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:

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:

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