K3 ATU readout

[Ralph Tyrrell]

Wayne gave us a way to read out what the ATU settings.

Does anyone have the  formula or formulae for using  "CT or CA and the L and C values to determine the impedance presented to the ATU?

Thanks,
Ty, W1TF, K3 #696

--------------------------------------
Wayne wrote:

Most of the time you'll let the KAT3 automatic antenna tuner do its thing and ignore it. It has a wide matching range and saves L-C information per-band and per-antenna, so you'll rarely need to re-tune.
 
(We do plan to add multiple stored segments per band, too.)

If you're ever curious about the actual L and C values used in the matching network, you can check them using a special setting of the KAT3 menu entry (in the CONFIG menu). Just set KAT3 to LCSET, then exit the menu. Next, tap "ATU TUNE". This will display the present L and C values.

For example, I just matched my K3 on a random wire antenna on 40 meters, went into LCSET mode, and saw this when I tapped ATU TUNE:

    CA 0.08 nF
    L 0.25 uH

The "CA" means that the capacitance ended up on the antenna side of the
 
L-network. The other possibility is "CT", or capacitance on the transmitter side. The capacitance is shown in nF (nanofarads) so it can fit into three digits on the VFO A display even when the value is over 999 pF. The value shown, 0.08 nF, could also be expressed as 80 pF.

Now, suppose you'd like to see what the effect of changing the L and C values would be on the match. (Or you're troubleshooting the KAT3.) You can simply rotate VFO A to change the C value, and rotate VFO B to change the L value. Tapping "ANT" alternates between "CA" and "Ct". Having made a change, tap ATU TUNE again to exit the L-C display. Then hold TUNE to go into transmit mode and see the new SWR value.

Manual view/change of LC settings is certainly fun and educational. But it could also be used to give me (your overworked firmware guy) feedback about a difficult matching situation. I'm always open to fine-tuning the KAT3's algorithm. So if you discover -- using LCSET --  that you're able to do better than the KAT3 in auto-tune mode, just let me know.

73,
Wayne
N6KR


     
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[hb9brj]

Ralph Tyrrell wrote

Wayne gave us a way to read out what the ATU settings.

Does anyone have the  formula or formulae for using  "CT or CA and the L and C values to determine the impedance presented to the ATU?

Had the same idea: Using my K3's ATU settings to determine the impedance of my antenna. The formula is easy. But besides L, CA or CT and the frequency, it contains the TX output impedance, which probably differs from 50+j0 ohms. Any opinions?

Markus

[Mike Scott-7]

>Wayne gave us a way to read out what the ATU settings.
>Does anyone have the formula or formulae for using "CT or CA and the L and
C values to determine the impedance presented to the ATU?

The K3 tuner looks like an L network with series L and shunt C that is
placed either on the antenna side or transmitter side of the inductor.

When the shunt capacitance is on the antenna side the impedance of the
antenna is higher than 50 ohms. When it is on the transmitter side the
antenna is showing less than 50 ohms.

Right now I show on my K3 CA = 0.16 nF and L = 0.70 uH, I am matched at
frequency of 7.025 MHz.

I now start cheating and use a program called L TUNER at:
http://www.smeter.net/feeding/l-network-terminating-impedance.php

I click on the L TUNER link and run the program (does not require
installation) and choose the topology (series inductor shunt capacitance on
the output or right side, network #1). I would choose network #3 if my
capacitance value was on the transmitter side.

I then enter the inductance of 0.7 uH, capacitance of 160 pF (convert from
nF shown on K3). Enter generator impedance (K3 transmitter) of 50 Ohms. And
now enter frequency of 7.025 MHz. And the program computes the following
values for the terminating impedance of the network assuming a proper
conjugate match to the 50-Ohms resistive load of the transmitter:

Series Resistance R = 67.9 Ohms

Series Reactance X = -8.8 Ohms


Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1  #1311



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[AC7AC]

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[KK7P]

Please keep in mind that the L C display tells what is selected in the
matching network.  There are stray capacitances and inductances on the
PC board.  If the indicated inductance or capacitance are very low, or
the matched impedance is highly reactive, these strays may be significant.

Enjoy!

73,

Lyle KK7P
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