asterisk users - Jun 2005 - Do I need a ring capacitor to use TDM400P cards in UK

Hello

I have played about with a TDM400 card and plugged in some standard analog
phones.  I am using the card in FXS mode - for analog extensions.  I did notice
that one of my phones did not ring and I wondered why.  I later read in Paul
Mahler's book VoIP Telephony with Asterisk that in his section on the TDM400
on page 127 he says "In the UK, you may need an adapter that provides a
ring capacitor, or the phone may not ring."

Can anyone confirm this.  Also what is one of those and where would I find a
good supplier?  I am in the trade so wholesale would be OK.

Angus Comber
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Hi Angus,
If you connect the phone directly to the outside line will it ring ?
The ring from the C.O. provides a  >90volt AC (30cps) and is capable of 
ringing a standard phone ( a real two tone gong bell)  My guess is that 
the TDM400 card does not supply enough current to actually do this. Most 
modern phones have an electronic ringer which requires a fraction of the 
power and will work fine.

I don't quite understand the reference to a capacitor unless your phone 
is as old as I am  in which case the phone has 2 x pairs of  wires going 
to the phone plug. The first pair of wires are the "voice pair" and
the
second pair are connected to the "ringer" if this is the case  your 
phone will  work normally but simply doesn't ring.
The fix is to connect two capacitors approx  *0.15 uf  250vw *from each 
wire of the voice pair to each wire of the ring pair  (you can do this 
inside the phone jack)
This should not cost much (about a dollar) and can be found in any 
electronics component shop (try Maplin electronics) . Concidering the 
time and effort you might want to buy a new phone.

                                     0.1uf                             
Wall Jack
 TDM400                  | ---||-----------yellow-------0
0-----------green------0-------------------------------0
0-----------red---------0------------------------------- 0
                                  | ---||-----------black---------0
                                     0.1uf


Hope this helps ...Henry
  * *


Angus Comber wrote:
> Hello
>  
> I have played about with a TDM400 card and plugged in some standard 
> analog phones.  I am using the card in FXS mode - for analog 
> extensions.  I did notice that one of my phones did not ring and I 
> wondered why.  I later read in Paul Mahler's book VoIP Telephony with 
> Asterisk that in his section on the TDM400 on page 127 he says "In the
> UK, you may need an adapter that provides a ring capacitor, or the 
> phone may not ring."  
>  
> Can anyone confirm this.  Also what is one of those and where would I 
> find a good supplier?  I am in the trade so wholesale would be OK.
>  
> Angus Comber
>  
>
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