Hello, Articles I read say that a 10MSPS rate gives better performance that a 8MSPS rate. I used the 8MSPS rate and still got good performance.
The oversampling is used in determining if the pulse is valid or part of interference. Some receivers use a huge ROM lookup table to convert all the sample values of the PPM slot into a one or zero. 73 Eric ----- Start Original Message ----- Sent: Sun, 24 Oct 2010 20:40:18 +0200 From: Andrea Montefusco <andrea.montefu...@gmail.com> To: discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] Gnuradio Mode S project released > On 10/24/2010 07:22 PM, Andrea Montefusco wrote: > > > is it thinkable to operate the decoder at a lower sample rate ? > > (e.g. at 2 MS/s or even less) > > I found this reference > > http://www.tech-software.net/adsb_decode1.php > > in a Eric A. Cottrell message that explains why we need an high sample rate: > > [...] > I thought that the USRP and DVB tuner board could also receive ADS-B and > Mode S. I did not know if my discone and long coax run would work. So > I did some experiments. > > I used the fft and oscilloscope programs to check for activity. I did > see activity on 1090 MHz. I then modified the oscilloscope program to > do AM detection with the gr.complex_to_mag() function. I saw various > pulse trains that look correct. There were some short ones that look > like old transponders and longer ones that look like Mode S. I found > the range of good gain settings was narrow (31 to 35) with 33 to be the > best. I found the decimation of 16 gave good pulse shapes. The pulse > timings are in 500 nS units so you need 250 nS sample times at least. > [...] > > So, I believe there is no hope to decode this stuff with HAM SDR hardware. > > *am* > > --------------------------------------------------------- > Andrea Montefusco iw0hdv http://www.montefusco.com > tel: +393356992791 fax: +390623318709 > --------------------------------------------------------- > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > ----- End Original Message ----- _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
