|
|
Post by robinastro on Oct 5, 2013 16:42:03 GMT
|
|
|
|
Post by robinastro on Oct 5, 2013 17:15:08 GMT
Correction:
Reading more carefully I see the setup uses two collocated antennae and the phase difference between the direct and reflected signal rather than measuring the reflected signal using spatially separated antennae forming a baseline. Still neat IMO though ;-)
Robin
|
|
|
|
Post by robinastro on Oct 6, 2013 1:11:11 GMT
a pair of RTS-DTR dongles That should of course have read "RTL-SDR dongles" (My excuse is I am currently working on a remote control system for a spectrograph flat and calibration lamp using the serial RTS/DTR lines) Robin |
|
|
|
Post by BillW on Oct 6, 2013 22:13:46 GMT
Very cool indeed, pity you need the great big transmitter as well  Recently I bought one of the Funcube pro+ sdr dongles to have a play with. Works really well, but on VHF my PC produces so much hash I can't hear the GRAVES radar reflections which I can even hear on a vertical antenna using a conventional radio.  cheers, Bill. |
|
|
|
Post by stewartw on Oct 7, 2013 10:15:37 GMT
Hi Bill, I asume you've placed the dongle some distance from your PC and have connected it using a USB extension lead - there's some discussion of this noise issue on page 48 of the BAA Radio Group's RAGazine at www.britastro.org/radio/downloads.htmlApologies in advance if I'm stating the obvious ... Best regards William |
|
|
|
Post by robinastro on Oct 10, 2013 1:14:55 GMT
Very cool indeed, pity you need the great big transmitter as well In this example it came FOC in the form of a local FM radio station. It relies on cross correlating the FM modulation to measure the delay. (There is an example in another link showing how it lost lock during a quiet period in the transmission kaira.sgo.fi/2013/09/passive-radar-update.html ) Must be tough to keep the direct signal out of the reflected signal path though. Presumably you put the line of sight direct signal into one of the deep nulls in the back scatter antenna. Cheers Robin |
|
|
|
Post by BillW on Oct 10, 2013 8:22:13 GMT
Hi Robin, Difficult indeed!, as how do you know where to direct the signal and null antennae? The meteors could come from any direction and the relative scattering paths would essentially be random  However you would pick up signals coming from a cone on the sky where these parameters were in correct phase. That would reduce the absolute detection efficiency in terms of numbers but would be perfectly valid over the long term since you know exactly where you're looking. It's interesting stuff. Have you tried anything like this? cheers, Bill. |
|
|
|
Post by robinastro on Oct 13, 2013 14:36:01 GMT
Hi Bill, It's interesting stuff. Have you tried anything like this? Not directly, beyond listening to meteor pings as a radio amateur back in the late 60s and the signal processing has something in common with the sort of paper machine diagnostics I was involved in during the 80's (correlation of signals from pressure transducers in pipework systems) Since this system depends on being able to hear the transmitter at all times, it is back scatter with the transmitter in the line of sight rather than the perhaps more usual forward scatter with the transmitter over the horizon. A first test could perhaps be done using a conventional meteor scatter setup with a directional antenna orientated to minimise the direct signal and listening for the pings from back scattered signals. If they can be heard then this sort of 2 channel rangefinding setup could be interesting to try. (Is knowing the range and approximate direction useful information? I guess the technique could be extended by correlating the range information from two locations, or even perhaps from one location using two transmitting stations. This could be used to pinpoint the location of the scattering source, in 2D at least) The software in this system is bespoke though by the looks. I dont know if any standard SDR packages would have the capability. I will try to contact the author to see what else I can pick up Cheers Robin |
|
