A week or so ago, I posted my ranger problem, (7.5m in the forest) expecting to flooded with ingenious solutions ;) Apart for a suggestion to use a chain, I got zip. Am I to assume that no-one had a better solution to offer?

I need your help PLEASE ! 

If you can help me with suggestions on a SIMPLE radio transmitter and/or receiver please e-mail me (antons@grindrod.co.za) or post to the list.

Transmitter.
Should be around 27MHz for legal reasons (no license rqd for low power).
Range required no more that 10 meters.
Absolute minimum parts, perhaps a simple colpits crystal osc?
Need to be able to turn the transmitter On and Off via PIC port pin.

Receiver.
27Mhz, 10meter - all I need is a carrier detection. Perhaps something similar to the old 'crystal' radio? (aerial coil, tuning cap, diode rectifier, low pass filter) followed by an op-amp comparitor. The output of this will be used to gate the ultrasonic sender.

The requirement was to measure 7.5meters in a wooded forest, to inscribe a circle. (about 12 measurements per circle). My plan was to have two units, one at the center (hub) and one roving unit for the perimeter (hand-held).
The hand held's PIC would turn on a radio transmitter, and start a timer. The hub would, upon detecting the radio signal, emit an ultrasonic ping. When the hand held detects this ultrasonic ping, the PIC would stop the timer. The time taken would be indicative of the distance.

Any help welcome

Thanks in advance

Anton Schoultz
antons@grindrod.co.za