[Elecraft] Level of K3S audio out to digital apps on Mac

[Bob McGraw K4TAX]

Regarding receiver set-up implementation, it is usually best when the no 
signal band noise is some 10 dB above the noise floor of the receiver.   
Per Sherwood Engineering data, the noise floor for the K3S is -135 
dBm.   Thus 10 dB above that would be -125 dBm. Now since one can't 
change noise floor one must use the correct amount of attenuation and RF 
Gain reduction to attain the -125 dBm target for the no signal band noise.

Here's the way I handle that.   This example, the no signal band noise 
is S-4 or -103 dBm.  That is determined with the Attn off and RF Gain at 
max.  Then the difference between my target of -125 dBm and -103 dBm is 
22 dB.  Thus I need 10 dB of attenuation and 2 S units of RF Gain 
reduction.      Lets take this a bit further.  The no signal band noise, 
no attenuation and RF Gain at max, is S-8 or -79 dBm.  To attain our 
target of -125 dBm we need a total of 46 dB of attenuation and RF Gain 
reduction.  If we choose 15 dB of attenuation then we need 5 S units of 
RF Gain reduction.   To easily accomplish this, I switch the radio from 
the antenna to a dummy load.  Then adjust the RF Gain until the S meter 
indicates S-5 where 1 S unit is = 6 dB.  Thus with 30 dB of RF Gain 
reduction the switch in 15 dB of Attenuation I have the required 46 dB 
or so.

Then to the audio.  Here I adjust the Recording Gain of the Windows 
mixer.  Normally this level is about -10 dB or 24% which ever you choose 
to display the value.    If the signal level on the WSJT-X is above 30 
dB then you should reduce the Windows mixer level a bit more to bring it 
into ideal range.

There is a caution in the K3S manual regarding advancing the K3S Line 
Output level which could cause distortion.  The default value is 10.

As to using AGC, on or off, from the WSJT-X help file:   "/Use the 
receiver gain controls and/or the computer’s audio mixer controls to set 
the background noise level (scale at lower left of main window) to 
around 30 dB when no signals are present. It is usually best to turn AGC 
off or reduce the RF gain control to minimize AGC action./" I find using 
my method for setting the receiver gain based on band noise, and the use 
of slow AGC will prevent any likely overload of the K3S audio path, the 
computer audio path, or the WSJT-X software processing.

The receiver setting of gain values works quite well for other modes as 
well.    But  today I hear hams say; "gotta have more gain to hear those 
weak signals".   Yep, 50 years ago this was correct, but not with 
today's receivers.

In looking at the Sherwood Engineering Test data 05/10/2019, the K3S has 
the lowest noise floor of any others at -135 dBm, it has the best 
sensitivity of any others at 0.27 uV, and it has the best 100 kHz 
blocking range of any others at 150 dB.   The point being.......you have 
a darn great receiver in front of you.  Now tweak its user parameters to 
obtain optimum performance which it is capable of providing.

Now for those that say "well I heard........" or that "someone told 
me......."  I say go research for yourself and learn the real facts.

73

Bob, K4TAX