Thanks for your input!
I looked over my hardware and tried different things but I get no good results. I think part of my problem is that I don't have one of the approved receivers yet. I think I put this on hold until the RXB6 I've ordered arrives in the mail.

See now that the Esp gives one row of output sometimes and other times three.

Nice there is some interrest! Indeed the pulses from the Esp are a bit strange. I made a new experiment. I took an old Arduino Duemilanove and connected a receiver, loaded the "ReceiveDemo_Advanced" sketch from RCSwitch library. I now have four readings from the Esp-12 setup and two from the Arduino ...

Ok great! I tried with 2775 and an old Nexa remote. It doesnt recognize it, but I get some output from debug: 20;01;RFDEBUG=ON; 20;02;DEBUG;Pulses=25;Pulses(uSec)=270,660,240,660,240,660,240,660,240,810,120,120,1740,660,720,210,240,660,720,210,240,900,30,450,150; 20;03;DEBUG;Pulses=35;Pulses(uSec ...

I tried Viktors mods with a Nodemcu. Compiles and uploads fine. The onboard led flashes irregularly, when I press a button on my Nexa remote it lights steady. But I dont get any output besides the start message ("RadioFrequencyLink - RFLink Gateway V1.1 - R33;"). The receiver I use is maybe not good ...