author) 4 years ago
Good point! I'll add a parts list to suit. The key goodie however is the Keymark/SpiritOn 433 MHz TX module.