At Deltron, specialists in 27MC, UHF/VHF communications, and scanners since 2008, we often receive questions about correctly tuning antennas. The internet is full of advice, but unfortunately, it's not always reliable. That's why, in this blog post, we're sharing the right information and practical tips for tuning your antenna, ensuring optimal performance of your transmission system.
What is SWR and why is it important?
SWR stands for Standing Wave Ratio. It's a measure of how efficiently your radio's transmit power is transmitted through the coaxial cable and antenna. An SWR of 1:1 is ideal: all the energy is utilized. The higher the value, the more power is reflected, which can lead to power loss and even damage to your equipment.
Standing waves explained simply
Think of it like a long rope that you tug at one end, causing the rope to "wave" and move to the other end and back again. This bounce is called a standing wave. This also happens with radio signals. With proper tuning, you minimize this reflection.
How SWR Affects Your Range
A high SWR doesn't directly limit your transmission range, but it does cause energy loss and can damage your output stage. With proper tuning, your antenna radiates more power, which indirectly increases your range.
What is a good SWR value?
An SWR below 1.5 is ideal. Up to 2.0 is acceptable. Above 3.0? Then you risk damage. Time to take action! Always ensure proper mounting with sufficient ground or ground plane. Only then will you get the most out of your antenna system.
Why you should never transmit without an antenna
Never use your 27MC transceiver without a connected antenna or a proper dummy load. Doing so risks damaging the output stage—which is never covered by the warranty. Want to test your radio? Connect one of the two correctly.
Mass is your best friend
Every standard antenna needs a ground (to compensate for capacitance) or ground plane to function properly. In vehicles, the metal chassis acts as the ground. For campers or plastic vehicles, it's best to use a no-ground antenna where the coax takes over part of the ground.
Adjust and measure
Many antennas are already properly adjusted at the factory, provided you leave the cable at the correct length and ensure a good ground. However, it's always wise to perform an SWR measurement after installation. This measures the signal reflection and prevents damage to your radio.
Use a multimeter to check the coaxial cable for breaks or shorts. Note: Base-loaded antennas such as Firestik no-ground and Sirio Turbo may short out during measurement—this is normal.
How to adjust SWR
- Connect your SWR meter (or SWR and Watt meter) between the transceiver and the antenna.
- If your SWR meter has an "SWR" setting, set it to this. If your meter doesn't have an SWR setting, you can skip this step.
- Set the transceiver to channel 20*
- Set the SWR meter to "Forward" (FWD)
- Squeeze and hold the handheld microphone
- Use the knob on the SWR meter to turn the needle in the display to "SET" or "CAL"
- Release the microphone
- Set the SWR meter to "Reflected" (REF)
- Squeeze the microphone again and hold it down
- The SWR meter should now indicate the lowest possible SWR value. Note : once the SWR meter reaches 2.5 or is in the red, don't hold the microphone depressed for too long. This can burn out your output transistor or, quite frankly, blow up your 27MC amplifier.
*The reason we're using channel 20 for SWR adjustment is because we're assuming a 27MC transceiver with 40 channels. The lower the number of channels, the lower the SWR, and the higher the number of channels, the higher the SWR.
Forward and Reflected Power
A standing wave is created on an antenna cable by two signals: forward (FWD) and reflected (REF) power. The forward power is the signal going from your transmitter to the antenna—this is the energy you actually want to transmit. The reflected power, on the other hand, is the part of that signal that isn't radiated by the antenna and therefore bounces back to the transmitter. An SWR meter measures both signals. If you set the switch to FWD, the meter measures the outgoing power. If you then set it to REF, you'll see how much power is reflected. These values together determine the SWR and provide insight into the efficiency of your antenna system.
What does the SWR value say about your antenna system?
- An SWR of 1:1 (or simply 1.0) means that all of your radio's transmit power is effectively absorbed by the antenna – ideal, but almost never achievable in practice. Cables and connectors always cause a small amount of reflection. An SWR of 1.2 or 1.3 is therefore considered excellent.
- At an SWR of 1.5, almost all of the power is still handled effectively by the antenna. Only a small portion is reflected, which doesn't pose a problem.
- An SWR of 1.8 deviates slightly from ideal, but most transmitters still function perfectly well at this level. Some broadband antennas even achieve values of up to 1.8 at the edges of their range – this is still acceptable.
- Starting at an SWR of 2.0, things become somewhat critical. While most transmitters can still handle it, it's wise to check and adjust your antenna system at power levels of 100 watts or above. Aim for an SWR of 1.5 or lower.
- An SWR of 2.5 or higher is simply too high. Some transmitters can be damaged by this. Don't use your transmitter with an SWR this high – time for a thorough system check!
Common problems when adjusting your SWR
- Is the SWR on channel 40 too high? Then you need to shorten the antenna boom. The method varies by antenna. Some require trimming mm by mm, while others have an adjustment screw that you can turn in and out.
- Is the SWR on channel 1 too high? Then you need to extend the antenna boom.
- If the SWR meter needle jumps into the red zone, there may be a short circuit in your antenna system. Adjusting it is pointless until the problem is resolved.
The causes of a too high SWR
- Bad or damaged coaxial cables
- Wrong or untuned antennas
- Bad ground or reflection
- Obstacles such as buildings or metal roofs during adjustment\
What is the result of a poorly tuned antenna?
A poorly tuned antenna can lead to power loss and increased stress on the transceiver, which can shorten the life of your equipment.
Tips for tuning your antenna
- Tune the antenna to an open area without obstacles
- Ask someone to help you, one person measures and the other person adjusts the antenna.
- Use the correct antenna for your application, for example, broadband transceivers also require a broadband antenna.
- Important: Do not stand near the antenna during measurements.
Additional resources
Use a cross-needle meter for more accurate measurements of both power (wattage) and SWR. Make sure you're using the correct cables and that the connectors are secure.
Daiwa CN-901HP3 cross-needle meter for measuring SWR and power
K-PO SWR-430 SWR and Watt meter
Digital vs. Analog SWR Meters: Which Works Best?
Although digital SWR meters are becoming increasingly popular, many experienced users still prefer analog meters. The reason? An analog needle offers a smooth movement that's easy to interpret. With digital meters, the numbers often change so quickly that they're difficult to read, unless the meter has a peak hold function that holds the highest value for a few seconds.
However, if you use FM or another constant carrier mode, digital meters are perfectly suitable, as the output power hardly fluctuates during modulation. For daily use and tuning, a reliable analog meter is often the most user-friendly choice.
Adjust the antenna in the correct environment
Tuning should be done in an open environment. So, not next to buildings, under trees or high-voltage power lines, and certainly not while someone is holding the antenna. Also, maintain a minimum distance of 30 cm between multiple antennas to prevent interference.
Pay attention to the entire system
The performance of your 27MHz transceiver depends on the entire system: antenna, base, and coaxial cable. Many problems arise from faulty cables, incorrect plugs, or a missing ground. Even a bad SWR meter can cause confusion. Think of your antenna like the speakers in a stereo system: good speakers make all the difference. The necessary interconnection cables , which allow you to connect an SWR meter or a linear amplifier to a 27MHz transceiver, are fitted with a soldered PL (UHF-Male) connector at both ends. These coaxial cables are available in various lengths, from 40 cm to 10 meters.
SWR tells you a lot about the health of your antenna system. Maintaining a low SWR prevents power loss, damage to your radio, and increases the effectiveness of your transmission system. Invest in a good SWR meter, cables, and antenna for optimal results.
Is your mobile antenna not working properly?
Do you have any questions after reading this blog, or is there something you don't quite understand? Please contact us; we're happy to help!
Frequently asked questions about tuning your 27MC antenna
What exactly is SWR?
SWR stands for Standing Wave Ratio. It indicates how well your antenna system utilizes its transmit power. The lower the SWR, the better your signal is radiated. A high SWR means power loss and can cause damage.
What is a good SWR value?
An SWR between 1.0 and 1.5 is ideal. Up to 2.0 is acceptable. Above 2.5, it becomes risky and can damage your 27MC transceiver. Regular measuring and adjustment is therefore crucial.
How do I correctly align my 27MC antenna?
Use an SWR meter and tune to channel 20. Measure both the forward and reflected power. Reduce the SWR by adjusting the antenna boom: shorten it if the SWR is too high on higher channels, and lengthen it if it's too high on lower channels.
Why are you never allowed to transmit without an antenna?
Transmitting without an antenna or a dummy load will cause immediate damage to your transmitter's output stage. Always use a connected antenna or a suitable dummy load when testing.
What is mass and why is it important?
Ground (ground plane) is essential for the operation of standard antennas. In vehicles, the metal chassis serves as the ground. Do you have a camper or plastic vehicle? Then you need a No Ground Plane antenna.
Can I measure SWR with a multimeter?
No, a multimeter doesn't measure SWR. You can, however, use it to check the coaxial cable for breaks or shorts. Always use an SWR meter to ensure the correct measurement.
What is the difference between forward and reflected power?
Forward power is the signal going from your transmitter to the antenna. Reflected power is what bounces back. An SWR meter compares these two to determine how efficient your antenna system is.
What are common causes of high SWR?
Common causes include: poor coaxial cables, incorrect antennas, no ground, or obstacles such as buildings during alignment. Also check your connectors and mounting location.
Which SWR meter should I use: digital or analog?
Analog meters provide smooth feedback and are user-friendly. Digital meters are accurate but can be difficult to read without a peak hold function. For beginners, an analog meter is often easier to use.
What should I pay attention to when tuning the antenna?
Tune in an open area free of obstacles, use the correct cables, and stay away from the antenna during the measurement. Also ensure sufficient distance from other antennas to avoid interference.
