On Thu, 14 Aug 2003 10:52:49 -0400, "Tarmo Tammaru"
wrote:

There is an FCC approved model for a telephone line input impedance at voice
frequencies. I can't remember the details, but it was something like two
resistors in series with a sum of around 1000 Ohms; the larger resistor
being shunted with a fair sized capacitor. You need this model to design,
for instance, a hybrid for a modem.


Hi Tam,

Sounds more like the model for the K-1 relay, or a hybrid decoupling
network or balancing network description. Telephone is the land of
600 Ohm specifications (min. 550, max. 850) for many good reasons
related to their networks.

The passband for voice frequencies does not demonstrate any simple one
time constant roll-off characteristic. Ma Bell couldn't afford that
kind of waste.

73's
Richard Clark, KB7QHC