RC RF directional beacon
January 11, 2009
I am still wondering if it is possible to create a simple, cheap, fairly accurate, directional beacon for outdoor use. And I keep thinking I should try to re-purpose an RC transmitter. So here it goes:
Would you deem it possible to create a directional antenna for an RC transmitter?
Would this antenna be able to rotate? Fully continous, or just 360 CW followed by 360 CCW?
Which RC system would you consider? There are so many frequencies in use. And modulation types.
Speaking of which, which freqs and mods are mostly used on the cheap RC toys anyway? Noone ever bothers to mention that when selling them second hand.
Here is the design (if I may use that word here) I have in the back of my head so far. Mind you, I never played with RC, let alone tinkered with these electronics.
Put a directional antenna on a rotation platform (maybe include the whole TX on there as well). Read the angular position of the platform (its "heading") using some sort of encoder. Use this position (0-359 degrees) to encode the signals like you would in servo communication. Zero degrees would come out as 1.0 ms wide pulses, 180 degrees as 1.5 ms wide and 359 degrees as 2.0 ms wide pulses.
Chris has demonstrated that the receiver can feed these pulses straight into a picaxe which could easily decode them back into degrees or rads.
Here's a thousand more words for ya:
The blue dot is my beacon. The yellow rectangle the receiving party (for arguments sake, lets call it a robot). The beacon in this position would transmit 1.11 ms wide pulses which the robot would translate back into 40 degrees. Thus the robot knows on which bearing from the beacon it is at that moment.
The beacon's transmitting beam would continue to rotate, further increasing the transmitted pulse width according to its heading. Every robot in the scanned area would be able to use this beacon passively.
Further calculating where the robot is exactly is beyond the scope of this post.