Questions about WBX daugtherboard

Hi everybody,

I received few days ago my new URSP2 with the WBX daugtherboard and i
have
some questions.
First there is two input: one labeled Tx/Rx and the other Rx2. Why is
there
two Rx input and which one i have to use for reception ?
Second, for my first test i plotted the spectrum of received signal
(without
any antenna) by using the usrp2_ftt.py example script. Looking at the
spectrum shape it appears there is a passband filter of about 8MHz
bandwidth
somewhere in the reception chain. I believed, according to datasheet,
that
the bandwidth was 30 MHz. An explanation ?
Third, the same spectrum shows lot of spurious harmonics relatively
powerful
(compared to the noise floor). Is it normal ?

Thanks in advance for your answers.

Damien


View this message in context:
http://old.nabble.com/Questions-about-WBX-daugtherboard-tp27938947p27938947.html
Sent from the GnuRadio mailing list archive at Nabble.com.

On Wed, Mar 17, 2010 at 04:09:09PM -0700, Damien Serant wrote:

Hi everybody,

I received few days ago my new URSP2 with the WBX daugtherboard and i have
some questions.
First there is two input: one labeled Tx/Rx and the other Rx2. Why is there
two Rx input and which one i have to use for reception ?

TX/RX is used for half duplex operation and can be either TX or RX, RX2
is used for RX-only or full duplex operation.

The input can be selected with the -A switch to usrp_fft.py, which
appears not to have been added to usrp2_ffy.py yet. Thus, the default
on usrp2_fft.py will be to use the TX/RX port.

Second, for my first test i plotted the spectrum of received signal (without
any antenna) by using the usrp2_ftt.py example script. Looking at the
spectrum shape it appears there is a passband filter of about 8MHz bandwidth
somewhere in the reception chain. I believed, according to datasheet, that
the bandwidth was 30 MHz. An explanation ?

The bandwidth is roughly 30MHz, perhaps you have your decimation rate
set to 100M/8M = 12.5 … so maybe 8 or 16?

Third, the same spectrum shows lot of spurious harmonics relatively powerful
(compared to the noise floor). Is it normal ?

There are clock multiples that show up, what sort of spurs are you
seeing?

Hi,
I forgot to thank you for your answers. So… thank you !
Concerning the spurs, they are peaks at precise frequencies. Their
position
and their strength depends on the LO frequency (I observe peaks around
698
MHz but not around 714 MHz as an example) but not on the decim rate. I
observed also an attenuation around the central frequency when I use LO
freq
above 1 GHz. Note that the usrp2 is used without its top (i don’t know
if
this precision has any importance)
I’m not really clear and i can add prints screen if desired.

Thanks Again
Damien

Jason A. wrote:

two Rx input and which one i have to use for reception ?
any antenna) by using the usrp2_ftt.py example script. Looking at the
powerful


Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio


View this message in context:
http://old.nabble.com/Questions-about-WBX-daugtherboard-tp27938947p28035497.html
Sent from the GnuRadio mailing list archive at Nabble.com.

Hi,
I forgot to thank you for your answers. So… thank you !
Concerning the spurs, they are peaks at precise frequencies. Their position
and their strength depends on the LO frequency (I observe peaks around 698
MHz but not around 714 MHz as an example) but not on the decim rate. I
observed also an attenuation around the central frequency when I use LO freq
above 1 GHz. Note that the usrp2 is used without its top (i don’t know if
this precision has any importance)
I’m not really clear and i can add prints screen if desired.

Are you seeing spurs at harmonics of the USRP2’s on-board 100 MHz
reference? In other words, if you tune your USRP2 + WBX to 501 MHz,
601 MHz, 701 MHz, etc., do you see the spurs that you’re referencing?
The 1 MHz offset is so that the DC offset correction doesn’t come into
play.

The ADF4350 used on the WBX does produce some spurious content, but
they are typically low-level (-60 dBc or lower from my experience).
The loop filter on the WBX is fairly narrow, so this should help
remove spurs on the LO.

If you can provide any additional information on the spurs you’re
seeing (screenshots of usrp2_fft.py would possibly be helpful), it may
help diagnose what’s going on.


Regards,
John O.
CEO/System Architect
Epiq Solutions
www.epiq-solutions.com

On 03/25/2010 02:57 PM, Damien Serant wrote:

Hi,
I forgot to thank you for your answers. So… thank you !
Concerning the spurs, they are peaks at precise frequencies. Their position
and their strength depends on the LO frequency (I observe peaks around 698
MHz but not around 714 MHz as an example) but not on the decim rate. I
observed also an attenuation around the central frequency when I use LO freq
above 1 GHz. Note that the usrp2 is used without its top (i don’t know if
this precision has any importance)
I’m not really clear and i can add prints screen if desired.

You are looking at frequencies in which there can be a lot of strong
local signals. They could be from TV, cellphones, 2 way radio, etc.
The first step is to put the enclosure on, terminate with a 50 ohm
terminator, and then report all the settings.

Matt

On 03/26/2010 09:44 AM, Damien S. wrote:

Thanks John and Matt for your answers.
Indeed Matt, in my band of interest there is DTV signals since I’m trying to
record them !! :).
Unfortunately, i can’t put the enclosure because the SMA connector is to big
to close the box. Indeed the MCX to SMA bulkhead connector wasn’t in my
package (there was the SMA to SMA instead - it’s normal Matt ?) and so i’m
using a MCX to SMA adaptator.

You should have gotten an MCX to SMA cable. Send me your shipping info
privately and we’ll get you one.

I have put some screenshots on my Picasa Album Web (i have put a 50 ohm
terminator but not the enclosure):
http://picasaweb.google.fr/damien.serant/USRP2WBXScreenshots?authkey=Gv1sRgCOPtyo2jg-6Nfw&feat=directlink

Your gain of 0 is unusably low. Set it to at least 20 or 25. Also,
you’re going to see harmonics of the motherboard clock at multiples of
100 MHz, but they will be smaller relative to your incoming signals once
you turn up the gain.

The next step it to put in a signal with a known amplitude to calibrate
the undesired signals against.

Matt

Thanks John and Matt for your answers.
Indeed Matt, in my band of interest there is DTV signals since I’m
trying to
record them !! :).
Unfortunately, i can’t put the enclosure because the SMA connector is to
big
to close the box. Indeed the MCX to SMA bulkhead connector wasn’t in my
package (there was the SMA to SMA instead - it’s normal Matt ?) and so
i’m
using a MCX to SMA adaptator.
I have put some screenshots on my Picasa Album Web (i have put a 50 ohm
terminator but not the enclosure):
http://picasaweb.google.fr/damien.serant/USRP2WBXScreenshots?authkey=Gv1sRgCOPtyo2jg-6Nfw&feat=directlink

Thanks for your precious time and your help.

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs