In Digi Modes ALC in Yellow?

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New user with question regarding ALC meter. Have noticed when getting Fldigi working that when transmitting the ALC meter is in the yellow.
- Is that OK as long as not in the red ?
- If not how does one adjust the audio drive level in digi modes in SSDR ?

73
Paul
w2eck
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W2ECK

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Posted 1 week ago

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John - AI4FR

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Excellent questions. I keep mine out of the red at all times! Even the tiny slot/dash in the SDR ALC scale is out of the red. I adjust mine using DAX.
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W2ECK

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I tried  the DAX Tx Gain adjustment and it seems like it was lowering the  Rf power out? 
Paul
w2eck
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Neal Pollack, N6YFM

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That is correct, backing off the audio drive will lower output power, while also reducing distortion and splatter. 

There are several points in the audio chain that can control TX audio level;

1.  Windows PC audio output level:
     https://www.youtube.com/watch?v=ko1A1qcqWWQ
     at about 3 minutes into the video, how to set output level for a specific audio channel.

2.  FLdigi Transmit Attenuator setting;
     Bottom of this page;  http://www.w1hkj.com/FldigiHelp/audio_adjust_page.html

3.  If using WSJT-X for FT-8, the PWR output slider on the right hand side of the
     program user interface screen.

Please understand that properly adjusted TX audio for a clean signal WILL result
in reduction of transmit power level, but also will avoid distortion, clipping, and
splatter across the radio band.

NOTE:  Modes like JT65 and FT8 are not sensitive to small amount of ALC action,
             but with phase sensitive modes like PSK, you should not let ANY ALC show
             on the meter.   [I have done extensive lab testing with JT & FT8 modes using
             a spectrum analyzer, as well as on the air coordinated testing, and moderate
             ALC on the rig meter does nothing to JT or FT8 modes.  You can't say the same
             for PSK modes, avoid ALC with PSK modes.]

Cheers
(Edited)
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Paul

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If you're overdriving, you will be producing unwanted frequency components (distortion). Those components contribute to the output power reading. So when you reduce the drive, much of the reduction in power reading can be attributed to those components no longer being present. The remaining signal itself is not significantly reduced.
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W2ECK

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Neal and all
thanks for the replies and help. Neal thanks for the results of you testing and the insights of ALC effects on PSK31 vs. the WSJT-X modes. I am coning from the elecraft K3 worked where you shot for 5 bars on the alc meter and if over you could adjust it down by using the mic gain knob and not have to touch the power knob. As I recall you could also adjust in the Windows Sound playback levels tab. But here we are using the DAX Tx gain adjustment.. 
- but still am not clear whether in FT-8 by lowering Tx gain to bring the ALC down (and thus power out) I will get the same results?
73
Paul
w2eck
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Neal Pollack, N6YFM

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Hi Paul:

Yes.   To affect your ALC meter setting (and audio gain/drive), you can adjust ANY  point in
the audio output path between WSJT-X and the physical radio.  This includes the audio level
slider on WSJT-X (right side of window), the MS Windows Audio Playback Level slider, the
Flex DAX TX gain slider, all of them are effectively in series.  Any one, or all, will control your
audio drive level.

Cheers,

Neal