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 [EMAIL PROTECTED]
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
---
http://www.elecraft.com
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