[Elecraft] KX3 Operating Tip: Determining the ATU's L/C values and L-net configuration

[Wayne Burdick]

Heinz (OE5EEP) wrote:
> The KXAT3 internal ATU works really great! I can match a dipole of  
> 2x 6.8m with 7m of double-wire feedline erected as inverted V on all  
> bands from 40 to 6m....  I wonder if there is a way to retrieve the  
> L/C combinations and values used to achieve a match. Is this  
> somewhere hidden in the menu?
>

You can't get L-network information via the menu. But you can send an  
"AK;" (ATU relay settings) command from the KX3 Utility Command  
Tester. This command is intended for use during automated factory test  
but may be of interest to operators as well.

The response format is “AKaabbcc;”, where:

   aa = inductance bitmap in ASCII hex format
   bb = capacitance bitmap in ASCII hex format
   cc = misc relays bitmap in ASCII hex format

At present only bit 0 of byte cc is defined:

   00 = capacitance on antenna side
   01 = capacitance on transmitter side

Example: Suppose you get back "AK031A01;". First convert the hex  
quantities to binary:

   03 => 00000011 (L)
   1A => 00011010 (C)
   01 => 00000001 (network selection)

Now compare these values to the KXAT3 schematic. 00000011 for L means  
that two smallest inductors are switched in. Add these together to  
determine the total L value. Similarly, add up the selected capacitors  
based on the binary value 00011010. Finally, you can determine the  
network configuration from the value 00000001. In this case, the  
capacitance is on the transmitter side of the series inductance.

If the ATU is not installed, or if the ATU MD menu entry parameter is  
set to one of the L/C test values, “AK000000;” is returned.

If the ATU is in “bypass” mode, quasi-bypass values are shown. (These  
were selected to approximately cancel out the ATU's own stray  
reactance on each band.)

In AUTO mode, the working auto-tuned values are shown.

Wayne