IF sampling in ISM band

Hi List,I am using an RFX2400 d’board, for IF sampling a signal which is
20MHz wide, centered at 2.4125GHz. I know it’s not possible to sample
whole 20Meg, but I am happy with a 16MHz version at this stage (which we
belive is the widest we can go). I am using

python usrp_rx_cfile.py -f 2404.5M -s --no-hb -8 -N 40000 data1.dat

  1. Am I correct in using 2404.5M to downconvert the IF signal at 10MHz?
    I need “real” IF samples at 10MHz, do I need to change something here?

  2. this frequency in the above command is LO frequency or incoming
    signal frequency?

  3. My signal is in the range 2402.5-2422.5MHz range, which is well with
    in defined range of RFX2400 (2.4-2.483GHz), do I still need to cut lines
    for ISM filter on-board, as one of my project mates was advised to do.
    If yes, can’t I use the other signal input on the board, which hasn’t
    got any filter around it?

  4. when I look at the spectrum of the IF samples collected using above
    command, they appear to have lesser bandwidth (4MHz) than the expected
    bandwidth(20MHz).

Sorry if any/all of these questions sound stupid, but consider me novice
:S

Regards Faisal

On Fri, Jul 04, 2008 at 12:21:25PM +1000, Phaysal Khan wrote:

Hi List,I am using an RFX2400 d’board, for IF sampling a signal
which is 20MHz wide, centered at 2.4125GHz. I know it’s not possible
to sample whole 20Meg, but I am happy with a 16MHz version at this
stage (which we belive is the widest we can go). I am using

python usrp_rx_cfile.py -f 2404.5M -s --no-hb -8 -N 40000 data1.dat

I’m pretty sure that the 8-bit support is still missing from the FPGA.
Until somebody fixes that, the highest rate you’ll be able to run at
is 8MS/s complex. That’s what you’ll get with -d 8.

  1. Am I correct in using 2404.5M to downconvert the IF signal at
    10MHz? I need “real” IF samples at 10MHz, do I need to change
    something here?

You set the frequency that you want to appear at DC in the complex
baseband.

  1. this frequency in the above command is LO frequency or incoming
    signal frequency?

The -f argument is the RF frequency that you want to appear at
zero in the complex baseband.

  1. My signal is in the range 2402.5-2422.5MHz range, which is well
    with in defined range of RFX2400 (2.4-2.483GHz), do I still need to
    cut lines for ISM filter on-board, as one of my project mates was
    advised to do. If yes, can’t I use the other signal input on the
    board, which hasn’t got any filter around it?
  1. when I look at the spectrum of the IF samples collected using
    above command, they appear to have lesser bandwidth (4MHz) than the
    expected bandwidth(20MHz).

With -d 8 you’ll get 64M/8 = 8MS/s complex. That’ll be +/- 4MHz.

Sorry if any/all of these questions sound stupid, but consider me
novice :S

Welcome!

Eric

On Thu, Jul 3, 2008 at 8:58 PM, Eric B. [email protected] wrote:

I’m pretty sure that the 8-bit support is still missing from the FPGA.

It was fixed in r6858 on the trunk and made it into release 3.1.2.


Johnathan C.
Corgan Enterprises LLC
http://corganenterprises.com/

On Fri, Jul 04, 2008 at 03:48:56PM +1000, Phaysal Khan wrote:

Hi,

Thanx Eric and Johnathan. I would be upgrading my radio to
3.1.2. But the actual question remains: Is there any way to bring
this incoming RF Signal down to some IF (say 10MHz)? and to get only
real samples?

Nope. Complex only.

It’s not that hard, just different than what you may be used to.

Eric

Hi,
I just upgraded my radio to 3.1.2, for getting 8-bit support. But the
acquired IF samples still show +/-4MHz spectrum (not +/-8MHz which I
required). Also, changing frequency on command line does not move
spectrum of IF samples, they still appear to be centered at zero freq.
Any Idea, what could be missing this time?! Faisal > It’s not that
hard, just different than what you may be used to.> > Eric

Hi List,
Just re-stating the issues I am having with capturing IF samples of an
RF signal: I am trying to sample a 16MHz wide spectral content from a
signal, originally centered at 2.414 GHz. I am using RFX2400, gnuradio
3.1.2 and using following command:

python usrp_rx_cfile.py -f 2404.5M -s --no-hb -8 -N 40000 data1.dat
using “-f 2404.5M” to get IF (downconverted) signal centered at 10MHz.
using “-s --no-hb -8” to be able to capture 16MHz wide bandwidth.
I am having following issues:

  1. I am getting a downconverted signal centered at zero freq and not at
    10MHz which I expected.
  2. I can see downconverted signal’s spectrum to be only +/-4MHz wide,
    and not +/-8MHz.

Any idea, what is causing these two problems here!? Faisal

Hi,
Thanx Eric and Johnathan. I would be upgrading my radio to 3.1.2. But
the actual question remains: Is there any way to bring this incoming RF
Signal down to some IF (say 10MHz)? and to get only real samples?

Regards

On Tue, Jul 08, 2008 at 10:16:53AM +1000, Phaysal Khan wrote:

Hi List,
Just re-stating the issues I am having with capturing IF samples of an RF signal: I am trying to sample a 16MHz wide spectral content from a signal, originally centered at 2.414 GHz. I am using RFX2400, gnuradio 3.1.2 and using following command:

python usrp_rx_cfile.py -f 2404.5M -s --no-hb -8 -N 40000 data1.dat
using “-f 2404.5M” to get IF (downconverted) signal centered at 10MHz.
using “-s --no-hb -8” to be able to capture 16MHz wide bandwidth.
I am having following issues:

  1. I am getting a downconverted signal centered at zero freq and not at 10MHz which I expected.
  2. I can see downconverted signal’s spectrum to be only +/-4MHz wide, and not +/-8MHz.

In the trunk (sorry, I didn’t take time to build 3.1.2), when I do
this, I see 16MHz of spectrum:

[[email protected] ~]$ usrp_fft.py -8 -f 92.1 -d 4

How do you know you’re not getting +/- 8MHz?

How wide is the signal that you want offset by 10MHz?

Eric

On Mon, Jul 07, 2008 at 05:27:40PM -0700, Eric B. wrote:

On Tue, Jul 08, 2008 at 10:16:53AM +1000, Phaysal Khan wrote:

Hi List,
Just re-stating the issues I am having with capturing IF samples of an RF signal: I am trying to sample a 16MHz wide spectral content from a signal, originally centered at 2.414 GHz. I am using RFX2400, gnuradio 3.1.2 and using following command:

python usrp_rx_cfile.py -f 2404.5M -s --no-hb -8 -N 40000 data1.dat

I note that you’re not specifying -d 4 to set the decimation rate.

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