Build a 160m Vertical Antenna
A quarter-wave vertical for 160m stands 130 feet tall — taller than a ten-story building and beyond the reach of most amateur stations. Yet 160m is one of the most rewarding DX bands, with long-haul propagation at night, genuine challenge, and a dedicated community of operators who have invested in effective antennas. The solution for most amateurs is a shortened vertical: a physical structure of 50–80 feet made electrically equivalent to a full quarter-wave through top loading, base loading, or a combination of both. This guide covers the physics of shortened verticals, top-hat and capacity-hat design, base loading coil construction, matching networks, radial system requirements, and the complete installation procedure for a practical 160m vertical that can be built on a typical suburban or rural property.
Why 160m Verticals Are Always Shortened
At 1.83 MHz, a quarter-wave vertical is 130 feet (40 metres) tall. Almost no amateur station can erect a self-supporting structure that tall. The practical approach is to build a shorter vertical — typically 50–80 feet — and compensate for the missing electrical length using loading techniques that make the antenna behave as if it were taller:
Loading Methods — Top, Base, and Combination
Three loading methods are used to make a short physical structure resonate at 160m. Each has different effects on efficiency, bandwidth, and construction complexity:
Top Hat Design — Capacity Hat Dimensions
The top hat (capacity hat) consists of horizontal wires radiating outward from the top of the vertical element. These wires add capacitance to the top of the antenna, increasing its electrical height without increasing its physical height. The top hat does not radiate significantly — its purpose is purely to load the antenna:
Base Loading Coil Design
When a top hat alone is insufficient to bring the antenna to resonance at 1.83 MHz — which is almost always the case for verticals under 80 feet — a base loading coil is added in series with the antenna at the feedpoint. The coil adds inductive reactance that cancels the remaining capacitive reactance of the shortened antenna:
| Physical height | Loading method | Top hat | Effective el. height | Radiation R | Est. efficiency (good radials) | Notes |
|---|---|---|---|---|---|---|
| 130 ft | None — full size | None | 130 ft (100%) | 36 Ω | ~90% | Rarely achievable; benchmark reference |
| 80 ft | Top hat only | 4× 40 ft wires | ~108 ft (83%) | ~25 Ω | ~83% | Excellent; good efficiency; requires tall support |
| 65 ft | Top hat + base coil | 4× 30 ft wires | ~86 ft (66%) | ~15 Ω | ~75% | Recommended — practical for most rural sites |
| 55 ft | Top hat + base coil | 4× 25 ft wires | ~73 ft (56%) | ~10 Ω | ~65% | Good; typical push-up mast height |
| 50 ft | Top hat + base coil | 4× 20 ft wires | ~64 ft (49%) | ~7 Ω | ~55% | Minimum practical for serious 160m operation |
| 40 ft | Base loading only | None | 40 ft (31%) | ~2 Ω | ~25% | Poor efficiency; marginal for 160m DX |
| 65 ft | Base loading only | None | 65 ft (50%) | ~7 Ω | ~50% | Acceptable; 15–20 dB worse than full-size |
Materials for a 65-ft 160m vertical with 4-wire top hat and base loading coil
Building the 65-ft Top-Loaded 160m Vertical
This guide builds a 65-ft vertical with a 4-wire top hat and a base loading coil for 160m operation. Work in this order: radial system first, then vertical structure, then top hat, then coil, then matching. The radial system is the most labour-intensive part — do not shortcut it.
Install the Radial System
The radial system is the ground plane for the vertical — it has more impact on 160m antenna efficiency than any other single factor. On 160m, ground losses dominate antenna performance for shortened verticals. Every additional radial added to a sparse system produces a measurable improvement in efficiency and radiated signal. Install as many radials as you can before erecting the vertical:
Connect all radials to the central radial plate at the antenna base. Solder each radial wire to the plate or use stainless steel ring terminals crimped to the wire ends and bolted to the plate. The radial plate must make good electrical contact — clean all surfaces before connecting and apply an anti-oxidation compound to all joints.
Build and Wind the Base Loading Coil
The base loading coil is the most critical electrical component in the shortened 160m vertical. Its Q determines how much loss the coil adds to the antenna system — a high-Q coil is essential for acceptable efficiency. Build the coil before erecting the vertical so you can test and measure it on the bench:
Erect the Vertical Structure
The vertical element can be a self-supporting tower (Rohn 25G, Trylon, or similar), a guyed mast (aluminium tubing sections), or a push-up fibreglass mast with a wire element running alongside it or through it. Whatever structure is used, the vertical element must be insulated from the ground at the base — the base insulator keeps the antenna element isolated from the radial system ground plane, so that RF current flows through the coil matching network rather than directly to ground.
Erect the structure according to the manufacturer's specifications for the tower or mast type used. For a guyed mast, attach guys at 1/3 and 2/3 height using non-conductive guy sections (fibreglass rods or rope) for the inner 10 feet of each guy nearest the mast — this prevents the guys from detuning the antenna. The guys beyond this non-conductive section can be standard wire or synthetic rope.
Install the Top Hat
The top hat consists of four horizontal wires radiating outward from the top of the vertical element, each 30–35 feet long. Attach four fibreglass spreader arms (arrow shafts, kite spars, or commercial fibreglass rods) horizontally at the top of the mast, evenly spaced at 90° intervals. The spreader arms support the top-hat wires at their inner ends; the outer ends of the wires are supported by thin ropes to nearby trees or by additional fibreglass poles.
Connect the Base Coil and Find Resonance
Mount the loading coil at the base of the vertical, inside its weatherproof enclosure, between the base of the vertical element and the radial ground system. The coil is in series with the antenna: the bottom of the coil connects to the radial plate (ground), and the top of the coil connects to the base of the vertical element. The coax feedline connects across a portion of the coil or through a separate matching network.
Connect the NanoVNA to the base of the antenna through a temporary connection and sweep 1.6–2.0 MHz. Look for the resonance point — a minimum in the impedance magnitude curve. Adjust the coil tap (the number of turns in circuit) until resonance falls at 1.83 MHz. Each tap point adds or removes inductance and shifts the resonant frequency:
Build and Tune the Matching Network
With the antenna resonant at 1.83 MHz, the feedpoint presents a resistive impedance of approximately 15–25 Ω. An L-network transforms this to 50 Ω for the coax feedline. The L-network consists of a shunt capacitor across the feedpoint and a series inductor between the feedpoint and the coax, or vice versa depending on the impedance relationship:
Verify Performance and Weatherproof
With resonance and matching confirmed, perform a final check with the NanoVNA across the full 160m band (1.8–2.0 MHz). Document the SWR curve — a shortened 160m vertical has inherently narrow bandwidth, which is normal and expected:
Use WSPR on 160m for a week after installation to build a receive map of your radiated signal. WSPR spot maps provide an objective assessment of your antenna's effectiveness — comparing your spots against similar stations in your region shows how your antenna performs relative to other 160m installations.
The Shunt-Fed Tower
If you already have an HF tower for other antennas, shunt-feeding it for 160m is one of the most effective and lowest-cost approaches to a 160m vertical — the tower becomes the radiating element at no additional cost for the vertical structure itself:
- How it works: a gamma match or omega match connects a feed wire to the tower at a point approximately 1/4 to 1/3 of the way up. The tower is grounded at the base (the yagis, rotator, and feedlines are not disturbed). The matching network resonates and matches the shunt-fed tower to 50 Ω coax.
- Tower height: a 70-ft tower shunt-fed for 160m produces excellent results — the tower height of 54% of λ/4, combined with a good radial system, gives radiation resistance of approximately 10–15 Ω and competitive 160m performance.
- Existing antennas: the yagis and other antennas on the tower are part of the 160m radiating structure — they act as additional top loading. This inadvertent top loading often improves 160m performance beyond what the bare tower height alone would suggest.
- Reference: the W8JI website contains extensive practical information on shunt-feeding towers for 160m — one of the most thorough treatments of this technique in amateur literature.
Vertical Wire on a Fibreglass Mast — the Budget Option
For operators who want a 160m vertical without tower expense, a 65-ft push-up fibreglass mast with a wire radiator and top hat is a cost-effective and practical solution. Several commercial fibreglass mast systems are designed for exactly this application:
- Spiderbeam 18m mast: a 60-ft heavy-duty fibreglass push-up mast widely used for 160m verticals. Non-conductive, light enough to erect single-handed, and takes wind loading well when guyed properly. A copper wire runs alongside the mast and serves as the radiating element.
- Jackite 31-ft telescoping pole: two sections nested together give 50 ft — compact storage, quick deployment, and popular for Field Day and portable 160m operation.
- Top hat attachment: at the top of the fibreglass mast, four fibreglass spreader arms (fishing rods work well) are attached horizontally, and the top-hat wires run from the spreader tips back to anchor points on the ground at 30–35 ft radius. The pull of the top-hat wires actually helps tension the mast — a self-guying effect.
- Cost: a 60-ft fibreglass mast costs $150–300. A homebrew 160m vertical on a fibreglass mast with 60 radials and a base coil can be built for $300–400 total and will outperform many commercially marketed 160m antenna systems.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| Cannot find resonance anywhere in 1.6–2.0 MHz sweep | Open circuit in vertical element, top hat not connected, or coil open | Check continuity from coax feedpoint through coil to top hat tip; verify top hat wires connect at mast top | Repair open connection; verify all solder joints; check coil continuity end-to-end |
| Resonance found but very broad and shallow — low Q | High ground resistance (poor radial system) or low-Q loading coil | Measure ground resistance with ohmmeter from radial plate to remote ground stake — should be under 5 Ω | Add more radials; re-wind loading coil with heavier wire on larger form; check for moisture in coil enclosure |
| Resonance too low — well below 1.8 MHz | Too much inductance in coil; or top hat longer than needed | Remove turns from coil (move tap upward) and re-measure; if resonance still too low, shorten top hat wires | Remove turns 5 at a time until resonance reaches 1.83 MHz; trim top hat if coil is already at minimum |
| Resonance too high — above 2.0 MHz | Too little inductance; or top hat too short | Add turns to coil and re-measure; check top hat wire connections at mast top | Add turns to coil; extend top hat wires; verify top hat connection to vertical element |
| SWR acceptable initially but rises within weeks | Corrosion at radial plate connections or base coil connections; moisture in coil | Inspect all base connections visually; check for green oxidation or white corrosion deposits | Clean all connections with wire brush; apply anti-oxidation compound; re-solder any suspect joints; reseal coil enclosure |
| Good SWR but poor signal reports — low efficiency | Inadequate radial system; coil Q too low; or base insulator leakage | Use WSPR to compare with known-good stations; add radials and measure again; check coil Q | Add radials to minimum of 32; replace loading coil with higher-Q version; clean or replace base insulator if cracked or dirty |
| SWR good at low power but rises at 100W | Arcing in matching network capacitor or coil tap contact | Listen for arcing during transmit key-down; inspect capacitor and coil tap for burn marks | Replace capacitor with higher-voltage-rated unit; clean or replace coil tap contact; verify all connections are properly soldered |
How many radials do I really need for 160m?
The practical minimum for a workable 160m vertical is 16 radials — below this number the ground loss dominates the system and efficiency is poor. For serious 160m operation, 60 radials is the commonly cited target that provides most of the benefit available from a radial system without excessive labour. Above 120 radials the improvement per additional radial is very small. The most important factor is getting radials in the ground — even 32 radials of 50-foot length makes a dramatically better antenna than 4 radials of 100-foot length. Prioritise count over length up to about 32 radials, then prioritise length for additional radials beyond that.
Can I use my 80m antenna on 160m with a tuner?
An 80m dipole or EFHW can be pressed into service on 160m with an ATU, but efficiency will be very poor — the antenna is extremely short electrically on 160m and the feedline loss at high SWR can be severe. A 66-ft 80m dipole on 160m presents a very low impedance with enormous capacitive reactance at the feedpoint, and an ATU that can match this is working at the limits of its range. It is usable for occasional 160m contacts on strong openings but is not a substitute for a dedicated 160m antenna. For regular 160m operation, even a modest dedicated vertical outperforms any 80m antenna pressed into double-duty on 160m.
How narrow is the bandwidth of a shortened 160m vertical?
A 65-ft top-loaded vertical typically has a 2:1 SWR bandwidth of 20–40 kHz — covering either the CW segment or the phone segment but not both simultaneously. This is inherent to the antenna's low radiation resistance and is not a construction flaw. To cover more of the band, an ATU at the feedpoint can be used to retune the system across the full 160m allocation. Alternatively, a relay-switched capacitor at the base can shift resonance 40–60 kHz on command from the shack — allowing instant switching between the CW and phone segments. Taller verticals (80–100 ft) have broader bandwidth and often cover the entire 160m allocation within a 2:1 SWR circle.
Is a 160m vertical better than a dipole?
For DX, yes — almost always. A vertical on 160m has low-angle radiation that travels along the earth's surface (ground wave) and radiates at low angles for skywave DX. A dipole at typical amateur heights (under 100 feet) on 160m radiates primarily straight up — good for regional NVIS contacts but weak at the low angles needed for transcontinental DX. The strongest 160m DX stations run tall verticals or arrays of verticals over extensive radial systems. A 65-ft vertical with 60 radials, even with its efficiency losses, typically outperforms a 135-ft 80m dipole for 160m DX because of this low-angle radiation advantage.
What is the best loading method if I can only build a 50-ft vertical?
For a 50-ft vertical on 160m, a combination of top loading and a base coil gives the best efficiency. First maximise the top hat — four wires of 25–30 ft each, and add a second set of four shorter wires if space allows. This brings the effective electrical height to approximately 65–70 ft. Then add a base coil to resonate the remaining capacitive reactance. A base-coil-only approach on a 50-ft vertical without a top hat produces much lower efficiency because the current distribution along the short wire is non-uniform, reducing effective radiation resistance. Even a modest top hat of four 15-ft wires provides a meaningful improvement over base loading alone.
How does the 160m vertical perform on 80m?
A 65-ft 160m vertical is approximately a half-wave on 80m — a reasonable antenna on 80m without modification. The loading coil and matching network designed for 160m are not in the correct configuration for 80m, so you will need either a separate 80m feedpoint that bypasses the 160m loading coil, or a relay that shorts out the loading coil for 80m operation. Many 160m vertical operators add a second relay at the base — when energised, it shorts the loading coil and connects the coax directly to the base of the vertical for 80m operation. This gives a single antenna system covering both 160m and 80m with relay switching between bands.