[Elecraft] KAT500 Performance Clarification

[Phil Hystad]

Dick,

Thanks, this is exactly the kind of clarification I was looking for.  Now, if you
or someone says this was described in the manual I will be ashamed and
embarrassed.   I already knew about the higher power at lower bypass
SWR.  But, I did not realize the lower power at higher bypass SWR.

phil

PEH's iPad


On Jan 23, 2013, at 9:58 AM, Dick Dievendorff <dieven at comcast.net> wrote:

> Hi, Phil.
> 
> Although the KAT500, like most tuners, will attempt to find a match whenever
> it can, it protects itself from the very high voltages and currents that can
> appear on internal components when the match is poor. We rate the tuner for
> 500 watts at 10:1 SWR.  When you use an antenna that shows 17:1 SWR (the
> "untuned" or "bypass" VSWR), the ATU measures the forward power and computes
> the power it can safely handle with the high mismatch.  It's less than 500
> watts.  You should be able to operate safely at 250 watts or so with that
> high a bypass VSWR.  If you exceed the ATU's safety values, it should
> illuminate the red FAULT led, make a fault log entry, and put the ATU into
> BYPASS at the next opportunity.  It should also interrupt the amplifier key
> line.
> 
> Dick, K6KR
> 
> 
> 
> 
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Phil Hystad
> Sent: Wednesday, January 23, 2013 8:48 AM
> To: elecraft at mailman.qth.net List
> Subject: [Elecraft] KAT500 Performance Clarification
> 
> Gang, I was surprised last night when I got a descent low SWR tuning my
> 80-meter (ladder-line fed into 4:1 balun) dipole on 160 meters.  I have had
> the KAT500 for a couple of months and I never bothered trying it on 160
> meters because on all previous attempts with other manual tuners I have
> failed to get a good match.
> 
> But, last night, just as a lark, I switched up to 160 meters and gave the
> KAT500 a try.  Sure enough it found a match of 1.05:1 at 1900 KHz with the
> Bypass VSWR reading about 17:1.  Given I have most of the transmission line
> in lower-loss ladder line helps with the losses to the antenna with that
> high bypass SWR.
> 
> This was at 100 watts out from the K3.  Now, I decided to give a try with
> the KPA500 in-line at about 475 watts and the best I could get is about 4:1
> tuned SWR.  Now, I am not quite sure I understand the dynamics of the KAT500
> with higher power.  This is what I did.  I tuned at 20 watts to the 1.05:1
> SWR (bypass was ~17:1).  At 100 watts, my LP-100A was still reading about
> 1.1:1 SWR.  But, when I turned on the KPA500 (switched out of standby) the
> reading was roughly 4:1 with a fault on the KPA500.  Question, how does the
> higher power affect the match of the KAT500.  I understand how higher power
> might stress the KAT500 with maybe arcing or something but I don't
> understand why the match actually changed unless that higher power caused
> some change in the KAT500 capacitor or inductor components.
> 
> 
> 73, phil, K7PEH
> 
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