How do I limit my RF reception range?

IR is fairly simple if it is line of sight - otherwise expect a large and highly variable drop in signal if one or more bounces are involved. Led life is unlikely to be a problem if you keep within the datasheet pulsed current limits - in any case, they degrade slowly.

Presumably the tag is the transmitter - how do you propose to adjust the transmitter LED output in response to received signal strength - you will need some sort of back channel from the tag to pass that information ?

Note also that if the tag is the receiver, then you may have a problem with battery life - you need to keep an amplifier for the received IR signal 'alive', and amplifiers take power.

Google 'Active Badge' for one approach

have fun ! Dave

I had originally envisioned configuring both the base stations and tags as transceivers. The base stations would send out periodic signals and the tags would respond as required. I chose this method because, during my initial planning, I thought that most of the power would be involved in transmitting. However, it is becoming clear (especially in light of your comments) that it would require more power to keep a receiver running constantly than it would to just have the tag periodically transmit a signal.

Oh, and thank you for that link about Active Badges. That is almost exactly what I am attempting to do!

Thank you.

Not really, can't you take the assigned people for an appropriate barbeque according to their needs and round up the BMW's while they are partying?

DNA

No need to pretend. It seems you have a very good grasp and you are correct.

Yes, your receiver is 15 dB less sensitive than my example. The sensitivity is usually referred to milliwatts into 50 ohms.

Yes, correct again on both counts.

You are correct in your transmitter power output calculations (assuming 50 ohms, as always).

I see no errors to correct.

I estimate that your receiver will achieve -80 dBm at 1 meter when your transmitter is emitting 1 mW (0 dBm) using a 1% efficient antenna and your receiver has a 1% efficient antenna. These antenna efficiencies are pretty ridiculous. Anything approaching .1 to .25 wavelength is usually more efficient than that. So, supposing that both your antennas are, say, 90% efficient, then I estimate that your receiver will achieve -80 dBm when your transmitter is putting .1 microwatts (-10 dBm) into its antenna.

Please realize that these are very crude estimates.

You are very welcome. I would like to stress that it is extremely difficult to guarantee a distance range with RF communications. There are many people watching this group who know much more than I. For example, I haven't the faintest idea of how you might manage data integrity in the presence of noise. This is a separate issue which should be addressed by the professionals here. Also, as I mentioned earlier, signal reflections are a significant factor. The list of problems goes on. However, please don't let this discourage you. It is through research and efforts such as yours that we advance.

Thanks. Everyone will benefit.

Sincerely, John

In message , dated Sat, 2 Sep 2006, John - KD5YI writes

-40 dBm.

-- OOO - Own Opinions Only. Try

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Thanks, John. I knew I would make a mistake somewhere.

John

At 2.4Ghz, a signal having an output power around 0...+4dBm will be send and received along the 3..4 feet without any transmission and receiving antenna, just the SMA connector itself (or with a small wire). The receiver it supposed to have around

-120dBm sensitivity (or greatest) .

greetings, Vasile

And if the transmitter doesn't have high SWR protection you may blow the output transistors. The trick is to put a tee connector with a terminator, and use a small mismatched antenna which won't cause a big drop in output impedance. Another method would be -20 dB directional couplers followed by a pad, and the original antennas.

last time I looked 3m was extreme range for radio-powered proximity tags - no battery.

you may want to see what's available...

Bye. Jasen