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I have had a Suresignal V3 for a few months after the initial one blew up.
The device is connected up correctly to my BT Hub, is working correctly and my phone has 5 bars in the same room as the Suresignal - even though it is not so good in the next room or further away in the house.
The problem I often run in to when on a phone call is that although I can hear what the caller on the other line is saying pefectly well, they often tell me that my line is terrible and that it is constantly breaking up.
I can't see how this can be the case if I have 5 bars? I have tried turning off all other devices that receive wifi to see if that made a difference, which it didn't.
I did a speed test which could provide some clues, as you'll see, pretty bad upload speeds but broadband has never been that great living a rural area, here are the results