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Coax loss calculator

Coax loss calculator

Every foot of cable between a radio and its antenna costs signal, on the way out and on the way in. Find out how much before you buy a longer run or a bigger antenna.

Cable

Length (ft)

Connectors and adapters (total dB) Add each connector's loss from its data sheet. We do not assume a figure.

Radio output (dBm) From the radio's spec. Example: the T-Deck Plus lists +22 dBm.

Antenna gain (dBi)

Where the numbers come from

Loss per 100 ft at 900 MHz from Times Microwave Systems (via RF Parts) and the LMR-400 data sheet. Older or damaged cable, and water in a connector, lose more.

Every 3 dB lost is half the power. Loss counts twice in practice: your transmit signal and the signal you hear both pass through the cable.

The US power rule

47 CFR 15.247 allows 1 W (30 dBm) conducted for digitally modulated systems in 902 to 928 MHz, reduced dB for dB when antenna gain exceeds 6 dBi. We do not count cable loss toward that limit here. Read the rules guide.

Mesh Radio Supply

Radios that message each other when the cell network can't.

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Mesh Radio Supply is an independent publisher. References to Project NOMAD, MeshCore, Meshtastic, Amazon, Adafruit and manufacturers describe third-party products or software and do not imply sponsorship, affiliation, endorsement or authorization.

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