[Elecraft] KAT100: Strange K2/100 Behavior During Tune

[Jonathan Taylor, K1RFD]

In this case the antenna is a simple coax-fed 40M dipole with a balun at the 
feedpoint.  Without the KAT100 in line the SWR is approx 1.2 to 1 at 7100 
where the problem occurs.

A quick check shows that yes, the problem seems to occur only on 40m.  I 
also noticed that other accessories on the same power supply re-set 
themselves when it happens, supporting the foldback limiting theory and the 
work-around that Tom posted and Mark pointed out.  However, it happens only 
when the KAT100 is in line; I cannot reproduce it at any frequency or power 
level when the KAT100 is disabled.


----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at earthlink.net>
To: "Jonathan Taylor, K1RFD" <k1rfd at k1rfd.com>; <elecraft at mailman.qth.net>
Sent: Saturday, September 16, 2006 4:47 PM
Subject: RE: [Elecraft] KAT100: Strange K2/100 Behavior During Tune


> If it is RF feedback, the proper way to deal with it is at the source - in
> your antenna system.
>
> An easy way to check it is to cut a quarterwave wire for each band that is
> troublesome - attach one end of the wires to the ground terminal on your
> tuner and the other end just stretches out and attaches to nothing excpet 
> an
> insulator.  There will be high RF Voltage on the open end of the wires, so
> keep them clear of human and pet contact and keep them far enough away 
> from
> objects to prevent arc-overs (treat the far ends sort-of-like the end af 
> an
> antenna).
>
> If these wires correct the problem, then you do have work to do on the
> antenna system.  If they do not help, then you can look further for a 
> K2/100
> or KAT100 problem.
>
> From your description, I would think something is causing a very high
> current draw (even for a very short time) - your power supply may be going
> into foldback limiting and the K2 powers off momentarily.  The other
> possibility is that the resettable fuse in th ebase K2 is tripping and
> causing the power off condition (yes - it is powering off since you see 
> the
> ELECrAFt on the display).
>
> Is this by any chance happening most frequently on 40 meters?
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>> I have a K2/100 with a KAT100.  For the most part, all works well as
>> expected.
>>
>> Intermittently, though, when I press the TUNE button, the KAT100 will
>> chatter briefly as if finding a match, and then it suddenly stops
>> and the K2
>> acts as if its CPU has been re-set; the bargraph and the LCD go blank
>> briefly, then the ELECrAFt sign-on message appears briefly and
>> finally the
>> frequency is re-displayed.  During this time, however, the power supply
>> indications are normal and the LCD backlight remains on.
>>
>> This problem seems to be frequency-dependent and seems to happen
>> more often
>> at high power, which leads me to think it is an RF feedback issue.
>>
>> However, I've noticed that turning the power down to bottom end of the
>> high-power range (approx 12 W) usually doesn't help, yet turning
>> it slightly
>> lower than that, to get into the low-power range (approx 10 W), does.
>>
>> Any advice on how to solve it?
>>
>> Thanks
>>
>
>
>