Empathy List Archives

AF

Andrés F A

Fri, Mar 23, 2012 6:52 PM

Hi,

I'm working with a USRP 1 plus a WBX, trying to receive the GPS L1 signal.
The WBX is feed through an external active antenna, powered via a BiasT,
which adds near 12db to the signal.

So far, this has not been working very good.

Here my questions,

Is it possible to find an offset relative to the center sampling frequency
as big as 400khz? When I request the USRP to sample on 1.57542Ghz, it seems
that I have the main NAV signal at 1.57502Ghz. Am I inside the expected
tolerance? This offset is too big for the algorithm I'm using to correlate
the gold code, I want to check I'm doing the things right.

When I change the requested center frequency or sampling rate or any other
ADC parameter, is it expected the offset to change? Not necessarily in a
linear fashion.

Thank you!

Hi, I'm working with a USRP 1 plus a WBX, trying to receive the GPS L1 signal. The WBX is feed through an external active antenna, powered via a BiasT, which adds near 12db to the signal. So far, this has not been working very good. Here my questions, Is it possible to find an offset relative to the center sampling frequency as big as 400khz? When I request the USRP to sample on 1.57542Ghz, it seems that I have the main NAV signal at 1.57502Ghz. Am I inside the expected tolerance? This offset is too big for the algorithm I'm using to correlate the gold code, I want to check I'm doing the things right. When I change the requested center frequency or sampling rate or any other ADC parameter, is it expected the offset to change? Not necessarily in a linear fashion. Thank you!

MD

Marcus D. Leech

Fri, Mar 23, 2012 6:55 PM

On 03/23/2012 02:52 PM, Andrés F A wrote:

Hi,

I'm working with a USRP 1 plus a WBX, trying to receive the GPS L1
signal. The WBX is feed through an external active antenna, powered
via a BiasT, which adds near 12db to the signal.

So far, this has not been working very good.

Here my questions,

Is it possible to find an offset relative to the center sampling
frequency as big as 400khz? When I request the USRP to sample on
1.57542Ghz, it seems that I have the main NAV signal at 1.57502Ghz. Am
I inside the expected tolerance? This offset is too big for the
algorithm I'm using to correlate the gold code, I want to check I'm
doing the things right.

When I change the requested center frequency or sampling rate or any
other ADC parameter, is it expected the offset to change? Not
necessarily in a linear fashion.

Thank you!

The frequency precision of the master clock on the USRP1 is 25PPM, so
the maximum error you'd expect on Fc would be about 40KHz.

If you have a laboratory signal generator, you can check the offset
fairly precisely. But 400Khz in 1.5Ghz is roughly 10 times too large.

--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

On 03/23/2012 02:52 PM, Andrés F A wrote: > > Hi, > > I'm working with a USRP 1 plus a WBX, trying to receive the GPS L1 > signal. The WBX is feed through an external active antenna, powered > via a BiasT, which adds near 12db to the signal. > > So far, this has not been working very good. > > Here my questions, > > Is it possible to find an offset relative to the center sampling > frequency as big as 400khz? When I request the USRP to sample on > 1.57542Ghz, it seems that I have the main NAV signal at 1.57502Ghz. Am > I inside the expected tolerance? This offset is too big for the > algorithm I'm using to correlate the gold code, I want to check I'm > doing the things right. > > When I change the requested center frequency or sampling rate or any > other ADC parameter, is it expected the offset to change? Not > necessarily in a linear fashion. > > Thank you! > The frequency precision of the master clock on the USRP1 is 25PPM, so the maximum error you'd expect on Fc would be about 40KHz. If you have a laboratory signal generator, you can check the offset fairly precisely. But 400Khz in 1.5Ghz is roughly 10 times too large. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org

AF

Andrés F A

Fri, Mar 23, 2012 8:58 PM

Thank you Marcus, I will check my configuration.
Any tips are welcome.

Cheers.

On Fri, Mar 23, 2012 at 3:55 PM, Marcus D. Leech mleech@ripnet.com wrote:

**
On 03/23/2012 02:52 PM, Andrés F A wrote:

Hi,

I'm working with a USRP 1 plus a WBX, trying to receive the GPS L1
signal. The WBX is feed through an external active antenna, powered via a
BiasT, which adds near 12db to the signal.

So far, this has not been working very good.

Here my questions,

Is it possible to find an offset relative to the center sampling
frequency as big as 400khz? When I request the USRP to sample on
1.57542Ghz, it seems that I have the main NAV signal at 1.57502Ghz. Am I
inside the expected tolerance? This offset is too big for the algorithm I'm
using to correlate the gold code, I want to check I'm doing the things
right.

When I change the requested center frequency or sampling rate or any
other ADC parameter, is it expected the offset to change? Not necessarily
in a linear fashion.

Thank you!

The frequency precision of the master clock on the USRP1 is 25PPM, so the
maximum error you'd expect on Fc would be about 40KHz.

If you have a laboratory signal generator, you can check the offset fairly
precisely. But 400Khz in 1.5Ghz is roughly 10 times too large.

--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org

USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

Thank you Marcus, I will check my configuration. Any tips are welcome. Cheers. On Fri, Mar 23, 2012 at 3:55 PM, Marcus D. Leech <mleech@ripnet.com> wrote: > ** > On 03/23/2012 02:52 PM, Andrés F A wrote: > > > Hi, > > I'm working with a USRP 1 plus a WBX, trying to receive the GPS L1 > signal. The WBX is feed through an external active antenna, powered via a > BiasT, which adds near 12db to the signal. > > So far, this has not been working very good. > > Here my questions, > > Is it possible to find an offset relative to the center sampling > frequency as big as 400khz? When I request the USRP to sample on > 1.57542Ghz, it seems that I have the main NAV signal at 1.57502Ghz. Am I > inside the expected tolerance? This offset is too big for the algorithm I'm > using to correlate the gold code, I want to check I'm doing the things > right. > > When I change the requested center frequency or sampling rate or any > other ADC parameter, is it expected the offset to change? Not necessarily > in a linear fashion. > > Thank you! > > The frequency precision of the master clock on the USRP1 is 25PPM, so the > maximum error you'd expect on Fc would be about 40KHz. > > If you have a laboratory signal generator, you can check the offset fairly > precisely. But 400Khz in 1.5Ghz is roughly 10 times too large. > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >

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USRP1, WBX and GPS L1 questions