Marcel, The control tower direction finder used a scheme that has been around quite a while in amateur radio direction finding circles. It was first published in QST magazine May 1978 as the "DoppleScAnt (short for Doppler Scanned Antenna). See http://www.harcnet.org/tdoardf1.pdf for another construction article on this technique from 1999. There is some ambiguity from multi-path, but it works pretty well (in my experience). Ramsey electronics also sells a kit. See http://www.ramseyelectronics.com/downloads/manuals/DDF1.pdf I think this technique could be extended to 3 axis with two arrays orthogonally polarized. Edward Gisske, P.E. Gisske Engineering 608-523-1900 gisske@offex.com ----- Original Message ----- From: "Mike Hawkshaw" To: Sent: Monday, April 05, 2004 1:33 PM Subject: Re: [EE:] 3-D tracking > 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 > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu