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Tomcsanyi, Domonkos domi at tomcsanyi.netHello 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/20201026/e8285f46/attachment.htm>