I want to acquire first the GPS L1 signal to get a basic idea of how
acquisition works and then move to Galileo E1 signal, but I am facing some
problems.
1. I am using RTL-SDR Dongle, with Rafael R820T Tuner, and I want to
acquire GPS L1 signal with that.
2. I am using GNURadio to receive the data. In GNURadio, in the RTL-SDR
Block, I am giving my sample rate of 2.048 Msps.
3. Incoming L1 signal has frequency of 1575.42 MHz and I am using GPS
active antenna with 40 db gain.
4. In RTL-SDR dongle, it will be down-converted to IF (that is unknown to
me), through local oscillator. and after the down-conversion, it will be
passed to ADC.
5. In some articles, I have studied that RTL-SDR dongle that I am using has
IF= (3.57 MHz or 4.57 MHz). (*http://superkuh.com/rtlsdr.html
<http://superkuh.com/rtlsdr.html>)*
6. Now my question is that if it is true, then the signal going into the
ADC has frequency of (3.57 MHz or 4.57 MHz) , and my sample rate is 2.048
Msps, that is below the frequency of the incoming signal, then it is not
following the Nyquist Criterion. Also, according to this, the incoming
signal must be at (3.57 MHz-2.048 MHz= 1.652 MHz). Is it Right? (screenshot
attached for reference)
7.The samples coming out of RTL-SDR are complex (I & Q). In one articles I
have studied that the I-part are the C/A codes and the Q-part are P-Codes
and these samples are at Baseband(zero-frequency). If I just want to
acquire C/A code, then shall I need to just take I-part of the output
samples coming out of the RTL-SDR? Or what should be my data on which I
need to do the further DSP?
These are my problems till now. I have studied dozens of web-pages and
articles, but couldn't find the fruitful answer. I shall be very thankful
for any help.
Thanks a lot for your time.
Regards,
Priyanka