Hi!

On Thu, Sep 12, 2013 at 7:33 PM, Marc Juul <juul@labitat.dk> wrote:

Hi!

Some of us at sudo room / east bay mesh are working on a low bandwidth disaster recovery mesh project based on software defined radios.

We're prototyping with a combination of USRP1 and RTL-SDR devices and GNU Radio.

We're having some issues getting the receivers to demodulate our data streams (using DQPSK and QAM modulation).

I never thought about doing much more than tuning to FM radios with my rtl-sdr, but that's a pretty cool project!

I think that depends what's your goal, if you want to decode qpsk frame from classic radios [1] I think rtl-sdr can do it.

If you want to Tx/Rx data accurately, I think you need a digital modulation chip [2]

(my understanding is that it works best at the hardware level if you want a decent bandwidth)

Something like this [3] could help, if you know someone who can program fpga cards ..

But it's a pretty cool project, maybe you can use an OFDM stream instead [4][5].

That's the hd tv data stream the chip RTL2832U [5] in the rtl-sdr is meant to demodulate in hardware.

.. I even found an opencore for ofdm modulation [7], which could (in theory) be loaded on an fpga ..

Cheers,

Matthieu

[1] http://en.wikipedia.org/wiki/Project_25

[2] http://www.maximintegrated.com/app-notes/index.mvp/id/686

[3] http://nuand.com/

[4] https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing

[5] https://www.youtube.com/watch?v=TQ0KDjxhXNk

[6] http://www.realtek.com.tw/products/productsView.aspx?Langid=1&PNid=22&PFid=35&Level=4&Conn=3&ProdID=257

[7] http://opencores.org/project,ofdm