I know next to nothing about radio wave transmission and detection. So can some of the more “radio-savvy” of the readership perhaps help me with the following:
Suppose we have a hypothetical horizontal circle (say 50 m in diameter) segmented into roughly six equal slices (“pies”). Now suppose that at any of the six points on the circumference (i.e. points about 60 degrees apart as seen from the focus) we have four radio transmitters emitting four different frequencies.
This means that there are four signals being received at the focus. There, there is a horizontal set of six receivers arranged in an approximate hexagon.
Would it be possible to construct a scheme whereby the strongest received signals from each of the 4 transmitters could be used to identify the receiver(s) receiving such signals? Such identification would then determine the direction(s) of origin of the signals.
The data gleaned could then be used by a Python sketch to derive my desired result - a secret, unless you have twigged onto what I am about!
I have a relatively new Raspberry Pi 400 and an old Arduino which I have not touched for 4 years.
Any help would be appreciated. Thanks.
An arrangement of aerials receiving from one transmitter (that is, on one of the several frequencies you mention) could, in theory, use the relative signal strength to indicate which receiver is closest to the transmitter and therefore the direction from which the signal is being received, with interpolation as required. The effectiveness of this would depend heavily on the calibration of the receiver sensitivity, the physical separation of the receivers, and the signal path from the transmitter to the receivers…
If you then switched all the receivers to a different frequency you could determine the direction of another of the transmitters, and so on.
Maintaining a fixed, known, relative sensitivity for the receivers might be a problem, although the requirement could be reduced by using directional aerials at the receivers.
Hi Michael.
What sort of frequencies are we talking about here. This will determine antenna size and the feasibility of doing this at a hobby level.
By far the easiest would be a directional antenna mounted on a rotator as used by amateurs the world over (and other users) but if you are talking hF (2 to 30MHz) believe me these directional antennas are HUGE. You would need about an acre to fit one in. The military use these but I don’t know of anyone else.
Cheers Bob
Hi Jeff. Michael.
Jeff. That once again depends on the frequencies in use to make a practical solution. The RX antennas would have to be several wavelengths apart to get any signal level comparisons. The different RX sensitivities could be overcome by using the one RX and switching antennas around the circle.
If VHF, one method goes back to WW11 where an array of vertical antennas is arranged in a circle. By rapidly changing the phasing of the individual antennas the main “lobe” can be made to rotate around 360º not unlike a radar antenna. The design of such a system requires Maths and Radio propagation nous far above my pay scale. When the engineers and scientists tell me this is what happens I believe them.
If the frequencies are high enough (so the antenna is a manageable size) I think the rotator mounting would be the easiest. The lack of any other information precludes any further attempt at guessing.
Cheers Bob
Some routers have a scheme like this. They call it Beamforming and Wikipedia has articles. The method has multiple antennae and by comparing the phases of a received signal between them can determine where the signal comes from. It is not something the home designer would attempt without considerable research.
Hi Alan
Yes, another way of using a circular array of vertical antennas. Probably better that the method I mentioned above which could be more use for transmitted signals. Indeed that is how TV transmitting antennas are fed. Each of the four sides is 90º out of phase with the adjacent side so in effect the signal spins around the centre of the antenna structure.
That is true. Period. With or without the considerable research bit. Even the mechanical tolerances involved to maintain impedance matching would be beyond most home experimenter/constructor. Not to mention the ability to measure phase differences accurately.
Cheers Bob
My suggestion about a rotator is looking better all the time.
Apologies for my late response. Thankyou Jeff, Robert and Alan for your input.
Would any of you be able to recommend actual equipment I could consider purchasing? One thing that springs to mind is something like garage door remotes, where maybe the user has to press a button (or not?). Could such tiny transmitters (and hopefully tiny receiver(s)) be used for my proposed project do you think?
Having some equipment knowledge would perhaps get me moving on the project instead of being only a concept in my head!
Mike.
Hi Michael,
Before you get too far into the details you still haven’t shared what frequency of radio signals you are trying to track. As @Robert93820 pointed out until we know what frequency band you want to operate in we don’t know if your antenna will fit in the palm of your hand or be several meters long.
Hi Trent! I have no idea what frequency band! All I want to do is receive signals which can determine direction (i.e. position) in each case; this data can then be processed by the software into the format I need.
Do you think infrared could be used rather than RF? Or any other radiation . . . ?
Mike
Why not go left field and set up some ESP devices with GPS and Wifi, and a Pi as base station running your Python script?
That has the advantage that the data points can be moved without needing any change to the software, and the receiver does not need to be at the centre of the array.
Hi Mike,
Infrared may be possible but in that case, I’d probably be using Bob’s idea and making your sensor rotate to check each direction.
This has the potential to be very challenging so it would be good to know what your vision is for an end goal of this kind of system. Did you want to track the direction the best phone reception is coming from in an area or TV broadcast signals? Every signal will require a different antenna to detect it so you’ll need to start by deciding what you want to track.
This device operates in the same band as a garage door remote. But it is designed to operate with another as a pair. One sends a code and if the code is correct the other responds. Wrong code and frequency and the receiving unit will ignore the transmission. It does not measure the received energy, so it could not work out the direction where the signal came from.
But if you used specific codes for each transmitter and the receiver keyed to the code would respond and not the others. It could be frequency that provides the difference also. I think these devices have over 30 channels you could use.
Finding a device that listens to a frequency and provides a signal level would, probably, be much more expensive.
Regards
Jim
EDIT: Reading the original post I don’t think this device is what is needed. It would only work if you have control over the transmitters as well as the receivers.
Hi All
Apparently Michael’s end result is a secret.
So a solution to this secret might have to remain a secret until we can find out what he wants methinks.
Cheers Bob
OK I’ll let the secret out! The six potential transmitting sites are croquet hoops and the actual transmitters are the four hoop clips! I simply want to determine the score of a game in realtime.
A potential problem, though, is interference with similar setups at adjacent courts; so the whole idea may not be feasible.
I tried GPS with an Arduino using a “CIROCOMM 595K” sensor which wasn’t accurate enough. I also have the packaging for a “GPS Module PMB-648 SiRF” but I’m not sure where the contents are! - unless it is said CIROCOMM.
Are the suggested GPS sensors superior to these? The period was 2017-18 when I tried it out.
To my knowlege no-one else has tried this project, but it seems an obvious one to have a go at. Maybe interference from other courts is a mitigating factor?
Mike
Hi Michael
Thanks. I don’t think too many people are going to pirate that idea.
Don’t know what these look like but you heed antennas and as these are physical things this will dictate to some extent the frequencies to use. The other factor is these frequencies have to be licence free.
Yes it could be. Not limited to adjacent courts either. With the popularity of “wireless” systems these days these frequencies are in widespread use. That is why there is a power limit on unlicensed devices, it is an attempt by the regulators to minimise interference problems.
The other potential problem is your system interfering with other existing services. That is why you have to stay within limits.
A Bluetooth system of some sort might work although the 50M might be a bit much.
Maybe even some sort of WiFi system but your interference problem might prevent this.
433MHz might be feasible.
If each station had an identifier (like in a I2C chain) the directivity would not be required. Try to solve the RF problem first then think about this.
I have not had much to do with the internals or nitty gritty of any of these systems but I feel sure there are people here who have so maybe they could jump in with ideas.
I don’t quite know what you mean by this. Are the clips going to be the antennas?? I don’t think too many here would know what they looked like so a couple of pics along with a description might help.
Cheers Bob
The Neo-6m has half the horizontal position error of the Cirocomm (2.5m vs 5m). It also has a much higher update rate and a much shorter time to first fix. At your quoted arrangement of 4 receivers distributed around the perimeter of a 50m diameter circle, that is more than adequate accuracy.
Hi Michael,
While I have heard these can be fiddly to get working, the following tech has good accuracy using radio:
https://www.decawave.com/product/evk1000-evaluation-kit/
And while very pricey, RTK can improve the accuracy of GPS units with a stationary reference:
https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all
The lower-cost solutions suggested above would be the way to go if the lower accuracy is acceptable.
Maybe a camera set up to track the objects instead?
-James
Thanks James, but at the moment I am going to try Jeff’s suggestion of the Neo-6m GPS sensor and see what improvement in accuracy of recorded data is, using my 4-yr-old Arduino. I can simultaneously use my phone to check the same locations using the GPS Coordinates app.
I have the software already written and if the data is acceptable I will then, later, need a way of transmitting the lat/lon data from each of the four croquet hoops to a receiver. (I would need three more Neo-6ms!).
I watched the video in this snooker quote (don’t know how to put the video in the quote) and I am amazed at the technology! I even remembered a movie about a man using a special calculation to determine the right shot in snooker, can’t remember the name of the movie. And now it’s a reality!
I knew nothing about croquet so I read about it and tried to work out what this has to do with transmitters and directional receivers. My assumption is the scheme is trying to track where the clips are in real time. The description I read says the clips are to be placed on the next hoop to be played by the ball of the same colour as the clip. And this can give the score at that point in the game. I may have this completely wrong.
If I’m right, then this may be solved by using something like RFID tags and readers. The reader transmits its identity and the identity of any tag (so if the reader is on the clip, the tag would be on the hoop and the clip transmits its own code and the hoop code. If the reader is the hoop, then it transmits its code and the clip code.) RFID tags are passive so only one of hoop and clip needs power (a battery). The RFID tags are cheap, so minimising cost says the hoops have the tags and the clips are the transmitters. But that would make the clips rather bulky, would people be happy to cart them around?
Just throwing random thoughts around.
