[Elecraft] KX1 losing its match (discussion and remedies)

[wayne burdick]

The KX1 should definitely not lose power output or the KXAT1 change its 
L-network settings under any normal circumstances. We've tested the 
tuner and the rig extensively, and I've never seen this happen.

The first things that come to mind are intermittent component failures 
or power supply brownouts that reset the MCU. However, using the tuner 
with a very poor (or non-existent) ground, and/or an antenna that is 
close to a half wavelength or a multiple thereof could also cause 
trouble. RFI in such cases is a challenge for almost any ATU. The usual 
remedies are (1) better ground counterpoise, (2) adjustment to antenna 
length, (3) balun. A 4:1 balun can be quite effective at reducing high 
RF voltages that might be present on the chassis or antenna, in many 
cases transforming a difficult match into one that's in range of the 
tuner.

If anyone has a KX1 that exhibits a consistent failure pattern, please 
contact me directly. I would need to know exactly how the failure 
occurs so I can determine whether it's likely to be due to RFI, a 
component failure, or some other cause. I'll also need to know what L, 
C, and network selections were in effect at the time. (The KX1, like 
the K1 and K2, provide ATU menu entries that allow you to determine how 
the tuner is configured. See the manual for details.) I will analyze 
and repair any KX1 that is demonstrated to have such a problem. But 
let's discuss it by e-mail first  ;)

I should mention one other possibility. If you have an antenna that you 
know presents high RFI to the rig, but you'd like to use it anyway, or 
if you just want to "ruggedize" the KXAT1, you could add a few bypass 
capacitors. I would place a very small .01 uF capacitor from each of 
the MCU's relay drive pins to ground. Since relays K1-K3 are so close 
to the KXAT1's MCU, you could place capacitors directly across the 
relay coil drive pins. The other four relays (K4-K7) are farther from 
the MCU, so it would be best to put the bypass capacitors right at the 
MCU itself, i.e. from pins 10, 11, and 12 to pin 5 (ground).

The Elecraft part number for these bypass capacitors is E530019. Anyone 
who wants to add these to their KXAT1 can request seven of them at no 
charge by e-mailing parts at elecraft.com.

Note that our new T1 ATU has such bypass capacitors on all relay drive 
lines (surface-mount capacitors, pre-installed on the board). We felt 
that the T1 should have this protection because it is a very wide-range 
tuner, capable of operation on 6 meters where RFI problems can be 
significantly worse than on the HF bands. Also, the T1 is rated at 20 
watts, and has been successfully used at twice this level on 40 meters 
and up (with "backpacker" amps, usually). The KXAT1, in contrast, is 
never going to be operated at high power levels and is only intended to 
cover 40, 30, and 20 meters. But in extreme cases, it too could benefit 
from the extra bypassing.

73,
Wayne
N6KR


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