Standing Wave Ratio (SWR) is one of the most discussed, and often misunderstood, topics in amateur radio and antenna design. While many strive for the perfect 1:1 SWR, it’s important to understand that SWR is not an indicator of your antenna’s efficiency or performance. This article aims to demystify SWR and explain its true implications for both transmission and reception.

What is SWR?

SWR is a measure of the impedance match between the transmitter, feedline, and antenna. It describes how well power is transferred from the transmitter to the antenna. A perfect match (SWR of 1:1) means all the power from the transmitter is delivered to the antenna, while a higher SWR (e.g., 3:1) indicates that some of the power is reflected back toward the transmitter.

As a side note, the reflected power does not travel on the braid (as some might think). It is not common-mode current, which is a separate issue caused by unbalanced feedlines or poor grounding. Reflected power travels as part of the normal wave propagation inside the coaxial cable on the inner core, bouncing between the mismatched impedance points as a wave reflection with decreasing amplitudes ...

Read more here: Feedlines, coaxial and balanced feedlines (ladderlines) 

Key Points About SWR

1. SWR measures the power transfer efficiency between components, not the radiating efficiency of the antenna itself.

2. A low SWR ensures minimal power is reflected back to the transmitter, protecting sensitive components. 

3. High SWR does not necessarily mean poor performance. Many efficient antennas operate at higher SWR values when designed for specific conditions.

SWR and Antenna Efficiency

A 1:1 SWR does not guarantee that the antenna is efficient. It only confirms that there is a good impedance match for power transfer. The antenna’s efficiency is determined by its radiation resistance and loss resistance, not the SWR.

Example: Efficiency vs. SWR 

 The lesson: Chasing a perfect SWR does not improve antenna efficiency.

SWR and Feedlines

The role of the feedline (coaxial cable or otherwise) is crucial in understanding SWR’s impact. Here’s what you need to know:

SWR Along the Feedline:

• SWR does not directly affect the antenna’s ability to radiate. It only impacts the efficiency of power transfer through the feedline.
• Power reflected back from the antenna due to mismatch travels along the inner core of the feedline, creating “standing waves.” This can increase losses in the feedline, particularly at higher frequencies and with longer lengths. 

Feedline Length and Multiband Antennas:

• With multiband antennas, feedline length can impact the impedance presented at the transmitter due to variations in feedline electrical length.
• The impedance at the feedpoint can differ dramatically at the transmitter end of the line depending on the cable’s length and the antenna’s impedance on each band.

Read more here: Does feedline length matter?

SWR and Reception

SWR is often misunderstood in the context of reception. On receive, SWR has minimal influence because most modern receivers are not affected by the small impedance mismatches caused by SWR. The receiver sensitivity is generally far greater than the signal losses due to SWR-related reflections.

Bottom Line for Receive:

• SWR does not significantly impact the signals your receiver picks up.
• Even with higher SWR, your antenna will still collect signals effectively.

Common mode pickup does affect the reception. Read more: Line Isolators / Common-mode choke why ?

Tuner Losses vs. SWR 

Many operators use tuners to achieve a perfect 1:1 SWR at the transmitter. However, using a tuner introduces additional losses:

Tuner Losses:

• Tuners use inductors and capacitors to match the transmitter to the feedline. These components can introduce noticeable losses, especially when matching high-SWR antennas.
• For example, matching a 5:1 SWR can lead to tuner insertion losses of several dB, depending on the tuner quality.

Direct Feedline Losses:

• Operating with a higher SWR without a tuner may lead to feedline losses, but these are often less significant than the losses introduced by an inefficient tuner. 

Example: Tuner vs. High SWR Without Tuner

• A feedline with a 3:1 SWR may introduce 1–2 dB of additional loss due to reflected power.
• Using a tuner to match 1:1 could add 2–3 dB of loss, depending on the tuner design and quality.

Takeaways About SWR

SWR is Not a Measure of Antenna Efficiency:

High SWR can coexist with an efficient antenna. It only indicates power transfer efficiency between the transmitter and the feedline.

Perfect 1:1 SWR Isn’t Always Necessary:

A slightly higher SWR (e.g., 1.5:1 to 2:1) is acceptable in most cases and avoids unnecessary tuner losses.

Feedline Losses Matter:

On high-frequency bands, or with long feedlines, minimizing SWR is more critical to reduce losses in the coax.

Tuner Use Has Trade-Offs:

Tuners are helpful for impedance matching but can introduce significant losses if used to force a 1:1 SWR on poorly matched antennas.

Multiband Antennas and Feedline Length:

On multiband setups, feedline length can interact with varying impedances, influencing SWR at the transmitter. Adjusting feedline length or using a balanced antenna design can help.

In short

SWR is an important tool for assessing power transfer efficiency but should not be viewed as the sole indicator of an antenna system’s performance. Focus on building efficient antennas with good radiation resistance and accept a reasonable SWR to avoid unnecessary losses. A well-matched but inefficient antenna wastes more power than an efficient antenna with a slightly higher SWR!

By understanding SWR in its proper context, you can optimize your station without chasing the elusive 1:1 SWR unnecessarily.