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.
I’ve spent quite a bit of time discussing length as it relates to dipole/inverted-V combo and end-fed antennas. Today, I’ll be shifting my focus to questions about the height of wire antennas. To read the first nine entries in this series, just enter “Trippy” in the OnAllBands search box above.
How high can my antenna be, and what about wavelengths in height?
Your antenna can be as high as you want it to be, depending on how much room you have and how high your city, township, or county government will allow.
We’ve talked about wavelengths in terms of length for wire antennas, which is very important for tuning your antenna. Now we’re going to talk about wavelengths in height. The higher the antenna, the better the wavelength and the better signal you have. In the book 73 Dipole and Long-Wire Antennas, it says, “With every half wave added to the antenna in height, you add more dB
gain.” Now is that awesome or what?
According to the article “Ham Radio dB Gain,” written by WA2OOO, “A long-standing rule of thumb: If you double the height of your antenna, you will gain 6 dB! That means if you had an antenna at 25 feet and decided to put it up on a small tower at 50 feet high, you’ll gain 6 dB!”
If you have the height to do it, you want your antenna to be at least 1 wavelength off the ground. So here is what 1 wavelength is in height for different bands using the 1 wavelength formula: 984 divided by the exact middle of each band:
- 10 meters: 34 feet
- 15 meters: 46 feet
- 20 meters: 69 feet, 4 inches
- 40 meters: 137 feet, 7 inches
- 80 meters: 262 feet, 4 inches
- 160 meters: 517, 9 inches.
Note: Since many people can’t get above 60 feet in height, 40 to 60 feet is good enough.
However, LB Cebik, in his book, Antennas from the Ground Up, notes that while many people think a half wavelength is the best height to put up an antenna on HF, this is not necessarily the case. He explains that a half wave has a dB gain of 6.9, but a 5/8ths wave has a dB gain of 7.9. Also, he says that people think the higher the antenna wavelength, the better on HF, but this isn’t always the case. For example, a 1 wavelength antenna in height has a dB gain of only 7.8 compared to 7.9 dB with a 5/8ths wave antenna in height.
Here’s an example of why striving for the 5/8ths wave I just mentioned is so important compared to trying to achieve a higher height. Years ago, I was renting a room in Illinois. The room had a piece of TV lead; I didn’t know what it attached to. I wanted to get back on HF, but I had no antenna to use. I had been off the air for almost five years since leaving home to go to college, and I was very depressed about my lack of time on the air.
One cold day in January 1989, Dennis, K0DB, said, “Trippy, I want to get you back on the air where you belong. I know someone who has a TV tower they’re not using. It doesn’t have a TV antenna and it goes up 40 feet! The tower will be an all band vertical with no radials on it! You know that TV lead in your room? It goes out of the house and connects to the TV tower. I can take this end of the TV lead that’s just hanging down in your room and connect it to the binding post on the back of your MFJ antenna tuner and you’ll be on the air today. How about that!”
So that’s what he did.
Here’s the awesome part: I was able to get out on SSB and CW on 10 through 40 meters, and CW on 80 meters. I didn’t know how good that TV tower would work as a vertical antenna, but I got my answer later that year in the CW Sweepstakes in November. Sunday morning, I got on 20 to make contacts in the contest, and one of the stations told me, “You’re the LOUDEST signal on this band!”
That just blew me away. Only 100 watts, a 40-foot tower with no antenna on it, NO RADIALS, and I was the loudest signal on 20 meters!
Why was this station the loudest on the band? Because the tower was up 40 feet, just below a 5/8ths wave in height on 20 meters (a 5/8ths wave vertical antenna on 20 meters is 43.38 tall). That’s much better than a quarter wave! If it would have been 43 feet, 4 inches, it would have been a 5/8ths wave vertical!
However, I could not get out on 80-meter SSB. Why? Because the tower was only 40 feet, not even a quarter wave vertical for 80 meters. Now if it was 65 feet, 6 inches high, it would have got out on 80-meter SSB.
Here’s another way to use a tower as a vertical: If you have a tower (TV or otherwise) with no antenna, make a snake antenna. This is just a piece of coax. Use a PL-259 connector at the shack end and run it from your antenna tuner up one side of the tower as high as it will go.
For example, if the base of your 40-foot tower is 100 feet from the antenna tuner in your ham shack, make a 140-foot snake antenna. Run the snake from the antenna tuner up to the top of the tower. Use a tie wrap, or zip tie, every so many feet (use your discretion regarding how many tie wraps to use), and I bet it will work! Unfortunately, I don’t have a yard that allows me to put up a tower, but if I did, I would do exactly as I’ve told you—and I’d get on the air! So try it. You might really love it, and if it works, let me know. If you want to know more about the snake antenna, email me and I’ll send you an article about it.
And if you want to know more about using a tower as a vertical, I recommend getting ahold of the book Low Band DXing by John, ON4UN.
Questions? Comments? Reach me at hebrown3rd@gmail.com.
