WOW MIKE THANKS! So that's the way I will be going. I, already, foresee a calibration phase so that is not a problem. Thanks again! Marcel Mike Hawkshaw wrote: > Marcel, > > If you use the phase information, then you will not loose accuracy by > downconverting to IF. You will find, however that to resolve phase > infomation at 1.5GHz directly, is impossible. > > With FSK, a phase locked loop should be able to recover the original carrier > fairly easily, but now I think about it again, you might not have to do > this, the phase difference between the two IF signals will be the same even > with the modulation present. > > You will probably have to do some sort of calibration, with the transmitter > in a known place wrt the reciever, to illiminate any odd phase shifts in the > reciever. e.g. in IF filters. > > I once looked round the control tower of my local airport, and they had a > device which recieved the local comms channel, and had a crt which "pointed" > in the direction of the incomming signal so the controllers could see where > the aircraft was who was talking to them. It had an array of 4 dipoles on > the roof of the control tower. Also look up "RF direction finding" > > Cheers.... Mike. > > ----- Original Message ----- > From: "Marcel van Lieshout" > To: > Sent: Monday, April 05, 2004 7:17 PM > Subject: Re: [EE:] 3-D tracking > > >> Mike, >> >> I am no RF-engineer, but even if I have to give this task to someone who is I would like to >> understand what is happening. >> >> Am I understanding you correctly that I will not loose resolution > (accuracy, etc) when mixing down to IF? >> My intention was to measure the phase-difference of the 2.4GHz carrier, > not the phase-difference of the >> modulation. It would be great if you can confirm that, by using the IF instead, I will not loose >> resolution. >> >> BTW: The modulation-type is GFSK. I have no control, whatsoever, of the transmissions. >> >> Mike Hawkshaw wrote: >>> Marcel wrote: >>>> The main obstacle I see now is: How do I extract the needed 2.4GHz carrier from all the signals >>>> (microwave-oven, wifi, bluetooth, etc) arriving at the antennas. "Normal" receivers do this by >>>> mixing with a slightly lower frequency resulting in an IF-signal. This I do not want, I want >>>> the carrier (with phase-info retained). I do know the frequency to look for, if that is of any >>>> help. >>> >>> If you mix the signal down to an IF, the phase information is retained. It >>> has to be, because if it wasn't , the modulation could not be recovered. >>> >>> For each recieving station, you will need a reciever(single LO) but with two >>> RF inputs. Mix the two inputs (one from each antenna) down to a manageable >>> IF, say 10.7Mhz using the same LO and then you can work on them. >>> >>> I'm not sure what modulation scheme the transmitters are using, but you will >>> need to recover the original carrier (at IF) of the signal i.e. removing the >>> modualation. (By this I mean, for example if the modulation was ssb, then >>> recover the carrier which was suppressed) This is the only really hard part. >>> I would think the modulation scheme will be something like QPSK or QAM >>> system, and recovering the original carrier will not be easy. You will need >>> a quick locking and stable phase locked loop. You can then compare the >>> phases of these two recovered carriers, and they will directly represent the >>> carrier phases of the two incident carriers at 1.5Ghz; this will then give >>> you a plane of possible locations per recieving station of where the >>> transmitter is. >>> >>> I am an RF engineer with considerable experience, and would shudder if >>> someone were to ask me to achieve what you are trying to do. You are working >>> right at the edge of what is possible. You will need a lot of luck. >>> >>> Some things to read about which would be on my research list are: >>> RF network Analysers - how do they work. >>> GPS - there is a carrier phase method which can be used to achieve greater >>> accuracy - how does that work. >>> RF reciever demodulation techneques - carrier recovery and PLLs. > > > --- > Outgoing mail is certified as Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.648 / Virus Database: 415 - Release Date: 31/03/2004 -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu