[Elecraft] K3 AF line out to mic attenuation

[Don Wilhelm]

Chris,

A simple voltage divider *may* be required, but I would suggest trying 
it without any attenuation first.  It all depends on where the soundcard 
controls the microphone gain - be on the lookout for overload in the 
soundcard, and if present, add an attenuator.  A series resistor may 
work just fine, or as you suggest, a voltage divider.

Impedance matching is not necessary nor desirable.  Audio devices 
operate well by using a low impedance source (able to provide more 
driving current than is required) and a high impedance sink (which will 
limit the current drawn).  The characteristics of the sink (in your 
case, the microphone input) will determine how much current is drawn 
from the source (the K3).  An analogy is to consider utility power 
wiring - the outlet receptacle provides a very low impedance source, and 
the device that you plug into that wall socket will determine how much 
current is drawn, therefore the amount of power that is transferred from 
the power company to your device.  Within limits, an audio source/sink 
combination works the same way, but the actual source impedance will not 
be as near zero as the power company source, it will have some finite 
value such that if the current drawn is too large, distortion products 
will be developed in the driver.

When the available source power is near the power to be dissipated (as 
in a transceiver/antenna situation), then impedance matching becomes 
important for maximum power transfer - because the source power is 
limited (or more correctly, not vastly greater than the power required 
by the sink).

73,
Don W3FPR


Chris Meagher wrote:
> Hello,
>
> I want to connect K3 audio line out to a Toshiba laptop which only has a 3.5 
> mic socket for audio in.
> Does anyone have recommendations for attenuation/impedance matching?
> I was thinking of a simple votage divider.
>
> Thanks,
>
> Chris VK2LCD
>
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