Q. USRP2+RFX2400 performances on dynamic range, and decim


#1

Hi guys,

Using my usrp2+RFX2400 and the GRC with gnuradio 3.2svn,
I’ve recorded a wimax signal out of a RF signal generator.

However, I found some issues with the result and ask you guys for some
help.
(I tried to search on these issues, but only found some about usrp.)

  1. The biggest problem is the dynamic range of the signal:
    The recorded signal showed only about 25dB between the in-band spectrum
    level(-25dBm/RBW) and the noise floor (-50dBm/RBW) while the original
    signal shows at least 45dB.

I wonder if this is normal with the given hardware of usrp2. If not the
case,
please let me know how to improve it.
(The input signal was CH power of -14dBm, which was chosen to avoid the
3rd order distortion.)

  1. I see the minimum decimation rate of usrp2 is still 4 with GRC, and
    wonder if there is any way to further reduce it such as 3 or 2?

  2. What is the data format of the usrp2_source()? I see that it is
    complex, but I’d like to know more precisely such as float, double,
    or… (pls forgive me if someone have answered on this question but I’d
    appreciate if you answer on this too.)


#2

On Thu, May 21, 2009 at 08:23:31AM +0200, Yc Park wrote:

The recorded signal showed only about 25dB between the in-band spectrum
level(-25dBm/RBW) and the noise floor (-50dBm/RBW) while the original
signal shows at least 45dB.

What gain setting are you using?
Have you tried lowering it?

Eric


#3

Eric B. wrote:

On Thu, May 21, 2009 at 08:23:31AM +0200, Yc Park wrote:

The recorded signal showed only about 25dB between the in-band spectrum
level(-25dBm/RBW) and the noise floor (-50dBm/RBW) while the original
signal shows at least 45dB.

What gain setting are you using?
Have you tried lowering it?

Eric

The gain was 10dB. With higher gain, the ACPR gets worse with the given
input power.

I’m sorry that I do not know how to upload the captured spectrum, but it
is exactly as I mentioned in the first place: The noise floor is about
-50dBm while the in-band signal is at -25dBm over the 8.8MHz of the
signal bandwidth.


#4

Yc Park wrote:

Eric B. wrote:

On Thu, May 21, 2009 at 08:23:31AM +0200, Yc Park wrote:

The recorded signal showed only about 25dB between the in-band spectrum
level(-25dBm/RBW) and the noise floor (-50dBm/RBW) while the original
signal shows at least 45dB.

What gain setting are you using?
Have you tried lowering it?

Eric

The gain was 10dB. With higher gain, the ACPR gets worse with the given
input power.

I’m sorry that I do not know how to upload the captured spectrum, but it
is exactly as I mentioned in the first place: The noise floor is about
-50dBm while the in-band signal is at -25dBm over the 8.8MHz of the
signal bandwidth.

Forgot to mention: I also tested the gain 0, -10(I guess the result with
negative gain was same with 0dB). But nothing much different with the
spectrum.