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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