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K3S current draw relative to KAT3A settings

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Nicklas Johnson

K3S current draw relative to KAT3A settings

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

--
*N6OL*
Saying something doesn't make it true. Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.
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Joe Subich, W4TV-4

Re: K3S current draw relative to KAT3A settings

> 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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Nicklas Johnson

Re: K3S current draw relative to KAT3A settings

On Tue, 12 May 2020 at 11:51, Joe Subich, W4TV <[hidden email]> 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

--
*N6OL*
Saying something doesn't make it true. Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.
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Joe Subich, W4TV-4

Re: K3S current draw relative to KAT3A settings

> 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 <[hidden email]> 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
>

Nicklas Johnson

Re: K3S current draw relative to KAT3A settings

On Tue, 12 May 2020 at 12:34, Joe Subich, W4TV <[hidden email]> wrote:

What do you see with: 1) a 50 Ohm load connected to the antenna port
> and the KAT3A bypassed,

See the "bypassed" column in the original chart.

> 2) a 50 Ohm load connected to the antenna
> port and the KAT3A removed (KANT3 board installed),

I purchased the K3S with the KAT3A installed, and as I don't have a KANT3
board handy to swap in, I am unable to tell you.

> 3) a 50 Ohm
> load connected to the antenna port and the KAT3A tuned for SWR =
> 1:1,

For 13W, on 40m, 6.71A; on 20m, 8.2A. (The dummy load isn't a perfect 50
ohm match unfortunately; it's off by a few ohms and I measure 57 ohms with
a DC meter.)

> 4) your "antenna" connected to the antenna port and the KAT3A
> tuned for minimum SWR?
>

For 13W, on 40m 6.9A, on 20m 9.4A. In both cases the ATU had no trouble
making a 1:1 match.

The actual measured SWR of the antenna system (ie, with an SWR meter) is
3.7:1 on 40m and 2.9:1 on 20m. Not a great match obviously, but expected
for what it is.

Nick

--
*N6OL*
Saying something doesn't make it true. Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.
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Bob McGraw - K4TAX

Re: K3S current draw relative to KAT3A settings

In reply to this post by Nicklas Johnson

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:

Nicklas Johnson

Re: K3S current draw relative to KAT3A settings

On Tue, 12 May 2020 at 13:41, Bob McGraw K4TAX <[hidden email]> wrote:

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.
>

Running the identical test, on 40m, I get 14.4A bypassed, 13A matched.

On 20m, I get 14.0A bypassed, 17.5A matched, a bit bigger delta than what
you saw, but perhaps not totally unreasonable.

The reported C/L values the ATU picked for 40 and 20 for this test with the
dummy load are 0 nF / 0.5uH and 0.06nF / 0.25uH respectively.

With my antenna, repeating the same test, I get 14A on 40m and 19A on 20m
(both with the KAT3A matched), so around an amp more than with the matched
dummy load.

> 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.
>

Thank you so much for taking the time to run these tests. I appreciate
it. I think the fact that we have a TX gain calibration per band also
implies that we'd see some differences in current draw for the different
bands too.

What I was really trying to determine is whether the results I'm seeing are
*typical*, and it sounds like the answer is "yes."

I guess what caught my eye in all of this is how much the configuration of
the matching network can affect the current draw of the amplifier. Not
having a great deal of engineering experience with RF amplifier engineering
myself, I kind of expected that presenting the amplifier with a nice 50 ohm
load would have implied similar characteristics regardless of what sat on
the other side of the network, vs causing the amplifier to draw another amp
or two. My expectation was that we'd see *loss* through the presence of
the matching network, but not so much an additional demand of current.

Kind of interesting, but not, it seems, abnormal or unexpected. Thanks
again for confirming!

Nick

--
*N6OL*
Saying something doesn't make it true. Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.
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Jim Rhodes-2

Re: K3S current draw relative to KAT3A settings

In reply to this post by Bob McGraw - K4TAX

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 <[hidden email]>
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
> >
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Message delivered to [hidden email]

--
Jim K0XU
[hidden email]
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