A THREE BAND INVERTED VEE ANTENNA
How would you like to build a simple, multiband antenna that requires no traps, coils, or radial system? I ran across this interesting challenge when gusty winds, a fallen tree branch, and nine days of heavy rains finally took their toll on my end-fed halfwave antenna this past Saturday (23 February 2013).
Two weeks ago, I took down my 20, 15, and 10 meter ground plane antenna (using balanced feeders) and the 40 meter inverted vee (using balance feeders) for routine maintenance. In their place, I erected a temporary end-fed halfwave antenna cut for 40 meters. The antenna was satisfactory for my casual operating schedule and I didn’t plan to erect the other antennas until early March. Since January, both my xyl and I have been teaching school at the Laupahoehoe Community Public Charter School, so my usual free time during the day has been cut short. Anyway, the forces of nature intervened and left me with a jumble of wire where a nice halfwavelength antenna once stood. Of course, the 40 meter loop under the house wasn’t affected by the severe weather. The loop is a winner for local contacts and interisland nets, but for dx purposes, the low-level loop is a hit or miss deal.
So, I cleaned up the mess, saved most of the wire, and got the weeds and mud off the still intact MFJ 33-foot (10.06 meter) fiberglass mast. Considering how many parts I have in the ole “junque” box, I figured a new inverted vee fed by balanced feeders (450-ohm ladder line) would be easy to build and get on the air. Unfortunately, my supply of 450-ohm ladder line was nearly exhausted, so I opted for some RG-8X coaxial cable to feed the new “skyhook.” Unlike balanced feeders, coaxial cable can’t handle the SWR extremes found in multiband antennas, so, I decided to make a segmented inverted vee to cover my favorite amateur radio bands–40, 20, and 15 meters.
I based by antenna design on several examples found in Edward M. Noll’s (W3FQJ) book,”Easy-Up Antennas for Radio Listeners and Hams.”
Because of limited space in my backyard, I opted to erect an inverted vee antenna. A horizontal dipole erected at 35 to 50 feet (10.67 to 15.24 meters) would be better, but available tall supports weren’t available after the storm took away the most promising branches of the nearest tree. I also wanted an antenna that didn’t require a radial field. My backyard is too small to lay down an extensive ground system. Although I’ve used vertical antennas with a tuned counterpoise system and even ground plane antennas (4 elevated radials), I just preferred to avoid the radial issue this time around.
The inverted vee antenna would use wire lengths based on the general formula, 468/f (MHz)=L (feet). Various antenna experts have suggested that the length of the antenna elements in an inverted vee system should be between 3% and 5% shorter than the elements of a horizontal dipole. I decided to keep the antenna a bit long, so I could trim the elements for the best SWR.
One 33-foot (10.06 meter) fiberglass or pvc mast. I had a spare MFJ fiberglass mast in the storeroom for this purpose.
Three, five-foot (1.52 meters) wooden stakes–2 for tying off the inverted vee antenna elements and 1 for mounting the mast.
One Budwig center coax connector (available from Fair Radio Sales).
Four ceramic or plastic insulators–two for each antenna element.
Fifty feet (15.24 meters) of RG-8X coaxial cable with UHF connectors.
Approximately 70-feet (21.34 meters) of #14 AWG household wire. Each antenna element would contain two quarterwave segments of wire, cut to the chosen 20 meter frequency of 14.200 MHz (approximately 16.5 feet or 5.03 meters). Each segment was attached to an insulator. A clip lead from the end of the first segment would be connected to a clip lead attached to the remaining quarterwave segment, thus producing a full 33-foot (10.06 meters) quarterwave wire for the chosen 40 meter frequency (7.088 MHz–the Hawaii Afternoon Net frequency).
If I wanted to operate only on 20 meters, I would unclip the second 20 meter segment from each side. The antenna would then be a 20 meter inverted vee. To operate on 40 meters, I would then connect both segments together on each element to get the full quarterwavelength on 40 meters. I used a “homebrew” swivel to lower the mast to connect or disconnect the various elements for the band in use.
Four ceramic or plastic insulators. One each to divide the 20-meter quarterwave elements on each wire. And one each to tie off the remaining 20 meter segment to a wooden post.
A static discharge unit connected to an 8-foot (2.43 meters) ground rod. The coax feed line would be attached to this unit before another shorter cable would be used to connect the antenna to the transmatch.
A transmatch. I relied on my trusty Drake (MN-4) to handle the small mismatch in the antenna system.
Dummy load and transceiver (in this case, my old Swan 100 MX).
The antenna was constructed on the ground. I cut 4 equal length 20 meter antenna elements for 14.200 MHz. Two segments would be used for each side of the inverted vee. The wire (#14 AWG housewire) was cut to 16.5 feet (5.03 meters).
The top segment of each element was connected to the Budwig center connector. Connections were soldered, painted with clear nail polish, and covered with several layers of vinyl electrical tape.
Clip leads were attached to each quarterwave section. Plastic bags covered the clip leads when they were connected or disconnected.
Before I connected the RG-8X coax to the center connector, I made a “choke balun” out of the coax to prevent rf coming down the outside of the feed line and possibly entering the shack. The balun consisted of 8 turns, approximately 6 inches (15.24 cm) in diameter. The “choke balun” was secured with vinyl electrical tape and attached to the fiberglass mast with nylon ties.
I ran the RG-8X straight down the mast to the 16-foot (4.87 meters) level. I tied off the coax with a few nylon ties.
I set the mast on its wooden support stake and tied off the antenna elements.
The antenna elements helped support the mast.
I then ran the coax feed line to a plastic hook in the garage and then onto the static discharge system. From there, a short length of RG-8X (10 feet or 3.04 meters) went to the Drake transmatch. Patch cords connected the transmatch to the dummy load and the Swan 100 MX.
The antenna seems to be working well. With the help of the transmatch, I can keep the SWR below 1:6 to 1 on both 20 and 40 meters. Most of my SSB contacts to the U. S. mainland have been in the 55 to 57 range, with the cw reports falling between 569 and 599. Power has not exceeded 20 watts.
Oh, yes…I mentioned three bands. You can use the 40 meter configuration (both 20 meter elements connected on each side) to operate on the third harmonic of 7.088 MHz (21.264 MHz). You can use your transmatch to handle the small increase in SWR encountered on 15 meters. When the antenna is used on 15 meters, it will perform as a 3/2 wavelength antenna, which will still present a good match for 50-ohm coaxial cable feed lines.
I’ll leave this antenna up for a few weeks before I take it down for storage. So far, so good.
Noll, Edward, M (W3FQJ). “Easy-Up Antennas for Radio Listeners and Hams. Limited edition, 1991. MFJ Enterprises, pp. 103-118.
Have fun with this antenna. It isn’t fancy, but it works.
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Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.