The install was : RTX +50 cm RG58 + AMP + 1m Aircom (like RG213) + SWR +15m
Aircom + G5RV. the built-in SWR of my RTX TS-570D read SWR 1:1. If my external
SWR
displayed an SWR 4 that means that it read the info AFTER it, what looks
in contradiction with what ARRL

Thierry, If your external SWR meter is after the amplifier, in a 50 ohm
system, and it read 4 it could possibly destroy your amplifier output devices.
The fact that the built-in SWR meter in the Kenwood read 1:1 only means the
input match to the Amplifier was good. If the 570 has a built-in tuner, it
will try to get a 1:1 match, no matter what is downstream. It doesn't mean the
output the Amp sees is good.
As for the ARRL, I haven't had the time to look, but I hope they are not
stating that a 50 ohm output Amp operating into 4 mismatch is a good thing.

73 Gary N4AST