[Elecraft] ALC implementation

[Bob McGraw K4TAX]

Well written generic paper for operation of FT-8 and other digital 
signals of like mode.   It does not totally nor correctly apply to 
Elecraft radios as power management is handled by a totally different 
means.   And those means and methods suggested in this paper are not 
applicable to Elecraft radios for power control.   From experience in 
set-up and operating different radios and different interfaces, I do 
believe that the WSJT-X operating panel which shows the right slider 
labeled PWR is very misleading and should be changed to some other 
description i.e. TX AUD.

While many radios use the control of audio level to adjust power output, 
this is somewhat misleading as there are control areas available such as 
SPKR level in Windows, and Line Gain for the radios or perhaps an 
external sound card device.   Again, the use of the acronym MIC is 
always a frighting term,  in as much as many systems produce a transmit 
audio level that will overdrive the microphone pre-amplifier input.  
Once this occurs, reducing MIC gain will not relieve the distorted audio 
as it occurs pre level control in the circuit.   Frankly, one should not 
connect the sound card to a microphone input without proper and correct 
means of attenuating the signal before it is connected to the microphone 
input.   In addition, this will always preserve the transmit 
Signal-to-Noise ratio.

As to "compression" I take that to mean Speech Processing, which should 
ALWAYS be off or set to a zero value.   Likewise for EQ, again always 
set to OFF or FLAT  for transmit and receive purposes as well.

As a mater of practice, there are three or perhaps four distinct places 
that audio levels can be controlled in the transmit path. First is SPKR 
level which is the audio level out of the computer. Second is the WSJT-X 
PWR slider, and third is the Line Gain within the radio.  A fourth, if 
used, would be an external interface such as a Signalink or 
Soundblaster.   If any of these points end up near minimum value or near 
maximum value, I strongly suggest further investigation as to why and 
remedial steps taken to more "normalize" the control values at all 
points in the system.

Some radios do have "meter" indicators which relate to ALC levels while 
others simply prove a visual means usually the illumination of a LED.  
In all cases, the indicators should be observed, and the radio operated 
accordingly with NO indicated ALC action occurring.    Again, regarding 
Elecraft radios, the first 4 bars on the "ALC Scale" are audio level and 
NOT ALC action.  The onset of actual ALC occurs at the 5th bar and higher.

73

Bob, K4TAX




On 6/28/2019 9:18 AM, Andy Durbin wrote:
> Does anyone know of any rig that uses "compression" rather than linear gain control to implement ALC?
>
> ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1
>
> 73,
> Andy, k3wyc
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