[Elecraft] Mic and headphone

[Jim Brown]

On 4/15/2014 1:36 PM, David Woolley wrote:
> 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. 

Yes and no. We discussed this a week or so ago. Zo is not a constant, 
nor is it resistive at most frequencies. See 
http://k9yc.com/TransLines-LowFreq.pdf

A telephone line may, indeed, too short to exhibit transmission line 
properties at audio frequencies, but it will certainly behave as a 
transmission line when it carries DSL, which has spectrum extending well 
into the MHz range. And a line several miles long WILL exhibit 
transmission line properties at high audio frequencies.

Thanks for the link to the document showing the termination. What that 
network is doing is to approximately match to the varying Zo of the line 
at audio frequencies, and to equalize the propagation delay shown in Fig 
1 and Fig 2 in my link.

73, Jim K9YC