[Elecraft] K3S current draw relative to KAT3A settings

[Jim Rhodes]

For your test to give you the results you are trying to find you need to
have a load that requires high C/low L and another which requires low
C/high L on EACH band, then have the tuner match it. Otherwise you are just
seeing how much energy can be dissipated in your tuner. One way to do this
is to use a dummy load and a manual tuner, set the manual tuner to
deliberately give you the type of mismatch you want and then have the
autotuner try to match it. doing it your way is just abusing your output
devices.

On Tue, May 12, 2020 at 3:41 PM Bob McGraw K4TAX <rmcgraw at blomand.net>
wrote:

> 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
> >
>
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-- 
Jim K0XU
jim at rhodesend.net