Radio Tracking - Triangulation

[Clyd3]

I did a search to see what had been discussed here, finding the location of a transmitter from more than one receiver.
Someone mentioned < i think it was Nigel > that radio waves travel quick, like or at the speed of light, and therefore there is a minimum distance of the entire system which you can calculate based purely on time, because you would need to process the signals you receive incredibly quickly.

Can you tell me, or rather, can we discuss measuring the strength of received signals to do similar triangulation and what the minimum distance of such a system could be. Accuracy and feasability versus distance between transmitter and receiving stations. As well as favourable frequencies for hobbiests to work at. I'm fully passionate...
I'm hoping to do this on as small a scale as possible, whatever scale that may turn out to be.

I'm hoping to try and keep all progress as documented as possible in this thread.

 

[Nigel Goodwin]

Triangulation is done using two, or more, receivers spaced a distance apart - you take a bearing from each receiver, draw the lines on a map, and the lines should cross where the transmitter is. It's usual to adjust the receiving aerials for minimum signal rather than maximum, as the null point will be sharper and more pronounced than the maximum point.

Frequencies used depend mostly on the size and types of aerial, for low frequency use loops or ferrite rods can be used, for VHF and above yagis can be used. There are numerous aerial types that are suitable, and people usually have their favourites.

You might try googling for 'DF hunt' which is a popular amateur radio pastime.

What actually are you wanting to do?.

 

[Clyd3]

i was hoping to have a really small system, eg. desk sized, but that may be a bit unrealistic, is it? If not, what do you think the smallest size i could hope for would be???
would the frequency be at all related to the overall size of the system?

i was thinking of drawing circles on the map, the centres being the receiving stations, and the circles illustrating the strength of the signal they receive.
Once i've got a basic system going, i want to computerize it, so it'll be faster... now let me do that df hunt quickly
btw. once it's computerized i want it to be relative measurements rather than actual sizes eg. m, mm...

Edit (Now that i've read up on df hunt)
Check out this page: https://en.wikipedia.org/wiki/Direction_finding
Look at the 3 methods of direction finding found at the bottom of the page, namely Single Chanel DF, Pseudo-Doppler DF Technique, and Watson-Watt w/ Adcock Antenna Array.

Even though they have it as the main heading, with the others as sub titles, I can immediately eliminate the first, Single Chanel DF, in its simplest form. It's not what we are looking for, because I intend to have more than one receiver, and I do not require mobility.

Now I have to decide between the last two, Pseudo-Doppler DF Technique, and Watson-Watt w/ Adcock Antenna Array.
Originally I was thinking of the later method, but i think you were referring to the former method. If however you were simply referring to using a directional antenna such as a yagi, I don't think that's what i'm looking for, because i do not want to have any motion in the receivers if possible.
Which of the two methods do you think I should pursue first, taking into consideration the degree and capability of each to run in the smallest areas possible?

 

[Nigel Goodwin]

i was hoping to have a really small system, eg. desk sized, but that may be a bit unrealistic, is it? If not, what do you think the smallest size i could hope for would be???
would the frequency be at all related to the overall size of the system?

No idea!, it's not something you would normally do on a desk top, as you can simply see the transmitter :lol:

i was thinking of drawing circles on the map, the centres being the receiving stations, and the circles illustrating the strength of the signal they receive.

Signal strength is affected by too many variables, it's the angle you measure and then plot a straight line - two such plots, from different locations, should cross where the transmitter is sited.

 

[Clyd3]

i was thinking of drawing circles on the map, the centres being the receiving stations, and the circles illustrating the strength of the signal they receive.

Signal strength is affected by too many variables, it's the angle you measure and then plot a straight line - two such plots, from different locations, should cross where the transmitter is sited.

The Watson-Watt technique uses the circle method, but as you say, signal strength is affected by too many variables. However, if in a very controlled environment, would you consider it feasable?
I'm gonna try this out, and I'll report back here. What frequency do you think i should play with??? I have two omnidirectional antennas capable of 300MHz up to around 800MHz, I think. Would you say they are suitable??? or should I go pick up a different frequency, which perhaps you or someone else here feels more comfortable or has had similar experience with?

 

[Nigel Goodwin]

The Watson-Watt technique uses the circle method, but as you say, signal strength is affected by too many variables. However, if in a very controlled environment, would you consider it feasable?
I'm gonna try this out, and I'll report back here. What frequency do you think i should play with??? I have two omnidirectional antennas capable of 300MHz up to around 800MHz, I think. Would you say they are suitable??? or should I go pick up a different frequency, which perhaps you or someone else here feels more comfortable or has had similar experience with?

I can only suggest you try it and see?.

 

[Clyd3]

well i guess it's time to start then.
In summary i need 2 receivers, capable of measuring the strength of a signal, and output the value in some way, say 1v to 3v or similar.
I also need a transmitter, as small as possible, and with as low range as possible. The transmitter needs to output a fixed signal, simply because it doesnt need to send a complicated signal.
I don't think i'll be needing any aerials, because they'll just make the range too high, so i'll do simple pc board etched aerials.

I've found it rather hard to find what I'm looking for, because normally when people do radio work, they try to make strong reliable systems, never with a range of 3m...
But what really makes it difficult is finding a really short range system, which is still constant and reliable...
Any help anyone???

 

[Nigel Goodwin]

One thought! - as you're wanting such an extremely short range, have you considered an inductive system? - rather than RF use a low frequency magnetic field, and detect it using a tuned coil. There's actually an existing thread about this, but that uses an inductive loop with the sensor inside - you should be able to use a tuned audio frequency coil (10KHz or so?) as a transmitter, and the same coils as receivers.

Easier than UHF, and should be simple to experiment with?.

 

[Clyd3]

sounds interesting, i'll give it a good look at...
Edit: I'm sorry, I can't seem to find the already existing thread, but I'm scratching around the net anyway

 

[docel]

near-field RDF

Clyde3, detecting direction at 1meter distance is pretty difficult nigh impossible at higher frequencies (RF). Nigel's suggestion would be the better method.
Near field detection is achieved by the combination of active attenuation and frequency off-set reception. This means we attenuate the signal >100db along with shifting the frequency away from the transmitted freq.

Eg. Our ham VHF fox hunts are in the 144-146Mhz. range; lets say 145.00MHZ. We build an offset attenuator at may be 4MHz and tune the receiver to 145MHz + or - 4Mhz. This will reduce the signal strength and prevent front-end overload, capture effect etc.,
The offset circuit is nothing but a diode mixer. The Bias is adjusted for attenuation. Difficult to explain but it is impossible to block / attenuate the direct signal wrt directivity at anything beyond 1/2 a mile!!

The magnetic field transmitter and receiver at audio frequencies will be the best choice for table top triangulated direction finding. It is nothing but an air cored transformer with the strength (along the flux lines) having a toroidal pattern from pole to pole. To be detectable at a distance of , say, 3ft, you'll have to make a pancake transformer coil af at least 2ft in diameter.
I suggest that you build a 2ft dia coil of 8-16 ohms impedance and plug it into a radio or tape or some other audio amplifier. This would be your transmitter. the receiver can be a ferrite loop=stick coil fo say 600ohms or so. This can be plugged into the Mic. socket of an AF amplifier.The earphone/speaker will then indicate the signal strength, with some led attached.
Another simple receiver would be a LM3914 type bargraph indicator with the loop coil at the input. The leds will then show the signal strength.

The ferrite loop will be bidirectional and show 'null' broadside and "max" along the coil.

 

[Clyd3]

Re: near-field RDF

Clyde3, detecting direction at 1meter distance is pretty difficult nigh impossible at higher frequencies (RF). Nigel's suggestion would be the better method.

Well that's an answer to a major question here, thanks 8)
So to what degree is a lower frequency beneficial?
Would it then be possible to use lower (perhaps extremely low) frequencies to detect over such a short distance?
Obviously cut me some slack here, curiosity makes me still want the answer, even though Nigel's suggestion is a better sollution.
I'm guessing that if it did require extremely low frequencies there would be strong disadvantages, such as extreme interference or something (i'm sucking a simple disadvantage out of my thumb until i find a real one - responsibility in a way)

As for actually putting the idea into process - i'm gonna read up and research for now.

Thanks a lot for the very useful replies.

 

[docel]

near-field RDF

Hello clyd3,
Here The frequency versus field strength is the deciding factor. Also , the power levels too play the contributary part.
Higher frequency waves are more 'penetrative', at a constant power levels. The theory of Transformer, mutual coupling and electromagnetic induction holds good at all AC frequencies. The question is : can you prevent the signal from getting into the receiving circuit, from anywhere other than the directional antenna.
A point source radiating field spreads in all directions away from each other. At some distance, they will be evident as 'individual lines of force'. At the and nearer to the radiating point, there will exist several lines of force per unit area. This will be confusing enough as 'near field' and 'far field'.

I mentioned AF amplifier, meaning Audio frequencies <15KHz. This is good enough for a 'triangulation' on a table top.
To give an example, sound waves too behave the same as Radio frequency waves. Light also behaves the same. The similarity is demonstrable, indeed on a table top. The real problem is in directing or channelising the waves into a small enough " detector " area.
In the case of Ultra sonic frequency radiation, there is a finite minimum distance below which the directional property cannot be demonstrated. This is about 8-10cms @40KHz. Even this is a little difficult and certain specific physical 'damping' has to be done to prevent the waves entering or vibrating the receiving transducer, from all around.
The human ear , is probably the best directional antenna ever.....but it does so with the help of some queer software written in the brain!

Perhaps a look at the excellent RFID tutorials via Google will help you better understand these weird behaviour of alternating waves. That willbe some job, considering the hordes of pages that will respond to your search!!

 

[yasser11]

Hi,

I have worked on Localization Algorithms in sensor networks.
There I had Chipocn Sensor nodes(they included a transceiver and microcontrollers etc. ). My main motive was to implement the algorithms and check their performances.
If u want to know anything more, reply..

 

[docel]

chipcon

Very nice. do you have a near-field signal strength Smith chart for 300- 450Mhz?

 

[Clyd3]

Hi,

I have worked on Localization Algorithms in sensor networks.
There I had Chipocn Sensor nodes(they included a transceiver and microcontrollers etc. ). My main motive was to implement the algorithms and check their performances.
If u want to know anything more, reply..

good game...
well, i think we need you to share your opinion on the questions i've posted so far, and what YOU would use to do localization as you call it in a really small area, eg within 3m. Also, i'm not that afraid of prices so it that's the problem let them fly high.
Btw, i would ultimately want 3dimensions, sounds fun eh??? hehe...

getting some pretty promising replies here, thanks
thanks to docel too, because you seem to understand what i'm asking for more than myself... this chart sounds fascinating - i'll get it, i promise, i learn fast