FeedlineEdit
Feedline refers to the transmission path that carries radio frequency (RF) energy between a transmitter (or receiver) and an antenna. The performance of any radio system hinges on how effectively this bridge handles impedance, losses, and environmental stresses. In practical terms, the feedline chosen for a given installation reflects cost, reliability, and ease of maintenance, as well as the frequency range and power levels involved. A well-designed feedline helps ensure that most of the transmitter’s power ends up radiated by the antenna, rather than reflected back into the equipment.
In many markets, feedlines are selected to balance simplicity and performance. Coaxial cables are ubiquitous in consumer and hobbyist setups because they are easy to install and tolerate a wide range of conditions. For high-power or long-distance work, more specialized options—such as balanced lines or rigid hardline—offer lower losses and greater robustness, at higher cost and with greater installation complexity. Across these choices, the common engineering goal is to minimize reflections, manage impedance, and protect equipment from electrical and environmental stress. The interplay between feedline design and antenna performance is a central concern in RF system engineering, and it is a major topic in the development of practical radio infrastructure. See also transmission line and antenna.
Types of feedlines
Coaxial cable
Coaxial cable, often simply called coax, consists of a central conductor surrounded by insulation, a conducting shield, and an outer jacket. Its characteristic impedance is a defining property, with common values around 50 ohms for many amateur and professional systems and 75 ohms for other specialized applications. Coax is valued for its flexibility, ease of routing, and commercial availability. Attenuation increases with frequency and length, and connectors (such as N-type connector or PL-259/SO-239 system) must be chosen to suit the frequency range and power level. For those who prioritize minimal loss at HF and VHF, higher-quality coax types (e.g., low-loss variants) are favored. See also coaxial cable.
Ladder line and balanced feeds
Ladder line, a two-conductor balanced feed, can offer very low loss at HF compared to many coax options, especially over long runs. Its higher characteristic impedance makes it attractive for certain antenna configurations, but it is more sensitive to weather, support conditions, and impedance tuning. Balanced feeding requires proper isolation from the transmitter’s unbalanced output, typically via a balun or unun to prevent undesirable currents on the shield. See also ladder line and balun.
Hardline and other rigid feeds
Hardline refers to rigid transmission-line systems (often metal tubes or bars) used in broadcast studios, radar installations, and some high-power RF plants. These lines can exhibit very low losses and excellent power handling, but they are expensive, bulky, and require careful mechanical installation and support. See also hardline and broadcasting.
Other options
In some installations, alternative or specialized feeds—such as twisted-pair or microstrip arrangements—may be employed for particular frequency bands or integration with equipment. Each option carries trade-offs in loss, bandwidth, and ease of use. See also twisted pair and microstrip.
Key concepts
Impedance, matching, and SWR
RF energy travels most efficiently when the feedline–antenna system presents the transmitter with its designed impedance (commonly 50 ohms in many systems). When the impedances are not matched, part of the power is reflected back toward the transmitter, creating a standing-wave pattern quantified by the standing wave ratio (SWR). Excessive SWR can heat components, reduce radiated power, and stress transmitters. Matching networks, such as a balun and sometimes a dedicated antenna tuner, help keep reflections to a minimum. See also impedance matching and SWR.
Loss, power handling, and skin effect
Feedline losses arise from conductor resistance, dielectric losses, and, at higher frequencies, the skin effect that confines current to the surface of conductors. Loss increases with length and frequency for many lines, so practical systems balance run length, line type, and power requirements to keep efficiency high. See also skin effect.
Environmental and installation considerations
Moisture ingress, temperature changes, and physical stress affect feedline performance over time. Weatherproofing connectors, proper strain relief, routing that minimizes bending radii, and secure supports help maintain performance and longevity. Proper grounding and protection against lightning and surge events are also important in many outdoor installations. See also grounding and lightning protection.
Power protection and safety
Feedlines carry significant RF voltages and currents, especially at higher power. Ensuring that connectors, weatherproofing, and shielding are appropriate for the operating conditions reduces the risk of arcing, corrosion, and equipment damage. See also antenna tuner.
Applications and debates
Amateur and hobby radio
In amateur radio, operators routinely choose between coax and ladder line based on their antenna configuration, available space, and comfort with maintenance. The debate often centers on the trade-off between the convenience of coax and the efficiency of ladder line on long runs or high-frequency work, with many system designs incorporating a balun to manage impedance and prevent unduly high current on the feedline shield. See also amateur radio and balun.
Broadcasting and professional systems
Broadcast and professional RF systems favor low-loss lines and robust construction to support steady operation and high power. The choice between flexible coax and rigid hardline reflects differences in installation cost, maintenance, and performance requirements. See also broadcasting.
Regulation and market dynamics
Policy perspectives on radio infrastructure tend to emphasize spectrum management, interference prevention, and reliability of service. While feedline design itself is largely a matter of engineering choice and market competition, outcomes are shaped by regulatory frameworks that govern authorizations, equipment standards, and interoperability. See also transmission line and regulatory affairs.