Let's Make Robots!

Radio mast navigator - idea :)

Hi, just got this idea, and thought perhaps it would interest one of the clever guys out there. Hope is that a vendor will take this up, after a couple of clever LMRians have talked more about the details that I am too stupid to get into :)


It is a board that always shows you "north" - a fixed point anyhow. Purpose is to navigate, for example in a football match.

Turn on board, and it has a radio, like a human-music-radio-thingey. Only it does not play music, it has the ability to tune in to a radio station, but only listens for the carrier wave.

It simply has a pointing areal, is "a crap radio that needs to be alligned to the sending mast", and an 0-5V signal is the
output, more or less, after how strong the recieved signal is.

On the board we place 3 such tuners. (I am sure they can be bought/made for nothing, no?)

The antennas on them points to each direction, sort of like a Mercedes logo.

The board has a small processing / logic part that compares all 3.

It finds the 2 strongest recievers, and according to their individual levels, the point between them is where "north" is.

Output is a direction (0-360 degrees), always fixed towards the radio mast.

There are more complex ones in the sales, where you have to place "the sending masts" yourself. but how cool is that, when you can just tune in to a radio station?

I think such a module could be build cheap, compared, and I think most roboteers would really like a sense of direction, cheap and easy!

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I am researching small uni-directional antenna. The problem with our size requirements is evident: we want our antennas to be so darn small! The laws of physics are not very accommodating.

For instance, a typical AM signal @ 800 kHz has a wavelength (lambda) of 375 m. A standard whip antenna has 1/4 wavelength ~ 94 m. Any shorter antenna would be less effective.

The higher we get in the RF spectrum, the shorter the waves get and also the antennas.
Typical FM signal @ 100 MHz -> lambda ~ 3 m.
Typical Wifi router @ 2.4 GHz -> lambda ~ 12 cm.

So here's the big question: would a Wifi router (or a cell phone mast) also work for our application?

Sure, WiFi routers and Cell Phone masts would be cool and the gang!

Since we do NOT want a perfect signal (because then there was nothing to measure in difference), would it not be cool with a crappy antenna? 1/8 of the wavelength or something like that?


On another node, to quote OddBot from a private mail: "3 simple crystal sets and a low power transmitter should work" - what ever he means by that (?)

A crystal set is a type of receiver that can receive AM radio. It uses no battery or other internal power source. The radio waves are picked up by an antenna, resonates on a coil/capacitor circuit and rectified through a diode. This signal can be strong enough to drive a crystal earphone (which has a very high impedance or internal resistance to audio signals). The receiver also needs a good "ground".

Oddbot is probably thinking that a Picaxe ADC also has high impedance and can replace the earphone. For our purposes, the antenna/ground combo would need to be highly "directional". And mobile. And small. I doubt if a smallish antenna would be able to provide a detectable signal. Please let someone prove me wrong!

An idea is not a problem to be solved. It is a suggestion for having fun. Ready made compass chips are slightly missing that point.

Also: I cannot open that link for some reason.

No, because that is a 404 - page not found!


that's weird its working normally over here :) and its not a compass module , its somehow a tutorial on how to make a compass using hall effect sensors , pretty interesting , i wanted to make it , but the parts needed are unavailable over here . if you want i can try and upload it somewhere :) ?

I see, a radio direction finder

You could mount a small pocket radio on a servo. The radio could be modified with a directional antenna (see here, how to do).

I guess not every radio station is based in the North, so you would need to pre-selected one certain radio station. I would not use 3 radios as they would interfere with each other.



I am .. well, try and read the above again :) I am not talking about a slow spinning of the antenna.

And we do not need to know where we are and all that, from a radio direction finder.

3 analouge signals, 2 of them are stronger than the third. The relationship between these 2 is our output.

I am talking about a simple little board that can be tuned to find any radio station, like you auto tune a radio. Then it constantly monitors the 3 radios, and tells you from 0-360 which direction the signal appears to be strongest.

You get a constant feed from it; Transmitter is now at 275, 277, 271, 265, 264..

As mentioned, the 3 radios will interfere with each other. I guess, it will also be not possible to get a 1° resolution with 3 fixed antennas. If you ever tried radio tracking you know what I mean :) Instead of the 3 radios I would use at least one, and switch/change the antennas in fast order :)