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.
In our continuing look at the benefits of using dipole/inverted-V combo and end-fed antennas and insights on how to build them, I’ll be answering a few more frequently asked questions in today’s blog post. To read the first five entries in this series, just enter “Trippy” in the OnAllBands search box above.
When putting up a dipole/inverted-V combo or end-fed antenna, is there a way that I could build them without need for an antenna tuner?
According to VE3BXN, a ham for over 40 years, when you put up a dipole/inverted-V combo or end-fed, always have the apex (meaning the center point which is the feedpoint of the antenna where the balun or unun is) as high up as possible and do not let the center sag.
For the dipole/inverted-V combo, drop the ends so each leg is sloped at a
52.5 degree angle, totaling 105 degrees. Note that each leg can be dropped at even more than 52.5 degrees. If you can do it, drop each leg straight down at a 90 degree angle for a total of 180 degrees.
For the end-fed, the wire leg can be sloped at a 45 degree angle, or if you can do it, drop it straight down at a 90 degree angle.
If you do this with your dipole-inverted-V combo or end-fed, when you check the natural SWR (check out Part 3 of this series), you should see that it’s, at most, 2 to 1 or even lower everywhere on all bands. That means you will not need to use an antenna tuner to bring down the SWR because it will already be very low.
I built a dipole/inverted-V combo for a ham who lives in an apartment. We sloped the one leg at 45 degrees and dropped the other leg straight down at 90 degrees for a two-leg total of 135 degrees. His SWR on 80 meters was 1.7 to 1 or lower across the entire 80 meter band, so he doesn’t need to use the antenna tuner on 80 meters—it’s incredible!
If you are unable to slope the dipole/inverted-V combo or end-fed at a 105 degree angle, try 90 or 45 degrees. But no matter what, just slope it the MOST angle you can. If the angle is less than 105 degrees, do a natural SWR check. If it’s higher than 2 to 1, use an antenna tuner.
What measured footage for a dipole/inverted-V combo or end-fed shoot I shoot for?
The measurements that work are all the traditional options recommended by other hams: half wave or multiples of half waves, like one wave, one-and-a-half wave, two wave, etc.
Note: If you want to only use it on one band—or use it on all bands—and you have the room to put up and string out a half wave dipole/inverted-V combo or end-fed instead of a quarter wave, do it—even if you don’t have the room. You can use coiling, which is a revolutionary way to put up dipole/inverted-V combos or end-fed antennas (see below).
At a half wave, these antennas have a radiation resistance which is much closer to the characteristic impedances of available coax, and normally much larger than the resistance of the conductors so that their efficiency approaches 100%, which is what you want with your dipole/inverted-V combo or end-fed.
What about ferrite chokes?
For your end-fed, you will also need to use at least two ferrite chokes, also called common mode chokes or line isolators. Snap one right next to the PL-259 connector at the shack end and the other next to the PL-259 connector at the feedpoint end.
I don’t have enough space to string out my half wave end-fed antenna. What do I do?
I have good news for you! Coiling is the answer. Below are the steps to take to coil an end-fed if you don’t have the room to string it out all the way.
- Using the same length of wire you would normally use for your end-fed, hang a 56 to 1 unun (I’ll discuss how to do this in an upcoming article).
- Measure how much room you have to string out the wire starting at the unun where the wire is connected to it as far as you can string it.
- Put some kind of marker at the six-foot point, which is six feet away from where the wire connects to the unun. You can use a piece of tape or a tie wrap for a marker.
- Take the coil of wire and connect one end to the unun.
- You will need someone to assist you with this next step. While holding onto the coil so it does not move from the six-foot point (but loose enough so the end of the wire that’s not connected to the unun can be gently pulled to the place where you cannot string any more wire), have your assistant pull the wire to its termination point.
- Take a porcelain insulator. You’ll notice it has four holes, two on each end across from each other. Put the end of the wire through one hole on one side, then across through the hole on the other side. After you get the tip of the wire through the second hole, it should be touching your thumb.
- With your thumb on the right hole and your other thumb on
the left hole, move the insulator to the left until there is enough
wire to go from that right hole, along your right thumb until your right
thumb meets your hand. Now you have enough wire. - Keep the insulator where it is, with your left thumb and finger to keep it from moving.
- Take the wire on the right side of the right hole of the insulator and bend it to the left so it will touch the wire that is to the left of the insulator.
- Bend that little piece of wire to the right of the wire it is touching until you cannot bend it anymore.
- Move the insulator to check to see if it comes off the wire. If it doesn’t, you’re set. If it comes off, repeat steps as necessary until it stays on.
- Take a tie wrap, put it through the coil, and lock it tight so the coil and the wire in the coil cannot move from that six-foot point.
Congratulations! You have just put your wire leg onto the end-fed!
Next week I’ll be discussing performance results of some popular antenna lengths for dipole/inverted-V combos and end-feds.
