I have the transmitter sold by pilight (looks like this: http://rely.sell.everychina.com/p-90880674-rf-transmitter-module-for-alarm-systems-tx1.html ), and made an antenna like this: https://www.elektor.nl/Uploads/Forum/Posts/How-to-make-a-Air-Cooled-433MHz-antenna.pdf
All was well with my outlet switches working every time (except a dimmer, which sometimes did not work correctly). Recently I had to place a switch close to the ceiling and it won’t work most of the times. I moved the homeduino to another place and I have now found that the simple 17.3cm wire works better than the coil antenna. When I made the coil antenna, it seemed to work better. Weird.
The transmitter is not far from the new ceiling receiver, something like 4 meters, but there’s a wall very close to the transmitter in the way to the receiver, and is placed near the ground (at knee height).
I would probably work better if it would be placed in a higher place, but I want it to be hidden.
I now tried bending the 17cm wire, making a 90 degree curve (not a cusp, but a smooth curve) and it seems to have improved it! Maybe now the RF wave is also sent vertically instead of going only horizontally?
Do you guys have any tips? I know I could increase the voltage up to 12V on the transmitter, but that would require another power supply.