Will I damage the transmitter if I run it without an antenna?
Yes, it is a risky practice. When the antenna is removed the mismatch theoretically goes to infinite SWR and all the generated power returns to the output stage; this produces heat and voltage stress. Range also drops practically to zero. Never energize a receiver or transmitter without its antenna fitted under any circumstances.
The antenna is the only path by which the power produced by the transmitter is carried away. With no antenna the power finds nowhere to go and returns from the feed line into the output stage. On low-power SRD transmitters this usually does not cause instant destruction, but continuous or repeated operation without an antenna markedly shortens the life of the output transistor.
Common mistakes:
- Energizing and testing the receiver during installation without its antenna fitted.
- Temporarily fitting a short piece of wire in place of the antenna on a receiver whose antenna has broken.
- Leaving only the coaxial cable in place of the antenna; this cable radiates like a bad antenna, distorts the radiation pattern and spreads interference.
What should be done: keep a spare antenna ready in the system, do not apply power without fitting the antenna, and replace a broken antenna with the correct antenna made for the same frequency band. A shorting wire or a cable of random length both leaves SWR high and gives much lower range than you expect. With the antenna removed the remote may still appear to work at short distance; that does not mean no damage has occurred.
Full article: 433 MHz or 2.4 GHz?