UmTRX

Sylvain Munaut 246tnt at gmail.com
Mon Jun 17 09:45:08 UTC 2013


Hi,

> I’m an engineer from Spain and I’m interested in a GSM receiver because I
> would like to study the internal signals for a research project. In
> particular, I’m interested in the analysis of the IF signal, but, as
> Alexander told me, the LMS6002D uses zero-IF architecture, so there is no
> real "IF" signal, there is only baseband signal.

Well, they also have a optional GSM front end board that has an IF.
However it has a very narrow IF filter since the goal was to about
in-band interference from neighbour channels ...


> I guess I could also use
> this signal for my purposes, but only if all 124 GSM channels can be found
> at that point. I’m not sure if this is possible, since there is a low-pass
> filter before. Does anybody know if I can extract that information, that is,
> the analogic 124 channels after the RF mixer?

The filters can be set to 28 MHz wide and the LMS has analog I/Q debug
outputs, so yes you could get the analog out.
But it's I/Q  not a single signals so you'll need two fast ADC to get
it digitized.

OTOH why wouldn't you just use the ADC in the LMS ? They're clocked at
26 Mhz (or could even be fed higher frequency) and so you should be
able to get the whole 25 MHz of P-GSM band.

Cheers,

    Sylvain




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