Saturday, 9 June 2018

950MHz 2G Spectrum

Here are some spectrum views of the 900MHz GSM phone band, captured with a SDRPlay RSP-1 and a 1/4 wave ground plane next to an upstairs window (looking north).
My Comet GP-15 tribander on the chimney, with over 25m of coax gave roughly the same signal for a mast which was line of site except for a few trees (the sector facing me is on 959.4). A mast only a few streets away with my best sector on 953.8 was much better on the GP-15 (about 15dB), it's on the opposite side of the house.
Vodafone using 951.4 - 954.8 (18x 200KHz channels 82-99), O2 using 955.2 - 959.8 (24x 200KHz channels 101-124). Most sites are now Vodafone and O2 into the same antennas. It looks like a lot of the newer sites which were built for 3G coverage (usually roadside poles) have been fitted with 2G 900MHz. 2G GSM is nowhere near finished yet in the UK, the cheapest phones are 2G only, and as the turnover of smartphones is faster, support for devices without 4G could be cut down to 2G voice/texts only before too long. 3G capacity is already being cut by refarming the 2100MHz band to 4G for up to 2/3 of the bandwidth. 2G GSM is used by a lot of remote control and slow data applications too, things like tracking devices, digital signage where the speed of sending a txt or GPRS data doesn't matter.
I'm not sure what's happening with the channels like 955.8MHz where the signal isn't continuous, seems to be an extra channel from the same sites.