What actually is the main purpose of the filter is to prevent the telephone SHORTING OUT the high frequency ADSL signal.
It has a minor effect of also reducing high frequency pick-up on in house wiring, but unless you have an RF noisy house, that's not normally an issue.
More or less yes and yes.
You will hear it on phones that are, as well.
More or less, the faceplate includes a choke too, but certainly worth disconnecting the bell wire first, most modern phones don't need it.
Thanks.
Some of us use proper dial telephones though. Even with them, there are ways of managing without a bell wire; for instance use the condenser in the phone itself, as you would with a fully traditional installation. I have a BT NTE2000 ADSL adaptor which has phone and ADSL sockets on its faceplate and a built-in filter. Any extension wiring is phone only. I currently have a good old Plan 107 (albeit with MF phones) connected to the phone port.
If you need to add the ring signal back to a socket having disconnected the ring wire, its fairly trivial to just wire a bipolar cap between the connections on the socket.
Thanks. Hopefully I will not be needing to do this but for anyone who does, what capacitor should they use (uF, V, etc)?
BTW on a telephony related note: I was wondering about this:
I know telephone sockets are normally daisy-chained but if you wanted to do a star arrangement, how would you join them at the hub if these boxes do not accept multiple wires?
Thanks.
The ADSL side is not filtred, only the POTS side to keep the ADSL signal out of phones and to maintain the RF line conditions when phones go on/off hook etc.
More likely that the modems just have good common mode rejection. Trouble is noise from the ring wire is injected asymetricallly onto the pair and thus isn't common mode...
There shouldn't be any need to filter a phone to keep the ADSL signal out, phones should reject the RF noise anyway. If they don't you will pick up radio stations.
Yep, that's what I said.
No, they do a lot of DSP processing to extract the signals. They use digital filters to select from hundreds (well they can on a good line, poor lines have to use less) of channels used simultaneously to send the data.
1.8uF 250VDC non-polarised is in a master socket. ADSL filters tend to use about 1uF but can only usually manage a REN of 2 as a result.
If you need a 1.8uF drop me a note - I have some removed from master sockets altered to slaves and you are welcome to one or two.
Yes, in practice you can usually fit 3 wires in if you take care to secure them where they exit the box so they can't flex. Bear in mind that the left hand set of terminals are connected underneath by PCB tracks to the right hand set of terminals (1 to 1, 2 to 2 etc).. Using two wires only you can, with a bit of cunning linking, fan out one line to 8 star wired extensions from 1 box using no more than two wires in each blade.
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