Faraday Cloth as Radials: Conductivity Is Not the Whole Test
Faraday Cloth as Radials: Conductivity Is Not the Whole Test
A conductive blanket, screen or mesh can carry RF current. That does not make every piece of “Faraday cloth” equivalent to a radial field. Material, contacts, footprint, soil and the current distribution of the complete installed antenna decide the result.
RF.Guru working definition: Common-mode current is the non-cancelling phasor-sum current in a specified set of conductors, evaluated at a defined cross-section and using a declared current-direction convention. In the intended differential transmission-line mode, the outgoing and return currents are equal and opposite, so their phasor sum is zero. When they do not cancel, the remaining current must close through another reference or return path—such as the outside of a coax shield, a mast, equipment chassis, station wiring, nearby structures, earth, the operator, or distributed coupling through the environment.
This broader working definition is especially useful in practical antenna systems. On transmit, non-cancelling current on the outside of the coax can make the feedline and connected structures part of the radiating antenna system unless that path is intentional, clearly defined and properly controlled—for example by providing the required return path and placing a suitable common-mode choke at the correct boundary.
Why Two Ham Florida Man Videos Belong Here
In Faraday Cloth Radials for Verticals. Magic Carpet Ride?, Mark, K3ZD—Ham Florida Man—credits the RF.Guru article written by Joeri Van Dooren, ON6URE, and closely reads its challenge to treating conductive cloth as an automatic radial replacement. The essential proposition survives: Conductivity is not enough. You need the right current distribution.
In Hams with Vertical Antennas Confuse “GROUND.”, Mark places the same question inside RF.Guru’s wider distinction between an RF return structure and protective or lightning earthing. These videos are the source conversation for this article, not laboratory proof. The engineering answer below keeps their practical question intact while making dimensions, radial counts and performance conclusions conditional on the installed system and its measurements.
My objection is not that cloth cannot work. A metal sheet, mesh, braid or plated textile can all become part of an RF return structure. My objection is to skipping the electrical and mechanical questions because the sales name contains “Faraday.” The antenna responds to complex impedance and current distribution, not to the label on the fabric.
My practical position: compare the complete installed return systems. A small cloth pad may help, do almost nothing, or redirect current into the soil, mast and coax exterior. A larger well-connected sheet or mesh may be effective. Wire radials can also be excellent or disappointing. None of those outcomes follows from the material name alone.
Conductive Cloth Can Carry RF Current
A conductive textile is not RF magic, but neither is it electrically invisible. If the coating, fibres and joints provide a continuous conducting network, current can flow through it. The sheet then contributes conductor resistance, inductance, capacitance to soil and nearby objects, and a distributed current path back toward the feedpoint.
That is already enough to reject both slogans: “cloth is the same as radials” and “cloth can never be a radial.” The useful question is whether a declared material and geometry provide the wanted current path with acceptable conductor, contact and ground loss over the operating bands.
“Faraday cloth” is normally an application description for shielding fabric. It is not a standard radial-system specification. Shielding effectiveness in a particular enclosure test, a DC continuity beep, or a surface-resistance value does not by itself establish the impedance, loss or pattern of an HF antenna installation.
Sheet Resistance Needs Its Test Conditions
Surface resistance is often reported in ohms per square. For a uniform rectangular sheet contacted across two complete opposite edges, the first approximation is:
R ≈ Rs × L / W
Rs is sheet resistance, L is current-path length and W is width.
Real fabric rarely matches that simple model perfectly. A woven or knitted material may conduct differently along its two axes. Plated fibres, coating thickness, folds, abrasion, moisture, temperature and repeated deployment can change the result. A narrow grommet or clip does not excite the full edge uniformly, so current crowding and contact resistance can dominate the first part of the path.
AATCC TM76 defines a controlled method for measuring the surface resistivity of fabrics with specified electrodes and atmospheric conditions. That makes a data sheet interpretable. It still does not turn the coupon result into an antenna-efficiency value. Frequency-dependent current distribution, joints, soil coupling and the return structure beyond the sample remain outside that number.
The Feedpoint Joint Is Part of the Radial
The current must enter the cloth through a physical connection. The connection’s width, pressure, contact area, plating, fastener system and environmental stability matter. A low-resistance sheet attached through one small oxidised eyelet can behave more like a narrow lossy lead feeding a large capacitive shape than like an ideal conducting plane.
For a repeatable portable system, record the actual joint: lug or clamp material, number and spacing of fasteners, contact preparation, strain relief and the condition after folding, rain and drying. Do not assume a copper-coloured surface is bulk copper. Do not mix metals outdoors without considering galvanic compatibility and drainage.
Four-terminal resistance checks across the joint and along both fabric axes are useful screening measurements. They do not replace powered RF checks, because the current distribution and dielectric environment change with frequency and installation.
Footprint and Soil Coupling Set the RF Problem
A ground-mounted monopole drives current through a distributed return system. Some current flows in intentional conductors; some couples into soil through conductive and displacement-current paths; some may use the mast, bonding conductors or outside of the feed line. Soil permittivity and conductivity vary with composition, moisture, temperature and frequency, so the same mat can behave differently at another site or after weather changes.
The cloth footprint affects where current transfers between the conductor and earth. Its edges, slots and seams can matter. Extending the conductive region can reduce loss in one system, but there is no universal cloth radius—whether expressed as metres or a fraction of wavelength—at which every installation becomes efficient. Radiator height and loading, frequency, ground properties and every unintended return path move that boundary.
ITU-R BS.705-2 treats a vertical monopole above earth using either a conducting disk or radial wires whose radius, count and conductor diameter are explicit model inputs. The recommendation does not collapse those geometries into one material label. That is the right discipline here: declare the geometry before claiming the result.
A Sheet, Mesh and Radial Wires Are Different Geometries
A continuous sheet offers many parallel current paths. A mesh removes conductor and introduces cell geometry and many junctions. Radial wires constrain current into separate branches. Fabric strips sit somewhere between a wide conductor and a network of fibres. All can form useful return structures, but they need not produce the same feedpoint impedance, current density, loss or radiation pattern.
Cutting a fabric into strips is therefore not an automatic upgrade. It changes current paths, edge length, capacitance to earth and the feedpoint connection. Keeping one sheet may be better for contact area and current spreading; strips may be easier to deploy or may extend the footprint with the same material. Ordinary wire may be lighter, tougher or easier to terminate. Which choice wins depends on the comparison constraint: equal material mass, equal footprint, equal cost, equal packed volume and equal deployment time are different experiments.
Count electrical branches rather than visual arms. Two crossed strips can make four physical directions while sharing continuous material at the centre. That is not automatically equivalent to four independent wires, and neither arrangement earns a fixed efficiency from its shape alone.
Elevated and On-Ground Systems Are Different Architectures
An elevated radial is a coupled antenna element. Its length, height, tuning, symmetry and nearby conductors affect current balance and pattern. An on-ground or buried radial couples strongly to lossy earth and normally behaves as part of a distributed ground screen. A fabric pad placed on soil belongs to the second family unless the entire geometry has deliberately been elevated and analysed as part of the radiating structure.
Rudy Severns, N6LF, measured both families and repeatedly bounded his conclusions to the tested antenna, frequency, height, soil and geometry. His surface-radial experiments show that length and count interact; his elevated-radial work shows sensitivity to symmetry and surroundings. Those results do not establish that a fixed number of elevated quarter-wave wires always beats every sheet, or that many short wires always beat fewer long ones.
The proper lesson is more valuable: choose a plausible architecture, then verify the installed current division and field. A convenient match can coexist with loss or unintended feed-line radiation.
A Percentage Field Change Is Not an Efficiency Certificate
Mark’s Faraday-cloth discussion also leads into comparisons stated as a percentage of “relative field strength.” Before converting such a result into decibels, identify the measured quantity. For an electric-field amplitude ratio under the same impedance conditions:
ΔdB = 20 log10(E2 / E1)
If the ratio is already a power ratio, use 10 log10(P2/P1). More importantly, a remote reading at one bearing and height can change because total radiated power changed, because the pattern moved, because coax-exterior current changed, or because the probe and test environment changed. A percentage without accepted power, geometry, repeatability and uncertainty is a comparison observation—not absolute radiation efficiency.
The companion RF.Guru analysis, Faraday Strip Radials: 23% of What, Measured Where?, handles that arithmetic and its evidence boundary in detail.
Measure the Installed Return System
- Define the baseline. Record radiator, loading, matching network, feed line, choke position, mast, bonding and every connected cable.
- Characterise the material. Measure fabric resistance along both axes and across the feedpoint joint. Record dimensions, seams, folds, moisture and surface condition.
- State the reference plane. Save complex feedpoint impedance and calibration location. Do not substitute shack-end SWR for a ground-loss measurement.
- Map current. Compare current around the cloth or mesh, on individual wires, on the mast and along the feed-line exterior. Look for current crowding at the connection and edges.
- Check powered stress. Inspect joint and material temperature at the intended mode, power and duty cycle. Watch voltage clearance and arcing at edges, seams and damp contamination paths.
- Compare accepted power. Hold or correct for power accepted at the same plane, including matching and feed-line losses.
- Measure more than one direction. Use a stable remote receiver or calibrated field probe at repeatable positions and polarisations. Multiple bearings help separate pattern movement from a broad efficiency change.
- Restore the baseline. Use an A/B/A sequence and record soil moisture and weather so drift does not become the result.
IEEE Std 149-2021 provides the wider discipline for antenna measurements. The exact amateur setup may be simpler, but the logic remains: define geometry, calibration, environment, quantities and uncertainty before generalising.
RF Radials Are Not Protective Earth
A conductor used to shape RF return current is not automatically a protective-earthing conductor or lightning electrode. Those functions have different fault-current, bonding, mechanical, corrosion and installation requirements. A cloth mat must not be treated as a personnel-safety earth or lightning-protection component merely because it is conductive.
Use the locally required protective and lightning bonding system independently of the antenna experiment. IEEE Std 81 addresses earth resistivity, ground impedance and surface-potential measurements for grounding systems; IEC 62305-1 sets the general principles for lightning protection. Neither is replaced by a low SWR or a successful portable radial test.
Primary Engineering Sources
- ITU-R BS.705-2 — HF transmitting and receiving antennas: vertical-monopole models with explicitly defined conducting disks or radial-wire ground systems.
- ITU-R P.527-6 — Electrical characteristics of the surface of the Earth: the dependence of ground permittivity and conductivity on material, moisture, temperature and frequency.
- Rudy Severns, N6LF — Ground System Performance for HF Verticals, Part 1: experimental method and the limits of generalising from selected ground-system configurations.
- Rudy Severns, N6LF — Ground System Performance for HF Verticals, Part 5: measured radial-count behaviour and the difficulty of making precise field comparisons.
- AATCC TM76 — Electrical Surface Resistivity of Fabrics: controlled fabric-resistivity method with defined electrodes and atmosphere.
- IEEE Std 149-2021 — Recommended Practice for Antenna Measurements: measurement geometry, instrumentation and uncertainty discipline.
- IEEE Std 81-2025 — Guide for Measuring Earth Resistivity, Ground Impedance and Earth Surface Potentials: grounding-system measurements distinct from antenna matching.
- IEC 62305-1:2024 — Protection against lightning, General principles: the safety function that an experimental RF radial structure must not be assumed to fulfil.
Practical Conclusion
A conductive cloth pad is not automatically a good radial system. It is also not automatically useless. Ask what it is made from, how current enters it, how far it extends, how it couples to the soil, where the rest of the return current flows and what the installed measurements show.
The myth is not the cloth. The myth is believing that one material label settles the RF system. Follow the current, measure the contacts, declare the baseline and let the complete installation answer.
Mini-FAQ
- Can conductive cloth work as an antenna radial or ground screen? Yes. It can carry RF current, but its material, joints, footprint, soil coupling and the rest of the installed return path determine whether it is useful and how much loss it introduces.
- Does a low resistance in ohms per square prove low antenna loss? No. It describes a material sample under stated test conditions. Contact resistance, RF current distribution, frequency, geometry and ground coupling still determine the system result.
- Is a small conductive blanket equivalent to a field of wire radials? Not automatically. A sheet and separate wires support different current distributions, and their feedpoint connections, footprints and soil coupling may differ substantially.
- Should conductive fabric always be cut into strips? No. Strips can extend the footprint or simplify deployment, while a sheet can improve current spreading and contact area. Compare both under the same installed conditions.
- Do a few elevated quarter-wave radials always beat cloth or on-ground wires? No. Elevated radials form a different coupled antenna structure and depend on tuning, symmetry, height, soil and surroundings. N6LF’s results do not establish a universal winner.
- Can one remote field-strength percentage establish efficiency? No. It may reflect accepted-power, pattern, common-mode or measurement changes. Use controlled power, multiple positions, current mapping, A/B/A restoration and stated uncertainty.