# Frequency good for tracking?

Discussion in 'Wireless & RF Design' started by Douglas Lovin, Feb 10, 2015.

1. ### Douglas Lovin Thread Starter New Member

Feb 10, 2015
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0
What type of frequency can be used between two devices to track the location of each other without GPS?

The devices emit some type of frequency that can be used so each device can "locate" the other device.. maybe not the exact distance away but at least the general direction of the other device.

Also how powerful would it need to be to be used in the woods within a 1-2 mil range or say in a city environment?

So here is the deal. Two people are in the woods, each have a device on them.

The devices emit some type of frequency that can be used so each device can "locate" the other device.. maybe not the exact distance away but at least the general direction of the other device.

Also how powerful would it need to be to be used in the woods within a 1-2 mil range or say in a city environment?

Apr 5, 2008
15,796
2,384
Hello,

This is trying to locate a hidden transmitter in the field using radio direction finding:

http://homingin.com/

Bertus

3. ### Douglas Lovin Thread Starter New Member

Feb 10, 2015
2
0
Interesting. Thank you. It points me in a better direction.

Do you think this technology could be squeezed down into something smaller.. Say a device the size of a tablet or phone?

4. ### MikeML AAC Fanatic!

Oct 2, 2009
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No. Reality is that Radio Direction Finding relies on directional antennas, and an antenna that exhibits directional properties is at least 1/2λ x 1/2λ in size. λ = 300/f, where f is in Mhz, so the wavelength λ is 3m at 100Mhz. 3m/2 = is a big antenna...

Other reality is that the best range of frequencies for RDF is about 100Mhz to about 300Mhz. Below 100Mhz the antennas get too big. Above 300MHz radio signals tend to bounce off smaller and smaller objects, and the directionality is diffuse and confusing.

I routinely participate in VHF RDF contests using the 144-148MHz amateur radio band. I have won a national contest against 30 other competitors, so I believe I know what I am talking about...

Telemetering GPS derived position using a radio link between two locations is the way to go.
Look at the Garmin Rino...

5. ### Art Distinguished Member

Sep 10, 2007
797
61

There is a commercial product for skiers to wear in case they get buried in avalanche.
They are direction finding and operate on 456 KHz, and work well.
They use two ferrite loop antennas mounted 90 degrees to each other.

This one has three axis.. the extra rod at bottom right.

Last edited: Feb 11, 2015
6. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
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Yeah, but their range is a few feet. The TS wants a range of ~1mi.