#368 NANOVNA Return Loss vs VSWR

Summary

The video discusses the differences in measurement practices between amateur radio enthusiasts and RF design professionals, focusing on SWR (Standing Wave Ratio) and return loss. While radio operators typically use SWR to gauge antenna performance, RF designers rely on return loss measurements. The presenter explains how to measure both parameters using a Vector Network Analyzer (VNA), provides mathematical relationships between them, and shares practical guidelines for acceptable values. A return loss of 10 dB or better and an SWR of 2:1 or better are suggested for optimal performance, emphasizing the convenience of using VNA features for these calculations.

Takeaways

• 📡 Understanding the differences between VSWR and return loss is essential for those in RF design and ham radio.
• 🔄 People in ham radio typically use VSWR measurements, while RF design professionals focus on return loss.
• ⚠️ A common misconception is that an SWR greater than 3 can damage radios, which emphasizes the need for proper education.
• 📈 Return loss is measured in decibels (dB), indicating how much power is reflected back to the source.
• 📊 When using a VNA (Vector Network Analyzer), two key traces are displayed: the Smith chart trace and the return loss trace.
• 🔍 The mathematical relationship between return loss and SWR is crucial for accurate measurements.
• 🧮 You can convert between return loss and SWR using specific logarithmic equations, but cheat sheets are available for convenience.
• 🛠️ Many RF engineers prefer to let the VNA perform calculations instead of doing them manually.
• 💡 General rules of thumb suggest that an SWR of 2:1 or a return loss of 10 dB is acceptable.
• 🚀 For optimal performance, striving for a return loss of 20 dB (or an SWR of 1.2:1) is recommended.

Q & A

What is the primary confusion mentioned in the transcript regarding VNA measurements?

The confusion arises between the VSWR (Voltage Standing Wave Ratio) measurements preferred in ham radio and return loss measurements used in RF design. Ham radio enthusiasts often focus on SWR, while RF designers typically emphasize return loss.

What does an SWR of less than 2:1 indicate?

An SWR of less than 2:1 is generally considered acceptable in ham radio contexts, indicating that the system is well-matched and efficient.

What are the typical misconceptions about high SWR values?

Many people believe that an SWR greater than 3:1 will damage their radio equipment. This reflects a misunderstanding of the relationship between SWR and return loss.

How are return loss and SWR related mathematically?

Return loss and SWR are related through logarithmic equations that define how much signal is reflected back. The transcript notes that there's a mathematical relationship between the two, but doesn't delve deeply into the complex calculations.

What tools can be used to visualize return loss and SWR on a VNA?

A Vector Network Analyzer (VNA) displays two traces: the Smith chart trace and the return loss trace, allowing users to visualize return loss and SWR measurements simultaneously.

What does a return loss of 10 dB imply in terms of SWR?

A return loss of 10 dB typically corresponds to an SWR of approximately 2:1, indicating a reasonable level of impedance matching.

What are some common return loss benchmarks mentioned in the transcript?

The transcript mentions that a return loss of 10 dB is acceptable, while 20 dB is considered good. For SWR, 2:1 is acceptable, while a SWR of 1.2:1 is excellent.

What is the purpose of using cheat sheets for return loss and SWR calculations?

Cheat sheets provide quick reference values to convert between return loss and SWR without needing to perform complex logarithmic calculations manually.

Why might someone prefer to display measurements in SWR rather than return loss?

Individuals who are accustomed to ham radio measurements may prefer SWR since it is a familiar metric in their field, while RF design professionals may stick to return loss as it is more common in their practices.

How does the VNA default display setting influence user experience?

The VNA typically defaults to display return loss measurements, as this is the standard in RF design, which might require users to change settings to see SWR if they are more comfortable with that measurement.