KX1: ATU and misc

[Andrea Borgia]

Hello.


Been playing around with my newly built ATU for the KX1 and I'm a bit
puzzled by a few minor things:

1) my G5RV, accidentally shortened because of a wind gust, cannot be
tuned by my IC-736 in 30m while the KXAT1 happily reports a perfect
match (r1.0). Is that plausible?

2) in order to debug the problem above, how can I force the ATU to
forget the 30m band L&C settings and retune, possibly without resetting
the main cpu? If I force a retune in 20m and 40m I hear lot of relays
clicking, while all is quiet on 30m. I checked the error code and it is
E00, so I'm stuck.

3) the pwr meter of the ATU reports 5.2-5.5W on 30m as opposed to
3.0-3.3W on 40m and 3.5-3.8W on 20m. No accurate calibration was done,
but the difference is striking. Any clues/things to investigate?


As a side-note (pun not intended), with respect to the KX1 power mods
suggested a while ago, I have a question: has anyone thought about
putting a fuse on the battery line? The potential for damage due to a
shorted Q6 is quite relevant even when running off internal batteries;
my external power cord is fused and this has already saved me once 8-)


B73,
Andrea.

--
Homepage: http://andrea.borgia.bo.it     /    Amateur radio: IZ4FHT
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[wayne burdick]

Hi Andrea,

As the designer of the KX1 and options I thought I'd chip in here.


> 1) my G5RV, accidentally shortened because of a wind gust, cannot be
> tuned by my IC-736 in 30m while the KXAT1 happily reports a perfect
> match (r1.0). Is that plausible?

Tuners in some commercial transceivers are limited either by power
handling or by firmware to 3:1. The KXAT1 is quite capable of matching
some (but not all) loads that are 10:1 or higher, thanks to the low
power of the KX1.


> 2) in order to debug the problem above, how can I force the ATU to
> forget the 30m band L&C settings and retune, possibly without
> resetting the main cpu? If I force a retune in 20m and 40m I hear lot
> of relays clicking, while all is quiet on 30m. I checked the error
> code and it is E00, so I'm stuck.

Just tune up into a dummy load on any band you want to "reset."


> 3) the pwr meter of the ATU reports 5.2-5.5W on 30m as opposed to
> 3.0-3.3W on 40m and 3.5-3.8W on 20m. No accurate calibration was done,
> but the difference is striking. Any clues/things to investigate?

If this happens even on a dummy load, the rig probably really is
putting out higher power on 30 m. The "knee" in the low-pass filter
moves around a bit and can have a large effect on per-band efficiency.
The knee can be adjusted to equalize the bands somewhat by squeezing or
spreading the low-pass filter toroid windings.


>
> As a side-note (pun not intended), with respect to the KX1 power mods
> suggested a while ago, I have a question: has anyone thought about
> putting a fuse on the battery line? The potential for damage due to a
> shorted Q6 is quite relevant even when running off internal batteries;
> my external power cord is fused and this has already saved me once 8-)

In general I recommend operating the KX1 at 4 W and lower. The extra dB
or two you get by exceeding this is usually not worth the risk.

As for fusing, I don't know of any cases of battery melt-down on the
KX1. Remember that the maximum power output when running from the
internal battery is about 2 watts. If you really wanted to fuse it, you
could use a very small self-resetting polyfuse -- see www.digikey.com
for possible types to use. The main problem in the KX1 is space, so
you'll need a *really* small fuse.

73,
Wayne
N6KR


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[Andrea Borgia]

wayne burdick wrote:


> Just tune up into a dummy load on any band you want to "reset."

Ok, I'll try that asap, but I'm still curious as to why there's no relay
activity on 30m when forcing a tune operation: the antenna is not tuned
to 30m natively, only on 20m, but on 20m the atu clicks and on 30m it
doesn't. Well, I'll get back to you when I have tried the dummy load
("no, I should build one" is the answer to the question you were
thinking to ask ;-)


> In general I recommend operating the KX1 at 4 W and lower. The extra dB
> or two you get by exceeding this is usually not worth the risk.

Sorry, I wasn't being clear: I was talking about the power-supply mods,
such as cutting a trace to use the jack's builtin switch. The scenario I
had in mind is a melt-down caused by a short-circuit, not extended
operation  at high power levels.


> internal battery is about 2 watts. If you really wanted to fuse it, you
> could use a very small self-resetting polyfuse -- see www.digikey.com
> for possible types to use. The main problem in the KX1 is space, so
> you'll need a *really* small fuse.

Yep, that's the same issue I thought of. Thanks for the infos and for
the pointer, I'll look into it.


B73,
Andrea.

--
Homepage: http://andrea.borgia.bo.it     /    Amateur radio: IZ4FHT
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