By "manually tuning" I mean using KPA1500 Utility
program to tweak the L and C. In most cases you
can get closer to zero reflected power than the
automatic routine can. Getting the SWR down as
close as possibly to 1.0:1 at all frequencies
most certainly flattens the gain/frequency response.
If you know how to use the Utility program try it. You might be surprised.
You should also investigate the ^PB command, very
useful if you have a high Q antenna. The ^PB
command chooses the stored setting for the lowest
SWR within a segment. I have this mapped to PF1
on the front panel and use it on 160M where the
tuning segments are wide compared to the fast
changing SWR (high Q) of my antenna. I also have
WET and DRY settings for one of my antennas that are selected by PF1 (^PB).
- Paul KW7Y
at 07:19 PM 11/18/2019, K9MA wrote:
There are a couple issues here. First, even if
the SWR is 1.2:1, about the best the KP1500 ATU
firmware can do, across the whole band, the
power can still vary a lot. It depends on the
actual load impedance, which, at 1.2:1 could be
anywhere from 42 to 60 Ohms. If you happened to
be at 42 Ohms when you set the power to 1500 W,
it could possibly go up to 2100 W elsewhere in
the band. (Except, of course, that the KPA1500
won't let you do that.) The other issue is the
temperature dependence: I find I have to reduce
drive by about 20 percent when the amplifier is
cold, or it will fault. Both of these problems
could be solved by a slow feedback mechanism
which adjusted the K3 output like we do
manually. It might even remember previous
settings as a function of PA temperature and
frequency. The second issue is that this is
nothing like conventional ALC, a relatively fast
feedback loop. ALC has proven to be highly
problematic, so let's not go into that again.
It's an entirely different issue. Yes, ALC that
really worked well with an amplifier would make
the above unnecessary, but I don't think anyone
has figured out how to do that. Until someone
does, a slow feedback loop adjusting drive power
would solve the problem above, not introduce any
distortion, and save us operators the bother of
riding the power control. 73, Scott K9MA On
11/18/2019 20:32, N4ZR wrote: > Jim, I think
Paul is talking about something different
here. On Page > 18 of the manual it describes
tapping the ATU Tune button again within > 3
seconds of completing the initial tune, to get
closer yet. I just > tried it, and it works
well so long as you have trained the tuner for >
both antennas on every segment. Unfortunately,
there appears to be no > way to actually
transmit the first character at full power
when > changing antennas or QSYing bigly. I
understand the tuner bypasses > the amp until it
has determined which setting it should use,
which it > can only do by learning what the load
looks like by actually sending > power into
it. > > 73, Pete N4ZR > Check out the Reverse
Beacon Network > at <http://reversebeacon.net>,
now > spotting RTTY activity worldwide. > For
spots, please use your favorite > "retail" DX
cluster. > > On 11/18/2019 8:18 PM, Jim Brown
wrote: >> On 11/18/2019 11:34 AM, Paul Baldock
wrote: >>> I have manually tweaked (with amp in
standby and running 50W) my >>> auto learned atu
settings to get as close to 0W reflected power
as >>> possible. >> >> Yes, and this is exactly
what the manual says to do -- before using >>
the amp, train the tuner by tuning at multiple
frequencies in each >> band, AND for each
antenna that you use on that band. The tuner
is >> smart enough to select between multiple
"trainings" when you use more >> than one
antenna. >> >> 73, Jim K9YC >>
______________________________________________________________
-- Scott K9MA [email protected]
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