[Elecraft] KPA1500 with P3 Transmit Monitor

[Ron D'Eau Claire]

I presume that by "draft" you are looking at a prelim copy of the KPA1500
Owner's manual.

To further simplify its block diagram the signal path is like this:

TRANSCEIVER (external) --> AMPLIFIER --> INTERNAL SWR BRIDGE --> ATU -->
ANTENNA SYSTEM (external) 

The SWR briege in the KPA1500 will report the SWR the amplifier "sees" going
into the ATU. As you know, the point of the ATU is to ensure the amplifier
itself is feeding a 52 ohm non-reactive load which is expressed as an SWR in
the link between the amp and the ATU. 

I doubt if you'll find a way to 'break in' to the link since the SWR and
Power output from the amplifier itself is already a part of the basic
measurements that is reported by the KPA1500.

You are quite right that putting a coupler at the Antenna output of the
KPA1500 (and so the output of the built in ATU) will simply report the SWR
the antenna system (including feeder) presents to the KPA1500. 

Of course if the ATU is in Bypass the internal SWR measurement will show
that of the antenna system since the ATU is no longer in the circuit. That
only occurs when the SWR presented by the antenna system is low enough to
feed directly. 

73, Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of James Wilson
Sent: Thursday, November 2, 2017 10:54 AM
To: Elecraft
Subject: [Elecraft] KPA1500 with P3 Transmit Monitor

Looking at a draft of the KPA1500 amplifier, it appears that the only place
to install  a TxMon or Wattmeter coupler is at the  -  output  -  of the
built-in tuner.

At that point, it will always show the SWR of the coax feedline, not the SWR
that the amplifier "sees" as adjusted by the built-in tuner.

Or, is there a coupler built-in inside the KPA1500 ?

What am I missing?

Jim - W4RKS