[Elecraft] KXAT2 vs. Other Elecraft Transceiver ATUs

[Wayne Burdick]

Mike,

Your analysis of combinations is correct. But the KXAT2 should be compared to the KXAT3 (etc.), not the T1. Here's why: 

The KXAT2 only has to cover 80-10 meters. The KXAT3 has one additional L and C, but it has to cover 160-6 meters. Over the range of 80-10 meters, for virtually any field antenna, the KXAT2 will perform just as well.

The T1 also has to cover 160-6 meters. To do this with 7L/7C, the L and C values in its array are spread out with a ratio of slightly greater then 2:1 from one to the next. This allows the array to cover a wider range of load impedances, but with an average final SWR more like 1.5:1 than 1:1.

The KXAT2, like the KXAT3, uses a ratio of very close to to 2:1, so average final SWR is very close to 1:1.

73,
Wayne
N6KR



On May 24, 2016, at 9:05 AM, Mike Morrow <kk5f at earthlink.net> wrote:

> Bill wrote:
> 
>> As to the ATU in the KX2, 7L/7C is the same range as the KX1, T1 and
>> I think the K2 ATU.
> 
> That is wildly inaccurate, especially for the KXAT1 ATU!!!
> 
> The reactance configuration for all Elecraft ATUs is an L-network of series inductance, with a capacitance connected to common before (radio side) or after (antenna side) the inductance (but not both) by a relay.  It is a classic simple low pass filter.
> 
> The total number of possible configurations in such a filter of L inductors and C capacitors, with the capacitor bank capable of being connected to either side of the series inductor, is:
> 
> Different Configurations = ( 2^L x 2^C x 2 )
> 
> Four (4) "don't care" (non-unique) configurations should be eliminated from total:
> 1.  Capacitor bank connected to inductor input, but all capacitors open.
> 2.  Capacitor bank connected to inductor output, but all capacitors open.
> 3.  Capacitor bank connected to inductor input, but all inductors shorted.
> 4.  Capacitor bank connected to inductor output, but all inductors shorted.
> 
> USEFUL Different Configurations = ( 2^L x 2^C x 2 ) - 4
> 
> For Elecraft transceiver ATUs before the new KXAT2, here are summaries (N is the network variable...capacitor connected to input OR output of inductor):
> 
> KAT1 (4L/5C/N) Configs=1020, L=0 to 4.9 uH (16 steps), C=0 to 300 pF (32 steps) 
> 
> KAT2 (8L/8C/N) Configs=131068, L=0 to 20.7 uH (256 steps), C=0 to 2420 pF (256 steps) 
> 
> KAT3 (8L/8C/N) Configs=131068, L=0 to 17.4 uH (256 steps), C=0 to 2600 pF (256 steps) 
> 
> KXAT1 (3L/3C/N) Configs=124, L=0 to 4.5 uH (8 steps), C=0 to 140 pF (8 steps) 
> 
> KXAT3 (8L/8C/N) Configs=131068, L=0 to 15.9 uH (256 steps), C=0 to 2680 pF (256 steps) 
> 
> T1 (7L/7C/N) Configs=32764, L=0 to 7.5 uH (128 steps), C=0 to 1300 pF (128 steps) 
> 
> Many already have the new KXAT2, but no circuit value information has yet been provided to those of the great unwashed masses like myself.  All I've seen is its description as 7L/7C/N, just like the T1.  If that is correct:
> 
> KXAT2 (7L/7C/N) Configs=32764, L=0 to ?.?? uH (128 steps), C=0 to ???? pF (128 steps)
> 
> The KXAT1 generates 124 unique matching network configurations. 
> The KAT1 generates 1020 unique matching network configurations. 
> The KXAT2, T1 generate 32724 unique matching network configurations. 
> The KAT2, KAT3, KXAT3 generate 131068 unique matching network configurations. 
> 
> Conclusion:  The KXAT2 is comparable ONLY to the T1.
> 
> 73, 
> Mike / KK5F 
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