Hello,
Im an engineer from Spain and Im interested in a GSM receiver because I would like to study the internal signals for a research project. In particular, Im 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. I guess I could also use this signal for my purposes, but only if all 124 GSM channels can be found at that point. Im 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? If it is not possible with this board, does anybody know if I can do it with another GSM transceiver board?
Thank you very much in advance.
Best regards,
Albert
If you need to extract them all simultaneously then you'd need about 25 MHz baseband bandwidth, which I think at the moment is a bit more than the UmTRX can do on one channel, you might be able to do something clever and look across both channels maybe. That's a whole lot of processing as well, I'm guessing you'll be analyzing the signals offline? USRP2 or USRP N series and do about 25 MHz sustained on one channel, you'll need some good network hardware on your PC to prevent overruns.
John
On 17 June 2013 10:23, Albert-Miquel Sánchez albertm@salleurl.edu wrote:
Hello,****
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. 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? If it is not possible with this board, does anybody know if I can do it with another GSM transceiver board?****
Thank you very much in advance.****
Best regards,****
Albert****
Thank you very much for your response. I didnt mention it, but I only want to extract the analog signal (the 25 MHz baseband bandwidth), in order to analyze the spectral content (I would capture this signal with another board developed by us). Therefore, I dont need to process it with the UmTRX. However I need the UmTRX in order to do this analysis while keeping a phone communication.
Best regards,
Albert
De: john.wilson@pathintel.com [mailto:john.wilson@pathintel.com] En nombre de John Wilson Enviado el: lunes, 17 de junio de 2013 11:41 Para: Albert-Miquel Sánchez CC: umtrx@lists.osmocom.org Asunto: Re: UmTRX
If you need to extract them all simultaneously then you'd need about 25 MHz baseband bandwidth, which I think at the moment is a bit more than the UmTRX can do on one channel, you might be able to do something clever and look across both channels maybe. That's a whole lot of processing as well, I'm guessing you'll be analyzing the signals offline? USRP2 or USRP N series and do about 25 MHz sustained on one channel, you'll need some good network hardware on your PC to prevent overruns.
John
On 17 June 2013 10:23, Albert-Miquel Sánchez albertm@salleurl.edu wrote:
Hello,
Im an engineer from Spain and Im interested in a GSM receiver because I would like to study the internal signals for a research project. In particular, Im 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. I guess I could also use this signal for my purposes, but only if all 124 GSM channels can be found at that point. Im 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? If it is not possible with this board, does anybody know if I can do it with another GSM transceiver board?
Thank you very much in advance.
Best regards,
Albert
Albert,
In this case yes, it's possible. You could get RXOUT values on the four test points at the north-west corner of the chip (TST5 - TST8). Note, that they are differential and separate I/Q.
To acquire 25MHZ you could set LPF to 28MHz, as Sylvain pointed or completely disable it. I strongly recommend you to use an external bandpass filter in the latter case.
On Mon, Jun 17, 2013 at 2:08 PM, Albert-Miquel Sánchez <albertm@salleurl.edu
wrote:
Thank you very much for your response. I didn’t mention it, but I only want to extract the analog signal (the 25 MHz baseband bandwidth), in order to analyze the spectral content (I would capture this signal with another board developed by us). Therefore, I don’t need to process it with the UmTRX. However I need the UmTRX in order to do this analysis while keeping a phone communication.****
Best regards,****
Albert****
*De:* john.wilson@pathintel.com [mailto:john.wilson@pathintel.com] *En nombre de *John Wilson *Enviado el:* lunes, 17 de junio de 2013 11:41 *Para:* Albert-Miquel Sánchez *CC:* umtrx@lists.osmocom.org *Asunto:* Re: UmTRX****
If you need to extract them all simultaneously then you'd need about 25 MHz baseband bandwidth, which I think at the moment is a bit more than the UmTRX can do on one channel, you might be able to do something clever and look across both channels maybe. That's a whole lot of processing as well, I'm guessing you'll be analyzing the signals offline? USRP2 or USRP N series and do about 25 MHz sustained on one channel, you'll need some good network hardware on your PC to prevent overruns.****
John****
On 17 June 2013 10:23, Albert-Miquel Sánchez albertm@salleurl.edu wrote:
Hello,****
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. 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? If it is not possible with this board, does anybody know if I can do it with another GSM transceiver board?****
Thank you very much in advance.****
Best regards,****
Albert****
-- *Dr. John Wilson* Product development engineer, Path Intelligencehttp://www.pathintelligence.com/ T +44 2392 388442 @pathintel DETECT • ANALYSE • PREDICT • INFLUENCE
Path Intelligence Limited, registered number 5176274. Registered in England, registered office at 1000 Lakeside North Harbour, Western Road, Portsmouth, UK, PO6 3EN ****
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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Albert-Miquel Sánchez -
Alexander Chemeris -
John Wilson -
Sylvain Munaut