In plain language: Twin-lead is a balanced two-conductor transmission line embedded or held in a continuous plastic web, historically common in television and lightweight antenna feed systems.
Why the station behaves this way
Its compact form is convenient but places more dielectric around the conductors than open-wire line, increasing loss and sensitivity to moisture in some types.
A common wrong turn
Calling all parallel line “300-ohm twin-lead” ignores products with different impedance, conductor size, dielectric, and power capability.
What to do at the radio
Use the specified impedance and power rating, route symmetrically away from metal, avoid crushing or tight bends, weatherproof transitions, and match it with a deliberately balanced network.
Operating boundary
Use current equipment instructions, legal operating limits, the exact signal path, and observed conditions. A connector, software label, transformer ratio, or forecast value does not prove complete-system performance.
