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.
Dipole/Inverted-V Combo and End-Fed Antennas: Some questions and answers.
Both dipole/inverted-V combos and end-feds are great antennas!
With a dipole/inverted-V combo antenna, each leg is connected to a 1 to 1
balun. The legs are stretched out horizontally as far as possible and dropped straight down at a 90 degree angle or sloped down at a 45 degree angle.
With a half-wave end-fed antenna, the coax goes from the radio to a
56 to 1 unun. One piece of wire is connected to the unun, strung out as far as possible, and connected to an insulator at the end of the wire.
I prefer the 56 to 1 compared to the 49 to 1 unun because, in the words of one antenna expert I consulted, “The 56 to 1 unun transformer gives a slightly better match on low bands than the 49 to 1 unun.”
Do you need a balun or an unun?
If you’re building a dipole/inverted-V combo, you absolutely need a 1 to 1 balun. If you’re building an end-fed, you absolutely need a 56 to 1 unun. I never build a dipole/inverted-V combo without a balun, or an end-fed without an unun. As I’ve mentioned in a previous post, I use a balun (MFJ-918) that has three I-hooks (one in the middle to hang it up and one for each leg of the dipole/inverted-V). I use this balun because my fingers do not work well when wrapping wire around binding posts or lug nuts. For a half-wave end-fed, I would only use a 56 to 1 unun, but the problem is nobody in the industry builds 56 to 1 ununs with I-hooks (or I-bolts).
For dipole/inverted-V combo antennas, should I use 4 to 1 baluns or 1 to 1 baluns?
If you’re dipole/inverted-V combo is balanced, meaning each leg is the
same length, then a 1 to 1 balun is better because it gives your antenna a perfect 1 to 1 SWR, and that is what you want! I agree with hams who say that open-wire/center-fed dipoles are the most efficient antennas for covering 5 to 7 bands. That is what we want—to cover as many bands as possible with just
one antenna.
However, I have GREAT news for you. Until now, people thought that if the antenna is not balanced (for example, one leg is 10 feet long and the other leg is 21 in an off-center-fed antenna), you would need a 4 to 1 balun. But because of coiling, it does not matter if you have less room for one leg of the antenna than the other. You still can use a 1 to 1 balun because you’re going to be putting up a dipole/inverted-V combo that has the same length for each leg—meaning no need for an off-center-fed antenna and 4 to 1 balun. Keep following my posts. There will be much more to come about this.
Which is better: A dipole/inverted-V combo or a dipole alone?
From my experience, a dipole/inverted-V combo is much better than a horizontal dipole. Here are some of its advantages:
- It lowers the feedpoint impedance from the nominal 75 ohms of a
dipole to just 50 ohms. This, of course, is ideal for matching the antenna
to standard 50-ohm impedance coaxial cable and makes for a better
match, because your antenna tuner and your radio both love, you guessed it, 50 ohms. - It is more omni-directional than a dipole. You want omni-directionality because it allows you to make contacts from all directions. There’s nothing worse in ham radio than having to turn a beam to work a station. I should know: I broke two rotors working 50 different stations
in different directions. After I broke the second one, I said to myself,
“The heck with this. I’m going omni-directional so I can work stations without having to turn an antenna.” - It has an excellent reputation for long-distance communication on the
lower-frequency amateur bands (160, 80, and 40M). - Where the installation of large verticals or high horizontal dipoles
is not practical due to lack of height and/or having enough space to
string them out, the dipole/inverted-V combo is better for portable operation. This is because the two legs of the dipole/inverted-V
combo drop straight down, or slope toward the ground, requiring less
horizontal room than a regular dipole. And you don’t have to have the
antenna up so high like you have to have for a vertical. For example, the dipole/inverted-V combo performs very well at low frequencies and will give good results on the 3.5 MHz ham radio band when the apex, meaning the center feed point, is only about 45 feet high or less.
On the other hand, the regular dipole does not perform well at 45 feet high or less, making the dipole/inverted-V combo a very attractive proposition for many amateur stations on 160, 75 or 80, or 40 meters.
Note: As a matter of fact, I no longer build dipoles at all, and I tell
all the hams I can to stay away from them and use a dipole/inverted-V
combo instead because of the above advantages.
What about using parallel dipole/inverted-V combo antennas?
I stay away from those because they are a group of antennas joined together at the center. I don’t want to mess with more than two wires because the goal should be to use one antenna for all bands, not more than one antenna.
Stay tuned for my next post in which I’ll be answering questions about measuring dipole/inverted-V combos and end-feds, advice on keeping these antennas up when faced with high winds, and what types of ropes to use for hanging them.
