Antennas, Coax Cables and RF Connectors

Frequency range first: the number that defines the job

An antenna is tuned to a band, so read the frequency range before anything else. A TV antenna covers tens to hundreds of megahertz, a cellular antenna lists bands such as 698 to 960 and 1710 to 2170 MHz, a GPS antenna centers on 1575.42 MHz, and land-mobile radio sits in its own VHF, UHF or 800 MHz ranges. Gain in dBi shows how tightly the signal is focused, and omnidirectional designs listen in every horizontal direction.

Connectors, impedance and cable loss

Connectors decide whether parts fit together. SMA and reverse-polarity RP-SMA look alike but are not compatible, TS9 appears on some mobile hotspots, BNC suits video and test gear, and NMO is a vehicle roof mount. Radio and cellular gear uses 50 ohm cable while TV and video use 75 ohm, so keep the impedance consistent. Every extra meter of coax adds loss, which grows with frequency, so keep runs short and use adapters sparingly.

Questions about Antennas, Coax Cables and RF Connectors

What does dBi gain on an antenna tell me?

Gain describes how strongly an antenna concentrates signal compared with an ideal radiator, in dBi. Higher gain reaches farther in a flatter, narrower pattern, so a high-gain omni can miss signals that arrive from above or below. Choose gain to match the geometry of where you use it.

Are SMA and RP-SMA connectors interchangeable?

No. The threads can fit, but RP-SMA reverses the center contact, so the two do not connect electrically. Check the connector type on both the antenna and the device, and use an adapter only to bridge a known mismatch.

Does coax cable length really matter?

Yes. Every length of coax loses signal, and the loss rises with frequency, so cellular and GPS runs suffer more than TV. Keep cables as short as practical, choose a low-loss type for longer runs, and match the cable's impedance to the equipment.