## electromagnetism question

## electromagnetism question

(OP)

I am currently working on a project and I have a problem i am not sure how to solve. I have two NRF2401AG 2.4 GHz transceiver with an omnidirectional antenna. Those 2 transceivers are located on point "X" and point "Y" respectively. I need to compute the distance between point "X" and point "Y" (distance between both transceivers).

Is it possible to use the Poynting Theorem to calculate this distance? i mean, I know the TX power and the RX power aswell, and i could use the formula

Prx=(Ptx*G)/(4*pi*R^2) .... where Prx is the RX power, Ptx is the TX power, and G is the TX antenna gain.

I also thought of the possibility of sending a signal and compute the time it takes to get to the receiver...but i do not know how to do that.

Thanks for your help!

Is it possible to use the Poynting Theorem to calculate this distance? i mean, I know the TX power and the RX power aswell, and i could use the formula

Prx=(Ptx*G)/(4*pi*R^2) .... where Prx is the RX power, Ptx is the TX power, and G is the TX antenna gain.

I also thought of the possibility of sending a signal and compute the time it takes to get to the receiver...but i do not know how to do that.

Thanks for your help!

## RE: electromagnetism question

TTFN

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## RE: electromagnetism question

## RE: electromagnetism question

Why can't you use GPS?

TTFN

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## RE: electromagnetism question

## RE: electromagnetism question

Another option is to buy/rent a variant of total station, which would be a theodolite and laser rangefinder. You can get rangefinders accurate to a few millimeters, which can only be matched by a high-performance differential GPS.

Frankly, you hanve't really given any information that precludes using a 25-ft tape measure, which is both cheap and accurate.

TTFN

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## RE: electromagnetism question

Signal strength is not a reliable method of measuring distance. There are too many variables besides distance. For example, antenna gain is not really a constant (example '2.4dBi'), but is typically a complex function of azimuth and elevation.

## RE: electromagnetism question

## RE: electromagnetism question

## RE: electromagnetism question

One system I worked on uses the changing amplitude measurement to approximate distance to a target.

Aircraft Storm Scopes listen to radiation from lightning to assess distance to a storm based on amplitude alone.

In general, it's not accurate, but amplitude alone can be useful. Especially if you set up an array and take amplitude data from every sensor.

kch

## RE: electromagnetism question

When these sorts of StormScope(TM) systems first started to appear, I was naturally very curious how they estimated the distance to each stroke (because it seemed obvious to me that it was not a trivial method - in other words, I couldn't figure it out!).

Azimuth is of course very easy using normal DF techniques. Trivial.

But since the strength of lighting strokes varies widely, signal strength alone would be a very poor indicator of accurate distance (certainly not commensurate with the distance resolution of the lovely graphical display).

That left me with a mystery to be investigated. So, at the time, I looked it up. The explanation that I found at the time mentioned something about measuring the signal at different frequencies and that the DIFFERENCE in those signals somehow related to the distance (accurately).

Tonight I found a related patent with more details:

http://www.freepatentsonline.com/5541501.html

"...determine the range of a lightning stroke by utilizing two narrow frequency bands in the field emanated by the lightning stroke and relying on the relationship between the energy levels detected in these bands to determine range."

(There may be other patents and perhaps other concepts.)

So, these sort of aircraft StormScope systems use something much more subtle than just plain amplitude (1/R^2) to estimate distance.

But there may be inexpensive pocket-size lightning detectors that provide only a rough indication using nothing but amplitude. But they'd probably have something like a crude three step display for 'approximate distance'.

## RE: electromagnetism question

Seems amplitude comparison of a lightning strike at frequencies higher than 2 and less than 5 gives a fixed distance from the lightning strike.

kch