[Elecraft] KPA-1500 wish list

[K9MA]

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
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>
> 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

k9ma at sdellington.us