Anybody know about radio and electronics?

Poster: Andy
Dated: Wednesday August 25 2004 - 14:36:37 BST

Hi All,

Does anybody know, or know somebody, that knows about electronics and radio signals.

I need a device that can transmit a radio signal to a receiver and tell me how long it took to get there.

It needs to be very accurate so I really need to talk to a scientist (I know it's a long shot) or somebody that has studied radio waves and frequencies to be able to say if what I'm looking at is either doable, or has already been done.

BTW - I'm not loosing the plot ( at least I don't think I am) just got a mad idea that's all.

Anybody?

Cheers
Andy

Poster: kevin3442
Dated: Saturday August 28 2004 - 4:51:13 BST

Hi Andy,

Talk about "Anything Goes!"

If I dredge up my physics from years ago accurately, Hertz messed around with measuring the speed of rado waves in the late 1800s, so you're in good company! Maybe we'll end up with a new unit of measure... the Woolley ("Um... yeah Dave, set that to 60GWo will ya?")

I'm pretty sure that any electromagnetic energy moving through open "free" space (i.e., a vacuum) travels at the speed of light: 186,000 miles per second (you'll have to do the metric conversion!). Any non-vacuum medium that the wave travels through will decrease the actual velocity: atmospheric conditions (barometric pressure, humidity, etc.), density of obstacles between the transmitter and receiver, etc. But I doubt that the decrease would be all that much in most situations. The frequency of the wave should not affect velocity.

So, I don't know about a direct timing device; I would think that since the energy travels so fast, an accurate timing device would be pretty difficult to make for reasonable distances. But if you get an accurate measure of the distance, and you know the velocity, you should be able to derive the latency between transmission and reception.

Don't know if that helps. But there's my two cents. Now I'm left wondering what you're up to.

Cheers,

Kevin

Poster: Andy
Dated: Wednesday September 1 2004 - 16:11:30 BST

Cheers for that Kevin.



Absolutely!!

Anyway, my idea is to have a device tell me how long it took a radio wave to reach its destination.

I'm guessing it can be done because that's the way laser measuring devices work. They just bounce a beam of light from one location to another and see how long it took to get there and back. A bit like radar I suppose.

Anyway, my main questions are: Will travelling through obstacles like brick walls and trees make the signal take longer to reach its target or will it just degrade the signal strength. I'm guessing it will just affect the signal strength but it is a guess. Do you know the answer?

Also, would be good if we could actually find out if a device can measure very minute amounts of time. Again, this must be how laser measurements are taken so guess it is possible.

Also, what do you know about triangulation? As somebody in your field of business I guess you'd be clued up about this for tracking devices etc.

Cheers
Andy

Poster: Ruth
Dated: Saturday September 4 2004 - 1:13:56 BST

I don't know if this site is anything. The guy talks about some device called Fluke, some kind of receiver/comparator, and about some experiments he did measuring frequency and time of radio waves [the one he's using is old, but Fluke seems to be a UK company that makes/designs measuring devices for numerous things.

Ruth

Poster: John
Dated: Saturday September 4 2004 - 19:57:31 BST

Fluke is one of the oldest and most respected names in test equipment of many kinds. Good find, Ruth!

Poster: Ruth
Dated: Saturday September 4 2004 - 22:13:18 BST

It was just a fluke

Ruth

Poster: John
Dated: Monday September 6 2004 - 1:02:03 BST

Oh, brother... Maybe Ruth should take this week off, too

Poster: kevin3442
Dated: Tuesday September 7 2004 - 21:55:16 BST

Hi All,

Sorry for the slow reply... didn't see the recent activity. So... I'll jump in late.


Awesome pun!


True, but in that case, the tansmitter, receiver, and timing device are all built into the same unit, because it's measuring the 'return'.

Yeah, although radar also uses the Doppler shift to figure out the speed of the targeted object. Radar, sonar, lidar... they all rely on a return signal. You're after a somewhat diffent thing. In your case, if I understand correctly, you're talking about a one-way transmission, so I assume the "measuring device" would be on the receiver side... more like GPS. In that case, your transmission would have to include not only the test signal, but also the time at which it was sent, so that the timer on the receiver end would have a start time with which to calculate a latency. Not a big deal in itself probably. But the tricks would be that (1) because the signal travels so fast, the timers would have to be extremely accurate to a small fraction of time, and as a somewhat bigger deal (2) the two timers would have to be synchronized as accurately as possible. Maybe there's a way to have each timer just display the time of transmission or reception (and you calculate the difference yourself), but you'd still face the problems of resolution and synchronization. I think these are two of the problems faced by (and overcome by) GPS, on a much larger scale of course! Maybe in your case, there's a way to use a single timer, which would simplify the problem. But it's beyond me how you'd do it or if there are commercial devices to do it. Maybe Ruth's link will lead to something. It also occurs to me that since GPS has esentially overcome the same problems, you might find some sort of Radio/GPS combination that can use the GPS unit's built-in timer to do the sort of thing you want to do.


I am certain that the speed is affected by the medium that the wave travels through... I seem to remember this being emphasized as the reason why work with electromagnetic energy refers to the speed being equal to c (speed of light) in "free space" (i.e., in a vacuum). I would think that the signal strength is also affected, but I have no idea to what degree.


Well... the U.S. Military already did the hard part... GPS! To that extent, I understand trilateration (part of how GPS works). Trilateration seems easy... to find the location of an unknown, all you need is its distance to a minimum of three known reference points (e.g., satellites), some spheres (or circles in 2D), and some simple math. To me, triangulation is more difficult. It only requres two reference points (in 2D), but then you have to know not only the distances between the unknown and the reference points, but the angles as well. That's when it starts to suck for me... trigonometry was not a favorite subject for me, and when you start talking about sines and cosines, I'll have ot go get a book, and even then I might be lost. What are you trying to locate?

Cheers,

Kevin