The Natural Philosopher wrote:
Eeyore wrote:


Mike J wrote:

curious wrote:

Only the phones need to have filters. The broadband modem doesn't need
one and it can cause problems if one is fitted or so I hear.


Not quite true (as kraftee says later)
The 'modem' side of a filter should (on decent units)have additional
components in it to isolate/protect the modem from the DC on the line,
the 25c/s ringing voltage and the dc changes caused by lifting/replacing
the handset on other phones.


No. Any components there may adversely affect the line balance and
impedance.
All the required 'protection' is in the modem itself. It would be nuts
if it
wasn't.





If the modem has a phone port, that will have its own low pass filter in
it. Another reason why you wouldn't want to do that sort of filtering
higher up the food chain: phones plugged into a phone socket on the
modem would NOT then work.



Graham

The other reason for using a filtered Master Socket is that then the
ADSL signal gets taken off the line as soon as possible and doesn't get
fed on to all the sockets around the house with possible mis-termination
and standing waves upsetting the signal.
I know people will say "what about the crappy BT joins outside your
house" but at least they usually stay the same.

Mike