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Leaky Feeder Design

Leaky Feeder Designer

Visually design and simulate radiating cable communications networks for mines, tunnels, and large indoor environments. Drag and drop components onto a canvas and get an honest multi-carrier RF link budget — cable loss, amplifier cascade, IM3 with duplexer passband filtering, DC power feed, bidirectional uplink and downlink, and over-the-air mobile radio coverage — all in the browser with autosave across sessions.

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Default demo network: two base stations → combiners → head end → two AGC amplifiers → end terminator.
Default demo network: two base stations → combiners → head end → two AGC amplifiers → end terminator.
Per-port levels on the canvas plus the Port Inspector with per-tone breakdown.
Per-port levels on the canvas plus the Port Inspector with per-tone breakdown.
Per-mobile Uplink Budget Panel covering mobile TX parameters, OTA path, network cascade, and link budget summary.
Per-mobile Uplink Budget Panel covering mobile TX parameters, OTA path, network cascade, and link budget summary.

Overview

Radiating cable, more commonly called leaky feeder, is the dominant radio coverage method in mines, road and rail tunnels, large industrial buildings, and any environment where conventional repeater plus antenna coverage cannot reach. The cable itself acts as a long distributed antenna, leaking RF energy along its length to provide continuous coverage in spaces that would otherwise be radio dead. The design problem is harder than conventional radio. Cable loss accumulates over hundreds of metres. Amplifier spacing must be sized against gain, noise, intermodulation, and DC power constraints. Coupling loss into the mobile listener changes with cable type and frequency.

The noIM₃ Leaky Feeder Designer is a browser-based design environment for these networks. The visual builder lets engineers drag radiating cable, line amplifiers, AGC amplifiers, attenuators, splitters, hybrid combiners, directional couplers, antenna taps, power inserters, DC blocks, terminations, base stations, head ends, donor antennas, test points, and mobile radios onto a canvas. Every component carries its full electrical specification (RF gain and noise figure, P1dB and OIP3, DC current draw, frequency band, optional duplexer downlink and uplink passbands) so the canvas is not just a diagram but the input to a multi-carrier RF simulation.

The simulation runs on every edit. It walks the graph from each signal source through the head end, the AGC chain, and out to the end terminator. Per-tone power, cascaded noise figure (Friis with inter-stage cable loss explicitly inserted), cascaded OIP3, headroom to P1dB, and IM3 products are recomputed at every amplifier and the head end. IM3 products falling outside the configured downlink or uplink passbands are dropped so a duplexer or cavity filter in front of the amplifier behaves the way a real one would. Mobile radios link over the air to any component on the canvas (draw the wire from the radio antenna port to the cable or amplifier) and the uplink budget runs the reverse path through the network back to the base receiver, applying the over-the-air coupling loss into the cable and the path through the cascaded chain.

Autosave persists the in-progress design to browser localStorage on every change, so a tab refresh restores the network rather than dropping it. A reset control rebuilds the default demo topology when the user wants to start over.

Capabilities

Visual network design canvas

Drag and drop radiating cable, line amplifiers, AGC amplifiers, attenuators, splitters, hybrid combiners, directional couplers, antenna taps, power inserters, DC blocks, terminations, base stations, head ends, donor antennas, test points, and mobile radios onto a canvas representing the tunnel, mine, or building. Every component carries its full electrical specification so the diagram is the input to the simulation rather than an afterthought. Connection validation enforces output to input on wired connections and a single antenna port on mobile radios that draws an over-the-air dashed link to any other component. Undo and redo, copy and paste, right-click context menus, and a context-aware properties panel cover design productivity.

Multi-carrier RF propagation engine

The Network Simulation Engine walks the network graph from each signal source through every wired component, accumulating cable loss (fitted to manufacturer datasheets), splitter and combiner insertion loss, amplifier gain, and AGC target-power regulation. Per-tone power is tracked at every port — a four-carrier bidirectional setup propagates eight tones (four downlink and four uplink) through the whole chain. The Port Inspector shows the composite power, noise floor, SNR, and the full per-tone breakdown at any selected port. The Enhanced Simulation Engine adds Friis-cascaded noise figure with inter-stage cable loss explicitly inserted (so the second amplifier in a chain is not credited with the first amplifier’s gain when the cable in between has erased it).

Intermodulation with duplexer / passband filtering

Computes two-tone (2a−b) and three-tone (a+b−c) IM3 products across the amplifier chain using vendor specific OIP3 and Rapp-soft compression. Each amplifier, AGC amplifier, and head end carries optional downlink and uplink passband ranges. When set, IM products falling outside both passbands are dropped from the analysis — the duplexer or cavity filter on the real device cannot pass them. The result is honest in-band IM3 that does not include 50 MHz mixer products contributing to a 150 MHz channel. The per-amp spectrum analyser modal shows the full IM product list, sortable by power or frequency, and the worst-case dBc figure that survives the passband filter.

DC power feed solver

Tracks the DC power feed across the cable run and amplifier chain. Solves voltage drop along the cable using the manufacturer DC resistance per 100 metres and the per-amp current draw. Identifies the headroom against the amplifier minimum supply voltage at each node. Useful for sizing where remote-powering by the head end reaches its limit and where additional power inserters are required.

Bidirectional analysis: uplink and downlink

The downlink (base to mobile) and uplink (mobile to base) are simulated separately. Every port renders a colour-coded composite-power label on the canvas against the configured target threshold, and the Port Inspector gives the full per-tone breakdown, noise floor, and SNR at any point along the run. The Uplink Budget Panel runs the reverse path for any selected mobile radio: mobile TX power minus body loss plus antenna gain, over-the-air free-space loss, coupling loss into the radiating cable, then back through the amplifier cascade to the base receiver. A pass / marginal / fail status is computed against the configured RX sensitivity. The Bidirectional Links summary table flags mobiles that pass on one direction but fail on the other and shows the limiting direction.

Over-the-air mobile radio coverage

Mobile radios sit on the canvas with a single ANT antenna port. Drag the wire from the ANT port onto any port on an amplifier, cable, splitter, or terminator and the radio is OTA-linked to that component (no real cable is created — the visual is a dashed antenna line). Validation enforces that the mobile sits exactly on an enabled carrier’s centre frequency (mobile TX equals the carrier downlink, mobile RX equals the carrier uplink) and that the mobile’s system type (TETRA, P25, DMR, Analog FM, or custom) matches the carrier’s system. Distance to the radiating cable, antenna gain, and body loss are first-class parameters in the OTA budget.

Off-air donor (repeater) link analysis

For repeater designs where the head end does not carry its own carriers but picks them up off-air from a parent macro cell, drop a donor antenna onto the canvas. The Donor Links table computes the donor signal level at the indoor-unit input (donor EIRP, free-space path loss to the donor, antenna gain, and feeder loss) and the system isolation margin — the gap between the network forward gain and the donor antenna isolation back into the radiating cable. Each donor is flagged OK, marginal, or unstable, because if the forward gain exceeds the isolation the loop oscillates. It catches the two failure modes of an off-air repeater (donor too weak, or isolation too tight) before commissioning.

Per-port spectrum analyser and uplink budget modals

Right-click any amplifier or head end and open the spectrum analyser modal: input and output power per tone, cascaded NF and OIP3, worst-case IM3 (after passband filtering), P1dB headroom, IM product list, cascade info, and DC power status. Right-click any mobile radio and open the uplink budget modal: mobile TX parameters, over-the-air path, full path through the network, link budget summary with the margin against RX sensitivity, and the downlink equivalent.

Validation and live warnings

A live validation panel surfaces orphaned components, cycles in the graph, unterminated cable ends (radiating cables exempted, head-end LF outputs exempted since the chassis terminates them internally), cable operating-band exceedances against the manufacturer datasheet range, mobile radio frequency or system-type mismatches against the network carriers, and AGC headroom advisories. Each warning is severity-tinted (error, warning, info) and click-locates the responsible component on the canvas.

Vendor cable database fitted to manufacturer datasheets

Radiating: RFS RADIAFLEX RCF12 (½″), RCF78 (⅞″), RCF78-MSHA, RLF114 (1¼″ PE jacket), RLKW114 (1¼″ rail-tunnel grade); CommScope RADIAX RXL-12-CL, RXL-78-CL, RXL-114-CL. Non-radiating: Times Microwave LMR-100A, LMR-195, LMR-240, LMR-400, LMR-600, LMR-900; Belden RG-213/U. Every cable carries longitudinal-loss coefficients (K₁ and K₂) least-squares refit to the manufacturer datasheet table — fit RMS error under 0.1 dB/100m across the operating band for the radiating and LMR cables (PE-dielectric RG-213 fits the √f model less cleanly at the band edges) — plus impedance, max frequency, max power, loop DC resistance taken from the datasheet, outer diameter, minimum bend radius, weight, velocity factor, temperature range, and fire-rating notes.

Autosave across sessions

The in-progress design is automatically saved to browser localStorage on every change. A tab refresh or accidental close restores the network exactly where the user left it. The Reset (↻) control in the toolbar clears the autosave and rebuilds the default demo topology — the explicit escape hatch back to defaults.

Standards & methodology

  • Vendor radiating cable specifications (RFS RADIAFLEX, CommScope RADIAX) for coupling loss and longitudinal loss
  • Times Microwave LMR and Belden RG-213 specifications for non-radiating feeder loss
  • ACMA radiocommunications licence conditions referencing radiating cable installations

When to use this tool

  • Designing radiating cable communications networks for underground mines
  • Designing leaky feeder coverage for road and rail tunnels
  • In-building radiating cable coverage for large industrial buildings, warehouses, and data centres
  • Sizing amplifier and AGC spacing across long underground runs
  • Validating amplifier headroom against in-band IM3 with duplexer passbands modelled honestly
  • Evaluating bidirectional uplink and downlink coverage for half-duplex mobile radio systems
  • Modelling the over-the-air coupling from a mobile radio (TETRA, P25, DMR, Analog FM) into the radiating cable along the run
  • Checking an off-air donor (repeater) design for adequate donor receive level and enough isolation margin to avoid oscillation
  • Sanity-checking a candidate topology against the multi-carrier composite power at each amplifier
  • Training new mine and infrastructure RF engineers on radiating cable design fundamentals

Is this the right tool for you?

Reach for the Leaky Feeder Designer in any of the following situations.

  • You are designing a radiating cable communications network for a new underground mine, tunnel, or large industrial site and need an end-to-end RF link budget with multi-carrier composite power tracked through the chain.
  • You are planning the leaky feeder system for a new road or rail tunnel and need amplifier spacing sized against cable loss, cascaded noise figure, and in-band IM3 with the head-end duplexer modelled.
  • You are responsible for in-building radio coverage in a warehouse, data centre, or large indoor industrial environment and want to evaluate radiating cable against distributed antenna systems.
  • You are sizing AGC amplifier headroom against the multi-carrier composite power in a TETRA + P25 mixed system and need to confirm none of the AGCs are pushed past 3 dB into compression.
  • You are evaluating a candidate carrier plan and need to confirm that the IM3 products generated by the amplifiers and head end do not land in a different carrier’s receive band, with duplexer passband filtering applied honestly.
  • You are checking uplink budget for handheld and vehicle-mounted radios at the worst case point on a long radiating-cable run, with over-the-air coupling loss into the cable applied per the cable’s coupling-loss curve.
  • You are training new mine and infrastructure RF engineers on radiating cable design and want an interactive environment where every edit re-runs the simulation in milliseconds.

Frequently asked questions

What is leaky feeder and where is it used?

Leaky feeder, more formally radiating cable, is a coaxial cable engineered to leak RF energy continuously along its length, acting as a long distributed antenna. It is the dominant radio coverage method in underground mines, road and rail tunnels, large industrial buildings, warehouses, data centres, and any environment where conventional repeater plus antenna coverage cannot reach. The trade-off against discrete antennas is consistent coverage along the cable run at the cost of higher cumulative loss over distance.

What does the simulation actually compute?

Per-tone RF signal propagation through every wired component, including matched cable loss fitted to the manufacturer datasheet, splitter and combiner insertion loss, amplifier gain, and AGC target-power regulation. Cascaded noise figure (Friis) with inter-stage cable loss explicitly inserted as a passive Friis element so the second amplifier in a chain contributes its full NF when the cable in between has erased the first amplifier’s gain. Cascaded OIP3 and per-amplifier P1dB headroom. Two-tone (2a−b) and three-tone (a+b−c) IM3 products with downlink and uplink passband filtering, so a duplexer or cavity filter on the amplifier or head end drops products outside both bands. DC power feed across the cable run. Bidirectional uplink and downlink. Over-the-air mobile radio coupling into the radiating cable.

How does the over-the-air mobile radio coverage work?

A mobile radio has one antenna port. Drag a wire from that port onto any component on the canvas (cable, amplifier, splitter, terminator) and the radio is over-the-air-linked to that component — the wire renders as a dashed antenna line rather than a real cable. The uplink budget then computes the mobile TX power minus body loss plus antenna gain, the over-the-air free-space path loss to the nominated coupling point, the coupling loss into the radiating cable per its 50% or 95% coupling-loss curve, and finally the path through the cascaded amplifier chain back to the base receiver. The downlink equivalent runs in reverse. Validation enforces that the mobile sits exactly on an enabled carrier’s centre frequency and that the mobile’s system type matches the carrier (so a P25 handheld will not silently link to a TETRA carrier).

How does the passband filtering on IM3 work?

Each amplifier, AGC amplifier, and head end carries optional downlink and uplink passband ranges (minimum and maximum MHz). When at least one passband is set the IM engine drops any IM2 or IM3 product whose frequency falls outside both bands. This models the duplexer or cavity filter in front of a real amplifier honestly — a 50 MHz mixer product does not contribute to in-band power in a 150 MHz VHF system. With passbands set the worst-case IM3 displayed in the spectrum analyser reflects only the products that physically survive the filtering, not the full theoretical IM product set.

What cables are in the database and are they accurate?

Radiating: RFS RADIAFLEX RCF12 (½″), RCF78 (⅞″), RCF78-MSHA, RLF114 (1¼″ PE jacket), RLKW114 (1¼″ rail-tunnel grade); CommScope RADIAX RXL-12-CL, RXL-78-CL, RXL-114-CL. Non-radiating: Times Microwave LMR-100A, LMR-195, LMR-240, LMR-400, LMR-600, LMR-900; Belden RG-213/U. Longitudinal-loss coefficients K₁ and K₂ for every cable are least-squares fitted to the manufacturer datasheet table and checked at four to five frequency anchors across the operating band, with a fit RMS error under 0.1 dB/100m for the radiating and LMR cables (PE-dielectric RG-213 fits the √f model less cleanly at the band edges). Loop DC resistance is taken from the datasheet for every cable with a published figure; the 1¼″ RFS variants and the CommScope RADIAX entries use the dimensionally-equivalent RADIAFLEX value as a DC-feed planning estimate.

Does my work persist if I close the browser tab?

Yes. The current design is automatically saved to browser localStorage on every change (debounced) and restored on the next page load. A Reset (↻) control in the toolbar clears the autosave and rebuilds the default demo topology when the user wants to start over. Multi-tab editing shares one autosave slot so the last write wins.

Does the tool produce a certified compliance artefact?

No. The validation panel surfaces design-time issues (coverage thresholds, cascaded compression, in-band IM3, mobile-radio frequency or system mismatch) as decision support for the integrator. Certification, mine-site approvals, and ACMA licence sign-off remain a Principal RF Engineer responsibility against the relevant local regulatory framework — the tool informs the design, it does not replace the regulator-facing review.