I have 2 wires terminated on A and B terminals - blue to A and white and blue to B. I can get a internet connection if blue wire is connected to the socket without the white and blue and get around 40 meg download (out of bt infinity 76 guaranteed) and vice versa when white and blue is connected without blue I get around 20 meg download. So which wire does the upload speed come from?
It does not work that way. You need to have both connected, and be able to hear dial tone on your landline phone.
If you do not get dial tone, then you have a fault.
Upload and download use different frequency bands within the VDSL spectrum.
Did you try this just as an experiment or had an issue ?, as already stated it’s not 1 leg upload the other leg download ,and it’s not by design that ‘broadband’ works ( albeit slowly) when 1 leg is disconnected , simply a unintended side effect ( and dependent on where the disconnection is relative to where the router is ) , why the download varies so much between a disconnect A leg and disconnected B leg is strange but irrelevant.
As far as upload , it uses the same path as the download , but differentiated from it by the frequency’s used.
Is it possible to dictate what frequency to be selected on? How can you tell which frequency you’re on?
This is the frequency spectrum. The upload connection speed is mostly determined by the high end frequency response of your line, which can be affected by the type of cable pair, and any interference that may be picked up.