Detect range from active RF target

Hi. I'm new to robotics, and I'm interesting in developing a range detector which will measure signal strenght from an active RF target.
The range I'm interested in is up to 1 meter (10cm-1m). I've been searching the net (and this group), but most range finding designs revolve around ultrasonic and IR detectors which work on measuring ping time. My toy is equiped with an RF transmitter (I'm transmitting data), so all I need to do is measure signal strenght and determine range based on received power. I cannot find schematics or preassemlbed kits anywhere.
Has anyone got any links to RF range detectors?
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The gadget you are looking for is a 'field strength meter'. The simplest form consists of an aerial, rectifier and a sensitive current detector. Details can be found in just about any ham radio reference book.
Some receivers have an output which indicates received signal strength, or may have a suitable voltage inside somewhere - possibly as part of an AGC system - eg, FM receivers will quite often have an RSSI signal inside.
The bad news is that it is unlikely to do what you want. The field strength depends not only on distance, but also on shape/type/orientation of any aerials involved, and will also vary considerably in the presence of any objects ...

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Hi,

Like the other reply said, you can't sense range this way. However, there may be other solutions to your problem based on what you're actually trying to achieve. For instance, if the real goal is to prevent the toy from driving outside the range of your telemetry signal, the receiver can keep track of BER and infer link quality from that. You could thereby localize the toy within one of several zones according to BER; "close" (0%), "middle distance" (say 25%) or "far" (say 50%).
If the goal is to locate the toy in space, then you CAN use RDF techniques if you install a second receiver. But this is very tricky and inaccurate.
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snipped-for-privacy@gmail.com (Zenja Solaja) wrote in message

I am interested in getting a little info myself about a similar issue. I am thinking about a method of locating a robot by a grid of wires underneath the carpet [or otherwise embeded in the floor]. The grid could be used as a transmitter or recieving grid, with the transmitter on the mobile robot. This would be similar in concept to the design of many digitizing tablets used as input devices on computers.
Any ideas about where to find info on the web of folks who have done this, or ideas about what kinds of words to Google for? (I haven't had success in my search efforts so far)
Joe Dunfee
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I`ve seen a commercial robot somewhere on the net which uses three transmitters positioned anywhere within range of it; the on-board computer calculates its "Trig" coordinates from the three signals. Simple Field strength RF meters are easy to make (see model aircrafts), but one to be able to judge the distance should be fairly impossible due to external interference from other RF absorbers and transmitters. Enlighten me though if anyone here should be able to find a simple design too. ----------------------------------------------------------------------- Ashley Clarke -------------------------------------------------------
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