Does an antenna extension cable reduce range, how many dB does it cost?
Yes, every metre of coaxial cable brings measurable loss. RG58C/U loses about 0.44 dB/m at 450 MHz, RG174 loses 0.55 dB/m at 400 MHz and 0.88 dB/m at 1000 MHz. Five metres of RG58 costs about 2.2 dB in the sub-GHz range; since a 6 dB loss halves the range, this alone wipes out roughly 23% of the theoretical range.
Cable loss applies on both the transmitter and the receiver side and increases with frequency. The same RG174 goes from 0.55 dB/m at 400 MHz to 0.88 dB/m at 1000 MHz; at 2.4 GHz thin cables give far heavier loss. That is why, instead of using thin cable over a long run, you should either move to a thicker, lower-loss cable or shorten the cable.
Make a comparison when deciding:
- Bringing the antenna outside the enclosure with 3 m of cable: about 1.3 dB loss with RG58.
- Leaving the antenna inside the enclosure: tens of dB of loss.
- In other words, the price of the extension cable is almost always far cheaper than staying inside the enclosure.
Practical advice: do not buy the cable longer than needed and coil the excess, cut it short. Tighten the connectors properly; a bad connector alone produces a few dB and unstable contact. Do not run the cable in the same duct as power cables and motor cables; besides loss, you will also pick up interference. Use a single piece for the antenna cable instead of splicing it.
Full article: 433 MHz or 2.4 GHz?