[Elecraft] KX3 and KAT500

[Dick Dievendorff]

Phil:

The KAT500 is not a QRP antenna tuner. The SWR bridge's voltage divider is
designed for the 500 to 1500 watt range.  At QRP levels the SWR bridge
voltages (and voltage differences) become quite small.   As reflected power
drops near zero, it becomes difficult to measure small SWR differences. It's
very difficult to find a minimum SWR when the ADC jitter exceeds the change
due to a different tuner setting.

We have a couple of antenna tuners designed for lower power: The KAT100,
KAT3 and KXAT100 are all 110-watt tuners. The T1 and KXAT3 are 20-watt
tuners.

But the KAT500 should be able to select from pre-tuned solutions (what I
have called a "memory recall tune") at any transmit level that is high
enough for the frequency counter to work.  5 watts should be plenty.

A "full search" tune is problematic at low power levels, particularly as
exciters fold back (reduce output power) when asked to deliver their maximum
specified output power into a varying SWR load during tuning. 

10 watts from a K3/100 is not difficult.  10 watts from a KX3 into a varying
SWR load is more difficult.

You're correct to bypass the KXAT3 when using an external tuner.

73 de Dick, K6KR


-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Phil
Hystad
Sent: Saturday, May 17, 2014 11:08 AM
To: Reflector Elecraft
Subject: [Elecraft] KX3 and KAT500

I have been experimenting with my KAT500 and the KX3.  Although I do have a
K3 and KPA500 configured with the KAT500 using the switched arrangement
described by the KE7X KX3 book, the K3 is powered off and the KPA500 is in
standby mode during these experiments.

Although the KAT500 user manual says that to start a tune cycle, at least 10
watts needs to be provided.  So, my KX3 is right on the border line and from
my experience in this setup, it DOES NOT initiate a tune cycle in the
KAT500.

Has anyone else been successful in initiating tune cycles for the KAT500 at
10 watts from the KX3.  My method is to VFO to the desired frequency, make
sure that the KAT500 is switched to the right antenna, and then key down for
tuning.  Note: I do not make use of the KX3 built in tuner (I am assuming
that I should not given I have a low SWR to the KAT500).


Also, given that my KAT500 is totally programmed across the bands for my two
antennas, will the KX3 provide enough power (at 10 watts or under) to
initiate the memory lookup for a tuned segment (I have programmed each 20
KHz segment on 80 and higher frequency bands using my K3).  Is 5 watts
supposed to be sufficient for locating the proper memory stored tuned LC
parameters?  I have not found this to be so (but, here I am not positive of
the starting conditions and may need to do this test over, it was getting
late last night).

Thanks for any help you can be.

73, phil, K7PEH

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