The coaxial cable between a radio and its antenna is easy to ignore, and that is exactly why it quietly wrecks so many links. Every foot of feedline turns a little RF energy into heat, and that loss subtracts directly from the link budget on both transmit and receive. A tall mast with a great antenna can be undone by a long run of thin, cheap coax. This guide explains what causes coax loss, how it scales with cable type, length, and frequency, and how to choose a feedline that does not eat your signal.
Coaxial Cable Loss in one line: Coaxial cable loss, or feedline attenuation, is the RF energy a coax cable dissipates as heat as the signal travels between the radio and the antenna, measured in decibels per unit length at a given frequency. It grows with cable length, rises with frequency, and depends heavily on cable construction - thin coax loses far more than thick low-loss types like LMR-400 or heliax. Because the loss subtracts from both transmitted and received signal, keeping runs short and choosing the right cable protects the link budget.
Coaxial cable carries RF between a center conductor and a surrounding shield, separated by a dielectric. Two mechanisms turn signal into heat along the way: resistive loss in the conductors, worsened at high frequency by the skin effect that pushes current into a thin outer layer of the metal, and dielectric loss in the insulator between them. Together these give the cable its attenuation, quoted as decibels of loss per hundred feet at a stated frequency.
Loss scales in three predictable ways. It is proportional to length - double the run and you double the decibels lost - so long cable runs are the enemy. It rises with frequency, so the same cable that loses modestly at VHF loses considerably more at 900 MHz or 2.4 GHz. And it depends strongly on cable diameter and construction: a fatter cable with a larger center conductor and better dielectric has lower loss per foot than a thin, flexible cable. These combine, so a long thin run at a high frequency is the worst case.
The impact on the link is direct and doubled. Feedline loss subtracts from the transmit power reaching the antenna and again subtracts from the weak received signal on its way back to the radio. A few decibels lost in coax at each end can quietly erase the fade margin that a taller antenna was supposed to buy, which is why the feedline deserves the same attention as the antenna itself.
Cable selection is a balance of loss, cost, flexibility, and run length. Thin flexible coax is cheap and easy to route but loses a lot per foot, so it is only acceptable for very short jumpers. For typical feedline runs up the mast, a low-loss cable in the LMR family is the common workhorse - LMR-400 offers substantially lower loss than thin coax while remaining reasonably flexible, and larger LMR sizes cut the loss further for longer runs. For very long runs or high frequencies, corrugated hardline such as heliax delivers the lowest loss but is stiffer, heavier, and more expensive to install.
The design logic is to match the cable to the run. Estimate the length, look up the cable's loss per hundred feet at your operating frequency, multiply, and see how many decibels it costs. If a thin cable would eat several decibels over the run, step up to a lower-loss type until the feedline loss is a small fraction of the link budget. There is little point mounting a high-gain antenna at the top of a mast only to feed it through coax that gives back most of that gain in heat.
Connectors and their installation matter alongside the cable itself. Each connector adds a small loss, and a poorly installed, corroded, or water-intruded connector can add far more, along with reflections that further degrade the link. Weatherproofing connections at the antenna and using quality connectors keeps the feedline performing as designed over years of outdoor exposure, which in the field is often where links silently decay.
In an oilfield radio network, feedline loss is one of the most common and most overlooked reasons a remote site underperforms. A site that was commissioned with a healthy signal can drift as coax weathers, connectors corrode, or water wicks into the cable, and the added loss shows up as a shrinking fade margin and rising comm failures. Because the coax is the least glamorous part of the installation, it is often the last thing anyone suspects.
Getting the feedline right at design time is cheap insurance. Keeping runs short by mounting the radio close to the antenna base, choosing a cable whose loss is small relative to the link budget, and weatherproofing every connection all protect the decibels the antenna worked to gain. On the longest or highest-frequency links, spending more on lower-loss cable up front is almost always cheaper than a repeat truck roll to chase a marginal link later.
A cloud SCADA such as Merobix helps catch feedline problems by trending each site's received signal strength over time. A slow, seasonal decline in a site's RSSI - especially one that worsens in wet weather - is a classic signature of coax or connector degradation adding loss. Seeing that trend lets an operator dispatch a crew to inspect and reterminate the feedline before the fade margin runs out and the site drops off the network entirely.
Feedline loss subtracts from both the transmitted signal reaching the antenna and the received signal returning to the radio, so it hits the link budget twice. A few decibels lost in a long or thin cable run can erase the fade margin a taller antenna was meant to provide. It is one of the most overlooked reasons a remote site underperforms.
Loss is proportional to length, so doubling the run doubles the decibels lost, and it rises with frequency, so the same cable loses more at 900 MHz than at VHF. Cable construction matters too - thick low-loss cable like LMR-400 or heliax loses far less per foot than thin flexible coax. A long thin run at a high frequency is the worst-case combination.
Match the cable to the run length and frequency. Thin flexible coax is fine only for very short jumpers; for typical mast runs a low-loss LMR-family cable such as LMR-400 is the common choice, and for very long or high-frequency runs, corrugated hardline like heliax gives the lowest loss. The goal is to keep feedline loss a small fraction of the overall link budget.
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