On 06/04/2018 05:38, Black Michael via wsjt-devel wrote:
Your picture didn't come through. But I did another collection using
Audacity via WASAPI and don't see it now.
The reason I looked was an apparent power jump on my wattmeter at the
start of the transmission.
Now that I'm watching via WASAPI I don't see the power jump anymore.
Quit Audacity and the power jump comes back.
Getting very irregular behavior. That starting amplitude sometimes
come in at 0.5V, sometimes at 0.1, sometimes at 1.0 -- can't quite
find a repeatable pattern. I guess I'd like to record directly from
WSJT-X to see if there's a comparison to be had.
And a friend of mine with an IC7300 was seeing the same thing on his
rig too. Plus others have now chimed in and said they see the power
jump too. Could it be random? What determines the level of the preamble?
Hi Mike,
Steve's image came through here as an attachment without issue. It was a
perfect constant envelope trace with a clean start up, which is exactly
what I would expect. I'm also sure that if he looked at the first few
cycles it would show the tone sinusoid starting exactly at zero
amplitude and raising cleanly to full amplitude.
Many rigs suffer ALC overshoot after initial switch to Tx mode, some
Icoms are particularly prone but almost all rigs suffer. The Icom
IC-7300 has menu settings to adjust the timing between switching to Tx
and modulation starting, I assume by adding some delay into it's Tx DSP.
Also anyone using transmitter VOX or an interface like the SignaLink USB
that is effectively VOX should be careful to check that their rig does
not overshoot it's output power as any ALC circuit has some loop delay
and cannot stabilize instantly. For rigs that suffer badly, particularly
when an external PA might be vulnerable to excessive drive power spikes;
one solution might be to reduce the audio input to control power rather
than any power control on the rig itself.
As an aside I suspect that may have this ALC overshoot issue without
knowing about it because their power output meters on their rigs or
externally are not able to respond fast enough to register it.
73
Bill
G4WJS.
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