Does shortening or extending the antenna cable affect the range?
Yes, adversely. An antenna and its cable are designed for a particular impedance and length match; cutting it shorter or splicing it longer spoils that match, the reflected power increases and the radiated power drops. Instead of coiling up slack cable, arrange it in wide loops, and if an extension is needed use a manufacturer-approved extension kit.
The antenna system is designed to work at a particular impedance with the transmitter/receiver circuit. Interfering with the cable upsets this balance:
- Shortening: the cable length and the connection point are part of the design. Cutting it and fitting a new connector spoils both the impedance and the sealing.
- Extending: every joint means loss; also, cheap cable has high attenuation per unit length. Rather than a long cable, moving the receiver closer to the antenna is the more correct solution.
- Coiling: winding excess cable into a tight coil creates inductance and stray coupling. Arrange it in wide loops, away from power cables.
Try to solve a range problem with placement rather than by extending the cable: bring the antenna outside the panel, put it in a vertical position, raise it, and separate it from metal surfaces and motor cables. In most cases these four steps remove the need for an extension.
If an extension is unavoidable, cable of a suitable, low-loss type and the correct connector must be used, and it is preferable that the work is done by someone experienced in RF. Afterwards, repeat the range test from the furthest point of the site.
The full topic: 433 MHz or 2.4 GHz?