Editor’s Note: Over the next several months, OnAllBands will be featuring a series of articles from Harry “Trippy” Brown, AC8S, longtime amateur operator and antenna builder/tester who’s never let his visual impairment stop him from enjoying the hobby he loves. As the title of this series states, we hope these articles provide you with invaluable insights as you pursue your own successful antenna projects.
SWR
When building an antenna, you want the lowest SWR (Standing Wave Ratio—
a measure of how well load is matched to a transmission line). The lower the SWR, the more power the antenna will transmit. For any multiband antenna, if you want to use the antenna on more than one band and have the lowest SWR on each band, it is essential to select a length for the antenna that is AT LEAST a half wavelength on the lowest band to be used. That way, you’ll have a better chance to have a low SWR on each band.
As Steve Ford, WB8IMY, says in his book, Small Antennas for Small Spaces, “If you want an even better SWR on all bands, make the antenna at least a half wave on the lowest frequency band that you’re going to operate.”
If you’ll be using a half wavelength end-fed long wire on the lowest band of operation, then use a 56 to 1 unun for the end fed, and use your coax, which is the second leg of the end-fed half wave, as a counterpoise between the radio and the unun.
Thanks to Steve’s advice, when I build dipole/inverted-V combo antennas, I NEVER build them less than a half wave. I only build antennas that are, in length, half wave multiples (for example, a half wave, one wave, one-and-a-half wave, and so on). Half wave multiples make for very easy matching because the impedance is lower at the center feedpoint of the antenna.
Also, antennas that are half wave multiples give me much more dB gain, and they’re easier to match on more bands than a quarter wave—how cool is that!
I’d love to build end-fed half wave antennas, but I cannot find any 56 to 1 ununs that have I-bolts (also called I-hooks). They all use binding posts, or lug and wing nuts, and my fingers don’t work well enough to deal with those. Check out my introductory post on the need for ununs with I-hooks.
The antenna needs to have the lowest SWR on all bands, and the most effective antennas have an SWR of 2 to 1 or lower. Note: I used to be a real stickler about having a 1 to 1 SWR until I read an article by a contester who wrote, “If you can get your SWR anywhere from 2 to 1 or below, you’re fantastic, be happy, and get on the air!”
How important is SWR? Check out these Transmit Percentages
- 1 to 1 SWR transmits 100% of your power out of the antenna.
- 1.5 to 1 SWR transmits 96% of your power out of the antenna.
- 2 to 1 SWR transmits 88.9% of your power out of the antenna.
- 2.5 to 1 SWR transmits 81.6% of your power out of the antenna.
- 3 to 1 SWR transmits 75% of your power out of the antenna.
Note: Internal automatic antenna tuners in radios only tune antennas with 3 to 1 SWRs or lower, but no higher than 3 to 1. You’ll realize this because if you try to tune an antenna with an SWR greater than 3 to 1 using a radio’s built-in antenna tuner, you’ll get a message indicating that it can’t handle the higher SWR. If you know the SWR will be higher than 3 to 1, buy a wide range antenna tuner.
Personally, I have had great success with my Elecraft KX3. The KX3’s internal wide range antenna tuner tunes antennas and transmits using those antennas, enabling me to make 40-meter contacts with a 22 to 1 SWR or lower on CW. I have also made sideband contacts with a 12.9 to 1 SWR on 10 meters, and got 57 and 56 signal reports in New Hampshire and Rhode Island from my location here in Michigan!
SWR and Transmit Percentages (Continued)
- 3.5 to 1 SWR transmits 69.1% of your power out of the antenna.
- 4 to 1 SWR transmits 64% of your power out of the antenna.
- 5 to 1 SWR transmits 56% of your power out of the antenna.
- 6 to 1 SWR transmits 49% of your power out of the antenna.
- 7 to 1 SWR transmits 43.7% of your power out of the antenna.
- 8 to 1 SWR transmits 39.5% of your power out of the antenna.
- 9 to 1 SWR transmits 36% of your power out of the antenna.
- 10 to 1 SWR transmits 33.1% of your power out of the antenna.
- 15 to 1 SWR transmits 23.4% of your power out of the antenna.
- 20 to 1 SWR transmits 18.1% of your power out of the antenna.
- 50 to 1 SWR transmits 7.7% of your power out of the antenna.
So what if you have an antenna up but don’t know its SWR?
If you have a radio with a built-in antenna tuner or an external antenna tuner, you can find the “natural” SWR just by checking the SWR without trying to tune it for the lowest SWR.
For me, as a blind ham, I check SWR by using the HamPod—a microprocessor-based text-to-speech device that provides speech output and accessibility to common station equipment (editor’s note: production of the HamPod was discontinued in 2021). The HamPod supports speech output for a range Kenwood, Icom, Yaesu, Elecraft, and Ten-Tec rigs.
Here’s how it works. Whether you’re in front of your radio with the antenna connected to it or by your radio with your antenna connected to an external antenna tuner, press the HamPod’s shift key, let it go, and press the 5 key on the device’s keypad. Hold it until you hear a beep. Then release the 5 key and it will tell you the natural match.
For example, say my all-band inverted-V is at 3.8 on 80 meters. If I press and release the shift button on the HamPod, press the 5 key and hold it until I hear the beep, then let that key go, it tells me my natural SWR without tuning the antenna (in this case, 4.7 to 1). That’s way too high, so I would now tune it for lowest SWR, which requires me to press the tune button on the KX3 to achieve an SWR of 2 to 1. I will not have to do any tuning for lowest SWR because 2 to 1, as noted in the quote above, is “fantastic.” Now I’m ready to operate!
Another way to find the natural SWR is with an antenna analyzer. This is a device that tells you the SWR as you move up or down the band, without pressing the tune button on your radio.
Questions? Comments? Reach me at hebrown3rd@gmail.com.
