Posted by
Joe Subich, W4TV-4 on
May 12, 2020; 6:51pm
URL: http://elecraft.85.s1.nabble.com/K3S-current-draw-relative-to-KAT3A-settings-tp7660811p7660814.html
> 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*?
Any solid state amplifier will draw more current if it is driving a
low impedance load than it draws driving a high impedance load. If
the KAT3/3A is transforming the antenna impedance to a low value,
you will see higher current than you would for a proper 50 Ohm load.
The only valid measurement is with a 50 Ohm dummy load attached to
the antenna jack and the KAT3/3A tuned for the 50 Ohm load (or
bypassed). You should *never* be operating with the tuner adjusted
for other than 50 Ohms to the PA.
> min C/max L max C/min L bypass not-inst
> 40m, 12w 3.55A 2.23A 3.4A 3.3A
> 20m, 12w 3.70A 1.99A 3.1A 3.0A
>
>
> 40m, 13w 11.5A 4.65A 7.3A 7.2A
> 20m, 13w 15A 5.63A 6.9A 6.8A
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.
73,
... Joe, W4TV
On 2020-05-12 2:31 PM, Nicklas Johnson wrote:
> I've had a few exchanges with support on this, but as Covid-19 is imposing
> some new burdens on the shop, I thought I might ask the larger community
> for input as well.
>
> I've been troubleshooting seemingly anomalous power consumption when
> transmitting. My K3S pulls way more current on 20m than on 40m for the same
> input signal and output power.
>
> After some experimentation, I found that the input current is related to
> whether the KAT3A is engaged, and which values of C and L are selected.
> The lowest power consumption comes from the highest value for C and the
> lowest value for L, and the highest power consumption comes from the lowest
> C and highest L. Here's a chart of what I found going into a dummy load,
> manually setting C and L values:
>
>
> min C/max L max C/min L bypass not-inst
> 40m, 12w 3.55A 2.23A 3.4A 3.3A
> 20m, 12w 3.70A 1.99A 3.1A 3.0A
>
>
>
>
>
> 40m, 13w 11.5A 4.65A 7.3A 7.2A
> 20m, 13w 15A 5.63A 6.9A 6.8A
> If that chart doesn't render well on the list, here's a screen shot of it:
>
https://imgur.com/GF4IUIy>
> (This was transmitting a 1500Hz tone, SSB at almost 100% modulation with
> 14v supplied, and is the value reported by the K3s, though my ammeter
> reports a similar value. I get similar results with FT8 going into an
> actual antenna instead of a dummy load.)
>
> 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?
>
> Nick
>
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