[GreenKeys] Far OT: audio inputs

[Don Robert House]

The characteristic impedance of H88 loaded cable is 1200 Ohms
Non loaded cable, as has been stated, is 600 Ohms
150 Ohm terminations are used to compensate for the attenuation  
distortion of non-loaded cable.
The above are used for voice frequencies within the band of 300 to  
3200 Hz.

135 Ohms is used to measure non-loaded cable for digital transmission.
The Nyquist frequency of a digital signal such as 50 Kilobit is one  
half the bit rate or 25 kHz
So to measure the loss to the 50 KB signal you use 25 kHz at 135 Ohms.

135 Ohms is also used when measuring cable for Asynchronous Digital  
Subscriber Line (ADSL)
and other wide-band services such as certain program channels.

Don
K9TTY



On 16 Feb 2009, at 2:44 PM, Jim Haynes wrote:

The impedance of an open-wire pair runs around 600 ohms as well.

I have see 135 ohms in some telephone test equipment, but I don't
know what kind of circuit has that impedance.


jhhaynes at earthlink dot net

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