2 Meter Backpack Quad Antenna
This 2 meter 3 element cubical quad antenna is small, light weight and portable. A backpack antenna that is easy to put together in just minutes and parts store inside the boom making it ready for travel or storage.
Three element quad antennas typically have about 2 db more gain than a comparable size yagi and should rival the performance of a five element yagi antenna.
In building this antenna for the first time I found that a large metal mounting bracket would not work well with the antenna. A large piece of metal or a metal boom tends to cause a slight problem with SWRs especially if the antenna is designed to be built with a non-conductive boom. If mounting the antenna to a metal mast a section of about four feet of PVC pipe, with a wood stiffener placed inside, should probably be added to the top of the mast to mount the antenna. The antenna builder should also be aware that this is an ungrounded antenna and that care should be taken.
I used the standard cubical quad formulas and used 146 MHz to caluclate the lengths of the wire elements but the antenna came out instead resonate closer to 147 MHz. Please keep this in mind if you would like to build the antenna for a lower frequency. The formulas used for calculating the antenna element and spreader lengths are discussed in the video Cubical Quad Antennas (watch on YouTube).
The boom needed to be large enough to fit the parts inside but also needed to be small enough to still fit the U-bolts. I decided to use a 1-1/4" PVC thick wall pipe for the boom. Being 30-7/8" long it is just slightly longer than the reflector spreaders. If I were to remake the antenna I might next time choose 1-1/2" PVC thick wall pipe for the boom just for a little extra storage space inside. Fitting the spreaders and wire elements inside the boom was easy but trying to get a plastic zip-lock bag containing the small parts inside proved to be a bit challenging. After a couple of tries I did manage to get all the parts inside of the boom. I found it best to leave the vinyl tubing on the spreaders and put just the nocks in the plastic bag then place the parts inside the boom. For a four element backpack quad antenna use 1-1/2" PVC thick wall pipe.
After drilling the holes in the boom, if the spreaders are a tight fit then use a small round file to just slightly enlarge the holes. The clear vinyl tubing is used to help hold the spreaders in place. Also, the clear tubing should shrink in the sunlight for a tighter fit if using the antenna outdoors for fixed use.
Left over glue from stickers can be removed from the fiberglass rods using a paper towel dampened in paint thinner or mineral spirits. Cleaning the rods with a wet paper towel may also reduce the amount of loose fiberglass splinters that may otherwise end up in your hands.
A New Set of Plans
The following two diagrams are different than those shown in the video. I have recalculated all of the element and spreader lengths in order to make the antenna more resonate in the center of the band. The measurements for the boom remain the same -- other than suggesting 1-1/2" PVC pipe for the boom. To see the results of the new measurements please click here to watch the follow up video.
When calculating the length to cut the spreaders deduct 3/32" (about 2 mm) for the 14 gauge stranded bare copper wire, and deduct the distance needed for the two nocks, from the total calculated spreader length. If the spreader is slightly too long then use a rasp to file down one end of the rod taking care not to file too much off at a time. Keep each pair of spreaders the same length.
Video Instructions Watch the video below to learn how to build this antenna.
The antenna can be built with either the square or diamond shaped elements using the same construction method. If you drill holes for a mounting clamp, while drilling holes for the spreaders, the antenna will be postioned with diamond shaped elements.
This antenna is fed directly with 50 ohm coaxial cable (RG-8X-mini 8). The distance from the ends of the two ring connectors, soldered on the end of the cable where the shield and center are separated, determines the amount to deduct from the total length of the driven element. The coax where separated becomes part of the driven element. On a diamond shaped driven element, fed on the side (vertical), push the coax outward on to the nock to match the shape of the insulator and secure the coax to the spreader with plastic ties or tape.
At least 21' (6.4 m) of 14 gauge stranded copper antenna wire.
Mast mount clamp and hardware.
Safety First! Please use caution and keep common sense safety rules in mind when installing an antenna. Never install antennas near power lines or in any location that would place people or pets within the near field radiation pattern of an antenna. All users understand and agree that the owner of this web site is not responsible for accidents or other mishaps that may have been caused directly or indirectly as a result of the information published on this web site and/or in any of the video presentations.