Cresta TX320 longer antenna

Last week I bought 5 sensors of the type Cresta TX320 for my Domoticz system. Unfortunately they have a very weak transmitting signal strength. One HR++ glass pane and a concrete floor is too much to reach the RFXTRX433e transceiver. I removed the old internal antenna and exchanged it with a solid wire matching the length of 1/4 of the wavelength of the 433Mhz band. That is 17,3 cm from the PCB to the end of the wire.

Please note that I routed the whole antenna out of the top of the device. Routing it downward causes quite a lot of the signal strength to be absorbed by the batteries, which then are close to the antenna.

This setup still has a weak signal strength, but just enough to reach my transceiver.