Receive GPS L1 Signal

GNU Radio
1

Hi all,

I have a USRP N210 and DBSRX2 daughter board, running on Ubuntu 10.04,
and I
would like to get the L1 signal by

using Gnuradio Companion to draw a GPS receiver flow graph (I have a GPS
Antenna), and I just need to get the IF signal into File

Sink to get the .dat so I can use MATLAB to deal with the data, I have a
book "A Software-Defined GPS and Galileo Receiver: A

Signal-Frequency Approach", there is a GNSS L1 front-end digram at p.55
(that is my only reference), but I have no idea how to

translate it into GNUradio Blocks.There is a ADC on that diagram, should
I
just ignore it, or I need some blocks to complete that ADC?

(There is no blocks called ADC)And there is several Band-Pass Filter in
the
diagram with center frequency and 3dB Bandwidth, but I

don’t know how to translate it to the information that blocks
needed.(Like
Low or High cutoff frequency, transition width …etc)

Can anyone help me? Or has an example .grc or some website for related
information?

Thanks,

Eddie

2

On Sat, Jun 11, 2011 at 11:12 AM, Eddie Sun
[email protected]wrote:

Signal-Frequency Approach",

This is the best book for software GPS.

there is a GNSS L1 front-end digram at p.55 (that is my only reference),
but I have no idea how to

translate it into GNUradio Blocks.There is a ADC on that diagram, should I
just ignore it, or I need some blocks to complete that ADC?

ADC. Do you know what ADC means? If you do then you already have an ADC,
which is the USRP. :wink:

(There is no blocks called ADC)And there is several Band-Pass Filter in the
diagram with center frequency and 3dB Bandwidth, but I

don’t know how to translate it to the information that blocks needed.(Like
Low or High cutoff frequency, transition width …etc)

A USRP is a baseband IF receiver. Tune it to the GPS L1 frequency with
the
right decimation rate so that you have your band of interest selected.
This
should give you the IF signal.

3

Thanks for the reply, but i still have some questions.

2011/6/21 John A. [email protected]

A USRP is a baseband IF receiver. Tune it to the GPS L1 frequency with the
right decimation rate so that you have your band of interest selected. This
should give you the IF signal.

The source block that i used is the “UHD:usrp_source block” for USRP
N210 in
gniradio companion, after setting the frequency to L1 frequency
1575.42MHz,
there is no “decimation” term can be set in the block(only usrp1_source
and
usrp2_source block have that term, not uhd), so should i use the
“Rational
resampler” block to instead of it? or other method to complete the
decimation.

The flow graph will only be
“UHD:usrp_source block”“Rational resampler”“File sink”
is that right?

And I’m still a little confused, why i don’t need to down convert the
frequency but just do the decimation, i thought decimation is to
slowdown
the sample rate.

Is that mean the flow graph output from “UHD:usrp_source block” is
already a
IF signal? If this is true, what is that signal frequency? It can’t
still
have the 1575.42MHz if it’s a IF signal, isn’t it?

Thanks,

Eddie

4

Hello Eduardo,

i have to mention i’m a newbie in this domain. but if i can help, no
problem.

use e-mail contact me.

Eddie

2011/7/5 Eduardo Lloret F. [email protected]

5

Hello Eddie,

I will try the same thing in a few weeks but using the USRP2 board. I
hope
your work is going great. Do you mind if I contact you for advice?

Greetings.

Eduardo.

2011/6/24 Marcus D. Leech [email protected]