The SWR Myth: The Story of the "Lost" Power That Isn't Really Lost
In amateur radio, few topics are as misunderstood—or as fearfully obsessed over—as Standing Wave Ratio (SWR). Many believe that “bad SWR” vaporizes power or instantly destroys a transmitter. The truth: SWR doesn’t measure efficiency, and most of your power isn’t vanishing into thin air. Let’s unpack the physics, bust the myths, and explain where your power really goes.
Here’s the perspective of Mark — K3ZD (better known as “Ham Florida Man” on YouTube). Watch his video below:
What SWR Actually Measures
SWR describes how closely the antenna system impedance matches the transmitter’s 50 Ω output. A 1:1 SWR is perfect; 2:1 means some reflection. Reflected power is not “lost” — it is a wave bouncing back and forth until it is either radiated or dissipated.
-
Reflection coefficient:
|Γ| = (SWR − 1) / (SWR + 1) -
Return Loss (dB):
−20 log10(|Γ|) -
Power delivered:
P_L = P_F (1 − |Γ|²)(ignoring line loss) -
Mismatch loss:
−10 log10(1 − |Γ|²)dB
These apply at the measurement plane; line loss modifies what the transmitter “sees.”
Where Does Reflected Power Go?
- It does not vanish in the feedline (unless feedline loss is high).
- It does not magically radiate from the coax shield (unless return currents are flowing due to imbalance).
- It does not evaporate into space.
In reality, reflected power bounces between antenna and transmatch (tuner). Over multiple cycles, most of it is eventually radiated. Real loss only comes from feedline attenuation and transmatch or transformer dissipation.
Visualizing the Power Flow
Inside a mismatched coax, forward and reflected waves form a standing wave pattern. Energy is still in the system, “sloshing” until it leaves as radiation or heat.
- The transmitter or transmatch (tuner) re-launches the reflected energy
- The antenna radiates the majority
- Some is dissipated as feedline or component heating
The Real Losses: Feedline and Transmatch (Tuner)
- Feedline losses: SWR raises current and voltage peaks, which increase coax I²R and dielectric heating. Long or thin coax makes it worse, especially at high frequencies.
- Transmatch (tuner) losses: The transmatch only hides mismatch from the rig. Heavy mismatch requires more L/C, increasing insertion loss. In some cases, transmatch loss exceeds the extra coax loss of leaving the mismatch.
Example: 30 m (~100 ft) RG-213 at 14 MHz, matched loss ≈ 0.9 dB
| SWR | |Γ| | Extra line loss | Total line loss |
|---|---|---|---|
| 1.5:1 | 0.20 | ≈ +0.1 dB | ≈ 1.0 dB |
| 2:1 | 0.33 | ≈ +0.2 dB | ≈ 1.1 dB |
| 3:1 | 0.50 | ≈ +0.5 dB | ≈ 1.4 dB |
| 5:1 | 0.67 | ≈ +1.1 dB | ≈ 2.0 dB |
Balanced open-wire line under the same SWR has much lower loss. Coax is the limiting factor, not SWR itself.
Practical Example
Consider 10 m of RG-213 coax with a 3:1 SWR at the antenna, tuned to 1:1 at the rig:
- Coax loss: ~1.5–2 dB
- Transmatch loss: ~1–2 dB
- Total system loss: 3–4 dB
Feeding directly without the transmatch could reduce it to ~1.5–2 dB loss—sometimes the better choice.
Myth: 1:1 SWR Means an Efficient Antenna
No. A dummy load shows 1:1 SWR and radiates nothing. Conversely, an antenna with 2:1 SWR can be highly efficient.
| Antenna | Radiation R | Loss R | Total R | Efficiency | SWR |
|---|---|---|---|---|---|
| Good design | 50 Ω | 2 Ω | 52 Ω | 96% | 2:1 |
| Poor radiator | 2 Ω | 20 Ω | 22 Ω | 9% | 1:1 |
Reception: Does SWR Matter?
Not much. Receiver input impedance is broad and sensitive; SWR adds negligible loss. Return currents and noise on coax are usually the culprit in poor RX, not mismatch.
Key Takeaways
- SWR ≠ efficiency. It is only a match indicator.
- Reflected power isn’t lost. It recirculates until radiated or dissipated.
- Feedline and transmatch are the real loss points.
- Tuner placement matters. At the rig is convenient; at the feedpoint minimizes mismatch loss.
- Reception is unaffected. Focus on return currents and noise suppression instead.
Final Word
SWR is a useful diagnostic, not the ultimate measure of antenna performance. A little mismatch won’t ruin your signal, and chasing 1:1 at all costs often adds more loss. Design efficient antennas, keep feedline losses low, and use transmatches wisely.
Mini-FAQ
- Does high SWR always waste power? — No. With a transmatch and decent coax, most power is still radiated; only line and component heating are true loss.
- Is 1:1 always the goal? — At the rig yes (for protection), but the antenna/feedline can run higher SWR efficiently.
- Should I fear 3:1 SWR? — Not on short, low-loss coax or OWL. The added loss is small compared to other station inefficiencies.
- Will a line isolator fix SWR? — No. It cures return/current imbalance (and common-mode issues), not impedance mismatch.
- What matters more than SWR? — Antenna efficiency, feedline choice/length, and suppression of unwanted return currents.
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