K3: Still unable to set power correctly - clarification

[Dave, G4AON]

There seems to be ambiguity as to what this problem is and its effect.

Several months ago, I and others noted difficulty setting power levels
on data modes. This was looked at by Lyle and Wayne with an improvement
but it still is an issue right up to the latest beta firmware (2.76).
This problem has little to do with the K3 pre-set power level as dialled
in with the PWR control.

Many of us have very accurate peak reading external power meters and
oscilloscopes to set peak power levels with - and know what power we
initially set. What happens is the ALC is fairly loose in operation with
a long time constant, while this may produce a clean signal when running
near full power on SSB, the peak power levels at less than full output
vary considerably. Not only is this a pain on data modes such as PSK31
where you are (a) not needing high power and (b) trying to produce very
low IMD products, but also when driving a linear which requires less
than 100W of drive.

Here in the UK the power limit is 400 Watts, driving my Acom 1000 linear
with typically 20 ~ 25 Watts of carrier will give 400 Watts measured on
an LP-100 power meter. However, during the course of an SSB QSO the
power output on peaks runs anywhere from 200 Watts to 600 Watts and that
is not good. Checking my K3 at 20 to 30 Watts output into a dummy load
also produces this variability.

We have been told the K3 ALC produces a cleaner signal than many other
transceivers with "tight" ALC control, I don't doubt the signal is
cleaner than many, however the problem of adhering to a legal power
limit still remains... Clean signal or not.

73 Dave, G4AON
K3/100 #80



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[Julian, G4ILO]

Dave G4AON wrote

There seems to be ambiguity as to what this problem is and its effect.

Several months ago, I and others noted difficulty setting power levels
on data modes. This was looked at by Lyle and Wayne with an improvement
but it still is an issue right up to the latest beta firmware (2.76).
This problem has little to do with the K3 pre-set power level as dialled
in with the PWR control.

Many of us have very accurate peak reading external power meters and
oscilloscopes to set peak power levels with - and know what power we
initially set. What happens is the ALC is fairly loose in operation with
a long time constant, while this may produce a clean signal when running
near full power on SSB, the peak power levels at less than full output
vary considerably. Not only is this a pain on data modes such as PSK31
where you are (a) not needing high power and (b) trying to produce very
low IMD products, but also when driving a linear which requires less
than 100W of drive.

Here in the UK the power limit is 400 Watts, driving my Acom 1000 linear
with typically 20 ~ 25 Watts of carrier will give 400 Watts measured on
an LP-100 power meter. However, during the course of an SSB QSO the
power output on peaks runs anywhere from 200 Watts to 600 Watts and that
is not good. Checking my K3 at 20 to 30 Watts output into a dummy load
also produces this variability.

We have been told the K3 ALC produces a cleaner signal than many other
transceivers with "tight" ALC control, I don't doubt the signal is
cleaner than many, however the problem of adhering to a legal power
limit still remains... Clean signal or not.

I understand your problem, Dave, but I don't think it is the same as the one I am complaining of.

Let me try to explain it as simply as I can. There are two ways of producing a plain carrier output. You can key down, or you can inject a pure sine wave into the audio stages in SSB mode. The output should look to all intents and purposes identical, and since it is not varying in amplitude or phase, issues of whether or not peaks are being detected do not apply.

If I set the power control to 5W and key down in CW mode, the K3 meter and my power meter show 5W.
If I inject the audio tone in SSB mode and increase the level, the output power limits at 5W, as shown on both the K3 meter and my own meter (which only reads RMS not peak.)
If I inject the tone in DATA A mode and increase the level, the output power doesn't stop increasing until about 10W, as shown by both the K3 meter and my external meter.

The problem is quite simply that the output on a pure tone in DATA A is twice the power requested, and twice what it would be in SSB mode. What's more, it's twice what the K3 firmware expects it to be, with the result that if you set the power control to 10W it will try to produce 20W with the PA switched out.

[wayne burdick]

On Jan 4, 2009, at 8:18 AM, Julian, G4ILO wrote:

> The problem is quite simply that the output on a pure tone in DATA A is
> twice the power requested, and twice what it would be in SSB mode.
> What's
> more, it's twice what the K3 firmware expects it to be, with the
> result that
> if you set the power control to 10W it will try to produce 20W with
> the PA
> switched out.

This, if true, would be a firmware problem. So noted.

Wayne

---

http://www.elecraft.com

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