[meteoestarreja]

Theoretically those modules are 433.92MHz which leads to a 1/4 wave antenna with 17.3cm, but using SDRSHARP I saw that the frequency is normally below that value, around 433.7Mhz.
I don't know about SDRSHARP precision, so this value may not be exact.

In fact while testing it, in some cases I saw a small deviation on frequency.
You can calibrate SDRSHARP, using a transmission that you know for sure the frequency, like an ordinary FM broadcast radio or a ham repeater (you will find some very close from our station TX frequency) and adjust the value on the software so the frequency meets the frequency that you already know.
About the antenna, how did you get the 17.3 cm value? From my calculation, 17.3 would be somewhere around 428,3 Mhz
Also, do not trust 100% antenna's size from the outside plastic, I encountered several antennas with a outside size, and the antenna inside the cover had smaller size

BTW, the project - when/if it came to day light - will not use any usb dongle, the parts needed will be all together on pcb.