[Elecraft] Re: KX1: ATU and misc

[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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