Re: Galileo Frequency Shifting and Filtering

[Daniel Estévez]

On 27/02/2023 18:59, David Dima wrote:
> Hi guys,
> I am trying to simultaneously record Galileo's E5a and E5b signals as 
> follows:
> imagen.png
> I have tried to record them separately by tuning the local oscillator in 
> the middle of the signals bandwidths and sampling at 25MHz and it 
> worked. But when I try to shift and filter to get the signals in a 
> different file, it does not work. I have no idea what am i doing wrong.
> Galileo's Signal Plan is as follows:

Hi David,

I see the following problems:

1. The "Sample Rate" parameter in the Frequency Xlating FIR Filter is 
the input sample rate. Hence it should be 50 Msps in your case, not 25 Msps.

2. An anti-alias lowpass filter to decimate from 50 Msps to 25 Msps 
should have a cut-off frequency of around 12.5 MHz, not 25 MHz.

3. The band plan you posted is slightly wrong. The distance between the 
AltBOC sidebands and the centre frequency is 15 * 1.023 MHz. See 
https://gssc.esa.int/navipedia/index.php/Galileo_Signal_Plan (the 
difference between this and what you used is a few MHz, so it may or may 
not matter depending on what you're trying to do with these recordings).

Best,
Daniel.

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