Antennas · Volume 15
Receive-only Loops & Specialty Receive Antennas
K9AY, beverage, terminated flag / pennant / EWE, ferrite-rod, active receive loops (Wellbrook ALA1530, LZ1AQ, Bonito MegaLoop) — antennas built for SNR, not radiated power
Contents
1. About this volume
Every other antenna in Vols 6-14 was designed for transmit — the goal was efficient radiation of an applied signal at the operating frequency. This volume is different: the antennas here are intentionally lossy because the loss is the noise rejection. A 30 m beverage has 20–30 dB less absolute output than a comparable dipole — but the signal-to-noise ratio (SNR) is 10–15 dB better because external atmospheric noise dominates the noise floor on the lower amateur bands, and a directional receive antenna rejects the noise from off-axis directions.
This is the central insight of receive-optimized antenna design: on HF below ~14 MHz, external noise (atmospheric, man-made, ionospheric) is at least 20 dB above the typical receiver’s internal noise. The receiver’s noise figure doesn’t matter; the antenna’s directional rejection of off-axis noise sources is what determines SNR. A more “sensitive” antenna (higher gain, broader pattern) picks up more noise from all directions, drowning the wanted signal. A less “sensitive” antenna (lower gain, sharper directional pattern) picks up less noise, lifting the wanted signal out of the noise floor.
This volume covers six families of receive-optimized antennas:
- Beverage (§3): the king of low-band receive. 1–4 wavelengths of horizontal wire, terminated at the far end. Sharp end-fire cardioid pattern with 20–25 dB F/B. Used by serious 160 m / 80 m DXers.
- K9AY loop (§4): small terminated loop with directional null. 25–30 ft of wire in a diamond shape. The “small lot” answer to the beverage.
- Flag and pennant (§5): rectangular terminated loops in very small footprints (10–15 ft per side). The most compact directional receive antennas.
- EWE (§6): truncated beverage, fed at one end through a 9:1 transformer. Compromise between K9AY and beverage.
- Ferrite rod / loopstick (§7): the AM-radio antenna. Tiny ferrite-cored coils, excellent for portable shortwave receivers.
- Active receive loops (§8): 0.5–1 m diameter loop + integrated low-noise amplifier (LNA). The Wellbrook ALA1530, LZ1AQ, MLA-30+ — the modern SDR-receive antennas.
Phased arrays of receive antennas (combining two beverages or two K9AYs with electronic switching) are covered in §9 and cross-referenced to Vol 32 (Antenna farms).
This volume closes Phase 3 of the Antennas deep dive (the wire-and-air cluster, Vols 6-15). The next phase (Phase 4) covers matching networks — Vol 16 (BALUNs / UNUNs), Vol 17 (Antenna tuners), Vol 18 (Passive splitters), Vol 19 (Active splitters / preamps).
2. Geometry & theory — antennas optimized for SNR
2.1 The external-noise dominance regime
The HF noise floor at a typical amateur location:
| Frequency | Atmospheric noise (dBμV/m/Hz) | Man-made noise (urban) | Typical receiver NF |
|---|---|---|---|
| 1.8 MHz (160 m) | -5 | -5 | -130 (NF = 10 dB) |
| 3.5 MHz (80 m) | -10 | -8 | -130 |
| 7 MHz (40 m) | -15 | -12 | -130 |
| 14 MHz (20 m) | -25 | -18 | -130 |
| 21 MHz (15 m) | -35 | -22 | -130 |
| 28 MHz (10 m) | -45 | -28 | -130 |
| 144 MHz (2 m) | -85 | -55 | -135 |
| 432 MHz (70 cm) | -100 | -65 | -140 |
On 160 m and 80 m, atmospheric noise + man-made noise is 100+ dB above the receiver’s internal noise. Even on 20 m, external noise is 70+ dB above receiver NF. On 2 m and above, the receiver’s NF starts to dominate because external noise drops to near-receiver-noise levels.
On HF below 14 MHz, the receiver’s noise figure is irrelevant. The antenna’s ability to reject off-axis noise is what determines SNR.
2.2 The “intentionally lossy” insight
A receive antenna with 30 dB of loss (relative to a dipole) but with a 25 dB front-to-back ratio gives:
- Forward signal: -30 dB (lossy)
- Forward noise: -30 dB (lossy)
- Backward noise: -30 - 25 = -55 dB (lossy + F/B rejection)
- Net SNR improvement: 25 dB (the F/B advantage)
The wanted signal arrives from the forward direction; the noise arrives from all directions (mostly the back of the antenna due to the geometry of typical noise sources). The 30 dB of “loss” is absorbed equally by signal and forward noise (cancels in the SNR ratio); the 25 dB F/B rejection is pure SNR improvement.
This is intentional — receive antennas are designed with high loss to enable directional rejection. The trade is unavailable to transmit antennas (transmit needs efficiency); receive antennas can afford to throw away absolute signal level for directional benefit.
2.3 The termination resistor as the design feature
Most receive-only antennas have a termination resistor at one or both ends. The resistor absorbs the energy that would otherwise reflect back along the antenna, killing the standing wave that would create a bidirectional pattern. With the resistor present:
- Forward wave: travels through the antenna, picked up by the feedpoint at the near end
- Backward wave: absorbed by the resistor at the far end, never reaches the feedpoint
- Net pattern: cardioid (one direction strong, the opposite direction nulled)
Without the termination resistor, the antenna would have standing waves and a bidirectional pattern (figure-8 pickup). The termination resistor converts a bidirectional antenna into a directional one — at the cost of dissipating energy in the resistor.
The termination resistor’s value matches the antenna’s characteristic impedance (~470 Ω for a beverage, ~900 Ω for a flag/pennant). The resistor is typically 2–5 W rated (since it dissipates only receive-level energy from the small forward signal). Non-inductive wire-wound or metal-film resistors work; carbon-composition is poor (inductive at HF).
2.4 Active vs passive receive antennas
Two design philosophies:
- Passive: a properly-sized antenna picks up enough signal that the receiver’s preamp can amplify it without contributing significant noise. Beverages, K9AYs, flags, EWEs are passive.
- Active: a small antenna picks up little signal, but an integrated low-noise amplifier (LNA) at the antenna boosts the signal above the local noise level before sending it down the coax to the receiver. Wellbrook, LZ1AQ, MLA-30+ are active.
The active approach is the right answer when:
- The antenna is constrained by space (need a small loop)
- The signal of interest is below the receiver’s sensitivity threshold (very weak DX)
- The local noise level is moderate (allowing the LNA to lift signal above receiver noise without amplifying coax loss to dominate)
The passive approach is the right answer when:
- Space is available (beverage needs 30+ m of straight wire)
- The local noise is high enough that signals are well above receiver noise anyway
- The operator wants the simplest possible signal chain (no LNA failure mode)
3. The beverage — long terminated wire, the king of low-band receive
3.1 The 1921 design
Harold Beverage and partners (RCA, 1921) developed the beverage antenna for transatlantic radio reception — RCA’s commercial point-to-point services on 50–500 kHz benefited from the beverage’s directional rejection of European noise. The antenna’s design hasn’t changed in 100+ years; the canonical specification:
- Length: 1 to 4 wavelengths at the operating frequency
- Height above ground: 1.5–3 m (just above head height)
- Conductor: insulated single wire (#14 to #20 AWG)
- Far end terminated in ~470 Ω (matching the antenna’s characteristic impedance)
- Fed at the near end through a 9:1 UNUN to 50 Ω coax
Side view of a beverage:
● feedpoint (9:1 UNUN to 50 Ω coax) ←──── desired signal direction
│
│
─────────────────────────────────────────● far end (470 Ω termination
to a ground rod)
↕ 1.5-3 m above ground (or supported on small wooden posts)
═════════════════════════════════════════════
groundThe wire is not horizontal — it’s slightly inclined upward (toward the feedpoint) or downward (toward the termination). This is a subtle but real design choice that affects the pattern.
3.2 Beverage performance
A 1λ beverage on 80 m (80 m of wire):
| Property | Typical value |
|---|---|
| Forward gain | -5 to -15 dBi (yes, negative — beverages are lossy) |
| F/B ratio | 20–25 dB |
| HPBW | 50–70° (broad-ish) |
| Bandwidth | 2:1 — quite wide because the antenna is non-resonant |
| Polarization | horizontal (the wire’s orientation) |
| SNR improvement vs dipole | 8–15 dB on most QSOs |
The “negative gain” of a beverage looks bad until you remember that the SNR is what matters. The dipole has more gain but picks up noise from all directions; the beverage has less gain but only picks up noise from the forward direction. Net SNR is 10+ dB better with the beverage.
3.3 The “real estate” requirement
A 1λ beverage on 160 m is 160 m of wire — usually impractical. A 1λ beverage on 80 m is 80 m. A 1λ beverage on 40 m is 40 m. Most amateur installations use fractional-wavelength beverages:
| Beverage length | Approximate fractional wavelength on 80 m | F/B |
|---|---|---|
| 100 ft (30 m) | 0.38λ | 12–15 dB |
| 200 ft (60 m) | 0.75λ | 18–22 dB |
| 300 ft (90 m) | 1.1λ | 22–28 dB |
| 600 ft (180 m) | 2.25λ | 25–30 dB |
| 1000 ft (300 m) | 3.75λ | 28–32 dB |
For 80 m, 200–300 ft of beverage is the practical sweet spot. For 160 m, 500–1000 ft beverages are common at serious-DX stations (the cost of 1000 ft of #14 wire + termination + posts is ~$200, which is the cheapest “directional 160 m antenna” available).
3.4 Why beverages dominate low-band DX
For serious 160 m and 80 m DXing, the beverage is the receive antenna because:
- The bandwidth is wide enough for any QSO (no retuning ever)
- The F/B ratio is 20–30 dB (rejection of QRN from the opposite direction)
- Multiple beverages in different directions are inexpensive (~$50 each in materials)
- A switching matrix selects which beverage to use per QSO (e.g. “north beverage for European DX, south beverage for South American DX, east beverage for African DX”)
ON4UN’s “Low-Band DXing” (the bible for 160/80m DXing) devotes substantial coverage to beverage antennas because they’re the difference between making and missing DX QSOs.
4. The K9AY loop — small terminated loop with directional null
4.1 The 1995 design
Gary Breed K9AY (1995) developed the K9AY loop as a “beverage substitute for small lots.” The geometry:
- 25–30 ft of wire in a diamond shape (4 sides, all equal length)
- Each diagonal of the diamond ~8–10 ft
- Top corner ~10–15 ft above ground; bottom corner ~5 ft above ground
- Termination resistor (470 Ω) at one bottom corner
- Feedpoint at the opposite bottom corner, via a 9:1 transformer to 50 Ω
K9AY loop (front view, looking along its axis):
● top corner (10-15 ft up)
╱ ╲
╱ ╲
╱ ╲
╱ ╲
╱ ╲
╱ ╲
● ●
feedpoint termination
(9:1 to coax) (470 Ω resistor)
bottom bottom
corner corner
~5 ft up ~5 ft up
═══════════════════════════════════════
groundThe K9AY’s cardioid pattern: gain peaks in the direction toward the termination, deep null in the direction toward the feedpoint. F/B = 25–30 dB at the design frequency.
4.2 K9AY performance
| Property | Typical value |
|---|---|
| Forward gain | -25 to -35 dBi (very lossy) |
| F/B ratio | 25–30 dB |
| HPBW | 90° (broad — useful for general-direction listening) |
| Bandwidth | 2:1 — wide (non-resonant) |
| Polarization | vertical (the loop’s geometry) |
| SNR improvement vs dipole | 10–15 dB on 160/80 m |
The K9AY is the “small lot beverage substitute” — a 25 ft × 30 ft footprint instead of 200+ ft. Performance is slightly worse than a full beverage (F/B is similar, but HPBW is broader so noise rejection is less precise) but the size advantage is decisive for any amateur on a small lot.
4.3 Two K9AYs at right angles = steerable
The standard K9AY installation is two K9AY loops at 90° to each other, with a phasing/switching box that selects which is active and electronically swaps the termination-resistor end (which flips the pattern direction). With two loops and the switching, the operator can select between 4 directions:
- Loop 1, normal: NE
- Loop 1, swapped: SW
- Loop 2, normal: SE
- Loop 2, swapped: NW
Four directions of cardioid pattern from two loops in a 30 ft × 30 ft footprint. This is the K9AY’s signature feature — directional receive with electronic switching, no rotator required.
5. Flag and pennant — terminated loops in small footprints
5.1 The geometric family
Flags and pennants are rectangular terminated loops in even smaller footprints than K9AYs:
- Flag: rectangular loop, ~14 ft × 5 ft (e.g. 14 ft long × 5 ft tall, vertical orientation)
- Pennant: triangular loop, ~14 ft × 5 ft (one side replaced with a diagonal)
- Termination resistor (~900 Ω) at one corner
- Feedpoint at the opposite corner via 16:1 transformer
The flag and pennant are the most compact of the terminated receive loops — 14 ft × 5 ft fits in spaces where a 30 ft K9AY won’t.
Flag antenna (side view):
●─────────────● feedpoint
│ │
│ │
│ │
│ │
│ │
│ │
│ │
●─────────────● termination resistor (~900 Ω)
14 ft tall × 5 ft wide5.2 Performance
| Property | Typical value (flag at 80 m) |
|---|---|
| Forward gain | -30 dBi (extremely lossy) |
| F/B ratio | 25–35 dB |
| HPBW | 100° (very broad) |
| Bandwidth | wide (non-resonant) |
| Polarization | vertical |
| SNR improvement vs dipole | 8–12 dB on 80 m |
The flag and pennant trade more loss for tinier footprint. For a renter or apartment dweller who has a 14 ft × 5 ft outdoor space, a flag is the only directional 80 m receive antenna option short of an active loop (§8).
5.3 Flag vs pennant difference
The pennant variant (triangular loop with one diagonal side) has slightly cleaner pattern symmetry and slightly better F/B (~2 dB more). The flag is mechanically simpler (rectangular geometry). For most amateur use, the flag is the default; pennants are for serious low-band-DX optimization.
6. EWE — Earl Cunningham’s truncated beverage
6.1 The 1995 design
Earl Cunningham (1995) developed the EWE as a “low-height beverage substitute.” The geometry:
- 30–40 ft of horizontal wire at 7–12 ft height
- Both ends terminated (left end has 9:1 transformer + 50 Ω coax; right end has 470 Ω resistor)
- Fed at one end through a 9:1 transformer
- Optionally uses ground rods at both ends for the termination network
EWE antenna (side view):
●━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━●
│ feedpoint │ termination
│ (9:1 to coax) │ (470 Ω + ground)
↕ ~7-12 ft above ground ↕
═══════════════════════════════════════════
ground6.2 EWE performance
| Property | Typical value |
|---|---|
| Forward gain | -20 dBi |
| F/B ratio | 18–22 dB |
| HPBW | 70° |
| Bandwidth | wide |
| Polarization | mostly horizontal |
| Footprint | 30–40 ft wide |
The EWE is a compromise between beverage and K9AY: shorter than a beverage (30–40 ft vs 200+ ft), simpler than a K9AY (single horizontal wire instead of a diamond shape), better F/B than a flag. For amateur use where the operator has 30–40 ft of clear space but not 200+ ft, the EWE is the right size.
7. Ferrite-rod / loopstick — the AM-radio antenna
7.1 The geometry
A ferrite-rod (or “loopstick”) antenna is a coil wound on a high-permeability ferrite core. The ferrite focuses the magnetic field, allowing a small antenna to have significant inductance and acceptable receive sensitivity at low frequencies (AM broadcast, LF, MF).
Ferrite-rod antenna:
●═════════════════════════════════════════● ferrite rod (5-30 cm long)
╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱
╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱
╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱ ← winding (50-200 turns of fine wire)
╱ ╱ ╱ ╱ ╱ ╱ ╱ ╱
to receiver input
(high impedance —
typically tuned tank circuit)7.2 Where ferrite rods win
The ferrite rod is the canonical AM-broadcast-band receive antenna. Inside every transistor radio of the last 60 years is a ferrite-rod antenna for the AM band (540–1600 kHz). Properties:
- Compact (5–20 cm typical, vs 75 m for a quarter-wave at 1 MHz)
- Vertically-polarized when the rod is horizontal (the loop coil is perpendicular to the rod)
- Figure-8 pattern with deep nulls
- Excellent for portable shortwave receivers (Tecsun, Sony, Eton models all use ferrite rods)
- Good for receiving lightning sferics on LF/VLF
The ferrite rod is not a transmitting antenna (very low radiation resistance) — strictly receive-only.
7.3 The SDR receive application
For SDR receive on AM broadcast / LF / MF, a ferrite-rod antenna is sometimes preferred over a discone or wire — the ferrite rod’s directional pattern allows the operator to null out a strong unwanted local AM station while listening to a weaker distant station. The Tecsun H-501, Sony ICF-2010, and similar portable shortwave receivers ship with built-in ferrite-rod antennas.
8. Active receive loops — Wellbrook ALA1530, LZ1AQ, Bonito MegaLoop
8.1 The active-loop concept
An active receive loop is:
- A small loop antenna (typically 0.5–1.0 m diameter)
- A low-noise amplifier (LNA) at the feedpoint
- A bias-T at the shack end that delivers DC power up the coax to the LNA
- A 50 Ω output ready for any receiver
The LNA’s job: amplify the loop’s tiny received signal up to a level where coax loss and receiver NF don’t dominate. The loop alone has very low radiation resistance and would produce a signal below the receiver’s sensitivity threshold; with the LNA, the antenna’s effective noise figure is set by the LNA (typically 0.5–2 dB) and the local noise floor.
8.2 The dominant commercial products
| Product | Frequency | LNA NF | Price (mid-2026) |
|---|---|---|---|
| Wellbrook ALA1530LN | 10 kHz – 30 MHz | 1.5 dB | $400 |
| Wellbrook ALA1530LFL (Loop For Listening, premium) | 10 kHz – 30 MHz | 0.5 dB | $600 |
| LZ1AQ wideband active loop | 10 kHz – 60 MHz | 1.5 dB | $300 (kit) |
| LZ1AQ Type C (commercial built) | 10 kHz – 60 MHz | 1.5 dB | $500 |
| Bonito MegActiv MA-305 | 9 kHz – 300 MHz | 2 dB | $350 |
| Bonito MegaLoop FX | 9 kHz – 300 MHz | 1.5 dB | $480 |
| MFJ-1886 | 100 kHz – 30 MHz | 3 dB | $250 |
| MLA-30+ (Chinese; the budget reference) | 100 kHz – 30 MHz | 3 dB | $50–80 |
The Wellbrook ALA1530LN is the canonical reference active loop in the amateur SDR community. The MLA-30+ is the budget alternative — performance is “close enough” to the Wellbrook for casual use at 1/8 the price.
8.3 Active loop performance
A 1 m diameter active loop has:
- Frequency range: 10 kHz – 30 MHz (or higher, depending on LNA bandwidth)
- Pattern: figure-8 in the plane of the loop, deep nulls perpendicular (similar to a small magnetic transmitting loop)
- Noise pickup: 6–10 dB less local-noise pickup than a comparable-size wire antenna
- Receive sensitivity: equivalent to a 60-foot wire antenna at the same height
The active loop’s signature feature: outstanding low-band receive performance in a 1 m × 1 m footprint. For an apartment dweller wanting to listen to shortwave + 160 m + 80 m DX, the active loop on a windowsill outperforms any passive antenna of similar size.
8.4 The DIY LZ1AQ kit
Joel Wallman LZ1AQ designed a kit active loop that’s become the de-facto DIY reference. The kit includes:
- LNA PCB (push-pull JFET + BJT design)
- Bias-T injector
- 12V regulator
- Schematics and PCB Gerber files (open-source)
The DIY LZ1AQ kit costs $50 in parts; the operator wraps wire into a 1 m loop, solders the LNA, and has an active receive antenna at 1/8 the cost of a commercial unit. The LZ1AQ community has extensively documented the build and tuning for various frequency ranges.
9. Phased arrays of receive antennas
9.1 The phased-array concept
Multiple receive antennas with switchable phase produces electronic beam steering. The standard configuration:
- Two beverages (or two K9AYs) at 90° to each other
- A combining network that adds (or subtracts) the signals
- A phase shifter that adjusts the relative phase of the two antennas
The combined output’s pattern depends on the phase setting:
| Phase setting | Pattern |
|---|---|
| 0° (in phase) | Wide pattern, modest F/B |
| 90° (quadrature) | Strong directional cardioid |
| 180° (opposite phase) | Sharp null in one direction, gain in opposite |
By adjusting the phase electronically, the operator can rotate the pattern’s main lobe (or its null) across the azimuth without rotating the physical antenna.
9.2 DX Engineering RAPS
DX Engineering’s Receive Antenna Phasing System (RAPS) is the canonical commercial product. RAPS combines:
- Multiple beverage or K9AY inputs (typically 2–4)
- Variable phase shifters (10° steps)
- Front-panel selection of input antennas + phase
- Switchable bandpass filters for each band
Cost: $1500–3000 (depending on input count and bandpass filter selection). Used by serious low-band DXers who want maximum SNR control.
9.3 SDR-based phased arrays
Modern SDR users can build software-defined phased arrays using:
- 4–8 SDR receivers (one per antenna)
- GPS-synchronized clocks for phase coherence
- DSP software that combines the antennas in real-time
This approach (KrakenSDR, RTL-SDR-based coherent receivers) gives infinitely variable phase + digital pattern synthesis. The setup is more complex than RAPS but more flexible.
Cross-link to Vol 32 (Antenna farms) for the deeper treatment of multi-antenna arrays.
10. Feedpoint impedance and termination resistance
10.1 Termination resistance per antenna type
| Antenna | Termination R | Feedpoint UNUN | Comments |
|---|---|---|---|
| Beverage (1λ on 80 m, 80 m of wire) | 470 Ω | 9:1 | Standard beverage |
| K9AY | 470 Ω | 9:1 | Standard K9AY |
| Flag | 900 Ω | 16:1 | Higher Z due to vertical geometry |
| Pennant | 900 Ω | 16:1 | Same as flag |
| EWE | 470 Ω | 9:1 | Beverage-like |
| Ferrite rod | high (untuned) or 50 Ω (with tuned tank) | N/A | Direct connection to receiver tank circuit |
| Active loop | 50 Ω (from LNA) | N/A | LNA provides 50 Ω output |
The 9:1 UNUN is the standard for beverage, K9AY, and EWE designs. Construction is the same as the EFHW 9:1 unun (Vol 10 §3.2) but typically built with a lower-power core (FT114-43 is sufficient since receive doesn’t require high-power handling).
10.2 Termination resistor selection
The termination resistor must be:
- Non-inductive: wire-wound resistors are NG (inductive at HF); metal-film or carbon-composition with care
- Adequately rated: 2–5 W is enough (the receive signal is tiny)
- Stable across temperature: the value shouldn’t drift with weather
- Properly grounded: the resistor’s far end connects to a small ground rod (or a few short radials)
Common choices: Vishay 1 W metal-film, Caddock high-power non-inductive, Bourns wirewound non-inductive (rare). DX Engineering and similar vendors sell pre-packaged termination resistor + 9:1 UNUN combo kits for ~$50 — the cleanest commercial option.
11. Radiation patterns — cardioid, figure-8, end-fire
11.1 Beverage pattern
A 1λ beverage has an end-fire cardioid pattern:
- Main lobe: 0° (along the wire, toward the termination end)
- Null: 180° (away from the wire, toward the feedpoint end)
- HPBW: 50–70°
- F/B: 20–25 dB
The pattern “points” away from the feedpoint (toward the termination). Operators install beverages with the feedpoint at the shack-side end and the termination at the far end pointing toward the desired DX direction.
11.2 K9AY pattern
A K9AY has a cardioid pattern:
- Main lobe: toward the termination end (90° HPBW)
- Null: toward the feedpoint end (20–30 dB deep)
- Vertical polarization
The cardioid is broad (90° HPBW) compared to a beverage’s 50–70°, which means the K9AY rejects only the opposite direction strongly and accepts everything off-axis.
11.3 Flag / pennant pattern
Flag and pennant patterns are cardioids similar to the K9AY but with:
- Slightly higher F/B (25–35 dB vs 25–30 dB)
- Slightly broader HPBW (100° vs 90°)
- Vertical polarization
11.4 Active loop pattern
An active loop has the same pattern as a small magnetic loop:
- Figure-8 in the plane of the loop
- Deep nulls perpendicular to the loop plane
- Vertical polarization (for vertical loop)
The pattern is not a cardioid (active loops don’t have termination resistors); it’s bidirectional with deep nulls on the perpendicular axis. Rotating the loop’s plane rotates the pattern.
12. Best-case use
The receive-only antenna family wins when:
- Low-band (80 / 160 m) DX receive: beverages and K9AYs are the solution. The 10–20 dB SNR improvement over a transmit dipole is the difference between hearing a faint DX station and missing it entirely.
- Urban / noisy locations: the directional null rejects the strongest local noise source. For an apartment dweller surrounded by switching power supplies, an active loop’s pattern rejects ~10 dB of local noise compared to a wire antenna.
- SDR receive across MF/LF/HF: active loops where space is constrained. The Wellbrook + an SDR is the de-facto modern shortwave-listening setup.
- Direction-finding receive: the sharp F/B null of a K9AY or flag is excellent for direction-finding (rotate the antenna until the wanted signal nulls; that direction is the source bearing).
- Multi-beverage low-band DX stations: phased arrays of 2–4 beverages at different azimuths give continuous-direction coverage for serious 160/80 m operations.
- Ferrite-rod portable shortwave receive: the standard handheld-shortwave-receiver antenna for AM broadcast and SW.
- Quiet receive on a 30-ft beverage: a 30 ft beverage outperforms a 60-ft tall vertical’s receive SNR on 80 m by 10+ dB despite the vertical’s better gain.
- SDR phased arrays: KrakenSDR or similar coherent-SDR setups for advanced direction-finding and signal-source location.
13. Worst-case use
The receive-only antenna family is wrong for:
- TX: these are receive-only. Do not transmit into a 470 Ω terminating resistor unless you want a smoke show. The resistor will burn open in milliseconds at typical amateur power. Separate transmit antenna is mandatory.
- VHF/UHF: receiver noise figure dominates atmospheric noise above ~50 MHz. High-gain antennas win. Beverages and K9AYs are irrelevant above 50 MHz.
- Daytime 20 m receive: the band is too high (external noise is below receiver NF), so a directional receive antenna provides minimal SNR improvement over a horizontal dipole.
- Casual broadband listening: a discone (Vol 12) is much better for casual scanning across wide frequency ranges.
- Mobile or portable operations: beverages need 30+ m of straight wire — impractical mobile. K9AYs are 30 ft × 30 ft — impractical portable. Active loops are the only portable option in this family.
- Receivers with very high noise figure (NF > 10 dB): a receiver with poor NF will limit SNR before the antenna’s directional advantage matters. Upgrade the receiver first.
14. Power handling — receive-only is the limit
These antennas are receive-only. Transmitting into them causes:
- Termination resistor failure (the 2–5 W resistor burns open at 100 W+ transmit)
- Active loop LNA destruction ($400+ smoke event for a Wellbrook)
- Ferrite-rod saturation (the ferrite core saturates at any non-trivial RF power)
- UNUN core saturation (the small toroid used in 9:1 / 16:1 receive UNUNs saturates at < 50 W)
If you share an antenna with TX:
- T/R relay: a sequenced T/R relay disconnects the receive antenna and connects the transmit antenna before keying the rig. Pre-built T/R relays are sold by DX Engineering, Acom, and others ($200–500).
- Separate antennas: simplest — TX antenna in one direction, RX antenna in another. No relay needed.
Never key the rig into a receive antenna without a T/R isolation step. The repair cost is far higher than the value of forgetting.
15. DIY build — a Wellbrook-style 1 m active loop
This is the canonical DIY active receive antenna. About 4 hours of work plus tuning. Total parts cost ~$60 USD.
15.1 Geometry
- Loop diameter: 1.0 m (3.14 m circumference)
- Loop conductor: #14 AWG wire (insulated for outdoor durability)
- LNA design: LZ1AQ Type C (the canonical DIY reference)
- Power: 12V at the shack end via bias-T
15.2 Bill of materials
| Part | Specification | Source | Mid-2026 price |
|---|---|---|---|
| Antenna wire | #14 AWG insulated copper, ~3.5 m | DX Engineering DXE-ANTW-14B or Wireman 534 | $5 |
| LZ1AQ Type C LNA PCB + components | Push-pull JFET front end + BJT driver | LZ1AQ website / community-sold kits | $25 |
| Bias-T injector | DIY (T200-2 toroid + caps + chokes) | Local | $5 |
| 12V supply | Linear or DC-DC | Local | $10 |
| Coax | RG-58 for short runs | Local | $5 |
| Weatherproof enclosure | Hammond 1591-XX | DigiKey | $8 |
| Non-metallic mast | 1″ fiberglass pole, 1.5 m | Local | $15 |
| Hardware (clamps, screws) | Local | $5 | |
| Total | ~$78 |
15.3 Step-by-step construction
Form the loop. Bend 3.5 m of #14 wire into a 1.0 m diameter circle. The wire’s ends will attach to the LNA’s differential input.
Build the LZ1AQ LNA. Follow the LZ1AQ schematics — the PCB is small (~5 cm × 5 cm) and uses about a dozen components: JFETs, BJTs, resistors, capacitors, a small ferrite choke. Solder the components onto the PCB.
Connect the loop to the LNA. The two ends of the loop wire attach to the LNA’s differential input. The LNA’s 50 Ω output drives the coax.
Install the bias-T. At the shack end (or anywhere convenient), install a bias-T that injects 12V into the coax. The coax shield is at ground; the bias-T’s series choke prevents the 12V from leaking into the receiver.
Mount the loop. Attach the loop to a fiberglass mast at the desired height. The LNA enclosure mounts at the bottom of the loop.
Test with NanoVNA. Power the LNA via the bias-T. Sweep the LNA’s output. Should see flat gain across 10 kHz – 30 MHz. Listen on the receiver — should hear AM broadcast stations + amateur HF signals.
15.4 Verification
A successful build shows:
- Gain at 1 MHz: +10 to +15 dB (gain of LNA + loop pickup)
- Frequency range: 10 kHz – 30 MHz with reasonable flatness
- Noise figure: 2–3 dB
- SNR comparison vs random wire: the active loop should pick up DX signals with 5–10 dB better SNR than a comparable-size random wire
If the LNA oscillates, check the supply decoupling and the choke at the bias-T. If the LNA has too low gain, check the JFET biasing.
16. Commercial buys
Sorted by tier (USD, mid-2026):
| Tier | Model | Frequency | Price | Notes |
|---|---|---|---|---|
| Budget | MLA-30+ (Chinese) | 100 kHz – 30 MHz | $50–80 | The dominant budget active loop |
| Budget | DIY LZ1AQ kit | 10 kHz – 60 MHz | $50 | The DIY reference |
| Budget | Tecsun H-501 with loopstick | AM BC / SW | $150 | Portable shortwave receiver |
| Budget | Tecsun PL-660 portable | 100 kHz – 30 MHz | $130 | With ferrite rod for AM band |
| Mid | Wellbrook ALA1530LN | 10 kHz – 30 MHz | $400 | The amateur reference active loop |
| Mid | LZ1AQ Type C (commercial built) | 10 kHz – 60 MHz | $500 | Built version of the LZ1AQ design |
| Mid | Bonito MegActiv MA-305 | 9 kHz – 300 MHz | $350 | Wider frequency range |
| Mid | Bonito MegaLoop FX | 9 kHz – 300 MHz | $480 | Bonito’s premium |
| Mid | MFJ-1886 | 100 kHz – 30 MHz | $250 | Budget commercial |
| Mid | DX Engineering K9AY kit | 80/160 m | $400 | Complete K9AY kit with transformer + termination |
| Mid | DX Engineering Beverage kit | 80/160 m | $200 | Wire + UNUN + termination |
| Premium | Wellbrook ALA1530LFL (LFL = Loop For Listening, premium) | 10 kHz – 30 MHz | $600 | Premium build, lower NF |
| Premium | DX Engineering RAPS Receive Phasing System | 80/160 m | $1500–3000 | 2–4 input phased array |
| Premium | DX Engineering RPA-1 | 10 kHz – 30 MHz | $800 | Premium-grade preamp + matching |
| Premium | Custom phased K9AY pair | 80/160 m | $1000+ | Custom-built 2-K9AY phased array |
| Premium | KrakenSDR + 4 antennas | 24 MHz – 1.5 GHz | $700+ system | Coherent SDR direction-finder |
What to avoid:
- Passive “loop antennas” claiming RX from 0–1 GHz with no LNA — below 1 MHz they’re inadequate; above 30 MHz they’re not really loops. Active LNA is mandatory for wideband coverage.
- “Mini beverage” antennas shorter than 30 ft — they don’t have the directional pattern that makes beverages useful.
- Cheap “RX-only loop” antennas with no published F/B spec — without the directional spec, the antenna’s value proposition (SNR improvement) is unverified.
17. Companion gear
- Bias-T injector for powering active loops via the coax — DX Engineering, Mini-Circuits, or DIY
- Termination resistor (non-inductive, 5–10 W) for beverages and K9AYs — Vishay metal-film, Caddock, DX Engineering pre-packaged
- T/R switching for shared antennas — DX Engineering RTR-1A, Acom T/R relays
- Phasing/switching box for K9AY arrays — DX Engineering, MFJ, DIY
- Ground rod + radials at termination ends — short ground rod plus 2–4 short radials at the termination resistor’s far end
- Lightning protection (Vol 20 §5) — required for outdoor installations
- Receive antenna pre-selector / bandpass filter — DX Engineering NCC-2 nullables, Inrad bandpass filters; rejects out-of-band signals that could overload the LNA
18. Common gotchas and myths
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“Active loops are noisier than wire” — false; properly designed, an active loop is quieter than a passive wire in the same space because the wire picks up noise the LNA-loop’s pattern rejects. The myth comes from poorly-designed active loops with high-NF LNAs.
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“Beverage needs a perfect ground at the termination” — moderately good ground suffices (a few 10-foot ground rods); the magic is in the resistor. ON4UN’s measurements show that adding a 16-radial ground at the termination improves performance by <0.5 dB over a single ground rod.
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“K9AY is omnidirectional” — no, it’s cardioid — that’s the whole point. The directional null is what gives it the SNR advantage; an omnidirectional pattern would defeat the purpose.
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“Receive antennas are easier to install than transmit antennas” — partially true. The mechanical install is easier (less critical to be at a perfect height), but the electrical install (termination resistor + UNUN + ground) is similarly fussy.
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“Active loops work fine inside a building” — partially true. The active loop’s small size lets it fit inside, and the LNA can amplify weak signals — but the building’s metal structure (ductwork, plumbing, electrical wiring) couples local noise into the loop. For best performance, an active loop wants to be outside (a windowsill or roof) where local noise is lower.
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“My active loop got blown by transmitting nearby” — yes, that happens. A 100 W transmit signal at the antenna’s location couples enough power into the active loop’s LNA to fry it. Keep the active loop electrically isolated (T/R switch) from any local transmit antenna.
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“Phased array F/B is the sum of two individual F/Bs” — sometimes. Two beverages combined in proper phase produce 30–35 dB F/B (vs 22 dB each). Phased arrays multiply directional benefit when properly aligned and aimed.
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“Ferrite rod has no preferred direction” — false. A ferrite rod has a figure-8 pattern with deep nulls perpendicular to the rod’s axis. Rotating the rod nulls out unwanted local AM stations — the standard “AM radio with ferrite antenna” tuning trick.
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“The receive antenna’s SWR doesn’t matter” — true within reason. A 3:1 SWR on a receive antenna costs <1 dB in receive performance. Beyond ~5:1 SWR, the receiver’s input impedance mismatch starts to affect receive sensitivity.
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“I can use a piece of coax as a beverage” — surprisingly, partially true. A length of coax with the shield grounded and the center conductor used as the antenna can act as a beverage substitute. Performance is degraded but the deployment is convenient.
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“All active loops use the same LNA design” — false. The Wellbrook uses a discrete-component differential amplifier; the LZ1AQ uses a JFET + BJT push-pull; the MLA-30+ uses a more conventional cascade design. Performance differences are real (Wellbrook has the best NF, LZ1AQ is close, MLA-30+ is acceptable for casual use).
19. Resources
- Beverage 1921 paper (Harold Beverage, “The Wave Antenna for 200 Meter Reception,” QST Magazine, 1922) — the original beverage paper.
- ON4UN, Low-Band DXing (5th ed.) — the canonical receive-antenna reference for 80/160 m DXers.
- DX Engineering RX antenna technical articles — published online; the modern commercial reference.
- LZ1AQ active-loop documentation — Joel Wallman LZ1AQ’s website with schematics, PCB Gerbers, build notes.
- Wellbrook Communications datasheets — published specifications for the ALA1530 series.
- Gary Breed K9AY’s original 1995 article — published in CQ Magazine; K9AY loop design.
- Earl Cunningham EWE article — original 1995 paper.
- John Devoldere ON4UN, Optimum Receiving Antennas — receive-antenna design theory.
- KrakenSDR documentation — the modern SDR-coherent-receiver direction-finding tool.
- DX Engineering RPA-1 user manual — premium-grade preamp design notes.
- Bonito MegActiv / MegaLoop technical documentation — published specifications.
- ARRL Antenna Book Ch. 13 (receiving antennas) — comprehensive coverage of the family.