E
Eeyore
Guest
Tomi Holger Engdahl wrote:
you're 100m from the exchange / C.O. or 5km !
I appreciate your other information but it sure isn't the way we do things here
in the UK.
Graham
True.Eeyore <rabbitsfriendsandrelations@hotmail.com> writes:
Salmon Egg wrote:
Tomi Holger Engdahl <then@pippuri.niksula.hut.fi> wrote:
600 ohms 1-to-1 matching transformers are quite rare in telephones.
Modern normal telephones are normally "floating" line powered
devices where electronics connect directly to line. The whole
small device is "floating" isolted from everythign else
so that gives good balance.
I know of no situation where something specified as say a 150 ohms
1-to-1 matching transformer would perform significantly different than
something specified as a 600 ohms 1-to-1 matching transformer. This
assumes that they both can support the same voltage over the same
(telephone audio) bandwidth. Am I missing something?
Twisted pair cable as used for telecoms has a nominal 100-110 ohm
inpedance. See the ADSL specs.
The twisted pair cable as used for telecoms has a nominal 100-120 ohm
impedance for high frequecies the ADSL system uses. The ADSL
system uses frequencies between 138 kHz and 1.1 MHz for downstream
data (and 25 kHz to 138 kHz ofr upstream). This 100-120 ohm
impedance holds pretty well for those frequencies above 100 kHz.
But that is NOT the 'characteristic impedance' and will vary depending whetherFor lower frequencies the the impedance of the telephone cable
is not anymore that 100-120 ohm, but something else.
For voice frequencies used on on normal telephone (300-3400 Hz)
the impedance is normally considerable higher than 120 ohms.
you're 100m from the exchange / C.O. or 5km !
I appreciate your other information but it sure isn't the way we do things here
in the UK.
Graham