Build a Discone Antenna
The discone is one of the most genuinely wideband antennas ever designed — a vertically polarised omnidirectional antenna covering a 10:1 or greater frequency range from a single feedpoint with no retuning and no ATU. Originally designed for aviation and military communications in the 1940s, it has become a staple of the amateur radio and scanning community as a base station antenna covering VHF, UHF, and everything in between. A discone tuned for a lower cutoff of 25 MHz covers through 300 MHz and beyond — spanning 10m, 6m, 2m, 70cm, and the entire scanning spectrum in a single fixed antenna. This guide covers the physics, disc and cone dimensions, wire versus sheet metal construction, feedpoint assembly, mast mounting, and SWR verification for a practical homebrew discone.
Disc, Cone, and Wideband Operation
A discone consists of two elements: a horizontal disc connected to the coax centre conductor at the top, and an inverted cone connected to the coax shield below it. The disc and cone together create a continuously frequency-independent impedance structure — as frequency changes, the effective electrical size of each element changes proportionally, and the impedance seen at the feedpoint remains near 50 Ω across an enormous bandwidth:
Disc and Cone Dimensions
The relationship between disc diameter, cone slant height, cone angle, and the gap between disc and cone top determines the discone's impedance, lower cutoff frequency, and bandwidth. These dimensions are related by fixed geometric ratios:
Wire Discone vs Sheet Metal — Construction Options
A true discone uses solid sheet metal or mesh for the disc and cone — the original military and commercial designs are built this way. For amateur construction, a wire approximation using radial spokes for both the disc and cone works almost as well and is far easier to build:
- Sheet metal discone: highest performance, closest to theoretical behaviour. Disc is a solid aluminium plate; cone is a spun or folded aluminium cone. Heavy, expensive, and difficult to fabricate without metalworking equipment. Used in commercial scanner antennas.
- Wire spoke discone: 8 to 16 radial spokes for the disc and 8 to 16 radial spokes for the cone, all connected at the feedpoint centre. Performance within 1–2 dB of a solid sheet design. Lightweight, easily transportable, and straightforward to build with common materials. The recommended approach for homebrew construction.
- Number of spokes: 8 spokes is the minimum for usable performance; 16 spokes approaches sheet metal performance. The improvement from 8 to 16 spokes is meaningful (approximately 1 dB); beyond 16 the improvement is negligible.
- Spoke material: aluminium rod (1/4-inch or 3/8-inch) is the best choice — lightweight, corrosion-resistant, and easy to cut and drill. Solid copper rod also works but is heavier. Steel rod corrodes rapidly. Avoid hollow tubing for spokes under 12 inches — it is harder to attach at the hub.
Radiation Pattern and Gain
The discone's radiation pattern is vertically polarised and omnidirectional in the horizontal plane — identical in concept to a vertical dipole or ground plane antenna. Its gain and elevation angle change with frequency across its wide operating range:
| Lower cutoff | Coverage range | Cone spoke length | Disc spoke length | Cone base diameter | Disc diameter | Best use |
|---|---|---|---|---|---|---|
| 25 MHz | 25–300+ MHz | 112 in (9.3 ft) | 78 in (6.5 ft) | 95 in (7.9 ft) | 78 in (6.5 ft) | 10m through UHF — very large structure |
| 50 MHz | 50–600+ MHz | 56 in (4.7 ft) | 39 in (3.3 ft) | 47 in (3.9 ft) | 39 in (3.3 ft) | 6m through UHF — large but manageable |
| 100 MHz | 100 MHz–1 GHz | 28 in (71 cm) | 20 in (50 cm) | 24 in (60 cm) | 20 in (50 cm) | FM/VHF scanner through UHF — popular size |
| 130 MHz | 130 MHz–1.3 GHz | 21.5 in (55 cm) | 15 in (38 cm) | 18 in (46 cm) | 15 in (38 cm) | 2m through 23cm — compact amateur all-band VHF/UHF |
| 144 MHz | 144 MHz–1.5 GHz | 19.5 in (49 cm) | 13.6 in (35 cm) | 16.5 in (42 cm) | 13.6 in (35 cm) | 2m through 23cm — purpose-built for amateur VHF/UHF |
| 200 MHz | 200 MHz–2 GHz | 14 in (35 cm) | 9.8 in (25 cm) | 11.8 in (30 cm) | 9.8 in (25 cm) | Compact scanner antenna — UHF and above focus |
Materials for a 16-spoke wire discone covering 130 MHz through 1.3 GHz — covers 2m, 70cm, and scanning
Building the 130 MHz Wire Spoke Discone
This guide builds a 16-spoke aluminium rod discone for 130 MHz–1.3 GHz using two 8-spoke arrays — one for the disc and one for the cone. The feedpoint is a chassis-mount SO-239 connector serving as the hub. Build the hub assembly on the bench first, then cut and attach the spokes.
Cut and Prepare the Spokes
Cut eight disc spokes to exactly 15 inches and eight cone spokes to exactly 21.5 inches from 1/4-inch aluminium rod. Precise length is important — the lower cutoff frequency is set directly by the cone spoke length, and all eight cone spokes must be identical. Use a fine-tooth hacksaw or aluminium-cutting blade in a mitre saw for clean, square cuts. After cutting, deburr all ends with a file and smooth with 220-grit sandpaper.
Drill a 9/64-inch hole through each spoke end at 1/2 inch from the tip — this is the mounting hole for the attachment screw. Drill perpendicular to the spoke axis. Use a drill press if available to keep holes aligned; a hand drill with care is also acceptable. Clean all aluminium shavings from the holes before assembly.
Build the Disc Hub Plate
The disc hub plate is a 3-inch diameter aluminium disc that holds the eight disc spokes and connects to the centre pin of the SO-239 feedpoint connector. The centre pin of the SO-239 is the connection point for the disc — the disc is the "hot" element connected to the coax centre conductor:
Assemble the disc hub plate with all eight spokes attached. The spokes should be equally spaced and all in the same horizontal plane — check by sighting down the assembly from above. Tighten all screws firmly with a wrench — loose spokes at VHF frequencies act as open stubs that disturb the impedance.
Build the Cone Hub Ring and Set the Cone Angle
The cone hub ring holds the eight cone spokes and connects to the SO-239 flange (the outer body, which connects to the coax shield). The cone spokes must angle downward at approximately 25–30° from horizontal — this angle is what sets the 50 Ω characteristic impedance of the discone:
Assemble the Feedpoint Hub
The feedpoint is the most critical part of the discone — it must provide a low-resistance, weatherproof connection between the disc (centre conductor), the cone (shield/ground), and the coax connector. The SO-239 chassis connector is the standard hub component for a homebrew wire discone:
Solder all electrical connections at the hub — the disc-to-centre-pin connection, the cone ring to flange, and any jumper wires. Use a high-power soldering iron and 60/40 rosin-core solder. Aluminium does not solder with standard solder — use copper jumpers or stainless steel screws to make the aluminium-to-SO-239 connections, soldering the copper parts only. Apply flux generously to all copper surfaces before soldering.
Bench Test with NanoVNA Before Mounting
Before mounting the discone on a mast, connect the NanoVNA and perform a bench sweep from 100 MHz to 1.3 GHz. The discone should show SWR below 2:1 across most of this range, with best match from the lower cutoff upward. A bench measurement with the discone sitting on a table is not perfectly representative of the installed antenna (nearby metal affects results), but it confirms the feedpoint assembly is correct and the dimensions are in the right range:
Mount on Mast and Weatherproof
The discone mounts on a standard antenna mast using a U-bolt bracket clamped to the coax connector housing or to a dedicated mast clamp plate bolted to the cone hub ring. Mount the antenna as high as practical — at VHF and UHF frequencies, height above local obstructions is the most important factor in receive performance. Orient the discone vertically with the disc on top and cone below.
Run the coax from the discone down the mast using cable ties every 18 inches. At the antenna end of the coax, form a drip loop — a downward U-bend in the coax just below the feedpoint connector that prevents water running down the coax into the connector body. Apply self-amalgamating tape over the coax connector body and any exposed coax connections, followed by a layer of electrical tape for UV protection.
Final SWR Verification and Performance Check
With the discone installed and the coax run to the shack, perform a final NanoVNA sweep from 100 MHz to 1.3 GHz. Compare with the bench sweep — the installed sweep should show equal or better SWR across the full range. Document the sweep with a photo or saved trace as a baseline for future troubleshooting.
For a quick practical performance check, connect a wideband receiver or SDR and scan through several frequency ranges: the 2m amateur band (144–148 MHz), the NOAA weather satellites (137 MHz), the aviation band (118–137 MHz), the 70cm amateur band (430–440 MHz), and cellular frequencies (700–900 MHz). Reception on all of these bands from a single antenna confirms the discone is performing as expected.
Where the Discone Excels
The discone's combination of wideband coverage, omnidirectional pattern, and vertical polarisation makes it the best single-antenna solution for several applications:
- SDR wideband monitoring: connected to an RTL-SDR, HackRF, or Airspy, a discone provides coverage from VHF through UHF on a single antenna — ideal for a station dedicated to spectrum monitoring, signal hunting, or general curiosity about the radio spectrum.
- VHF/UHF amateur base station: a discone covering 130 MHz to 1.3 GHz operates on 2m, 1.25m, 70cm, and 23cm from a single feedpoint — an all-band VHF/UHF base antenna without switching or separate antennas for each band.
- Scanner/airband monitoring: covers the entire civil aviation band (118–137 MHz), marine VHF (156–174 MHz), NOAA weather (162 MHz), railway communications, and all public safety bands in a single antenna.
- Portable or field station: a 144 MHz discone disassembles into spokes and a hub for transport, and reassembles in minutes at a field site. Useful for POTA, SOTA at VHF, or portable monitoring stations.
- No-tune operation: no ATU, no switching, no retuning between bands. Plug in and operate on any frequency in the range — the defining operational advantage of the discone over all alternatives.
Discone Limitations — When to Use Something Else
Understanding where the discone falls short helps set realistic expectations:
- Gain: at its lower cutoff frequency the discone has approximately 0 dBi gain — equivalent to an isotropic radiator. A 2m Yagi with 10 dBd gain will outperform the discone by 10+ dB in its favoured direction. For weak-signal work, satellite communication, or EME, a directional antenna is needed.
- Transmit power: a wire spoke homebrew discone handles 100W comfortably on 2m and 70cm. At higher power levels (500W+), the spoke connections and SO-239 hub can become the limiting component. Commercial discones are rated 200–300W continuous. For high-power transmit, a dedicated band-specific antenna is a better choice.
- HF coverage: a discone sized for 130 MHz lower cutoff does nothing useful below 100 MHz. Extending it to cover 50 MHz or 25 MHz requires a much larger structure (see dimensions table). For HF and 6m coverage from the same antenna, a log-periodic dipole array (LPDA) is a better wideband solution.
- Noise environment: an omnidirectional antenna receives noise from all directions equally. In a noisy urban environment, a discone picks up all local noise sources simultaneously. A directional antenna pointed away from noise sources (a Yagi or beam) provides better signal-to-noise ratio in noisy conditions.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| High SWR across entire frequency range — no flat region | Open circuit at feedpoint — disc not connected to SO-239 centre pin, or cone not connected to SO-239 flange | Check DC continuity from SO-239 centre pin to disc spokes; check continuity from SO-239 flange to cone spokes | Re-solder centre pin connection; tighten all flange bolts connecting cone ring to SO-239 body |
| SWR good from 200 MHz up but poor at 130–150 MHz | Normal — approaching the lower cutoff frequency; or cone spokes slightly short | Compare measured lower cutoff with expected f_low = 234/L_cone; if shifted high, spokes are slightly short | Accept lower cutoff shift of 5–10% as normal; if shift is larger, add small wire extensions to cone spoke tips |
| Deep SWR nulls at specific frequencies (narrow spikes) | One or more spokes are loose and resonating as an open stub at those frequencies | Grasp each spoke individually and wiggle — a loose spoke will shift the null when touched | Tighten all spoke attachment screws firmly with a wrench; apply thread-locking compound (Loctite) to prevent future loosening |
| SWR good at one point on compass, high at 180° | One cone spoke bent out of its correct angle — asymmetry in cone spoke angles | Sight down the cone assembly from below — one spoke pointing differently than the others is visible | Straighten or re-angle the deviant spoke to match the others; all cone spokes must be at the same angle from horizontal |
| Good SWR but poor receive sensitivity across all frequencies | High-loss coax or coax too long for the frequency range; or water in coax connector | Try connecting receiver directly to antenna with a short jumper coax — if sensitivity recovers, long coax is the problem | Replace with LMR-400 or equivalent low-loss cable; weatherproof all connectors; cut coax to minimum length needed |
| SWR degrades after several months outdoors | Corrosion at spoke-to-hub connections or at SO-239 connector contacts | Inspect all connections visually for white (aluminium oxide) or green (copper) corrosion deposits | Disassemble, clean all connections with fine sandpaper and contact cleaner, reassemble with anti-oxidation compound; re-weatherproof SO-239 with fresh self-amalgamating tape |
| Antenna physically unstable — spokes drooping or bending | Cone spokes too long or too thin for the spoke angle; or attachment screws not tight enough | Check that 1/4-inch rod is used — thinner rod (3/16-inch) droops at 21-inch length | Use 1/4-inch or 5/16-inch aluminium rod for spokes over 18 inches; add a fibreglass hoop at spoke tips to maintain cone shape and add rigidity |
Can I transmit on a homebrew discone?
Yes — a well-built wire spoke discone handles 100W continuous on 2m and 70cm without issue. The limiting components are the spoke-to-hub connections and the SO-239 connector. At 100W on 2m the current at the feedpoint is modest and the connectors remain cool. At 200W and above, verify that all connections are mechanically and electrically solid — loose or high-resistance connections heat up under sustained carrier at these power levels. For digital modes (FT8, WSPR) which transmit at 100% duty cycle, keep power at or below the antenna's rated level and check the hub for warmth after a 15-minute operating session.
How does the discone compare to a collinear for base station use?
A collinear antenna on a specific band (say, a 5/8-wave collinear on 2m) provides 3–6 dBi gain over the discone on that band by compressing the vertical radiation pattern — more of the power goes toward the horizon. The discone at its lower cutoff frequency has approximately 0 dBi gain. For a single-band base station application where maximum range matters, a collinear is the better choice on that band. For a multi-band or wideband application where coverage from VHF through UHF from a single antenna is needed, the discone is unbeatable — no collinear covers the same frequency range.
What is the minimum number of spokes for a usable discone?
Eight spokes (four disc, four cone) is the practical minimum. A four-spoke discone works but has noticeable azimuth variation in SWR and radiation pattern — the pattern is not truly omnidirectional with so few elements. Eight spokes per element produces an acceptably uniform pattern and impedance. Sixteen spokes (eight disc, eight cone) approaches the performance of a solid sheet metal discone and is the recommended configuration for a permanent installation. Beyond sixteen spokes the improvement is negligible for typical amateur and monitoring applications.
Can I use the discone on HF bands below its lower cutoff?
Below the lower cutoff frequency the discone's SWR rises sharply and it becomes an inefficient, unmatched antenna. An ATU can force a match but the radiated efficiency will be very poor — the antenna is far too small electrically for HF operation below its design range. For a 130 MHz discone, operation on 10m (28 MHz) is about five times below the lower cutoff — the antenna is essentially non-functional on HF. If HF coverage is needed alongside VHF/UHF, a separate HF antenna is required. The LPDA (log-periodic dipole array) is the closest wideband alternative that covers both HF and VHF from a single structure.
Should I use SO-239 or N-type connectors?
For a discone with an upper frequency limit below 500 MHz, SO-239/PL-259 connectors are adequate. Above 500 MHz the PL-259 connection begins showing increasing insertion loss and the connector body can resonate at UHF frequencies, causing SWR anomalies. For a discone intended to cover through 1.3 GHz (23cm), N-type connectors are strongly recommended — they maintain consistent 50 Ω impedance through 10 GHz and their weatherproofing is superior to the PL-259. The N-type connector costs slightly more but the performance difference at 70cm and 23cm is measurable. If your discone is purely for VHF (2m and below), SO-239 is perfectly adequate.
Do I need a balun on a discone?
No — the discone is an unbalanced antenna. The coax shield connects directly to the cone (the ground element), and the coax centre conductor connects to the disc. This is inherently an unbalanced feed configuration — no balun is needed or appropriate. Adding a current choke (ferrite beads on the coax below the feedpoint) can help prevent common-mode current from flowing on the outside of the coax shield if the antenna is installed near metal structures, but this is a common-mode choke, not a balun, and is optional rather than required for normal installations.