With practical examples, measurement errors and common myths
SWR is one of the most discussed—and yet least understood—topics in the 27MC world. Many users measure a value, see a number, and then don't know what it means in practice.
In this guide, Deltron clearly explains what SWR is, why it's important, and how to correctly measure and interpret it.
What does SWR mean?
SWR stands for Standing Wave Ratio. It indicates how much of the transmitted radio signal:
- Actually transmitted by the antenna
- And how much is reflected back to the radio
The lower the SWR, the better your installation will perform.
Why SWR is more than just a number
A low SWR means:
- More efficient transmission power
- Better reach
- Fewer disruptions
- Longer life of your transceiver
A high SWR means:
- Energy loss
- Worse audio
- Risk of damage to the output stage (output transistor)
So SWR is a health meter for your entire installation.
What is a good SWR value?
| SWR value | Meaning |
|---|---|
| 1.0 – 1.3 | Excellent |
| 1.3 – 1.5 | Very good |
| 1.5 – 2.0 | Acceptable |
| > 2.0 | Adjustment necessary |
*In practice, 1.3–1.5 is more realistic than aiming for exactly 1.0.
How do you measure SWR correctly?
Basic lineup
- Radio
- SWR/Wattmeter
- Antenna
The meter is placed between the 27MC transceiver and the antenna using an intermediate cable.
Measurement procedure
- Measure on channel 1
- Meet on channel 40
- Compare the values
- Adjust the antenna length
- Repeat until balance is achieved
SWR measurement outcome
- SWR on channel 1 higher than channel 40? Antenna too short
- SWR on channel 40 higher than channel 1? Antenna too long
Common Measurement Errors (and Why SWR Sometimes Isn't Right)
- Measuring in a garage or next to buildings
- Door or hood open during measurement
- Bad ground /earth
- Wrong coaxial cable
- Magnetic antenna in an unsuitable location
Always measure outdoors, in open terrain (not too close to houses or buildings).
Myths about SWR (debunked)
- “1.0 is always necessary” > No, stability is more important than perfection
- “An expensive radio solves high SWR” > No, the antenna is decisive
- “SWR only says something about transmission” > No, it also affects reception
Practical examples
Truck
- Long antenna
- Steel roof = good mass
- Get SWR low quickly
4x4 with roof rails or rack
- Mass is usually a problem
- Additional grounding is often required
- SWR is often underestimated
Agricultural vehicle
- Lots of metal, but irregular
- Placement more important than length
When should you re-measure SWR?
- New antenna
- Other mounting location
- Other coaxial cable
- Bad reception
- After damage, bending or hard blow (due to low-hanging branches, storm, etc.)
Conclusion
SWR isn't a mystery, but a logical component of good radio communication. Understanding what you're measuring will help you get more out of your system and avoid unnecessary problems.
Frequently Asked Questions about SWR
What exactly is SWR?
SWR (Standing Wave Ratio) indicates how efficiently an antenna transmits a radio's transmitting power. A low SWR means the signal is being transmitted effectively; a high SWR indicates energy loss and potential damage to the transceiver.
What is a good SWR value?
An SWR between 1.0 and 1.5 is considered very good. Values up to 2.0 are acceptable. Above 2.0, adjustment is necessary to protect performance and equipment.
Can I use my radio with a high SWR?
This is not recommended. A prolonged high SWR can lead to overheating, power loss, and damage to the transceiver's output stage (transistor).
Does SWR affect reception or only transmission?
SWR mainly affects transmission, but a poorly tuned antenna almost always has a negative impact on reception quality as well.
Why does my SWR change when I drive?
While driving, the antenna's environment changes (other vehicles, buildings, and terrain). This can cause slight SWR fluctuations, which is normal.
Is an SWR of 1.0 always better than 1.3?
Not necessarily. In practice, a stable SWR of 1.3–1.5 is often better than an unstable 1.0 that is sensitive to environmental influences.
Can a bad coaxial cable cause a high SWR?
Yes. Poor quality, damage, or incorrect length of the coaxial cable can increase the SWR and make measurement results unreliable.
Do I need to re-measure SWR after moving my antenna?
Yes. Any changes to the mounting location, antenna, coaxial cable, and/or vehicle require a new SWR measurement.
Does SWR measurement also work with a magnetic antenna?
Yes, but magnetic antennas are more sensitive to: placement, mass and vehicle type
This allows the SWR to vary more quickly than with fixed mounting.
Can I measure SWR without an SWR meter?
No. An SWR meter or combined SWR/wattmeter is necessary to measure reliable values and adjust them correctly.
