# Looking for transmitter

May 28, 2013
3
Currently, I am working on a project that involves navigation using trilateration. This method requires knowing the distance between one point and three reference points. I need a transmitter that can broadcast an RF signal that is ONLY used for its strength and has a range of at least 300 ft. The transmitter does not need to have anything other than itself broadcast.

Any suggestions?
Thank you

#### BobK

Jan 5, 2010
7,682
Yes, figure out a different way to do this. Signal strength is not a reliable measure of distance.

Bob

#### davenn

Moderator
Sep 5, 2009
14,260
Yes, I agree with Bob on that one.
too many things, especially enviromental, will affect any signal strength reading you get

Dave

May 28, 2013
3
In that case, would it be possible to time the signals and calculate the distance based on the time from transmitter to reciever to transmaitter?

#### davenn

Moderator
Sep 5, 2009
14,260
that would be a better method.
you are going to need some serious timing circuits for distances that short

Tho thinking about that a bit more ... you are going to still run into some similar problems
You will never know if the signal you are timing is a reflected signal ( will take longer) or a direct signal

its only going to work if ...
1) its a line of sight path
2) there are no building, trees, other terrain etc that could cause reflections
3) you use microwave frequencies where you can make use of narrow beamwidth signals

Thats why cops use laser or 24 GHz microwave. the beam is VERY narrow
a laser is pencil thin, a 24GHz beam with appropriate antenna is a couple of degrees

Dave

#### duke37

Jan 9, 2011
5,364
It may be better to use sound, with a slower speed it will be much easier to time the signals. I believe the military used this in WW1 and still use it.
There will still be problems with obstructions and sound propagation speed.

#### differential equasions

May 30, 2013
2
Currently, I am working on a project that involves navigation using trilateration. This method requires knowing the distance between one point and three reference points. I need a transmitter that can broadcast an RF signal that is ONLY used for its strength and has a range of at least 300 ft. The transmitter does not need to have anything other than itself broadcast.

Any suggestions?
Thank you

Use a computer router and a USB antenna - Linksys is a good cheap option.

They have a range of about 200' inside of a building and about 300' in a free space.

The USB antenna is very directional and the weak microwave signal won't cause any type of interference with other radio services.

Use lap top computers and use the signal strength bar and calibrate it with a signal analyzer / generator.

A service monitor and 900 MHz would be a good second choice.
1 watt in the free - above 900 MHz band in the USA would work ok as long as nothing else in the neighborhood interfered with it.

You would need to make a field survey ahead of time before you attempted to do your experiement.

All signals reduce at the square of the distance away..
Simple physic's 101

#### davenn

Moderator
Sep 5, 2009
14,260
..........

All signals reduce at the square of the distance away..
Simple physic's 101

no its not that simple, for the reasons already outlined in the posts above

you apparently havent had any experience in dealing with RF measurement and the problems caused my multiple reflections etc

Dave

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