[KAT500] Tune operation question

[W5UXH]

Apparently my subscription to the mailman list got lost, so this is a second attempt to get this query out there:

First, the Rev C. manual says the following:

The Elecraft KPA500 is designed to have its key line switched to disable or enable the amplifier even
while it is producing full RF power, but many other amplifiers may be damaged doing that. To protect
those amplifiers, the KPA500 is supplied configured so that the key line will not be switched if more than
29 watts of RF power is present.

I am guessing this paragraph should say "the KAT500 is supplied configured....."?

I am getting close to ordering the KPA500 and KAT500 to go with my K3/100 and the tuning process is not clear in my old brain yet.  The manual states:

A tune operation begins when RF power between 10 and 100 watts is applied and the SWR is above the
tuning threshold in AUTO mode, or when the TUNE switch is tapped in either AUTO or MAN modes.

I am not able to fully grasp how this all works.  Part of my confusion is the upper limit of 100 watts.  Typically I will run the amp at more than 100 watts driving into the tuner.  What am I missing?  I hope tuning is automated such that all I have to do is key down shortly (a dash at 30 wpm I think I read somewhere) and the tuner will kick the amp offline if retuning is needed, do the tuning, and kick the amp back online.

Any comments will be appreciated.

Chuck, W5UXH

[Dick Dievendorff-3]

Yes, the KAT500 is supplied configured for an amplifier other than the
KPA500 rather than the KPA500 coming configured...  I'll mention this to our
manual author.

The antenna tuner does its tuning with exciter (K3) power.  The KAT500 has a
relay that interrupts the amplifier's keying line.  If the antenna tuner
finds a need to change its settings, it interrupts the amplifier keying
line, changes ATU relays, and reconnects the amplifier key line.  Perhaps
this is essentially one step (if it's recalling a prior tuner setting),
maybe it's several steps if it's tuning to a setting that hasn't already
been memorized.

Some amplifiers (the KPA500) are able to make this transition while the key
is down (RF present).  Other amplifiers work better (last longer) if you
avoid hot switching the amplifier's keying relay while RF is flowing. That's
why the antenna tuner provides the choice.

If you are using a KPA500 and the KAT500 is configured appropriately, the
KAT500 interrupts the amplifier key line, waits for forward power to drop to
a reasonable level (exciter power level), changes the antenna tuner relays,
and then restores the amplifier key line.  RF can be flowing during all
this, because the KPA500 tolerates these transitions with key down. It uses
solid state switching devices.

For other amplifiers, such as those with frame or reed keying relays that
should not be hot switched, the KAT500 waits for RF to drop below the
threshold power before interrupting the amplifier key line, makes its
changes, and then waits for the power to drop to essentially zero before
reconnecting the amplifier key line.  This is intended to protect the
amplifier's keying relay from destructive hot switching.

Some amplifiers also provide some protection for the keying relay by not
changing it while RF is present.  

73 de Dick, K6KR

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of W5UXH
Sent: Thursday, September 19, 2013 10:25 AM
To: [hidden email]
Subject: [Elecraft] [KAT500] Tune operation question

Apparently my subscription to the mailman list got lost, so this is a second
attempt to get this query out there:

First, the Rev C. manual says the following:

/The Elecraft KPA500 is designed to have its key line switched to disable or
enable the amplifier even while it is producing full RF power, but many
other amplifiers may be damaged doing that. To protect those amplifiers, the
*KPA500* is supplied configured so that the key line will not be switched if
more than
29 watts of RF power is present./

I am guessing this paragraph should say "the *KAT500* is supplied
configured....."?

I am getting close to ordering the KPA500 and KAT500 to go with my K3/100
and the tuning process is not clear in my old brain yet.  The manual states:


/A tune operation begins when RF power between 10 and 100 watts is applied
and the SWR is above the tuning threshold in AUTO mode, or when the TUNE
switch is tapped in either AUTO or MAN modes./

I am not able to fully grasp how this all works.  Part of my confusion is
the upper limit of 100 watts.  Typically I will run the amp at more than 100
watts driving into the tuner.  What am I missing?  I hope tuning is
automated such that all I have to do is key down shortly (a dash at 30 wpm I
think I read somewhere) and the tuner will kick the amp offline if retuning
is needed, do the tuning, and kick the amp back online.

Any comments will be appreciated.

Chuck, W5UXH



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[W5UXH]

Good, I thought it had to be this way, but am easily confused.  I looked at the manual again and specifically noticed this statement:

Clicking on Optimize for the KPA500 automatically selects that setting.

which does make it even clearer.  Having the default at 29 watts is quite reasonable.

Thanks Dick and Ron.

Chuck