How to read the vswr?

Today, let me walk you through the concept of VSWR (Voltage Standing Wave Ratio). If you’ve been following along with previous topics, you might have encountered terms like reflection coefficient or return loss. VSWR is closely related to these concepts, and understanding it will help you better analyze the performance of antenna systems, especially in terms of signal transmission and quality.

What is VSWR?

VSWR is a measure of how efficiently RF (Radio Frequency) power is being transmitted from the source to the load (usually the antenna). Essentially, it tells you how much of the signal is being reflected back from the antenna due to impedance mismatches. The goal is always to minimize the reflections because too much reflection can result in poor signal quality, leading to dropped calls or weak network connections.

VSWR is calculated by comparing the maximum and minimum voltage amplitudes in the transmission line. A low VSWR indicates that the power is being transferred efficiently with minimal reflection, while a higher VSWR means that a significant portion of the signal is being reflected back, leading to inefficiency and potential performance issues.

How to Interpret VSWR Values?

Now, you’re probably wondering what exactly constitutes a good or bad VSWR. Let me explain that in simple terms:

VSWR = 1:1: This is the ideal case. It indicates perfect impedance matching, meaning no signal is being reflected back. This is rare in practical systems but is the goal for optimal performance.
VSWR = 1.5:1 to 2:1: This is generally considered a good range. It means that the reflection is relatively low, and the signal is being transferred efficiently. You might encounter this in most well-tuned systems.
VSWR = 3:1: This is still an acceptable level in many cases, but it indicates a higher reflection. While the system will still work, performance might degrade, especially for sensitive applications like 4G/5G communications.
VSWR > 3:1: This is typically a poor VSWR, indicating a significant amount of power is being reflected. This should be addressed immediately, as it leads to inefficiency, increased loss, and potential damage to equipment over time.

How to Measure VSWR?

There are several methods to measure VSWR, but one of the most common tools used is a VSWR meter, which is designed to directly calculate the ratio. Here’s how it works:

First, connect the VSWR meter to the transmission line between the transmitter and the antenna.
The meter will measure the forward and reflected power.
It then calculates the ratio between the reflected power and the total power to give you the VSWR value.

It’s worth noting that there are also handheld tools, like antenna analyzers, that allow you to measure VSWR on-site for antenna systems. These are handy for quickly diagnosing antenna performance issues in the field.

Understanding the VSWR Graph

Many tools provide a graph that shows the VSWR across different frequencies. This graph is especially useful for identifying which frequencies or frequency bands have high VSWR values. If you notice large spikes, that indicates that there are frequencies where the antenna is not performing well, and you may need to make adjustments to improve impedance matching.

As we talked about earlier in this article, keeping VSWR values low is key to ensuring the quality of your RF system. If the VSWR is high, it could result in energy loss, lower signal strength, or even equipment damage. By regularly measuring and adjusting your system’s impedance, you can ensure maximum efficiency and performance.

VSWR and Antenna System Performance

In an ideal antenna system, the VSWR is close to 1:1. However, achieving a perfect 1:1 ratio is very difficult in practical systems, so anything between 1.5:1 and 2:1 is generally acceptable. If you notice that your system’s VSWR is consistently high, it could indicate a mismatch in the antenna or cable, or even a fault in the equipment itself. Identifying these issues and correcting them ensures that your antenna system is functioning optimally, giving you a stronger and more reliable signal.