Antenna switches and station switching

What it is

An antenna switch routes one radio to any of several antennas (or several radios to one antenna) without moving connectors. It also gives you a place to park a dummy load for testing, and a way to ground unused antennas.

Kinds of switch

Type	How it works	Good for
Manual coax switch	a rotary or push-button switch in the shack	a few antennas, one feed line each
Remote switch	relays in a weatherproof box near the antennas, with a control cable or DC sent on the coax	several antennas on one coax, towers and long runs
Multi-radio switch	connects any of several radios to any of several antennas	stations that share antennas between radios

A remote switch saves running a feed line for every antenna, but adds a control cable and an outdoor part that can fail. Keep that control wire away from the RF feed line, and use ferrite chokes or bypassing to stop RF getting into it.

What the ratings mean

• Frequency range. A switch rated to HF can behave badly at VHF or UHF: loss rises and isolation falls. Check it covers every band you use.
• Power rating. Choose one rated well above your power, including any amplifier, and rated for the SWR it will see. Ratings usually assume a good match.
• Insertion loss. A good switch adds only a small fraction of a dB at HF.
• Isolation. How well a port that is not selected is kept out of the one that is. Isolation is expressed in dB: at 60 dB, 1500 W is reduced to about 1.5 mW, and at 50 dB to about 15 mW. Isolation drops as frequency rises, and it matters most when two radios share a site, or one antenna sits close to another.

Operating safely

• Never switch while transmitting. Switching under power can arc the contacts, and many rotary switches momentarily open the line, a severe mismatch that can damage the radio or an amplifier. Stop transmitting, or turn the power down, before switching.
• Label every position, and check that the right antenna is selected before you transmit. A wrong position is a common cause of a sudden high SWR; see Power output and SWR protection.
• A grounded position is not lightning protection. It helps with static build-up. For storms, the safest practice is to physically disconnect feed lines and move them away from equipment, together with surge arrestors where the lines enter and a bonded ground system.

• With two radios on one antenna, an interlock or transmit inhibit stops the second one from keying while the first is in use. A transmitter connected to another radio's receiver input can destroy it.

Related

• Lightning protection and groundingProtecting people, equipment and antennas.
• Lightning safetyStaying alive during storms.
• Dummy loadsTesting a transmitter without radiating.
• Coaxial cableConstruction, types and choosing a coax.
• RF connectorsPL-259, N, BNC, SMA and when to use each.
• Station layout and ergonomicsArranging a safe, efficient shack.
• Linear amplifiersAdding power: tubes, solid state and the limits.