Re: [Elecraft] K2 SSB Power Overshoot on First Syllable

[Michael Carter via Elecraft]

Hi Karin,

You've resurrected a topic that was once very
active on this same Elecraft reflector:

https://www.mail-archive.com/elecraft@mailman.qth.net/msg27397.html

It's a long thread.  I recommend skipping down if you're
in a hurry to read the post by David, M0DHO:

https://www.mail-archive.com/elecraft@mailman.qth.net/msg27499.html

While David's post is not conclusive, it reveals some
information that numerous other posts do not.

Suffice it to say, you're not the first to make this
observation.  The presence of TX power overshoot
on SSB and not CW may also be correlated to
which version of MCU firmware and KSB2 firmware
one is running. It's not clear if the SSB power overshoot
issue was ever fully addressed by K2/KSB2 hardware modifications
or firmware upgrades.

You might contact Dave, W8FGU, who is now the
legacy K2 repair guy after Don's (W3FPR) long stint
in that role.  Dave's web page is 
https://w8fgu.com/index.html .
Dave may know if there was any resolution of this issue.

73,
Mike, K8CN
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Re: [Elecraft] K2 SSB Power Overshoot on First Syllable

[David Woolley]

This is all, unfortunately, in the proprietary part of the K2, the 
firmware. The K2 doesn't have a gain calibration tables, and I'm not 
sure if it even saves gain settings between transmissions.


With CW it will know that the first transmit level it sees is full 
power, so my guess is that it starts low and builds up to that, but for 
SSB, it won't know when the peak has been reached, so it is going to set 
the transmit gain before it reaches peak and then back it off, but there 
will be a delay in backing it off.  Remember it is primarily a CW 
transmitter.


I would guess, to minimise this, you should set your audio drive levels 
low enough that it gets the correct power open loop.


To make things safe for your amplifier, I guess you would have to add an 
attenuator, so that maximum power will not overdrive the amplifier. 
However, I'm not sure that running at maximum power is good for clean 
signals.


I don't know if there is any open loop control between the power control 
and the transmit gain, or whether it totally relies on closed loop power 
control.  Any open loop control would have to be a compromise, because 
of production spreads in the gain, so, on most instances, would end up 
too high, so as not to limit the maximum output.


I believe there is a gain calibration procedure on the K3 and K4, that 
allows those to make a reasonable open loop power setting at the start 
of a transmission.


--
David Woolley (owner K2 06123)

On 18/12/2023 22:42, Karin Johnson wrote:

Has anyone ever figured out why the Elecraft K2, either base version or with
KPA100 amplifier, has a pronounced
power overshoot on the first syllable using SSB.  I did an internet search
for this problem and did not find
a lot of discussion about it.  Difficult to use an external high power
amplifier as the amplifier may trip on
excessive drive.  My Elecraft K2 works just fine on CW.


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[Elecraft] K2 SSB Power Overshoot on First Syllable

[Karin Johnson]

Hello Group:
Has anyone ever figured out why the Elecraft K2, either base version or with
KPA100 amplifier, has a pronounced
power overshoot on the first syllable using SSB.  I did an internet search
for this problem and did not find
a lot of discussion about it.  Difficult to use an external high power
amplifier as the amplifier may trip on
excessive drive.  My Elecraft K2 works just fine on CW.
Inquiring minds want to know.

Regards,
Karin Anne Johnson  P.E.  K3UU
Palm Harbor, Florida

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