Build an 80 Meter Base-Loaded Vertical Antenna
A true quarter-wave vertical on 80m is roughly 62 feet tall — well beyond what most residential installations can support. The base-loaded vertical solves this by combining a shorter physical mast (typically 25–33 ft) with a loading coil at the base that electrically extends the antenna to resonance. The trade-off is a somewhat reduced radiation resistance and a narrower bandwidth than a full-size vertical, but for most operators this is the only practical way to get an effective 80m vertical into a normal-sized yard. This guide covers sizing the loading coil, building a solid ground/radial system to compensate for the reduced radiation resistance, and tuning the finished antenna for the phone or CW portion of the band.
Why Base-Loading Is Necessary at 3.75 MHz
A full-size quarter-wave vertical for 80m is impractical for the vast majority of installations, which is why nearly every homebrew and commercial 80m vertical uses a shortened, loaded design instead:
Sizing the Loading Coil
The loading coil must supply enough inductive reactance to cancel the capacitive reactance of the "missing" top section of the antenna — the length between your actual physical mast height and the full 62.4 ft electrical quarter-wave:
Center-loading (coil partway up the mast rather than at the base) is slightly more efficient for the same coil Q, since it places the coil where element current is higher — but base-loading is mechanically simpler and is what this guide builds. If you have the mechanical means to support a center-loading coil partway up a two-section mast, it is a worthwhile upgrade once the base-loaded version is working.
Why the Ground System Matters More on 80m
A shortened, loaded vertical has meaningfully lower radiation resistance than a full-size quarter-wave — often 15–25 Ω instead of the theoretical 36 Ω of a full-size design over perfect ground. Ground/radial loss resistance that would be a rounding error on a full-size vertical becomes a much larger fraction of total resistance on a loaded design, directly costing you real transmitted power:
- Minimum viable system: 8 on-ground radials, each 60–66 ft if space allows (shorter radials still help — see FAQ).
- Recommended: 16+ radials for a meaningful efficiency gain over 8.
- Space-constrained lots: elevated radials (4 at full quarter-wave length, raised a few feet off the ground) are a strong alternative when a full on-ground radial field won't fit.
Construction Options
- Aluminum tubing mast + base coil box: telescoping aluminum sections (common: 2 in OD base tapering to 3/4 in tip) totaling 28 ft, with the loading coil housed in a weatherproof box at the base between the mast and the ground mount. The most durable, most common homebrew approach.
- Military-surplus or push-up mast + wire: a surplus push-up mast (many hams use 25–33 ft steel or fiberglass push-up masts) with a wire element taped along its length, feeding into the same base coil arrangement. Lower cost, slightly more wind-sensitive.
- Commercial resonator-style: several commercial multi-band vertical systems (e.g. Hustler-style resonators) use exactly this base-loaded principle with a purpose-built coil/whip combination — useful as a reference for coil dimensions if you want to cross-check your homebrew coil against a known commercial design.
| Target frequency | Band segment | Full q-wave (ft, reference) | Loading coil (uH, 28 ft mast) | Notes |
|---|---|---|---|---|
| 3.525 MHz | CW center | 66.4 ft | ~21.6 uH | Cut/wind here for CW-only operation |
| 3.600 MHz | CW/digital | 65.0 ft | ~20.9 uH | Common digital-mode segment |
| 3.750 MHz | Phone center (recommended) | 62.4 ft | ~19.7 uH | Best all-band compromise for mixed operation |
| 3.900 MHz | Phone (upper) | 60.0 ft | ~18.6 uH | Common phone operating segment |
| 4.000 MHz | Band top | 58.5 ft | ~17.9 uH | Upper edge — not recommended as sole design point |
Vertical 80m Calculator
This design has published dimensions for more than one band. The default shown below is the first/most common one on the page -- change the frequency and recalculate for the other bands.
A note on narrow bandwidth
Materials for an 80m base-loaded vertical with 16-radial ground plane
What the NanoVNA Will Show
A loaded 80m vertical presents lower feedpoint resistance than a full-size design, and the exact value depends heavily on your ground system quality:
Guying and Mechanical Considerations
- 28 ft is genuinely tall: plan for at least one guy point around 18–20 ft and, ideally, a second near the top. Non-conductive guy line (Dacron/polyester rope) is preferred to avoid detuning the element.
- Loading coil box placement: keep the coil box a few inches off the ground on a small stand or the base mount itself — direct ground contact invites moisture ingress and corrosion at the coil taps.
- Wind load: a 28 ft tapered aluminum mast has meaningfully more wind load than the shorter verticals in this series — verify your base mount and guy anchoring are rated accordingly, especially in areas with regular high wind or ice loading.
Building the 80m Base-Loaded Vertical
This guide builds a ground-mounted, base-loaded aluminum vertical with a 16-radial on-ground system. Winding and trimming the loading coil is the step most different from a full-size vertical build — take it slowly.
Select the Site and Plan Guying and Radials
Choose a site with at least 60 feet of clear ground in one or more directions for radials, plus room for 1-2 guy points around the mast. Unlike the shorter verticals in this series, both the mast height and radial length here demand more space — a corner of a larger yard, or a site backing onto open space, works best.
Wind the Loading Coil
Wind the loading coil on a 3-4 inch diameter PVC form using #12-14 AWG enameled or insulated wire. Start with roughly 15% more turns than your calculated target (for 19.7 uH at 28 ft/3.750 MHz, wind for approximately 23 uH) so you have room to remove turns during tuning rather than needing to unwind and rewind entirely. Space turns evenly and secure the winding with cable ties or a clear coat of exterior varnish once tuning is complete.
Build the Base Coil Box and Feedpoint
House the coil in a weatherproof enclosure mounted at the top of the base mount, below where the aluminum mast sections begin. Bring the coil's lower end to an SO-239 feedpoint connector (center pin) and the upper end to the mast's bottom section. The radial hub connects to the SO-239 shell, same as a full-size vertical.
Assemble the Mast and Radial System
Assemble the telescoping aluminum sections to a total height of 28 ft above the coil box, securing each joint per the tubing manufacturer's clamps or set screws. Run 16 radials of #14 AWG copper at approximately 60 ft each (or your best available length) from the radial hub, spaced at 22.5° intervals, staked flat to the ground every 6-8 feet.
Raise the Mast and Install Guys
Raise the assembled mast into the base mount with at least one helper — 28 ft of aluminum is not a one-person lift safely. Attach guy lines at the planned point(s) using non-conductive rope, tensioning evenly in three directions. Install the current choke (5-6 turns of coax through an FT-240-31 toroid) at the feedpoint before final weatherproofing.
Initial SWR Measurement
Connect the NanoVNA at the shack end of the coax. Sweep 3.4-4.1 MHz and locate the SWR minimum.
Trim the Coil Tap to Final Resonance
Using your tap points from Step 2, move the active tap by one turn at a time and re-measure. Unlike trimming a full-size element's length, this is a reversible, low-labor adjustment — take advantage of that to sweep several tap positions before soldering the final connection permanently.
Verify Final SWR and Weatherproof
Weatherproof the coil box thoroughly with silicone sealant at all cable entries, and self-amalgamating tape at the SO-239 connection. Install a ground rod at the base connected to the radial hub for lightning protection, and a coax lightning arrestor at the shack entry.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No SWR dip visible across 3.4-4.1 MHz | Coil tap or feedpoint wiring fault | Check continuity from coax center through the coil tap to the mast base | Re-verify coil winding direction and tap solder joints |
| SWR minimum far below 3.750 MHz even at minimum turns | Coil wound with too much inductance for this mast height | Compare actual turns count against the calculated starting point | Remove turns in larger steps; verify mast height matches your design assumption |
| Bandwidth is extremely narrow (usable SWR under 40 kHz wide) | Coil Q too high relative to radiation resistance, or poor ground system | Compare against expected bandwidth in this guide's SWR table | Improve the radial system first — low radiation resistance narrows bandwidth further when ground losses are high |
| Good SWR but noticeably weak signal reports vs full-size verticals | Reduced radiation resistance combined with an inadequate ground system | Compare WSPR/FT8 spots against similarly-powered full-size vertical stations | Add radials — this design is far more sensitive to radial count than a full-size vertical |
| Resonance drifts noticeably with temperature or humidity | Coil form or winding absorbing moisture | Compare SWR readings dry vs. after rain | Seal the coil box more thoroughly; consider a coil form rated for outdoor RF use |
Why not just build a full-size 62 ft vertical instead?
If you genuinely have the space and support structure (a tall tree, an existing tower, or a very large lot), a full-size 80m vertical is more efficient and has meaningfully wider bandwidth than any loaded design. This guide exists because most residential installations cannot accommodate 62+ feet of self-supporting or guyed structure. If a full-size option is available to you, it's the better-performing antenna — the base-loaded design here is the practical compromise for everyone else.
Can I use shorter radials than the recommended 60 ft?
Yes — radials shorter than a full quarter-wave still contribute significantly, just with somewhat reduced effectiveness per radial. A radial at half the recommended length still captures a meaningful fraction of the benefit. If your lot only accommodates 30-40 ft radials in some directions, use what fits rather than skipping radials in those directions entirely — more shorter radials generally outperforms fewer full-length ones when space is the limiting factor.
Is base-loading or center-loading better?
Center-loading (placing the coil partway up the element rather than at the base) is slightly more efficient for a given coil Q, because it positions the coil where element current is higher, reducing the fraction of power dissipated in the coil's resistance relative to power radiated. The difference is real but modest — often under 1 dB in practice for a well-built coil either way. Base-loading is significantly simpler to build and service, which is why it's the more common homebrew approach and the one this guide builds.
How much does the loading coil reduce efficiency?
Every loading coil has some resistive loss, which reduces radiated power compared to a lossless full-size element. A well-built air-core coil with heavy-gauge wire and a Q of 200+ typically costs only a modest fraction of a dB in a base-loaded design at this height — the bigger efficiency factor by far is the ground/radial system, not the coil itself. Prioritize radial count and coil construction quality (thick wire, air-wound rather than tightly packed on lossy plastic) over chasing the last percentage point of coil Q.
Can this design work on 160m and 80m together?
Not with a single fixed coil — the 160m band needs substantially more loading (160m's full quarter-wave is roughly double 80m's). Some builders use a relay-switched second coil tap or a separate tap point to add extra turns for 160m operation, effectively making this a switchable dual-band loaded vertical. That's a meaningful step up in build complexity from this guide's single-band design — worth attempting once the 80m version is proven and working well.
What mast height should I use if 28 ft doesn't fit my property?
The dimensions table in this guide gives the reference calculation for a 28 ft mast — the same loading-coil approach scales to other heights. A shorter mast (say, 20 ft) needs a larger coil (more missing length to compensate for); a taller mast (say, 35 ft) needs a smaller one. As a rule of thumb, shorter physical heights trade coil size and Q-related loss for mechanical convenience — there's a practical floor around 15-18 ft below which the coil losses start becoming a significant fraction of your total system loss.