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Mobile phones and distance from cell site….

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  • #182775
    John MM0CCC
    Member

    As those at VHF FD will have seen, I recently bought a small yagi for 1800-2100MHz intended to improve our internet connection at the site. Having proved it worked well at home, when used at the FD site it easily locked onto a near full strength signal across the Solway Firth in Cumbria. Immediately after doing so however, the connection attempt would fail and the signal would change to zero. I know QSB can be fast at these frequencies but not that sudden, and suspect this is due to the maximum distance that you can be from a cell site, beyond which you should, in theory, have latched onto a new (closer) cell.

    Does anyone have any info on this? Have tried a few Google´s without success and would be interested to hear if there is any workaround for this or if you are locked out that is it.

    This is one of three sites I have trouble with /P connections. Next up is IOTA, where there is a T-Mobile site just a few miles to the north, but unless I walk out of the shack with phone in hand up to the Church, no signal is present. The yagi on a mast should improve this and will report back on this to see how it went.

    #182776
    Geoff MM5AHO
    Member

    I think this is to do with the multiplexing system, whereby the return signal must be error checked or something. This all must happen in a time slot, and that time limits the distance to shorter than the RF will propagate. So the signal can be enough, but the time delay (radio only travels at 3×10^8metres per second) caused by that distance snookers the connection.
    That doesn’t explain the apparent signal strength drop, but maybe that indication isn’t really RF strength, but connection strength? (ie including the comms)

    I noted a mobile tower, just at the intersection of the track and the main road (Kirkcudbright – Auchencairn road), but don’t know what network that was. It was not Vodaphone according to my signal strength when passing.
    What network are you using?

    #182777
    mm0gpz
    Member

    Hi Geoff/John. I don’t claim to know anything about this. Strangest part for me was that the O2 signal was strong and the modem connected and picked up an IP address. Why then it never communicated I am unsure. I would have thought if it could make the connection, it should have worked??

    I thought the same Geoff but I think that the time division was only on the original GSM standards. It is described here: Particularly this bit:The maximum range of a mast (where it is not limited by interference with other masts nearby) depends on the same circumstances. Some technologies, such as GSM, normally have a fixed maximum range of 35 kilometres (22 mi), which is imposed by technical limitations. CDMA and IDEN have no built-in limit, but the limiting factor is the ability of a low-powered personal cell phone to transmit back to the mast. As a rough guide, based on a tall mast and flat terrain, it is possible to get between 50 to 70 km (30–45 miles). When the terrain is hilly, the maximum distance can vary from as little as 5 kilometres (3.1 mi) to 8 kilometres (5.0 mi) due to encroachment of intermediate objects into the wide center fresnel zone of the signal.[3] Depending on terrain and other circumstances, a GSM Tower can replace between 2 and 50 miles (80 km) of cabling for fixed wireless networks.[4]

    Also read this read the Timing issue that limited connections to 35 Km’s

    However, these seem to be concerned with voice which is different from data. Data can be delayed and work fine whereas voice has to arrive on time obviously.

    Why not ask GM0GAV. He will be able to tell you exactly why the T-Mobile never connected I imagine.

    Cheers.

    Gordon

    #183058
    John MM0JXI
    Keymaster

    I think Gordon is in the right area, the transmitted signal from your phone will be much lower when received at the cell site so even though you get a good receive signal the return path isn’t good enough to sustain a connection.
    The theoretical range of a cellsite is about 30 miles but that distance shrinks rapidly with the bandwidth required for a data connection.
    I think what John was seeing was the cellsite handing off to another site based on whatever preprogrammed limitations are set for signal to noise, delay etc.

    #183059
    John MM0CCC
    Member

    Cheers for replies/suggestions so far folks. I agree with the mismatch between the dongle’s QRP and the higher power from the cellsite however this would throw up another question:

    Why, eslewhere, can I maintain a solid (though not usually as fast) connection when my received signal drops to 1 or 2 bars? Surely the mismatch would be even greater then, and the chance of connection even slimmer?

    Geoff, FYI I’m on Orange/EE. Benbecula site is near a T-Mobile cell which is ropey for voice calls. Hopefully the EE merger allows me access and the yagi increases the signal.

    #183061
    John MM0JXI
    Keymaster

    There is some interaction between the dongle and the cell site to set the output powers, if you’re getting a big signal on receive, the system may turn down the power as it thinks there is a good link.
    If you are only getting 2 bars, the phone will raise its output power as it thinks the link is poor, but that uses more battery

    Also the faster the connection, the better the signal needs to be and so the range of the cell reduces.
    If you could limit the speed of the connection you’d get better range but everything seems to be set up to give max bandwidth. Unfortunately you don’t get to choose speed v range, the system adjusts for a reliable signal.
    Too many errors and the cell will try to hand off to another.

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