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Sipos Csaba dchardware at gmail.comIt works! Long story short: the LimeSDR-Mini was off by 3.5kHz, and not the phone. Even after 30 years, the phone is only off by 14Hz, what a performance. Made in West Germany :-)) After the recalibration of the LimeSDR Mini, the phone successfully updated the TA and went to normal idle state. Calls are also possible, SMS will be tested when a capable phone arrives. All TA combinations were tested (1-15). Will create an updated patch for the country specific settings, now that it is tested. The lesson is: trust but verify :-) Especially with cheap hardware. Regards, Csaba Tomcsanyi, Domonkos <domi at tomcsanyi.net> ezt írta (időpont: 2020. okt. 26., H, 19:54): > Hello Csaba, > > I am not sure if you know this, wanted to mention it: you could easily > measure your SDR’s oscillator accuracy using the kalibrate tool. It uses > nearby GSM BTSs if I am correct to give you a good estimation about how > much off your oscillator is. > I used to use it with rtl-sdr a lot, because those USB dongles are crazy > off in terms off accuracy. > Once you have an offset figured out for the current temperature I guess > you could try to offset the frequency set by osmocom by that amount. Maybe > even try to expose it as a variable if needed. > Other solution would be using some kind of a GPSDO or similar 10 MHz input > if the LineSDR supports it. > > Sorry again if this is known info, but wanted to chime in with some > hopefully helpful bits. > > Cheers, > Domi > > > 2020. okt. 26. dátummal, 16:08 időpontban Sipos Csaba < > dchardware at gmail.com> írta: > > > Hi Ralph, > > I attached the patch for the country specific settings for Hungary, you > can apply it against "master" . TAs are not yet verified, but the phone > goes "green" with all TAs from 1 to 15. The RF part and country code are > verified. > > > One thing, maybe your MCR has drifted, due to ageing?! > > Well, that was my first impression too, as if you look at my picture ( > http://www.imagebam.com/image/d17e881357285965 ) you will see that the > center of the downlink and uplink transmissions are not exactly 10MHz > apart, they have a couple kHz drift. On the picture the two markers are > indicating the nominal frequency of the channel. As you can see the uplink > burst is actually closer to the nominal frequency, compared to the > downlink. It is not in the standard (or I was not able to find it, in > general the RF spec is not very detailed...), so I am not sure if the SDRs > downlink signal is off, and the phone is correct or the other way around. > Although it sure looks like a low layer fault, as the NMT network is not > even detecting is as bad or incorrect frames. > > I did a loopback test with a jumper between the TX and RX of the SDR and > that seemed to work (frame level and frame quality were 90+%). On the other > hand if the local oscillator would be off, the phone would not be able to > lock on the DL signal as well. I have no high precision counter at home, > but with a relatively primitive multimeter I was able to measure 12.7999MHz > on the 12.8MHz local oscillator. And both identical phones behave the same. > > The question is if I can somehow offset the uplink frequency on the SDR > side or via config/source modification to remove this couple kHz drift? > > If someone has seen a lot of these signals and can take a look at the > image above, would be lovely to hear if any of the signals are off. > > I will also get another more "modern" phone hopefully soon, so I can try > with that. > > Regards, > Csaba > > Ralph A. Schmid, dk5ras <ralph at schmid.xxx> ezt írta (időpont: 2020. okt. > 26., H, 15:33): > >> Hi Chaba, >> >> >> >> I have a Nokia handheld phone from Hungary, I can try with your settings >> and let you know. >> >> >> >> Andreas seems to be difficult to reach these days, I found the same :/ >> >> >> With best regards >> >> >> Ralph. >> >> >> >> >> >> >> >> *From:* OpenBSC [mailto:openbsc-bounces at lists.osmocom.org] *On Behalf Of >> *Sipos Csaba >> *Sent:* Monday, October 26, 2020 3:16 PM >> *To:* openbsc-request at lists.osmocom.org <openbsc at lists.osmocom.org> >> *Subject:* Fwd: NMT-450 - partial success >> >> >> >> Hi, >> >> >> >> I know it is a bit off topic, but as osmocom-analog has no dedicated mail >> list and my every attempt to contact Andreas lead to silence, I thought >> this is the closest one to discuss it. >> >> >> >> I try to create an NMT-450 network with Motorola MCR4800XL phones, and a >> LimeSDR-mini. As the phones are locked to "Hungary" using a specific raster >> and a large gap in the middle, first I needed to dig out the details, find >> out the country code and create a patch so at least the phone is willing to >> lock onto the DS signal. I managed to do all that, so now the phone is >> actually able to decode the network and lock onto the signal. >> >> >> >> My issue is with the uplink: when the phone tries Traffic Area update >> (the phone's uplink transmission burts is clearly seen with a spectrum >> analyzer), the network side is not able to detect the uplink burst at all. >> Not even as bad, or incorrectly formatted frame. Andreas has a site which >> describes how to set up the uplink side and do some tests: >> >> >> >> http://osmocom-analog.eversberg.eu/docs/sdr.html >> >> >> >> I followed that guide and when the uplink burst from the phone arrives, >> the RX IQ constellation monitor indicates a correct burst with proper power >> (the burst is nicely round and in the green area). If I try to set up a >> call to the phone using the correct country code and phone number, the >> phone clearly responds to the paging request, as the 3 paging attempt >> generates 3 uplink bursts. Again, with no reception/decoding on the network >> side. Tried with two phones of the same type, the effect is the same. >> >> >> >> I have two questions: >> >> >> >> 1. Where to send patches for the osmocom-analog project? >> >> 2. Does anyone have an idea what can be wrong with my setup? >> >> >> >> One more thing I noticed: compared to the channel frequency used to set >> the NMT network up, the uplink is a couple kHz shifted: >> >> >> >> http://www.imagebam.com/image/d17e881357285965 >> >> >> >> As it can be seen, the uplink burst appears 3-4kHz left relative to the >> downlink signal. >> >> >> >> The network is started with the following command: >> >> nmt -k 239 -k 235 -Y HU,1 --limesdr-mini --sdr-rx-gain 20 >> >> >> >> Any and all help is appreciated. >> >> >> >> Regards, >> >> Csaba >> > <0001-Add-country-specific-settings-for-Hungary.patch> > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/openbsc/attachments/20201027/82afc0ad/attachment.htm>