Software Defined Radio

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by kj6dzb » Thu Apr 26, 2012 7:45 pm
GHPSDR3-alex has all the FFT comps running in openGL and the AMD FFT kernel.

We just got the Android aHPSDR client to do OpenGL waterfalls last night.

There are quite a few SDR hardware boards supported in GHPSDR3... +1

Gordon could you explain????

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by zemned » Fri Apr 27, 2012 2:46 pm
I'm that guy gsh / kj6zdzb!

I am looking at how to expose an SDR module API in the RPi that would allow us to tap into the DSP elements of the RPI; these can perform raw processing of floating point numbers many times faster than the ARMv6.

The ultimate aim is to get the API shipped in the RPi binaries distribution and provide a DAB reference design with the configuration and data acquisition (from rtl-sdr) being done on the ARM and the actual hard work being performed by the high performance DSPs on RPi.  As the API would effectively configure and connect functional blocks such as decimation filters, FFT etc.. and all the acquisition is on the ARM side, others should be able to develop more radio designs without severe limitations.

Regarding graphical display of waterfall graphs etc, the RPi supports OpenGL ES2 so that is all possible at the moment.


zemned (m1zem).
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by kj6dzb » Fri Apr 27, 2012 5:11 pm
Thats wonderful... I dought im telling you but there is a significant performance increase when the GPU and CPUs stream line the FFT.

You should seriously check out the GHPSDR3 server...   Once RPis start to arrive in California we can test the GL code. We have integrated the AMD FFT kernel , Arm FFT, but with no RPi.....

Please we have worked for over a year building this up and there is still some good! stuff to come around the end of the year(roadMap).  If you would consider participating in the RPi +  GHPSDR3 love baby!

I hope SDR enthusiast start moving toads board like the HiQSDR, enabling wide bandwidth sampling, thats were streamlined FFT computations are going to come in to play.

73 Mathison KJ6DZB
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by katzohki » Fri Apr 27, 2012 7:34 pm
I would love to be a part of this! Let me know if there's any way I can be involved.

My senior project in college was a SDR (not a very good one) and I've always wanted to do more in SDR. My specialty is sort of DSP too.


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by Dave_G_2 » Sat Apr 28, 2012 9:07 am
Haven't read all the posts here in great detail (too many of them) so apologies if this has been covered before.

Why not bring the signals (I & Q) down to around 10KHz then feed them to a 16bit SPI type ADC?

Manufactures like TI, MAXIM, NXP and National make several low cost ($5 to $10) 16bit ADCs, some are even 8 channels.

According to the datasheet, the Pi can set it's SPI clock as high as 125MHz.

The bits (31 - 20) to set the frequency of the SPI_CLOCK can be found in the AUXSPI1/1_CTL0 register at address 0x7E215080.

Certainly more then good enough for sampling "audio" in the 10 to 20KHz range.

The SPI could of course also be used to set the frequency of a DDS chip acting as the local oscillator thus allowing for a fully tunable SDR radio.
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by katzohki » Mon Apr 30, 2012 4:54 am
I forgot to mention this. I'd like to see this used as a VLF receiver.
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by kj6dzb » Mon Apr 30, 2012 5:16 am
Katzohki, Lets see the server post on 

Dave G2, get this to work: GC6016 or the ADC12D1800. Then we can really benchmark the CPU a TMS320C6713B-300 for the FFT and networking and Pi of sort for a Qt radio... Ive heard of a lot of VLF signals... never watched the band...

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by Dave_G_2 » Mon Apr 30, 2012 12:39 pm
Hi kj6dzb

I suspect that the ADC12D1800 might be a bit of an overkill.

It's a 3.6Gbs/s ADC which the Pi will probably struggle to make full use of.

From the casual glance at the chips specs, it also seems to have a 12 bit parallel output which would pretty much use up a large majority of the Pi's available I/Os  and leave very little for other possibly required functions such as a tunable front end pre-selector.

I was thinking more along the lines of a 16 bit SPI ADC which can handle say 100 or so Ms/s.

Surely this will be sufficient to digitize the 10KHz (or so) I&Q signals?

I'm not a radio ham, so possibly I'm under estimating the task at hand.
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by kj6dzb » Sat May 05, 2012 6:30 pm
The ADC12D1800 board is not only for the RPi.  The RPi could lock onto the FFT stream over Ethernet, or if programed the FPGA could send it's streams to another DSP server or over Ethernet your Qt-radio client running on a RPi or what ever...  I dought the Pi is going to have a hard time running up against any hard hitters that run DSP servers processes large chunks of spectrum.

Broadband spectrum sampling has to take place on a custom FPGA based system, if its with GC6016 or ADC12D1800 or something else. Every one is bouncing off the walls on this RPi SDR thing....  There are lots of ways to set up 10 to 192khz sampling systems,  the hacked usb tuner cards do about 2mhz, but to really get a SDR to Sample and synthesize RF with out specialized circuits for a one band or another.... I think we must  tackle FPGA based SDRs.

The HiQSDR is a good example of a FPGA SDR, but If the design operated on the assumption that its going to feed a Qtradio interface or even stream to another DSP server and the size of the board could come down.

The GHPSDR3 wiget group is discussing possible FPGA's  to accomplish the task. If the board is developed to from specks from thou out the community, then we may be talking about a new line of SDR board for mid scale production.


Mathison KJ6DZB
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by caulktel » Sun May 06, 2012 6:48 pm
I also am very interested in using the Pi for SDR, in fact I have almost finished my SoftRock lite II kit. Can't wait to get it cranked up and start listening.

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by PaulTech » Wed May 09, 2012 9:47 pm
caulktel, after getting my RTL SDR I decided to buy a soft66lite which was quite easy to build, I'm now trying to get a DDS attached to a arduino to control the frequency. And I'm looking at an old scanner trying to work out the best way to attach a connector to the 10.7MHz IF. Maybe use the 232 port on the arduino to control the scanner too.

So now I will have quite a bit of SDR gear if my RPi ever arrives, I'm probably down for the 100,000th.
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by caulktel » Fri May 11, 2012 1:00 pm
I'm in the same boat as you, hurry up and wait. and I ordered mine about 8 hours after it went on sale. I would like to get familiar with the Arduino also, just not sure which one to buy. Thanks for the soft66lite info, I didn't know about that one. There are a lot of SDR radios out there and I would like to find a good USB radio a give it a try. The softrock lite II that I built works okay but seems to have lots of birdies, maybe it will perform better when I get it in a case and shielded. The local oscillator after being divided down is sitting at 7.056Mhz and obliterates most of the entire spectrum within the tuning range. Could be the SDR software I'm using also, Rocky.
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