SparkFun Forums

[rppearso]

Are there any micro controlers that can accept 2.4 GHz radio frequency inputs from an antenna and that can be programmed to measure the time delay between the 2 waves and accept mathematica or matlab programing for a voltage vs phase curve that outputs a voltage.

[Mee_n_Mac]

In a word ... no.

I assume there's some reason for not using the normal test equipment ?

You might marry an AD8302 to a micro or SoC to measure relative phase and report it.

[Dave Mueller]

I was going to suggest the AD8302 as well, but it needs 2 distinct inputs which you can't get from a single antenna.
Once you split into two antenna systems, then you need a way to match the systems to have identical phase delay. Narda makes (made?) a small phase trimmer with SMA connectors that would allow for precise matching.

I believe you can also use a double balanced mixer as a phase detector for two signals close in frequency, as long as the IF port goes down to DC.

What's the path length? Unless very short and line of sight, the phase difference could be from propagation as well as differing distances.

[Mee_n_Mac]

I was going to suggest the AD8302 as well, but it needs 2 distinct inputs which you can't get from a single antenna...

Well if the OP has only 1 antenna and there are 2 signals identical in frequency input to it, then all there is at that antenna's output is a single signal w/some "combined" phase. There's no way to separate them once added together. So I assume he's got 2 antennae.

Once again we're given insufficient info to give a good answer.

http://blockyourid.com/~gbpprorg/mil/in ... index.html

[waltr]

This one does sound like a university physics/engineering project.

But until he/she states exactly what they want to accomplish we can only guess at solutions.

[Dave Mueller]

I just remembered it is possible, but probably not for this application. I worked on a distributed HDTV network in NYC. It was multiple transmitters all on the same frequency, everything GPS locked, called an SFN - single frequency network. Each transmitter had a unique ID embedded in its data stream. We had a box (sorry, can't remember what make/model) that you connected to a receive antenna. It would analyze all of the signals and provide a graph of time delay between each stations. Since it was able to decode each transmit stream separately and measure the time difference between them, it could probably figure out phase as well since it's related. I doubt the OP has a 6 or 7 figure budget for this problem though

[skimask]

Sounds like something close to GPS-RTK?

[jremington]

Then there is this wild leap of the imagination:

accept mathematica or matlab programing

[Mee_n_Mac]

Yeah, obviously the OP doesn't recognize the difference between a micro-controller (MCU) and an system on a chip (SoC) or a PC. I'll opine that the OP has some grand intention in mind that he's yet to tell us about (Ssssh, Top Secret). Still ignorance isn't arrogance ... and we may yet hear what he really wants to do.

carnac-the-magnificent_huh.jpg

[rppearso]

Thank you so much for the replys, my first degree is in chemical engineering and I am working on a BS/MS in EE now. This is my first attempt at undertaking a real life project and not just doing math and matlab models. I have half a block diagram sketched out and will finish soon and post it. I have matlab code that allows me to do imedance matching and I would accomplish that by just verying the length of cable to the antenna (which is the simplest way, and just coil it up with a zip tie). There will be 2 antennas, one that is constantly transmitting from an osscilator from a DC power supply and the other will be reciving (the recieving antenna will be recieving the signal that I am broad casting plus any other signals out there. As I understand antenna operate on frequency so one freqeuncy will be from what I am broadcasting and the other from where ever (but the same frequency) so I guess that would only be one input with one frequency of 2 different phases, I appologize for that. Then the phase shifter will always be working to ensure that the phases are 90 out of phase but I have to have a way to meause the difference in order to send the proper signal to the phase shifter.

I am sure this is possible the issue is cost, I am now willing to spend 3 grand on a spectrum analyser so this one block may kill the project. The other angle is I could perhaps build a spectrum analyser but the entire device has to be somewhat small.

[Mee_n_Mac]

There will be 2 antennas, one that is constantly transmitting from an osscilator from a DC power supply and the other will be reciving (the recieving antenna will be recieving the signal that I am broad casting plus any other signals out there. As I understand antenna operate on frequency so one freqeuncy will be from what I am broadcasting and the other from where ever (but the same frequency) so I guess that would only be one input with one frequency of 2 different phases, I appologize for that. Then the phase shifter will always be working to ensure that the phases are 90 out of phase but I have to have a way to meause the difference in order to send the proper signal to the phase shifter.

Hmmm, what ? I'm afraid I'm not understanding your experimental setup. Nor do I understand what the purpose of your measurements is ? Perhaps a block diagram of the setup or some further description of what you're trying to do will help.

Antennae have both a frequency range (over which they work well) and a spatial range (over which they will transmit and/or receive w/o much loss). Are you transmitting a signal (of some sort) from 1 antenna to another and then trying to measure ... what, exactly ... ??? Where does the phase shifter (mentioned above) figure into this all ? Are you trying to create a PLL ?? If so, why ? Is the transmitted signal just an un-modulated carrier or ?? Are you trying to detect it's presence given that there's other interfering signals, or demodulate some information impressed onto it ??

I have a gut sense you're trying very hard to complicate something that, for an "RF person", is actually pretty simple. If you can describe what you're trying to do, instead of asking how to do it your way, you may get better answers.

[Dave Mueller]

If the two signals are exactly the same frequency, and both received by one antenna, it is impossible to separate them to measure their phase difference. They would appear as a single signal on a spectrum analyzer. The amplitude of the signal will depend on the strength of the two signal plus their relative phase. Also, a spectrum analyzer measures amplitude vs frequency, it can't measure phase.

[stevech]

for low cost/home electronics, and at 2.4GHz, it's impractically expensive to determine the relative phase difference between two antennas for one signal.

An interferometer for three antennas is more complex yet but can get you the direction of arrival if you have analog processing at a few nanoseconds speed. You also always have to have a way to remove the ambiguities of multiples of 180 or 360 degrees in phase difference.

To determine bearing angle at 2.4GHz, and from combinations of that, using time difference of arrival, one can get location. Companies like Ekahau make such for 2.4GHz, but they're costly.

[rppearso]

So what im hearing is that if there are 2 different antennas somewhere in space tranmitting at the same frequency but different phase it would be very difficult to measure that phase difference? I guess I should define low cost, I would be willing spend a few hundred bucks or maybe a bit more on this but the only reason I brought up cost is becasue when I started looking for 2.4 ghz range osillascopes they were like 30 grand. The company that makes them gave me the information and permission to build one if I wanted too but I will have to make time (lots of time). Another individual from a different company also makes a frequency analyzer but those are 3 grand which is pricy but not outside the relm of possibility.

In theory when those 2 signals hit the antenna they are in fact traveling at different phase down the "transmission line" into the circuit but it sounds like capturing that difference will be a task.

There has to be a way to do it, it cant be impossible. Or cost tens of thousands, espeically if the cirucit was built from scratch or broke down into multiple 40$ components. All the other parts to the project I have found for about 40$ a "block". phase shifter, trangle wave generator, ossilator, amplifier, antennas, filters. I might have to have a custom made board to connect the modules but thats not too big of a deal as long as im mindful of matching but I dont think I need to worry about matching for super short runs in the radio frequency.

[rppearso]

it looks like the AD8302 might do the trick. I could design the cirucit so that the tranmitting antenna does not turn on unitl the recieving antenna gets a signal from the band pass filter the AD 8302 could then measure the signal between the bandpass filter and the ossilator. It would not be active phase shifting but I could get decent signal cancelation from the first incoming signal. Once I started transmitting then the reciever antenna would be getting 2 signals unless I was able to design the antennas so that they did not interfere but that would be tough and likely impractical.