[Elecraft] K3 SSB Power Control and ALC Metering

[wayne burdick]

There's been some recent discussion of how to properly set up the K3 in 
SSB modes. I meant to respond sooner but was out of town for several 
days.

MIC GAIN SETTING:  Adjust MIC gain for an ALC meter peak at around 5 to 
7 bars during normal speech (rev. D owner's manual, page 28). This 
applies even to TX TEST mode, meaning you can set it off-air. This 
indication does not mean that you're "hitting the ALC really hard." 
When you get to around 5 bars, you'll be "tickling" the DSP's ALC. More 
on this below.

ALC METERING:  The K3's ALC meter is a bar graph, not an analog meter, 
and we felt that 5 bars would provide the right granularity at the 
target ALC level. The 5th bar of the ALC scale is heavier than the 
others, serving as a reminder of the this level.

ALC DESIGN GOAL:  The K3 was designed to minimize transmit splatter and 
other effects that plague some rigs. To achieve this, we apply all ALC 
*before* the crystal filter, and minimize the application of ALC in 
general. The levels have been carefully calibrated to that 5-to-7-bar 
level mentioned above. The result is that the crystal and DSP filters 
remove the types of artifacts that in many other rigs end up as 
transmitted wideband noise or clicks. I believe this is why we continue 
to hear excellent reports from K3 users regarding their on-the-air SSB 
signals. (We've also heard, from some experts in the subject, that the 
K3's compression is among the most effective they've ever measured.)

PER-BAND POWER CONTROL: With some vocalizations, speech energy may 
build up within a narrow crystal filter to produce a slight peaking 
effect. Because of this, the user must set the K3's power output level 
such that it peaks at or below the safe level for any external 
amplifier under all speech conditions. To facilitate this, you can use 
per-band power control (refer to the PWR SET configuration menu entry). 
We have many customers using this method. It compensates for per-band 
gain variation in the external amp or the K3 itself, again reducing the 
need for ALC. For example, all crystal filters have a small amount of 
ripple (typ. +/- 0.5 to 1.0 dB) that can result in a slight difference 
in average power output between LSB and USB with some voice 
characteristics. But since you typically use only one of the two 
sidebands on a given ham band, per-band power control can conveniently 
compensate for small variations.

TX GAIN COMPENSATION FOR VOICE MODES (TXG VCE): If you find that your 
speech peaks are routinely above the desired level (i.e., higher than 
CW power output using TUNE), you can adjust the TXG VCE menu parameter 
downward in 0.5 dB steps. Conversely, if your normal speech 
characteristics result in lower power output compared to CW TUNE, you 
can increase TXG VCE above the 0.0 dB level.

I'll be happy to answer any further questions. Our goal is to improve 
the manual to make the above as clear as possible.

73,
Wayne
N6KR

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OK?

W




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