Forum: GNU Radio Support for 8-bit USB samples in GRC

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558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2009-01-30 14:18
(Received via mailing list)
Josh, et al:

Do you have plans to support 8-bit sample settings in the GRC USRP
objects?

--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
4252201ac30d6dd44d8090ce1070e35f?d=identicon&s=25 Josh Blum (Guest)
on 2009-01-30 17:54
(Received via mailing list)
There are plans now...

Any example code would help
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2009-01-31 21:13
(Received via mailing list)
Josh Blum wrote:
> svn up!
>
> let me know if something goes wrong
>
Intersesting.

When I use 8-bit samples with decim=8 or higher, things are peachy.

But when I use decim=16 with 8-bits samples, I get a continuous stream
of -423dB out of the FFT Log Power sink.

I think what I'm getting is a pile of 0s from the USRP when decim=4.

Can anybody confirm that decim < 8 actually works on the USRP?



--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2009-01-31 21:32
(Received via mailing list)
Marcus D. Leech wrote:
>
> But when I use decim=16 with 8-bits samples, I get a continuous stream
> of -423dB out of the FFT Log Power sink.
>
> I think what I'm getting is a pile of 0s from the USRP when decim=4.
>
> Can anybody confirm that decim < 8 actually works on the USRP?
>
>
>
>
OK, let's try that again with my brain actually engaged.

Anything with decim=8 or higher, in 8-bit mode, produces "sensible"
samples.

Anything with decim lower than 8 (like 4) produces nonsensical results
in the Log Power FFT sink (a continuous block
  of -423dB).  I suspect that with decim=4, there ain't nothing but
zeros going across the USB.

So, does decim=4 actually work on the USRP, or do I need different
firmware?




--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
4252201ac30d6dd44d8090ce1070e35f?d=identicon&s=25 Josh Blum (Guest)
on 2009-01-31 22:54
(Received via mailing list)
According to this:
http://gnuradio.org/trac/browser/gnuradio/trunk/gr...

if you dont like half band filters or you want to decimate by 4,
"std_4rx_0tx.rbf" is the firmware for you

-------->

so, it seems that the correct thing to do in grc would be to set this
special firmware if your desired decim is 4 and its a usrp source.

Does that make sense (to someone in the know)?

-Josh
3d593de8acbe2510722af740d8668352?d=identicon&s=25 Firas Abbas (Guest)
on 2009-01-31 23:39
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Hi,

When working with 8 bit samples, you must disable FPGA halfband filter
see (http://gnuradio.org/trac/wiki/UsrpFAQ/DDC).

To do so, the USRP (via GRC) should load the "std_4rx_0tx.rbf" image.


Best Regards,

Firas
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2009-02-01 00:17
(Received via mailing list)
Josh Blum wrote:
> special firmware if your desired decim is 4 and its a usrp source.
>
> Does that make sense (to someone in the know)?
>
> -Josh
That sounds like the right strategy.

For the DBS_RX (which is the card I use for radio astronomy), it has
built-in programmable low-pass filters on the I and Q
  baseband outputs anyway.

--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2009-02-01 00:27
(Received via mailing list)
Firas Abbas wrote:
>
>
>
>
I have confirmed that using the "std_4rx_0tx.rbf" firmware works OK.   I
tested this by patching in that firmware
  into the grc_gnuradio/usrp  code, but a more-general solution is
definitely called for.

Perhaps there's should be a "firmware" parameter in the USRP source/sink
blocks.

--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
4252201ac30d6dd44d8090ce1070e35f?d=identicon&s=25 Josh Blum (Guest)
on 2009-02-01 01:19
(Received via mailing list)
> Perhaps there's should be a "firmware" parameter in the USRP source/sink
> blocks.
>

I want to avoid this if possible. If we only need to use this firmware
when decim < 8, then that can be done inside the grc usrp code.... But
if someone wants to disable the halfband filters and TX when decim >=8,
i would have to actually add this option into the blocks.

So, is there a case when someone needs to disable the half band
filters... in general, in grc?

just trying to keep the simple usrp blocks -> "simple"
-Josh
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