[Elecraft] Mic and headphone

[David Woolley]

Actually, the network termination impedance for two wire phone lines is 
important, as it is an important parameter in the design of the two to 
four wire hybrid.  http://www1.btwebworld.com/sinet/351v4p5.pdf gives 
specifications for the UK network, which are somewhat higher than 600 ohms.

Note these are the system values at audio frequencies; they are not the 
characteristic impedance of the line.  The line will typically be too 
short for that to be significant.

-- 
David Woolley
Owner K2 06123

On 15/04/14 07:37, Jim Brown wrote:
> On 4/14/2014 4:46 PM, Harry_Yingst wrote:
>> Phone lines are Typically 600 ohms
>
> Actually, the Zo of phone lines at radio frequencies is about 80 ohms,
> and varies widely with frequency in the audio spectrum. That
> characteristic is determined by the diameter, spacing, and insulation of
> the twisted pairs used to carry the signal. They have not been 600 ohms
> for at least 75 years. More than 40 years ago, it was standard practice