Antennas · Volume 20
Grounding, Counterpoise, Radials, Lightning Protection
RF ground vs DC ground vs safety ground, radial field design, single-point ground, polyphaser arrestors, the building ground bond, ground loops, and the cost of getting it wrong
Contents
1. About this volume
Grounding is the most-neglected and most-load-bearing element of any antenna install. The vertical’s pattern, the receive system’s quiet, the rig’s survival in a lightning event — all gate on the ground system. This is the volume where multiple disciplines (electrical safety, RF performance, lightning physics, NEC code) converge, and where the cost of doing it wrong ranges from “noisy receive” to “house fire” to “operator electrocution.”
Three separate “grounds” coexist in any well-designed station — safety ground (NEC requirement, protects against shock and fault current), DC ground (the power supply’s negative reference), and RF ground (the image plane for verticals, the counterpoise return for end-feds). These three are different things — they can be the same physical conductor, or three separate systems, but they must be bonded correctly. The single-point ground architecture (§7) is the canonical solution.
The volume covers:
- The three-grounds taxonomy and why confusing them is dangerous (§2)
- RF ground theory — radial fields for verticals (§3, §4) with full efficiency tables
- Counterpoise for end-fed antennas (§5)
- Safety ground bonding per NEC code (§6)
- Single-point grounding for lightning protection (§7)
- Polyphaser arrestors and the commercial-arrestor market (§8)
- Ground rods, ground rings, Ufer / butt grounds, chemical grounds (§9)
- Ground loops — the hum-on-the-receiver symptom (§10)
- DIY radial field for a 40m vertical + single-point ground panel (§11, §12)
- Commercial-arrestor reference parts (§13)
Cross-references are heavy: Vol 8 (Fixed verticals) for the radial-field-as-image-plane content, Vol 10 (Random wire & end-fed) for the counterpoise-for-EFHW content, Vol 16 (BALUNs / common-mode chokes) for the choke-balun-and-grounding interaction.
The Phase 5 cluster (Vols 20-23) covers the physical-deployment realities — grounding, mounting, weatherproofing, stealth. Together they’re the practical “how do you actually install this antenna” playbook.
2. Three different “grounds” — and why confusing them gets people killed
2.1 The three grounds
| Ground type | Purpose | Code requirement | Conductor |
|---|---|---|---|
| Safety ground | Protect against AC shock + fault current | NEC 250 mandatory | Equipment-grounding conductor (green wire) bonded to service entrance |
| DC ground | Reference for circuit voltage | Internal to equipment | Power supply negative rail / chassis |
| RF ground | Image plane for vertical antennas; counterpoise for end-fed | Performance, not safety | Radial field or buried wire/rod system |
The three can be the same physical conductor (e.g., a single ground rod that’s bonded to the AC service ground and also serves as the antenna’s RF ground) or three separate systems. What matters is how they connect — specifically, whether they bond at a single point (good) or form a loop between disparate ground points (bad).
2.2 The “two grounds” problem
If you have an AC ground rod at the electrical service entrance and a separate antenna ground rod 50 feet away with no bond between them, you have a ground loop: a closed conductor path that picks up induced currents from EMI, ground potential differences, and lightning-induced voltages.
The symptoms range from mild (audible hum in the receive audio) to severe (RF in the shack, blown equipment) to catastrophic (lightning strikes one ground rod, current flows through the entire shack to reach the other rod, frying everything in between).
The fix: bond the antenna ground rod to the service entrance ground via a thick copper strap. Specifically:
- 2” × 1/8” copper strap (or equivalent #4 AWG copper)
- Direct buried run from antenna ground to service entrance
- Mechanically secure connections at both ends (UL-listed grounding lugs)
Per NEC 810 (radio and television equipment grounding), this bond is mandatory for any installed antenna ground. Skipping it is a code violation and a safety hazard.
2.3 The “RF ground is safety ground” trap
A common amateur mistake: assuming the ground rod under the operating bench is the antenna’s RF ground. It’s not (it’s the safety ground for the rig). And using it as the antenna’s RF ground:
- Doesn’t provide the proper image plane for a vertical (the rod is single, not a radial field)
- Couples RF noise into the safety ground system (the rest of the house electrical)
- Creates a ground-loop path through the building wiring
- Violates NEC 810 (the AC ground must bond, not substitute for, the RF ground)
Keep them separate, but bond them together at a single point — the single-point ground panel (§7).
2.4 The dangerous version: “I’ll just use a long wire to a ground rod”
A vertical antenna’s “ground” is not a single ground rod connected to the antenna’s coax shield by a long wire. That setup:
- Has very high inductance (a 10-foot wire is ~10 μH at the antenna’s resonance)
- Doesn’t function as an image plane (the rod is a point, not a plane)
- Creates RF voltage on the coax shield (the rig is now part of the antenna)
- May produce RF burns on the operator
The correct vertical antenna ground is a radial field (§3-§4) — multiple wires, each λ/4 or longer, laid in a star pattern from the vertical’s base. The wires together form an effective image plane.
3. RF ground — the image plane for verticals
A vertical antenna above ideal ground (e.g., salt water) behaves like a dipole — the antenna’s radiation is mirrored below the ground plane, producing a symmetric pattern. Above real ground (lossy soil), the radiation pattern is distorted:
- The radiation lifts (the peak elevation angle increases from ~25° toward zenith)
- The gain drops (energy is dissipated as heat in the soil)
- The pattern asymmetry increases (less omnidirectional, more sensitive to local terrain)
The radial field’s job is to make the soil look “ideal” to the antenna. A properly-designed radial field reduces ground losses to ~0.5 dB and restores the antenna’s pattern to near-ideal-ground performance.
3.1 The soil conductivity / dielectric constant problem
Real ground has finite conductivity and dielectric constant:
| Soil type | Conductivity (S/m) | Relative dielectric ε_r | Quality |
|---|---|---|---|
| Salt water | 5.0 | 80 | Excellent (best possible without engineering) |
| Wet farmland | 0.03 | 25 | Good |
| Average soil | 0.005 | 13 | Mediocre (typical residential) |
| Dry rocky soil | 0.001 | 8 | Poor |
| Dry sand | 0.0001 | 4 | Very poor |
| Desert | 0.00005 | 3 | Bad |
A vertical antenna’s pattern over soil depends on these parameters. The vertical’s elevation pattern shifts from ~25° peak (over salt water) to ~50° peak (over desert) — a major degradation for low-angle DX work.
A radial field replaces the soil’s lossy current return path with a low-loss artificial conductor. The radial field’s quality is what determines how much of the soil’s deficiency the antenna can compensate for.
3.2 What radials do, electromagnetically
When a vertical antenna’s current flows up the radiator, an equal and opposite current must flow back to the feedpoint via the ground system. This return current:
- In soil: flows through the resistive soil, dissipating energy as heat
- In radials: flows on the radial wires (which are low-loss copper), then back to the feedpoint with minimal loss
The radial field intercepts the return current before it enters the soil, routing it through the radials’ low-resistance path. The wire’s resistance is much lower than soil’s effective resistance at HF; the radial field improves efficiency dramatically.
3.3 The 5.15 dBi vertical gain
A quarter-wave vertical over an ideal ground (the textbook reference) has gain of 5.15 dBi in free-space terms (or 2.15 dBi over a dipole reference, +3 dB because the vertical is one-sided).
In practice:
- Salt water, 60 radials: 5.0-5.5 dBi (matches textbook)
- Average soil, 60 radials: 3.5-4 dBi (1-2 dB below textbook)
- Average soil, 16 radials: 2-3 dBi (3 dB below textbook)
- Average soil, no radials: -2 to +1 dBi (6-8 dB below textbook)
The “no radials” performance is worse than a dipole — the soil losses eat most of the antenna’s potential.
4. Radial fields — buried vs elevated
4.1 Buried radial fields
A buried radial field consists of multiple wires laid radially outward from the vertical’s base, buried 1-6 inches deep in soil. The standard:
- Number of radials: 60-120 for “broadcast quality” performance
- Length of each radial: λ/4 at the lowest operating band
- Wire size: #14-#16 AWG copper or copper-clad steel (CCS — the broadcast-industry standard, $0.20/ft)
- Spacing: evenly distributed in 360° (e.g., 60 radials = 6° apart)
- Depth: 1-6 inches in soil; deeper doesn’t help (the magnetic field penetration into soil is shallow at HF)
The efficiency-vs-radial-count curve:
| Number of buried radials | Efficiency (typical soil) | Cost / effort |
|---|---|---|
| 0 | 5-20% | None |
| 4 | 25-40% | One afternoon |
| 8 | 40-55% | A weekend |
| 16 | 55-70% | Two weekends |
| 32 | 70-82% | Multiple weekends |
| 60 | 82-90% | Serious commitment |
| 120 | 90-95% | Broadcast-grade |
| 240 | 92-96% | Diminishing returns |
The takeaway from this table:
- 0 → 8 radials gains 30+ percentage points of efficiency — the biggest single improvement available
- 8 → 32 gains another 30 points
- 32 → 120 gains 15 more
- Diminishing returns after 120
For amateur use, 32-60 radials is the practical sweet spot — substantial improvement at reasonable effort. 120+ is overkill except for low-band DX stations.
4.2 Elevated radials (the alternative)
An elevated radial field consists of 2-4 radials lifted above the ground (at λ/8 to λ/4 elevation) rather than buried in it. The radials act as a counterpoise (a balanced return path) rather than as a soil-loss compensator.
| Number of elevated radials | Efficiency | Notes |
|---|---|---|
| 1 | 30-50% | Highly asymmetric; not recommended |
| 2 (opposite each other) | 75-85% | Minimum sensible configuration |
| 3 | 85-93% | Adds rotational symmetry |
| 4 | 90-95% | The standard — sweet spot |
| 6 | 93-96% | Marginal improvement |
| 8 | 94-97% | Diminishing returns |
The 4-radial elevated ground plane outperforms a 16-radial buried field in most installations. The elevated radials don’t interact with lossy ground at all; their efficiency depends only on the radials themselves.
Sloped radials (at 30-45° downward from horizontal) provide an additional benefit: they shift the feedpoint impedance from the natural ~36 Ω (perfectly horizontal radials) toward ~50 Ω (perfectly 45° sloped radials), giving a natural 50 Ω match without a transformer. See Vol 8 §6 for the full sloped-radial impedance table.
4.3 The buried-vs-elevated decision
| Choose buried radials when | Choose elevated radials when |
|---|---|
| You can ground-mount the vertical | You need to mount on a roof, tower, or above obstructions |
| You have the space for radials extending outward | Lot constrains horizontal radial space |
| You’re willing to lay wire on/in soil | Soil is rocky, paved, or otherwise inaccessible |
| Local soil is moderate-to-good conductivity | Local soil is dry/rocky (elevated avoids ground loss entirely) |
| Multi-band operation (radials work on all bands equally) | Single-band or trap-multiband (elevated radials are band-specific) |
For multi-band trap verticals (Hustler 6-BTV, Cushcraft R-9), buried radials are the conventional choice because elevated radials would have to be sized differently for each band.
4.4 The “radial counterintuition” reality
A vertical with too few buried radials shows a better SWR than a vertical with too many. The reason: ground loss adds resistance to the feedpoint impedance, lifting the 36 Ω toward 50 Ω.
- 4 radials, poor soil: feedpoint Z ≈ 65-90 Ω, SWR ≈ 1.3-1.8:1 (ground loss adds resistance)
- 60 radials, same soil: feedpoint Z ≈ 36-42 Ω, SWR ≈ 1.2-1.4:1 (no ground loss)
The 4-radial vertical reads “1.5:1 — looks great!” but is dissipating most of the power in soil heating. The 60-radial vertical reads “1.2:1 — a bit low” but is radiating efficiently.
SWR alone is not a measure of antenna efficiency. The radial field’s quality is what matters.
5. Counterpoise for end-fed and random-wire antennas
A counterpoise serves a different purpose than a radial field: it provides a controlled return path for the RF current at the UNUN’s ground side, preventing the coax shield from becoming part of the antenna.
5.1 The counterpoise specification
For an end-fed half-wave (EFHW) or random-wire antenna:
- Length: 5-10% of the antenna length (NOT λ/4 — see §5.2)
- Position: lies on the ground or hangs below the antenna’s near end
- Material: same wire as the antenna (#14 or #18 copper)
- Connection: bonded to the UNUN’s ground terminal (the side that connects to the coax shield)
For a 40 m EFHW (~66 ft), the counterpoise is 6-7 ft (10%). For an 80 m EFHW (~132 ft), the counterpoise is 12 ft (10%).
5.2 Why NOT a quarter-wave counterpoise
A common misconception is that the counterpoise should be λ/4 long (resonant). It should not:
- A λ/4 counterpoise becomes a resonant element itself, with its own current distribution
- The resonant counterpoise shifts the EFHW’s tuning (typically downward by 5-10%)
- The counterpoise’s pattern adds asymmetry to the antenna’s radiation
The 5-10% counterpoise is deliberately non-resonant. It provides RF current return without behaving as a separate radiator.
5.3 Counterpoise placement
The counterpoise should run:
- Horizontal along the ground (preferred — gives controlled return path)
- Vertical down from the UNUN (acceptable if no horizontal space)
- Sloped if the antenna is sloped (matches the antenna’s geometry)
Avoid:
- Spiraled / coiled counterpoise (the coil adds inductance, shifting tuning)
- Buried counterpoise (soil losses defeat the purpose)
- Touching metallic structure (the structure becomes part of the antenna)
5.4 Cross-link to Vol 10 (Random wire & end-fed)
The counterpoise length and configuration details for each end-fed antenna type are covered in Vol 10 §7. This volume covers the grounding philosophy — the counterpoise is the EFHW’s RF ground equivalent, not the antenna’s safety ground.
6. Safety / AC ground bond
6.1 NEC 250 — the AC service ground
The National Electrical Code (NEC) Article 250 governs how AC electrical services are grounded. The key points:
- Service entrance ground: the AC mains’ neutral and equipment-grounding conductors bond at the service entrance (where the AC enters the building)
- Grounding electrode system: ground rods, ground rings, or ufer grounds connect the service ground to earth
- Equipment grounding: every outlet’s third-wire (green) bonds back to the service entrance ground
The service-entrance ground typically achieves 10-25 Ω resistance to earth. This is not low enough for proper RF grounding (which wants <5 Ω), but it’s adequate for AC safety.
6.2 NEC 810 — antenna grounding
NEC Article 810 specifically covers radio and television equipment grounding:
- Antenna ground rod required: every installed antenna must have an antenna ground rod at its base or mounting structure
- Bond to AC service ground: the antenna ground rod must be bonded to the AC service entrance ground (mandatory) with a #6 AWG copper conductor minimum
- Antenna discharge unit: a lightning arrestor (Polyphaser, Alpha Delta, ICE) is required where the antenna feedline enters the building
- Single-point ground: all antenna grounds bond to a single point at the building (the single-point ground panel — §7)
The “antenna ground separate from AC ground” approach is explicitly prohibited by NEC 810. The bond between them is what prevents step potential differences during a lightning strike.
6.3 Why the bond matters
If your antenna ground rod is at 100V and your house ground rod is at 0V during a lightning event, every conductor between them (coax shield, RF feedline, control cables) carries the 100V difference. The current path: lightning → antenna ground → conductor → house ground → earth.
If the conductors are inside the building, the entire building wiring becomes part of the lightning path. Equipment between the two grounds — rig, computer, anything plugged into the wall — sees the full voltage difference.
The bond between antenna ground and house ground equalizes the potential. During a strike, both ground rods rise to roughly the same voltage; equipment between them sees only the small (~10V) IR drop across the bond, not the full lightning voltage.
6.4 The bond conductor
- Minimum: #6 AWG copper wire (per NEC 810)
- Recommended: 2” × 1/8” copper strap or #4 AWG cable
- Why strap over round wire: the strap has lower inductance at HF (the surface area matters for high-frequency current)
- Routing: as direct as possible, avoiding sharp bends; buried 18-24” deep
The longer the bond, the higher the inductance, the less effective the equalization during a strike. Keep it short and direct.
7. Lightning protection — single-point ground architecture
The single-point ground (SPG) architecture is the canonical lightning-protection topology. All antenna feedlines and rotator/control cables enter the building at one point, pass through lightning arrestors at this point, and are bonded to a common grounding point.
7.1 The SPG topology
Single-point ground panel architecture:
Antenna 1 ──────●
│
Antenna 2 ──────●
│
Antenna 3 ──────● ← SPG panel (cable entry to building)
│
Rotator cable ──●
│
AC mains ───────● (via AC service ground bond)
│
● Grounding bus
│
│ Heavy copper strap (2" × 1/8" or #4 AWG)
│
● Earth ground (rod, ring, or ufer)The SPG panel:
- Sits on the exterior of the building, at the cable entry point
- Holds lightning arrestors for each antenna feedline
- Bonds all arrestor grounds to a common bus
- Connects the bus to the AC service entrance ground via heavy copper strap
7.2 Why single-point matters
If antennas enter the building at multiple points (e.g., one antenna comes in through the south wall, another through the east wall) and each has its own ground, those grounds will be at different potentials during a lightning event. The building wiring connects them, and current flows through the equipment between them.
With single-point entry, all antennas reach the same ground voltage during a strike, and no current flows through the equipment.
7.3 The grounding bus
Inside the building (after the single-point ground panel), the rigs are bonded to this single point — never a separate ground rod elsewhere. Each rig:
- Connects to the equipment-grounding bus on the panel
- Does not have its own ground rod
- Does not connect to the AC ground via the third-wire (the rig’s AC plug)
This ensures that all equipment shares the same RF ground reference, preventing ground-loop noise pickup.
7.4 The “I’ll just disconnect during storms” alternative
A common amateur shortcut: disconnect the antennas during thunderstorms. This is insufficient:
- Disconnect physically (unplug PL-259), not just electrically (turn off the rig)
- Coax dangling in the shack is still a lightning conduit
- Even disconnected coax that’s touching the equipment can carry lightning current
- The proper disconnect is to coil the coax in a metal-grounded container outside the shack
The single-point ground architecture works whether you disconnect or not. It’s the only safe approach for permanent installations.
8. Polyphaser and other lightning arrestors
8.1 Lightning arrestor topology
A lightning arrestor is a device that:
- Passes RF signals normally (low loss, no insertion loss above 0.5 dB)
- Blocks high-voltage transients (lightning, static buildup, ESD)
- Is replaceable after a strike (the gas-discharge tube or spark gap is sacrificial)
The two common arrestor topologies:
Gas-discharge tube (GDT): a small sealed tube containing rare gas at low pressure. Trigger voltage 70-1000V; when exceeded, the gas ionizes and conducts to ground in nanoseconds. Self-resets after the surge passes. Replaces the gas tube periodically (after each major strike or every few years).
Spark gap: physical gap between two electrodes. Strikes ionize air, conduct. Older technology, larger trigger voltage, less reliable than GDT.
Hybrid (GDT + MOV): combines a fast-acting GDT with a slower, higher-energy metal-oxide varistor for both transient speed and capacity.
8.2 The canonical arrestors
| Model | Type | Connector | Trigger V | Insertion loss | Price |
|---|---|---|---|---|---|
| Polyphaser IS-50UX-C0 | GDT | UHF-N | 230V | <0.3 dB to 1 GHz | $80 |
| Polyphaser IS-B50LU-MA | GDT + bias-T | N | 230V | <0.5 dB to 6 GHz | $200 |
| Polyphaser IS-NEMP-C0 | GDT-only N | N | 230V | <0.3 dB to 6 GHz | $90 |
| Polyphaser DSXL-LP | DC-pass coaxial | N | 230V | <0.3 dB | $130 |
| Alpha Delta Coax Arrestor (ATT3G50UFP) | GDT | UHF | 200V | <0.5 dB to 500 MHz | $45 |
| Alpha Delta Coax Arrestor (Pulse) | GDT | N | 200V | <0.3 dB | $60 |
| ICE Series 300 | GDT | UHF | 200V | <0.5 dB | $55 |
| Times Microwave LP1U-NFNF | GDT | N | 230V | <0.3 dB | $90 |
| Astatic AT-1500 arrestor | GDT | UHF | 350V | <0.5 dB | $25 |
| DX Engineering DXE-RTL-1 | GDT | N | 230V | <0.3 dB | $75 |
| Generic eBay GDT arrestor | varies | varies | varies | varies | $10-40 |
The Polyphaser IS-50UX-C0 is the amateur reference arrestor. Polyphaser’s commercial broadcast experience translates directly to amateur reliability.
8.3 Selection criteria
| Application | Recommended arrestor |
|---|---|
| Coax antenna at HF | Polyphaser IS-50UX-C0 or Alpha Delta ATT3G50UFP |
| Coax antenna at VHF/UHF | Polyphaser IS-NEMP-C0 |
| Bias-T-powered LNA antenna | Polyphaser IS-B50LU-MA (DC-pass) |
| Rotator control cable | Polyphaser DRX series |
| Data lines (Ethernet, USB) | Polyphaser DSXL series with data-line variant |
8.4 The “post-strike replacement” reality
Lightning arrestors are sacrificial. After a direct strike (or even a strong nearby strike), the gas-discharge tube in the arrestor may be damaged even if the strike didn’t trigger it visibly. After any lightning event near the antenna:
- Visual inspection: check the arrestor housing for soot, discoloration, or cracks
- Performance test: verify SWR through the arrestor; if SWR climbed significantly, the GDT is damaged
- Replace: GDT tubes are inexpensive ($5-20 each); replace after any suspected damage
For high-strike-frequency installations (Florida, Texas), some operators replace GDTs annually as preventive maintenance.
9. Ground rods, ground rings, ufer / butt-ground / chemical grounds
The earth-connection technologies, ranked by quality:
9.1 Single ground rod
- 8 ft copper-clad steel (CCS) rod, 5/8” diameter
- Driven vertically into earth (or angled if rocky soil)
- Resistance: 5-50 Ω depending on soil moisture and conductivity
- Cost: $15 + a sledgehammer
The single ground rod is the minimum acceptable ground. Adequate for safety bonding but typically too high a resistance for proper RF grounding.
9.2 Multiple rods in a star
- 3-6 rods, each 8 ft, spaced 6-10 ft apart
- Bonded together with #6 AWG wire or copper strap
- Resistance: 2-10 Ω
- Cost: $50-200 + significant ground prep
The standard “good amateur ground” — adequate for both safety and RF grounding.
9.3 Ground ring around building
- Continuous #4 AWG or #2 AWG copper conductor buried 18-24” deep, encircling the building
- Bonded to all corner ground rods at the building perimeter
- Resistance: <1 Ω achievable
- Cost: $200-500 + trenching cost
The commercial-quality ground for buildings with significant electrical needs. Required for tower-mounted antennas.
9.4 Ufer ground (concrete-embedded)
- Steel rebar embedded in the building’s foundation concrete
- The rebar bonds to the AC service ground
- Resistance: <0.5 Ω (concrete is a surprisingly good conductor when wet — and the building’s foundation stays moist year-round)
- Cost: bundled with new construction; can’t be retrofitted
The best ground available for new construction. Per NEC 250, Ufer grounds are explicitly recognized.
9.5 Butt-ground (utility pole base)
- Bonded to the structural steel of a utility pole or tower
- Resistance: <0.5 Ω
- Used in commercial broadcast / cellular sites
For amateur installations, the tower base + ground rod combination is the equivalent.
9.6 Chemical ground
- Cylinders filled with bentonite + gypsum, slowly absorbing soil moisture
- Resistance: 1-5 Ω in dry soil (where standard rods are 50+ Ω)
- Used in arid climates where standard ground rods are inadequate
- Cost: $200-500 per cylinder
Common in commercial Arizona / Nevada installations. Amateur use is rare due to cost.
10. Ground loops — and why your audio hums when the antenna is up
A ground loop is a closed conductor path formed when two grounds at different potentials are bonded by a signal cable. The loop picks up induced currents from nearby AC mains, RF, and EMI, producing hum, buzz, and unwanted noise in the receive audio.
10.1 The classic ground-loop diagram
Ground loop in shack:
Rig 1 Rig 2
│ │
●──────● ●──────●
│ │ │ │
│ AC outlet 1 AC outlet 2 │
│ │ │ │
│ ●●● ●●● │
│ │ │ │
│ ground ground │
│ bond bond │
│ │ │ │
│ │ conductor between │
│ └─────────────────────┘ │
│ │
●─────── signal cable (audio cable) ●
↑
Ground loop: 1) rig 1 → AC ground → 2) rig 2 → audio cable shield → 1) back to rig 1
Induced currents in this loop produce hum/buzz in audio10.2 The cures
Single-point grounding (the canonical fix): bond all equipment to a single ground point (the single-point ground panel). No alternative paths exist; no loops form.
Audio isolation transformer: a 1:1 audio transformer breaks the DC ground connection between two pieces of equipment. The transformer’s two windings are galvanically isolated; no DC current flows between them.
Ground-lift switch / cheater plug: lifts the AC ground connection on one piece of equipment. Use with caution — this defeats the safety ground. NEC may consider this a code violation in some installations.
Common-mode choke: a ferrite choke (Vol 16 §17) on a signal cable suppresses the common-mode current that’s the loop’s mechanism. Doesn’t fix the loop but reduces its effect.
Bond the two grounds together (counter-intuitive but works): if the two ground points are at different potentials, bonding them together (with a thick conductor) equalizes them. This is the single-point grounding principle in reverse — instead of avoiding loops, you ensure the loops have zero potential difference.
10.3 Diagnosing ground loops
Symptoms:
- 60 Hz hum in audio (US/Canada AC mains frequency)
- 50 Hz hum (Europe/UK AC mains frequency)
- 120 Hz buzz (full-wave-rectifier ripple from the AC supply)
- Antenna-related hum that disappears when the antenna’s disconnected
Diagnosis:
- Disconnect the antenna; does the hum persist? If yes, it’s not antenna-related.
- Move the rig to a different AC outlet; does the hum change? If yes, the AC ground topology is involved.
- Replace each audio cable with a known-good cable; does any cable cure the hum? If yes, the cable’s shielding was inadequate.
- Add an audio isolation transformer between the rig and the next stage; does the hum disappear? Confirms ground loop.
11. DIY build — a 60-radial field for a 40 m vertical
About 2-3 weekend days of work (the labor is in the digging/laying, not the design). Total cost ~$200.
11.1 BOM
| Part | Specification | Source | Mid-2026 price |
|---|---|---|---|
| Radial wire | 60 × 10 m of #14 CCS (copper-clad steel) | Wireman 522 or DX Engineering DXE-RADIAL-1 | $120 |
| Ground rod | 8 ft copper-clad steel, 5/8” | Local hardware | $20 |
| Common-bond conductor | 2” × 1/8” copper strap, 1 m | Local hardware | $15 |
| Ground-rod clamps | 5/8” cable lugs | Local hardware | $10 |
| Cable ties | 100-pack for radial-to-stake | Local | $5 |
| Optional: stainless ground stakes | 60 × 6” stainless | Local | $30 |
| Total | ~$200 |
11.2 Procedure
Plan the layout. A 60-radial field at λ/4 = 10 m needs a 20 m × 20 m clear area (the antenna at the center, radials extending 10 m outward in all directions). Avoid laying radials over driveways, sidewalks, or structures.
Pre-cut the radials. 60 lengths of #14 CCS, each 10 m. Use a tape measure or pre-marked rope; consistency is more important than perfect length.
Center marker. Drive the ground rod into the center of the antenna location. The rod’s top will be the antenna’s grounding point.
Lay the radials. From the ground rod, lay each radial outward at evenly-spaced azimuths (6° apart for 60 radials):
- Use a marked rope or stakes to mark azimuth angles
- Lay each radial directly on the ground (no need to bury at this stage)
- Pin each radial with cable ties to ground stakes (or just to grass with U-stakes) every 2 m
- The far end of each radial can be loose
Bond the radials at the center. Strip the inner end of each radial; bond all 60 to the ground rod’s clamp. Use a separate bonding ring (5/8” copper plate with multiple holes) if the rod’s single clamp can’t fit all 60.
Bury, optionally. Within 6 months, the radials will be naturally buried by grass growth and topsoil migration. To accelerate: use a sod-cutter or rented utility plough to slice a 1” slit along each radial’s path, push the wire in, close the slit. Don’t bury deeper than 2-3 inches — magnetic field penetration is limited.
Bond to the rest of the ground system. Connect the ground rod to the AC service entrance ground via the 2” × 1/8” copper strap. Direct route, buried 18” deep. This connection makes the radial field a legal ground system per NEC 810.
11.3 Verification
- SWR at the antenna: a 60-radial 40 m vertical should show ~38-42 Ω feedpoint impedance (SWR 1.2-1.4:1)
- Receive noise: significantly lower than with no radial field
- Lightning protection: the ground rod + radial system provides a low-impedance path during strikes
12. DIY build — a single-point ground panel for the shack
About 4 hours of work. Total cost ~$120.
12.1 BOM
| Part | Specification | Source | Mid-2026 price |
|---|---|---|---|
| 1/4” copper plate | 12” × 24” | Online Metals or local | $40 |
| Bulkhead-mount lightning arrestors (3-6) | Polyphaser or Alpha Delta | DX Engineering | $200-400 |
| AC outlet with isolated bond | NEMA 5-15R | Local | $15 |
| Copper strap | 2” × 1/8”, 2 m | Local | $30 |
| Stainless mounting bolts | 5/16” hardware | Local | $10 |
| Conduit/wire-management | Optional but recommended | Local | $20 |
| Total | ~$315 (with 3 arrestors) |
The big cost item is the arrestors themselves; the panel and hardware are <$100.
12.2 Mounting
Mount the panel on the exterior wall at the cable entry point, where:
- The shack’s wall meets the outside world
- Sheltered from direct rain but accessible for maintenance
- Adjacent to the AC service entrance (so the bond strap is short)
- Within 6 ft of the ground rod system
12.3 Construction
Lay out the panel. Plan the layout: arrestors on the outside, bulkhead connectors that pass through the wall to the shack, AC outlet at the bottom, bond bus at the center.
Drill and mount the arrestors. Each arrestor mounts in a hole through the copper plate. Use stainless hardware. Bond all arrestor grounds to a common bus (an internal copper strap connecting all the arrestor grounding lugs).
Bond to the AC service ground. Connect the bus to the AC service entrance ground via the 2” × 1/8” copper strap. Direct route, buried 18” deep if going outside.
Route the cables. Antenna feedlines enter from outside, terminate at the arrestor inputs. Jumpers (short coax pigtails) from arrestor outputs go through the wall into the shack.
Inside the shack: bond all equipment (rigs, computers, etc.) to a separate grounding bus that connects to the SPG panel via a wall-mount conductor (#6 AWG copper minimum).
12.4 Verification
- AC outlet test: GFCI outlet near the SPG should test clean (no ground faults)
- Continuity: check that all arrestor grounds bond to the common bus
- AC ground bond: verify with a meter the bond between the panel’s bus and the AC service ground
13. Commercial buys — Polyphaser, Alpha Delta, ICE
| Tier | Model | Type | Price | Notes |
|---|---|---|---|---|
| Budget | Alpha Delta Coax Arrestor (ATT3G50UFP) | GDT, UHF | $45 | Reliable amateur-grade |
| Budget | Astatic AT-1500 | GDT, UHF | $25 | Budget option |
| Budget | Generic eBay GDT arrestor | varies | $15-30 | Verify spec sheet before buying |
| Mid | Polyphaser IS-50UX-C0 | GDT, UHF/N | $80 | The amateur reference |
| Mid | ICE Series 300 | GDT, UHF | $55 | Mid-tier alternative |
| Mid | Times Microwave LP1U-NFNF | GDT, N | $90 | Times Microwave commercial |
| Mid | Polyphaser IS-NEMP-C0 | GDT, N | $90 | N-connector version |
| Mid | DX Engineering DXE-RTL-1 | GDT, N | $75 | DX Engineering version |
| Premium | Polyphaser DSXL-LP | DC-pass GDT | $130 | For bias-T-powered LNAs |
| Premium | Polyphaser IS-B50LU-MA | GDT + bias-T | $200 | Combo arrestor + bias-T |
| Premium | Polyphaser DSXL bulk panels | Multi-arrestor panels | $400-1500 | Multiple integrated arrestors + grounding bus |
| Premium | ICE Bulkhead Panel | Multi-arrestor + bus | $500-1500 | Pre-built single-point ground panels |
What to avoid:
- Used arrestors without performance test data — GDTs degrade after strikes
- “Universal” arrestors claiming 1 MHz – 6 GHz coverage — most have narrower useful ranges
- Cheap eBay arrestors without published trigger voltage specs
14. Common gotchas and myths
-
“I have a ground rod under my desk” — that’s a new ground; if not bonded to the AC service ground, it’s a death trap during an AC fault. NEC 250 violation.
-
“Lightning arrestor isn’t needed if you disconnect” — disconnect physically (unplug PL-259), not just electrically (turn off the rig); coax dangling in the shack is still a lightning conduit. The proper disconnect is to coil the coax in a grounded metal container outside the shack.
-
“My HF antenna doesn’t need grounding because it’s a dipole” — the coax needs the choke balun (Vol 16) and lightning arrestor regardless. The dipole’s antenna doesn’t need a ground, but its feedline does.
-
“More radials = always better” — diminishing returns after 60-120 buried radials. The 121st radial adds <0.1 dB.
-
“4 elevated radials = same as 60 buried radials” — the elevated approach is better in poor soil but equivalent in good soil. For typical residential soil, 4 elevated is a better investment than 16 buried.
-
“My SWR is 1.0:1 so my ground system is fine” — SWR alone doesn’t measure efficiency. A vertical with poor radials and high ground loss shows better SWR than a vertical with proper radials and low ground loss.
-
“The bond between antenna ground and AC ground is optional” — no, it’s NEC 810 mandatory. Skipping it is a code violation and a lightning safety hazard.
-
“I don’t need the bond if I’m not in lightning country” — partially true for amateur use, but the bond also prevents ground loops, RF in the shack, and step potentials during AC faults. Always include it.
-
“Polyphaser arrestors are forever” — they’re sacrificial. After a major strike, the GDT tube may need replacement (visible by soot or discoloration). Inspect and replace as needed.
-
“Ground loops only affect audio” — false. Ground loops also cause receive noise (50/60 Hz hum), RF leakage into the shack, and ground-fault interrupter trips. They affect the entire signal chain.
-
“I’ll install the grounding later” — every “I’ll install it later” is a future house fire. Install grounding first; antennas second.
-
“My ground rod is at 5 Ω so I’m safe” — partially true. 5 Ω is excellent for AC safety; for lightning protection (where strike currents reach 30 kA), even 5 Ω produces 150,000V across the rod’s resistance. The grounding system’s inductance matters too.
15. Resources
- ARRL Antenna Book Ch. 23 (grounds and grounding) — canonical amateur reference.
- NEC 250 / NEC 810 (National Electrical Code) — the legal requirements for AC grounding and antenna grounding respectively.
- Polyphaser application notes — published lightning protection design.
- ON4UN, Low-Band DXing — covers radial field optimization in depth.
- Sevick, Transmission Line Transformers — covers common-mode choke design.
- IEEE 142 (“Green Book”) — industrial grounding standard.
- BICSI grounding design manual — telecommunications grounding standard.
- ARRL Operating Manual Ch. 25 — shack wiring and grounding.
- W2DU “Reflections” — clarifies the SWR/grounding interaction confusion.
- AC6V’s grounding articles — community-published amateur grounding reference.
- Lightning Protection Institute (LPI) standards — commercial lightning protection.
- ARRL Tech Bulletin TIS-22 — bonding requirements per NEC 810.