LF: 500kHz and ADSL

[Andy Talbot <andy.g4jnt@googlemail.com>]

I've been doing some tests with the BT Internet ADSL connection and trying to find out if there is any mutual interference.   

 

The 500kHz beacon transmission  seems to make no difference whatsover to my ADSL connection, it certainly doesn't affect the results of a speed test whether it is on or off.  And I can detect no discernible different in noise level whether the modem is off or on and operational.

 

So it looks as if my modification to the domestic phone wiring did what it was supposed to.   I got into the wiring from the master socket and  installed a microfilter - the sort that is supposed to be used on EACH extension -  between it and the rest of the house wiring, and connected only the ADSL wire direct to the incoming pair.  This removed the original third wire from the part of the circuit carrying the ADSL signal and reinstated it, via the micro-filter on the low-pass-filtered audio path.   The BT master socket no longer has its third ringer wire going anywhere.

 

Consequently, the ADSL signal is not being forced to travel all over the house on and unbalanced three core cable asking for interference to be injected / radiated.    I never liked the original concept, as supplied, of sending the ADSL all over the house on and unbalanced cab;e, then having to filter it out individually at each phone unit.   Its a nasty bodge, and just a cop-out to save them from having to install a proper diplexer on teh incoming line.

 

Mind you, its fortunate all my phones are the modern type that only need two wires for ringer.   I'm not sure the tiny ringer capacitor in the microfilter could do the job of ringing all the extensions I have connected.

 

The old BT Voyager modem does go away and retrain a lot more than it used to since the service was "Supposed" to have been upgraded, so dropping the connection for a minute or two several times a day, but the times it does this are not related to the 500kHz beacon signal coming on line.

Andy
www.g4jnt.com