[Elecraft] K3S current draw relative to KAT3A settings

[Bob McGraw K4TAX]

I just ran quick tests on my K3S on all bands, first with the KAT3a 
bypassed and then with the KAT3a allowed to resolve a match.  Both cases 
were using a 50 dummy load and external power meter to measure the power 
into the load.  The current values were from the K3S display.

In all cases I found that the current was less with the KAT3a in bypass 
just as expected.   There is always some loss through any antenna 
tuner.  Some more than others and it will vary by band. The L network 
used by Elecraft is one of the more efficient and lower loss ATU designs.

Specifically:  100 watts indicated into dummy load via external power 
meter.

for 40M the current was 15.3 amps {KAT3a bypassed}  and 15.75 amps with 
KAT3a active/AUTO and resolved a match

for 20M the current was 18.5 amps {KAT3a bypassed} and 17.26 amps with 
KAT3a active/AUTO and resolved a match.

As concluded from my tests, the radio will draw different amounts of 
current on different bands for the same given and measured power 
output.   Seems normal to me.

73

Bob, K4TAX

On 5/12/2020 1:31 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
>