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Merge multiple complex streams

Imre
Playing around with GRC for a few months now, sorry if this question is
from a dummy.

I've a bunch of rtl dongles laying around, and wonder if it's possible to
combine more then one to a single baseband signal.

The goal is to create a super cheap full HF band web reciever like or for
' websdr'

I managed to create multiple channels, where the 2nd dongle is tuned to an
offset, equal to the samplerate of the first. (for example 2 x 2 Msps = 4
Msps baseband)

Is such a thing possible with GRC?

Imre Biacsics





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Re: Merge multiple complex streams

Mike Jameson-3
If you make an FFT block for each rtl-sdr source you can then interleave them all together and take your pick using the 'M in N' block. At the edges of each rtl-sdr frequency it will probably get quite messy as the clocks are not synchronised.

An example of the use of the FFT and 'M in N' blocks is in my scanoo_rx app which will give you a head start.  The 'M in N' block is used to pick out the channel from the output of the FFT block:
I've always found that in order for it to work at first you must double click something in the flowgraph and then click cancel... some random erroneous bug in GRC.

Mike

On Mon, May 12, 2014 at 4:49 PM, Imre Biacsics <[hidden email]> wrote:
Playing around with GRC for a few months now, sorry if this question is
from a dummy.

I've a bunch of rtl dongles laying around, and wonder if it's possible to
combine more then one to a single baseband signal.

The goal is to create a super cheap full HF band web reciever like or for
' websdr'

I managed to create multiple channels, where the 2nd dongle is tuned to an
offset, equal to the samplerate of the first. (for example 2 x 2 Msps = 4
Msps baseband)

Is such a thing possible with GRC?

Imre Biacsics





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Re: Merge multiple complex streams

Martin Braun-2
In reply to this post by Imre
On 12.05.2014 17:49, Imre Biacsics wrote:

> Playing around with GRC for a few months now, sorry if this question is
> from a dummy.
>
> I've a bunch of rtl dongles laying around, and wonder if it's possible to
> combine more then one to a single baseband signal.
>
> The goal is to create a super cheap full HF band web reciever like or for
> ' websdr'
>
> I managed to create multiple channels, where the 2nd dongle is tuned to an
> offset, equal to the samplerate of the first. (for example 2 x 2 Msps = 4
> Msps baseband)
>
> Is such a thing possible with GRC?

A couple of things, on top of what Mike said:

- HF bands go lower than the frequency of the dongles. Keep that in mind.
- As Mike said, clocks aren't sync'd. So, if you're using data from
multiple dongles, that'll most likely be corrupt.
- To make things worse, they drift differently too. So, little chance in
fixing things.
- If all you want is an (inaccurate) "spectrum analyzer" for more than 2
MHz, then this is actually not a bad idea. If you have N+1 dongles, you
can use N of them to monitor N*2MHz of spectrum, and the other one to
receive at frequencies you're interested in.

M


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Re: Merge multiple complex streams

madengr
In reply to this post by Imre
How about the PFB synthesizer detailed by TR?  I'd think all the dongles would have to be phase locked and references tones (or comb) used to calibrate the channels.  If your signals are not crossing channels then maybe you could get away without that.

http://www.trondeau.com/examples/2014/1/23/pfb-channelizers-and-synthesizers.html


Imre Biacsics wrote
I've a bunch of rtl dongles laying around, and wonder if it's possible to
combine more then one to a single baseband signal.
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Re: Merge multiple complex streams

Imre
(Something went wrong with my mails, hopefully doing it right now, sorry Mike, replied directly to you)

Using Mike's example and some fiddling around:

http://www.livep2000.nl/code/grc/multichannel_input.grc

Tuning on a FM channel shows the mentioned mess,
interconnect the hardware clock? Maybe like this:

http://lists.gnu.org/archive/html/discuss-gnuradio/2013-09/msg00387.html

I'am give the polyphase synthesizer a look



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Re: Merge multiple complex streams

Marcus D. Leech
On 05/13/2014 03:02 PM, Imre wrote:

> (Something went wrong with my mails, hopefully doing it right now, sorry
> Mike, replied directly to you)
>
> Using Mike's example and some fiddling around:
>
> http://www.livep2000.nl/code/grc/multichannel_input.grc
>
> Tuning on a FM channel shows the mentioned mess,
> interconnect the hardware clock? Maybe like this:
>
> http://lists.gnu.org/archive/html/discuss-gnuradio/2013-09/msg00387.html
>
> I'am give the polyphase synthesizer a look
>
>
>
>
>
>
>
> --
> View this message in context: http://gnuradio.4.n7.nabble.com/Merge-multiple-complex-streams-tp48146p48191.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
>
> _______________________________________________
> Discuss-gnuradio mailing list
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All you channels will not only need to be phase-coherent, but also have
zero phase offset.  That's the only way you can reasonably simulate
   having much wider bandwidth by "gluing together" a bunch of smaller
bandwidths.

My own experiments with the RTLSDR gear is that achieving phase
coherence across significant bandwidth appears to not be possible, even
   with a common, high-quality master clock.


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Re: Merge multiple complex streams

Imre
We must not forget that each device has its own USB connection.
One reason that getting all in sync on a ' per sample'  base must be impossible.

Still a multi user system like the websdr can achieved by overlapping the channels and let the software decide what channel the user's choice fits.

For a nice graphical representation (Spectrum analyzer, waterfall) this principle could work well.

Imre



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Re: Merge multiple complex streams

Vanush Vaswani
What about the passive radar - didn't the author daisy chain the clocks of several RTLSDR?

Regards,
Vanush


On Wed, May 14, 2014 at 4:31 PM, Imre <[hidden email]> wrote:
We must not forget that each device has its own USB connection.
One reason that getting all in sync on a ' per sample'  base must be
impossible.

Still a multi user system like the websdr can achieved by overlapping the
channels and let the software decide what channel the user's choice fits.

For a nice graphical representation (Spectrum analyzer, waterfall) this
principle could work well.

Imre







--
View this message in context: http://gnuradio.4.n7.nabble.com/Merge-multiple-complex-streams-tp48146p48198.html
Sent from the GnuRadio mailing list archive at Nabble.com.

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Re: Merge multiple complex streams

Martin Braun-2
On 14.05.2014 09:03, Vanush Vaswani wrote:
> What about the passive radar - didn't the author daisy chain the clocks
> of several RTLSDR?

That was two dongles sharing a clock. Not exactly daisy-chained, and it
didn't look easily extendible :)

http://kaira.sgo.fi/2013/09/passive-radar-with-16-dual-coherent.html

M

>
> Regards,
> Vanush
>
>
> On Wed, May 14, 2014 at 4:31 PM, Imre <[hidden email]
> <mailto:[hidden email]>> wrote:
>
>     We must not forget that each device has its own USB connection.
>     One reason that getting all in sync on a ' per sample'  base must be
>     impossible.
>
>     Still a multi user system like the websdr can achieved by
>     overlapping the
>     channels and let the software decide what channel the user's choice
>     fits.
>
>     For a nice graphical representation (Spectrum analyzer, waterfall) this
>     principle could work well.
>
>     Imre
>
>
>
>
>
>
>
>     --
>     View this message in context:
>     http://gnuradio.4.n7.nabble.com/Merge-multiple-complex-streams-tp48146p48198.html
>     Sent from the GnuRadio mailing list archive at Nabble.com.
>
>     _______________________________________________
>     Discuss-gnuradio mailing list
>     [hidden email] <mailto:[hidden email]>
>     https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
>
>
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