Build a G5RV Dipole Antenna
The G5RV is one of the most enduringly popular multi-band HF antennas in amateur radio — designed by Louis Varney G5RV in 1946 and still widely used today. It is a centre-fed dipole 102 feet long, fed through a specific length of open-wire or ladder line matching section before transitioning to coax at the shack. The matching section is not a balun or a tuner — it is a resonant transformer that presents a usable impedance to coax on several HF bands. Used with an ATU, the G5RV covers 80m through 10m from a single antenna requiring only two supports. This guide covers the theory, wire dimensions, matching section construction, feedline routing, and installation for a full-size G5RV.
The G5RV Is Not a Magic Antenna
The G5RV is often misunderstood. It is not resonant on all bands without a tuner, and it does not present 50 Ω on every band. What it is: a half-wave dipole on 20m (its design frequency), fed through a matching section of specific electrical length that transforms the centre impedance to something an ATU can handle across multiple HF bands. Louis Varney's original design used a 34-foot section of 300 Ω twin-lead, which presents approximately 70–90 Ω to the coax on 20m — a reasonable match without a tuner. On other bands the mismatch is higher, and an ATU is required.
The Matching Section — What It Does and Doesn't Do
The 34-foot matching section of open-wire or ladder line is the most misunderstood part of the G5RV. It is not a balun. It is not a transmission line that carries the signal to the shack. It is a specific electrical length of high-impedance transmission line that performs an impedance transformation at the antenna's centre feed point:
The matching section must be kept clear of metal objects, gutters, and walls — it is a balanced transmission line and proximity to conductors upsets the balance and increases loss. Route it straight down from the antenna centre, at least 6 inches from any metal surface.
Full-Size vs Half-Size G5RV
The half-size G5RV (also called the ZS6BKW's predecessor or Junior G5RV) uses a flat-top of 51 feet and a proportionally shorter matching section. It covers 40m through 10m. Compared to the full-size version:
- Half-size flat-top: 51 ft total (25.5 ft each side) — a half-wave on 40m, 3/2 waves on 15m
- Half-size matching section: approximately 16–17 ft of 300 Ω twin-lead or 450 Ω ladder line
- 80m performance: the half-size is very short on 80m — high impedance mismatch, ATU may struggle; best treated as a 40m–10m antenna
- Space: the half-size fits a 60-ft span, making it practical for smaller gardens that cannot accommodate the 110-ft span the full-size needs with end insulators
- Recommendation: if you have the space, build full-size — the 80m capability is genuinely useful and the extra wire is cheap
ATU Requirement and Feedline Considerations
The G5RV requires an ATU on all bands except 20m (where the SWR may be acceptable without one on some installations). The combination of matching section plus coax presents a complex impedance to the ATU that varies widely by band:
- 20m: SWR to coax typically 1.5:1 to 2.5:1 — many rigs will load directly; ATU gives cleaner match
- 40m: SWR to coax typically 3:1 to 6:1 — ATU required; most antenna tuners handle this easily
- 80m: SWR to coax typically 4:1 to 8:1 — ATU required; use low-loss coax and keep coax run short
- 15m and 10m: can be quite high SWR — verify your ATU can tune these; a wide-range ATU (like the LDG AT-100Pro or MFJ-993B) handles the G5RV better than a narrow-range internal rig tuner
- Coax length matters: the SWR on the coax side of the G5RV junction is not flat — it repeats with coax length. Specific coax lengths perform better or worse on specific bands. A 50-ft or 100-ft run of RG-8X is a reasonable starting point; avoid coax cuts of exactly λ/4 at any operating frequency
- Use a 1:1 current choke balun at the coax-to-ladder-line junction — this suppresses common-mode current on the coax shield, which causes RF in the shack and pattern distortion
| Version | Flat-top length | Each side | Matching section material | Matching section length | Primary bands | Notes |
|---|---|---|---|---|---|---|
| Full-size (original) | 102 ft (31.1 m) | 51 ft | 300 Ω twin-lead (VF 0.82) | 27 ft (8.2 m) | 80m–10m | Varney's original spec; 34 ft was for higher-VF ribbon |
| Full-size (ladder line) | 102 ft (31.1 m) | 51 ft | 450 Ω ladder line (VF 0.91) | 30 ft (9.1 m) | 80m–10m | Lower loss than 300 Ω twin-lead; preferred choice |
| Full-size (open-wire) | 102 ft (31.1 m) | 51 ft | 600 Ω open-wire (VF 0.975) | 32 ft (9.8 m) | 80m–10m | Lowest loss; requires careful routing away from structures |
| Half-size (Junior) | 51 ft (15.5 m) | 25.5 ft | 450 Ω ladder line (VF 0.91) | 15 ft (4.6 m) | 40m–10m | Poor on 80m; good for smaller gardens |
| Band | Flat-top in wavelengths | Approx. SWR at coax | ATU required? | Radiation pattern | Notes |
|---|---|---|---|---|---|
| 80m (3.5 MHz) | ~0.18 λ | 4:1–8:1 | Yes | Broad, near-omnidirectional | Short on 80m — lower radiation resistance; still useful |
| 40m (7.1 MHz) | ~0.37 λ | 3:1–6:1 | Yes | Broadside, moderate gain | Good performer; ATU tunes easily on most radios |
| 20m (14.15 MHz) | 3/2 λ | 1.5:1–2.5:1 | Sometimes | Multi-lobe, gain ~2 dBd | Design frequency; best native match |
| 17m (18.1 MHz) | ~1.9 λ | 3:1–5:1 | Yes | Multi-lobe | Works well with ATU |
| 15m (21.1 MHz) | ~2.2 λ | 2:1–4:1 | Usually | Multi-lobe, moderate gain | Good performer |
| 12m (24.9 MHz) | ~2.6 λ | 3:1–6:1 | Yes | Multi-lobe | Works with wide-range ATU |
| 10m (28.5 MHz) | ~3.0 λ | 2:1–5:1 | Usually | Multi-lobe, higher gain lobes | Good when band is open; many lobes |
| 30m (10.1 MHz) | ~0.53 λ | 6:1–12:1 | Yes — may struggle | Broadside | High mismatch; some ATUs cannot tune; consider a separate 30m antenna |
Materials for a full-size G5RV using 450 Ω ladder line matching section
Building the Full-Size G5RV
This guide builds the full-size G5RV with 450 Ω ladder line matching section and a 1:1 current choke balun at the feedline junction. Work from the centre outward — construct the matching section and centre insulator first, then measure and attach the flat-top wires.
Prepare the Flat-Top Wire
Cut two lengths of #14 AWG stranded copper wire to 52 feet each — one foot extra per side beyond the nominal 51 feet, to allow for end loops and the connection at the centre insulator. Strip 2 inches of insulation from one end of each wire. If using bare copper-clad steel wire, simply form a loop at each end — no stripping required.
At the stripped end of each wire, form a small loop by folding the wire back on itself and twisting tightly — 4–5 turns — to create a secure mechanical termination. This loop will attach to the centre insulator. Solder the twist for permanence. At the far end of each wire, form a similar loop through the hole in the end insulator and fold back, twisting and soldering to secure the wire to the insulator.
Build the Centre Insulator and Matching Section Connection
The centre insulator connects the two flat-top wires and provides the attachment point for the matching section. For a home-built G5RV, a simple and effective centre insulator can be made from a 6-inch length of 3/4-inch PVC pipe or a commercial antenna centre insulator with solder lugs.
Cut the 450 Ω ladder line to 31 feet — 30 feet of matching section plus one foot for the connections at top (centre insulator) and bottom (balun). Separate the two conductors of the ladder line at each end by 3 inches. At the top end, connect one conductor to one flat-top wire, and the other conductor to the other flat-top wire. The connection must be mechanically secure before soldering — wrap the conductors tightly together, then solder all joints with rosin-core solder. Apply self-amalgamating tape over all solder joints for weatherproofing.
Install the 1:1 Current Choke Balun at the Coax Junction
At the bottom of the matching section, install a 1:1 current choke balun between the ladder line and the coax. This balun performs two critical functions: it provides the transition from balanced (ladder line) to unbalanced (coax) transmission line, and it suppresses common-mode current on the coax outer shield that would otherwise cause RF in the shack, distorted radiation patterns, and interference to nearby equipment.
Mount the balun at or near ground level, on the mast or a fence post, where the ladder line transitions to coax. Do not route ladder line horizontally — it should hang vertically from the antenna centre as far as possible before any bends.
Select and Prepare the Support Points
The G5RV requires two end supports separated by at least 110 feet (102 ft flat-top plus room for end insulators and rope catenary) and at least 30 feet high for reasonable HF performance. Trees are the most common support — attach a halyard to a branch at 35–50 feet using a throw bag and rope, not spikes or screws that damage the tree.
The antenna should be as straight and horizontal as possible. Inverted-V configuration (centre elevated, ends lower) is acceptable and reduces the required horizontal span — with a centre height of 50 feet, the ends can be at 20–25 feet over a much shorter horizontal distance. Performance differences between flat-top and inverted-V configurations are modest on most HF bands.
Raise the Antenna and Route the Feedline
With both end supports prepared, raise the antenna: attach halyards to the end insulators and haul up each end simultaneously if possible — this reduces stress on the centre junction as the antenna lifts. Tie off both halyards with enough tension to keep the flat-top reasonably straight but not under extreme mechanical stress.
Route the 450 Ω ladder line vertically downward from the centre, keeping it clear of metal structures, gutters, and walls. The ladder line must maintain at least 6 inches of clearance from any metal surface for its entire run. Where the ladder line must change direction, use a smooth curve — never a sharp bend, which causes mechanical stress on the conductors and can change the electrical length slightly.
Connect the Coax and Run to the ATU
At the balun, connect the coax run from the balun to the ATU input. Keep this coax run as short as practical — excess coax adds loss that is significant when the SWR on the coax is high (as it will be on several bands with the G5RV). Use RG-8X (low-loss, flexible) or RG-213 (low-loss, less flexible) for the coax run. Avoid RG-58 for runs over 30 feet — its higher loss becomes significant at elevated SWR.
ATU Adjustment and Band-by-Band Verification
With the antenna installed and coax connected to the ATU, verify that the ATU can achieve a match on each intended band. Work through each band methodically:
- 20m: the ATU should tune easily — some rigs will load without the ATU at all. Note the ATU position for future reference.
- 40m: the ATU will work but requires more range. If the ATU cannot tune, check that the coax is not an awkward electrical length — moving the balun position by 5–10 feet often resolves this.
- 80m: ATU will tune but the antenna is short — expect lower efficiency than a resonant 80m dipole. Digital modes (FT8) are effective; SSB is workable; CW is good.
- 30m: high mismatch — if the ATU cannot tune on 30m, do not force it. The G5RV is a poor 30m antenna and a separate 30m wire is a better solution.
- 15m, 10m: should tune readily; the multi-lobe pattern provides coverage in several directions simultaneously.
ZS6BKW — The Optimised G5RV
The ZS6BKW (designed by Brian Austin ZS6BKW in the 1980s) is a computer-optimised version of the G5RV concept that provides direct 50 Ω matches on more bands without an ATU. The flat-top is slightly shorter (93 ft) and the matching section length and impedance are adjusted for best multi-band match:
- ZS6BKW flat-top: 93 ft (46.5 ft each side)
- Matching section: 39.5 ft of 400 Ω window line (use 450 Ω ladder line as the closest practical equivalent)
- Direct match bands: 40m, 20m, 17m, 12m, 10m — SWR below 2:1 without ATU
- ATU still needed: 80m, 30m, 15m
- vs G5RV: the ZS6BKW requires a wider-range ATU for bands it doesn't match natively, but eliminates the ATU entirely on five bands — ideal for rigs with limited internal ATU range
If you are building from scratch and have the choice, the ZS6BKW is generally the better design. The hamradiobase ZS6BKW build guide covers this antenna in full detail.
Practical Improvements for the G5RV
Several modifications improve the stock G5RV design for fixed-station use:
- Replace 300 Ω twin-lead with 450 Ω ladder line: lower loss, better power handling, and the same function. The only difference is a slightly longer physical matching section length.
- Add a 4:1 balun instead of 1:1 at the coax junction: some G5RV installations benefit from a 4:1 voltage balun at the ladder-line/coax junction — it presents a better impedance to the coax on several bands. Experiment with both; the 1:1 current choke is almost always at least as good.
- Raise the ends: the G5RV's performance on 40m and 80m improves meaningfully as the antenna is raised. Every 10 feet of additional height over 30 feet improves low-angle radiation. The antenna is worth building even at modest heights but performance rewards increased height generously.
- Separate 30m antenna: rather than fighting the G5RV's poor 30m match, a simple 33-ft dipole for 30m run parallel to the G5RV and switched in as needed is a low-cost solution that covers the one band the G5RV handles poorly.
- Weatherproofing: apply self-amalgamating tape over all outdoor solder joints. Inspect connections annually — copper oxidation at the centre insulator and balun junctions is the most common failure point for installed G5RVs.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| ATU cannot tune on 40m | Coax length presenting awkward impedance to ATU | Try adding or removing 10–15 ft of coax between balun and ATU — impedance at ATU input changes with coax length | Adjust coax length in 5-ft increments until ATU tunes; 50 ft and 100 ft total runs are generally good starting points |
| RF in the shack — chassis buzz, mic feedback | Common-mode current on coax shield — missing or inadequate balun | Measure voltage between coax shield and mains earth — should be near zero; touch the coax connector and feel for RF tingle | Install or replace the 1:1 current choke balun at the ladder-line/coax junction; add a ferrite choke (5–10 turns RG-8X through FT-240-31 core) at the rig end of the coax |
| SWR on 20m is 5:1 or higher | Flat-top length incorrect, or matching section wrong length or material VF | Sweep with NanoVNA — check that resonance minimum is near 14.15 MHz; if shifted, flat-top or matching section length needs adjustment | Add or remove wire from flat-top ends in 1-ft increments; verify matching section length against VF of actual feedline material used |
| No performance on 80m — cannot make contacts | 80m efficiency is inherently low — short antenna on 80m is normal | Check ATU is tuning; run WSPR on 80m and compare spot reports to expected; antenna IS working — efficiency is just lower than a resonant 80m antenna | Accept lower 80m performance or add a dedicated 80m dipole; use digital modes (FT8) where the G5RV's reduced efficiency matters less |
| Ladder line touching house wall — detuning | Imbalance from proximity to conductive surface | Check SWR change when ladder line is moved away from wall; significant change confirms the problem | Install standoff insulators to hold ladder line 6+ inches from all metal and masonry surfaces; use porcelain or UV-stabilised nylon standoffs at 3-ft intervals |
| Antenna sags excessively in summer heat | Nylon rope stretching with temperature; wire elongation in heat | Inspect rope tension during hot weather | Replace nylon rope with Dacron/polyester rope; use antenna wire with a steel core (copper-clad steel) which has lower thermal expansion than bare copper |
| Performance dramatically worse after rain | Water ingress at centre insulator solder joints or balun | Check for visible water or corrosion at all outdoor junctions; SWR change with rain confirms moisture ingress | Re-weatherproof all outdoor solder joints with self-amalgamating tape; inspect balun enclosure seal; apply silicone sealant around all cable entries |
Can I use the G5RV without an ATU on 20m?
Often yes — on 20m the G5RV's matching section was designed to present a near-50 Ω impedance to the coax, and many installations produce SWR of 1.5:1 to 2.5:1 on 20m without any ATU. Modern transceivers tolerate SWR up to 2:1 without activating protection circuits. Whether your specific installation achieves this depends on the exact matching section length relative to your feedline's velocity factor, and the coax length to the rig. Measure with a NanoVNA before assuming — the 20m match without ATU is not guaranteed and varies between installations.
Does the G5RV work on 60m or 160m?
On 60m (5.3 MHz), the G5RV flat-top is roughly 0.1 wavelengths — very short — and the impedance will be very low with high reactance. A wide-range ATU may be able to tune it but efficiency will be poor. On 160m the antenna is even shorter relative to wavelength and is not practical. For 60m and 160m, purpose-designed antennas (an inverted-L or loaded vertical for 160m, a short dipole or loaded wire for 60m) are a better approach than trying to use the G5RV on bands it was not designed for.
Why is 30m so difficult to tune on the G5RV?
At 10.1 MHz, the G5RV flat-top is approximately 0.53 wavelengths — just past half-wave — and the impedance at the feedpoint is very high, in the range of several thousand ohms. The matching section then transforms this further into an impedance that can be very challenging for a typical ATU to match. The problem is not with the ATU but with the impedance presented to it. Solutions include: accepting 30m is unavailable with this antenna, using a dedicated 30m wire, or experimenting with different coax lengths between the balun and ATU to find a length that presents a more manageable impedance on 30m.
Commercial G5RVs — are they worth buying?
Commercial G5RVs from reputable manufacturers (Fritzel, Cushcraft, Vine Antennas, W8AMZ) are ready-made and use appropriate wire gauges and matched matching sections — they work as well as a carefully built homebrew version. The build cost difference is modest since the major G5RV costs are wire and ladder line rather than labour. The main advantage of building your own is the ability to use 450 Ω ladder line (many commercial G5RVs still use 300 Ω twin-lead for convenience) and to verify the matching section length precisely against your feedline's actual velocity factor. If buying commercial, verify the matching section material and length before installation.
How high does the G5RV need to be?
The G5RV benefits significantly from height. At 30 feet it is a functional HF antenna but with a high radiation angle on 40m and 80m — good for regional contacts, less effective for DX. At 50 feet the low-angle radiation improves noticeably on 40m and 20m. At 70 feet and above it is an excellent DX antenna on 20m and higher bands. For a fixed station where DX is a priority, getting the centre as high as possible (even at the cost of drooping the ends) is worthwhile. For a new installation where 30 feet is all that is achievable, the G5RV still performs — particularly on 20m, 15m, and 10m — and is far better than no antenna at all.
What power level can the G5RV handle?
The flat-top wire (#14 AWG copper) handles legal-limit power (1500W in the US) without concern. The limiting factor is the matching section and balun. Quality 450 Ω ladder line handles 1500W comfortably — it has very high power ratings. The 1:1 current choke balun must be rated for your power level — quality commercial choke baluns are rated 1–5 kW. At 100W, any well-built G5RV handles full power without issue. At higher power levels, verify the balun rating and ensure all solder joints are properly made with no high-resistance connections that could overheat under sustained carrier (digital modes, RTTY).