KX1 losing its match

[Lloyd Lachow]

  Lately, there have been a bunch of times when I
power my KX1 with a 12V supply, activate the tuner to
get a match, and the result is 4-5W and a good match.
Then, while operating, or just while it's sitting, not
being operated, I'll sometimes hear a few relays
chatter for a split second, and the match seems to
have been lost. When I transmit, I see that the power
out is down to 2W or so. I need to activate TUN again,
which will restore the match and the higher power out.

  Where can I look for the answer to this one...?

  thanks,

  LL/K3ESE
  K1#379,KX1#11,K2#4442(in the works)


               
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[David Pratt-3]

I get a very similar problem with my KX1, Lloyd, and it has put me off
using it.

I can tune it up and it matches nicely, producing almost 4W output. Then
unexpectedly while in the middle of a QSO the relays will start
clattering and the power goes down to 1 to 2W.

I have rewound all my toroids and checked everything for dry joints and
solder bridges, but the problem still persists.  It doesn't happen every
time I use it, but it is unreliable.  Any pointers that anyone can give
as to the possible cause will be much appreciated.

73 de David G4DMP

In a recent message, Lloyd Lachow <[hidden email]> said....
>  Lately, there have been a bunch of times when I
>power my KX1 with a 12V supply, activate the tuner to
>get a match, and the result is 4-5W and a good match.
>Then, while operating, or just while it's sitting, not
>being operated, I'll sometimes hear a few relays
>chatter for a split second, and the match seems to
>have been lost. When I transmit, I see that the power
>out is down to 2W or so. I need to activate TUN again,
>which will restore the match and the higher power out.
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[Trev - K6ESE-2]

I'd really like to hear if this is an issue and if there is a solution. I've
been thinking of building a KX1 for the fun of it, but don't want a buggy
rig...

>From my point of view it sounds like an RF on the rig problem...high voltage
at the antenna connector may be triggering the ATU into some wierd tune
state? It's just a guess, but in the past I've had similar problems with
other rigs when this was the case, a voltage node at the rig...

73's Trev K6ESE
----- Original Message -----
From: "David Pratt" <[hidden email]>
To: "Lloyd Lachow" <[hidden email]>
Cc: "List Elecraft" <[hidden email]>
Sent: Thursday, April 14, 2005 11:00 AM
Subject: Re: [Elecraft] KX1 losing its match

> I get a very similar problem with my KX1, Lloyd, and it has put me off
> using it.
>
> I can tune it up and it matches nicely, producing almost 4W output. Then
> unexpectedly while in the middle of a QSO the relays will start
> clattering and the power goes down to 1 to 2W.
>
> I have rewound all my toroids and checked everything for dry joints and
> solder bridges, but the problem still persists.  It doesn't happen every
> time I use it, but it is unreliable.  Any pointers that anyone can give
> as to the possible cause will be much appreciated.
>
> 73 de David G4DMP
>
> In a recent message, Lloyd Lachow <[hidden email]> said....
> >  Lately, there have been a bunch of times when I
> >power my KX1 with a 12V supply, activate the tuner to
> >get a match, and the result is 4-5W and a good match.
> >Then, while operating, or just while it's sitting, not
> >being operated, I'll sometimes hear a few relays
> >chatter for a split second, and the match seems to
> >have been lost. When I transmit, I see that the power
> >out is down to 2W or so. I need to activate TUN again,
> >which will restore the match and the higher power out.
> _______________________________________________
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> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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[g4ilo-2]

I had an identical problem a few years ago with an SGC-239 autotuner that I
originally used to tune my attic loop at the feedpoint. It was worst on 10
metres. It was suggested to me that RF could be getting in to the tuner. I
thought that was a bad joke, because an ATU ought to be pretty immune to
RF, especially if it is capable of being used at the antenna feedpoint.

I thought about this when I ordered the T1. I seem to recall Wayne saying
that one reason the T1 doesn't automatically retune if it senses a mismatch
is because this can sometimes cause problems. Because of my experience with
the SGC-239, this seemed like a definite advantage to me.

SGC sent me a new controller for the 239 that greatly reduced the incidence
of this trouble, presumably by reducing the threshold at which it did a
re-tune. I'm guessing that if there is an issue with the KX1, Elecraft
could resolve it with a firmware change too, by making it work more like
the T1 and only retuning if you change band or specifically tell it to.

Julian, G4ILO
G4ILO's Shack: http://www.tech-pro.net/g4ilo

"Trev - K6ESE" wrote:

>From my point of view it sounds like an RF on the rig problem...high
voltage at the antenna connector may be triggering the ATU into some wierd
tune state? It's just a guess, but in the past I've had similar problems
with other rigs when this was the case, a voltage node at the rig...


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[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 [hidden email].

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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