Dick,
Thanks for the notes on adjusting DRIVE/Po/ALC. Since my spike problem
occurs most often in CW mode, it seems more likely that it isn't caused by
misadjustment, but by a genuine problem with the rig's ALC circuit. For CW
on the '950SDX, you set POWER OUT to the desired level and advance the
CARRIER (drive) control to get an ALC indication within the ALC zone (no
more than halfway on the meter.) I assume it's the same on the '950SD. I've
generally found that changing POWER OUT on CW doesn't require readjustment
of the CARRIER control. But when following the correct procedure, I still
get spikes on 10M and 15M when the first CW element is sent.
Now that I think about it, I sometimes set the ALC level to just below the
top of the ALC zone (never beyond.) While this should be OK, it's possible
that this is too close to the edge for this rig, or that the ALC meter is
out of adjustment. If the rig still spikes when it gets back from service,
I'll try setting it at 1/4 ALC scale and see if that helps.
An intesting note is that the Yaesu rigs I have here (1000mp and 990) don't
have any provision for adjusting drive power in CW at all. You simply adjust
RF PWR out for the desired level. Does this represent an advance in circuit
design or is there some advantage in the 950's ability to set drive and
output power independently? Seems to me that the control is there on the
'950 because drive power tends to vary depending on the band (I sometimes
have to readjust the CARRIER control to bring ALC into the zone after
changing bands.) Evidently, that's not a problem for Yaesu.
As for SSB mode, I rarely see fault 17 there. On the '950SDX, I generally
adjust POWER OUT to suit the amp and MIC gain to set the ALC within the zone
on voice peaks. A little back and forth is needed to keep the amp peaking at
or below 1500W and keep ALC in the zone. When using the speech processor, I
set peak power output to suit the amp, compression below 10 dB, and ALC to
no more than half scale. If that boosts the power too much, I pull back on
the power and readjust the ALC (although that doesn't seem to be necessary
very often.) The procedure is basically the same for the FT-990. However,
the 1000mp ALC meter is different. Like the other rigs, you set compression
(with PROC) to 5-10 dB and drive power (with MIC) to mid-scale on the ALC
meter. But the ALC meter reading then *increases* if you reduce RF PWR or
*decreases* if you increase RF PWR. That's not what the meter does on the
other rigs, and I'm puzzled as to what's going on here. It seems like the
amount of ALC needed is automatically reduced (or increased) as the ratio
between DRIVE and Po decreases (or increases). Sound reasonable?
Anyway, I think the the whole concept of voice peaks presents an ALC
adjustment problem and probably explains why we hear so much distortion and
splatter on the bands. The question is, just how does one set the rig
correctly for voice peaks? I find that voice levels are notoriously
variable -- especially in contests. With the '950, I'm always keeping one
eye on the power/compression/ALC meters, and find readjustment is necessary
more often than I would like. The only times I have gotten a fault 17 in SSB
mode is when reflexively "shouting" into the mic during a contest. One fast,
sharp syllable at the right volume level will drive the heck out of the rig,
especially if the ALC is slow to ramp up.
Seems to me that in this day and age it should be possible to design an ALC
circuit that would 1) rise fast enough to prevent spikes, and 2)
automatically determine the correct level of ALC, so that the user would
only have to adjust one control -- POWER OUT (or mic gain/CW drive) -- to
obtain the desired power output level. After all, if a person can think it
through, the CPUs in today's modern rigs can, too!
73, Dick, WC1M
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