[Elecraft] K3S current draw relative to KAT3A settings

[Joe Subich, W4TV]

 > I'm not talking about the difference in measurements in the chart
 > vertically; I'm talking about the difference horzontally.

The measurement horizontally - at least min C/max L and max C/min L -
mean absolutely nothing because the tuner is not tuned properly.

What do you see with: 1) a 50 Ohm load connected to the antenna port
and the KAT3A bypassed,  2) a 50 Ohm load connected to the antenna
port and the KAT3A removed (KANT3 board installed), 3) a 50 Ohm
load connected to the antenna port and the KAT3A tuned for SWR =
1:1,  4) your "antenna" connected to the antenna port and the KAT3A
tuned for minimum SWR?

I do not have the tuner component values in front of me so I can't
calculate the impedance you are creating by min C/max L and max C/min L
but if the tuner has a 10:1 matching range you are running between
at least 5 and 50 Ohms or 50 and 500 Ohms depending on whether the
C is on the input output side of the inductor (basic L network).

The roughly 2:1 difference in current is believable for the 10:1
impedance mismatch - particularly if the controller is reducing
the drive (power output) as the mismatch exceeds 2:1 or 3:1.


73,

    ... Joe, W4TV


On 2020-05-12 3:08 PM, Nicklas Johnson wrote:
> On Tue, 12 May 2020 at 11:51, Joe Subich, W4TV <lists at subich.com> wrote:
> 
>>
>>> So I guess the question is this: is it expected to see such a large
>>> variance in power consumption for the same output power based on the
>>> values of C and L for the KAT3A?
>> Is the KAT3/KAT3A *tuned correctly*?
>>
> 
> This came up because the rig is drawing a lot more current on 20m vs 40m,
> when the KAT3A is tuned for the antenna (which is a better match on 20 than
> on 40).  For the dummy load, no, the KAT3A won't be tuned correctly when I
> manually choose values for C and L; I just used it as a way to better
> characterize the nature of the behavior that I was seeing and to reduce the
> number of variables.  However, as I mentioned, the behavior is similar when
> running FT8 with the tuner correctly tuned for the antenna.  If memory
> serves, the difference in current draw was something like 6 amps between 40
> and 20, though I can go measure that again if an exact value is useful.
> 
> You are comparing apples and oranges here.  At 12W the 100 W amplifier
>> is bypassed.  At 13W the 100W amplifier is engaged.  The differene you
>> see is due to the 100W amplifier.
>>
> 
> I'm not talking about the difference in measurements in the chart
> vertically; I'm talking about the difference horzontally.  I did the
> measurements twice deliberately, specifically because PA is
> bypassed/engaged, because I wanted to see if there was any relationship
> there as well.
> 
>     Nick
>