The driving force for constructing my hamstick minibeam was for Field Day use, exclusively for PSK31 operation on 20 Meters and QRP. I wanted an antenna that exhibited some gain, is portable, lightweight and easy to erect. Thanks to Russ Wilson VE6VK, the designer of the hamstick minibeam, I was able to achieve this goal. By mirroring his antenna dimensions but re-designing the hardware, the minibeam can be broken into transportable pieces and can be easily deployed in the field.
The photos are self explanatory and give you an idea about the specifics of the hardware components, this project required access to a machine shop facility.
The 12 foot long boom consists of two 6 foot sections of aluminum tubing of 1 inch OD. An 8 inch long telescoped aluminum coupling tube is glued (marine epoxy) 4 inches into one of the 6 foot boom sections. The other section is slotted and slides over the coupling tube. The two sections are clamped together with the clamp/antenna mounting post. The reflector and director mounts are 3.5" x 3/4" x 3/4"; the ends are tapped 3/8" X 24 TPI for mounting the hamsticks. The post and mounts are machined from aluminum.
The driven element mount is 3.5" x 1.5" x 3/4": it is machined from a block of Delrin, a very durable insulating material; the mount insulates itself from the boom. The ends of the mount are wrapped with copper sheeting for the electrical connections. Threaded into each end of the mount and contacting the copper sheeting is a machined aluminum coupler of 1" x 5/8" OD, tapped 3/8" x 24TPI for mounting the driven element hamsticks. The reflector, the director and the driven hamstick mounts all have a .060" deep groove milled into the base for square seating to the rounded boom. They are fastened down with a 2.5" long 8-32 stainless steel bolt with nut.
A block of machined Delrin, 1.5" x 1.5" x 3/4", with a 1 inch hole attaches the RBA 1:1 current balun to the boom. The antennas electrical connections are 1/4" wide copper sheeting strips cut to length and shaped to fit. They are soldered to the ends of the driven element mount and the other ends are bolted to the tapped 10-32 banana posts of the balun. A hairpin match is soldered across the driven element. It is constructed from a T-44 toroid core (red, a 2mix) wound with 7 turns of #18 magnet wire. The inductance measured 1.8 micro henries with a "Z Meter".
The minibeam weighs in at 3.8 lbs and was mounted on top of a 21 foot telescoping Wonder Pole for tuning. A 50 foot length of RG-8U coax cable was connected to the balun and the antenna was adjusted for a VSWR of 1:1 at 14.070 Mhz. The length of the hamstick rod (whip) is dimensioned from the tip of the rod to the "tapered" end of the rod ferrule. The dimensions are: Director - 34", Driven Element 38 5/16", Reflector - 44 5/16". The VSWR measured: 14.00 Mhz - 1.7:1, 14.036 Mhz - 1.5:1, 14.070 Mhz - 1:1, 14.140 Mhz - 1.5:1, 14.160 Mhz - 1.7:1, 14.190 Mhz - 2.0:1. If you wish to contact Dietmar you may email him at firstname.lastname@example.org
1 - Minibeam on 21 ft Wonder Pole.
2- Reflector and Director mounting block
3 - Clamp/mounting Post, Driven Element mounting block, Aluminum Coupler, Hairpin match and Balun, Electrical connections.
4 - Break down of antenna - transportable pieces.
5. Boom sections with coupling tube
-Clamp/Antenna mounting Post.
"V" Beam Pictures.
6 - "V" beam on Wonder Pole
7 - Reflector mount.
8 - Driven Element mount.
- Hairpin match and Balun
- Aluminum coupler
- Electrical connections
Two photographs of the "V" Beam.
One on the ground and the other up in the air.
MINI-HORIZONTAL "V" 2 ELEMENT HAMSTICK 20M BEAM.
4 20M hamsticks
1 inch square aluminum boom 4 ft 6 inches long.
1 mounting bracket driven element.
1 aluminum mounting bracket reflector.
4 insulated CB mounting kits 3/8" by 24 TPI (2 can be un-insulated for reflector.
Wire for hairpin match, .1/8" welding rod 24 inches long.
Coaxial balun 12.5 ft RG58 wound on a 1-1/4 inch white PVC 8 inches long, or regular 1:1 balun.
Bolts, nuts, lock washers for mounting.
Two brackets are made. One out of nylon or heavy plastic for the driven element and scrap aluminum for the reflector. The reflector bracket is bent into shape as per the photograph to allow element kits to be mounted so the elements are at 90 degrees from one another. The driven element insulator is also formed so that the hamsticks will be 90 degrees from one another. The reflector required some reinforcement so a cover was formed and fastened with self tapping screws. This prevented bending of the element.
At 15 ft off the ground, measurements were made of the Driven element using an electrical 1/2 wave length of RG58 as a 1:1 transformer. Using the antenna analyzer from the ground the following measurements were noted.
Impedance 25 ohms
The antenna was resonated to 14250 Khz.
A hairpin match was made using 1/8 inch welding rod. Two lengths 24 inches long are required. NOTE: (As the impedance is 25 ohms an Inducto match can be substituted for the hairpin. This would be 10T #12 guage 8T per inch. This would go across the driven element center. Reresonate and adjust spacing of turns slightly for a 1:1 SWR.)
The two rods have solder lugs placed on them at one end. These ends are connected to each mounting kit terminal for the Driven Element. The wires are spaced 1-7/8 inches from each other and are arranged so they are approximately 1 inch above the boom. See photographs for details. A couple of plastic spacers are used to keep the wires separated. Also a piece of 3/8 inch thick plastic is mounted on the boom, 2 holes drilled for the wires to pass through for extra supposrt. After the hairpin is mounted and a temporary shorting bar placed across the hairpin, the antenna is placed in its original position and further readings taken, adjusting the sliding short across the hairpin, until the impedance of 50 ohms is reached. A little juggling of the whips to bring the driven element back to 14175 Khz is necessary. After a few minutes of testing and adjustment of the hairpin short and the whips, the resonant frequency of 14175 Khz is reached and the impedance reads 50 ohms. The short on the hairpin can be permanently set using the bolts in each end.
Measure the length of the whip on the driven element, multiply this by 6% and add this to the length of each driven element whip. In my case it was 38.5 inches. 2.3 inches was added to each reflector whip. The boom length was experimented with and the length shown seemed to be optimum for the short boom. If you wish to operate CW or any other preferred frequenc you can choose by figuring out the frequency response of the beam is approximately 200Khz. The photographs should assist in figuring out the brackets etc. If you tune the antenna to the high end, say to 14260 and you wish to work on CW, use 4 clips, one on each hamstick, This will take you down into the CW portion of the band. Similar to what is described in the hamstick dipole above. Information on a hair-pin match can be obtained from ARRL Antenna Handbook and other publications.
A coil can be substituted for the hair-pin. Once the impedance is known coil calculations can be obtained from graphs.
The two photographs above show on the left the mounting bracket for the driven element, the balun underneath, the hairpin connection and insulator. Portion of the 1 inch square boom is also shown. The mounting studs are 1 inch with 3/8 inch by 24TPI mounting holes. The photograph on the right shows the mounting bracket with the studs mounted and some reinforcing to prevent any bending of the bracket. The antenna and antenna supports can be carried in a shortened ski bag, or equivalent, together with any tools required.
The above mounts, brackets, hairpin etc. were made by my good friend VE6YV Dick. Excellent workmanship! Dick is building another antenna for his portable operations.
Parts required: A 1:1 balun. Make your own balun using a 6 or 7" piece of 1-1/2" PVC pipe, 2 caps, 1 female coax connector, a 5" piece of 1/2" ferrite rod, #12 enamel copper wire, two adapters and insulator to support the weight of the hamsticks. 2 hamsticks of the band chosen. I chose 20M so the information following is for 20M only. Other bands can be set up the in the same manner. Use the information contained in the A.R.R.L. handbook for the 1:1 balun.
Once the balun is completed mount it on the selected pipe support with a "U" bolt. Attach the hamsticks to each side of the balun and using a multiple of a 1/2 wave of coax, attach an Antenna Analyzer to the end of the coax. This will act as a 1:1 transformer and allow you to be away from the dipole for the measurements. Tune the dipole to your selected portion of the band. The dipole has a reasonable bandwidth but if you tune it to the high end of the 20M band say 14.250 and you wish to have the same SWR at the bottom end of the band for CW or PSK add a metal clip to the junction of the whip and the hamstick on each side. This will lower the frequency and give you a very low SWR. No tuner required. Photographs below.
A Three - Element Yagi Mini-beam Using Hamsticks
by Russ Wilson VE6VK
Rick NE8Z and I were having a very long discussion about minibeams and credit for suggesting the use of hamsticks must go to Dr. Rick. I thought it was a great idea and well worth building one. I needed something light, easy to install and reasonably efficient with some directivity. Almost immediately I started building the boom and the feed point insulator and then ordered the hamsticks. After lots of experimenting the results are shown below.
BOOM = 12 feet (365.76 cm) x 1-1/4"(3.175 cm) diameter aluminum tubing [4' sections, (121.92 cm)]
BOOM ELEMENT SPACING:
Driven Element to Director spacing = 5' 9" (175.25 cm)
Driven Element to Reflector spacing = 6' 3" (190.5 cm)
DIMENSIONS FROM BOOM TO TIP OF HAMSTICK ROD:
Reflector = 7' 6.5" (230 cm)
Driven Element = 7' 2" (218 cm)
Director = 6' 9" (205.5 cm)
DIMENSIONS OF HAMSTICK ROD (WHIP) FROM END OF HAMSTICK COIL:
Reflector = 3' 8.3" (112.5 cm )
Driven Element = 3' 3" (98.5 cm )
Director = 2' 10.4" (87.5 cm )
IMPEDANCE USING OMEGA BRIDGE =
48 ohms at 15 feet off the ground.
FEEDING = 1 wavelength of RG58U and a 1:1 balun
FREQUENCY COVERAGE = 14.070 to 14.295 flat
TOTAL WEIGHT (INCLUDING CARRYING TUBE) = 12 lbs.
Note: I color code my Hamsticks for ease of assembly. Also for further information on the mounting of the elements to the boom look below the large photograph.
The support for the minibeam is 22 feet high and is constructed of telescoped aluminum. The following photograph is of the fully deployed minibeam. The fittings for the minibeam are shown below the large photograph.
Many enquiries have been received regarding the use of hamsticks for a mini-dipole. This is also described below.
OTHER BUILDING TECHNIQUES ARE SHOWN BELOW THE 2EL BEAM
3 ELEMENT MINIBEAM CONSTRUCTION DETAILS BY BERNIE NP2CB.
The following construction details were configured by Bernie NP2CB. A great deal of thought went into this project and Bernie is to be congratulated on a job well-done!
The boom is 13 feet long and uses a 10 ft, 2.25 inch OD EMT material with an additional 3 ft section connected with a coupler. PVC caps were placed on each end to keep out the critters. A 2x2x4 inch thick wall electrical termination box for each hamstick element was added. Each box has mounting ears and these were used to guide a 2.25 inch U bolt at each end using a pair of aluminum spacers to take up the slack between the bottom of the boom and the U bolt surface. A hole was drilled in each side of the box to accept the Hamstick element mounting hardware, including a 2 inch washer required for reinforcement. After each element, (all six Hamsticks) were mounted in this fashion, a balun was wound, a 26 ft. section of 50 ohm coax was tightly wound around a 13 inch length x 2.25 inch OD length of PVC. The ends were passed through holes drilled into the ends of the PVC which were rounded. Then, one end was terminated into a PL259 and the other end into a pig- tail to secure to the center conductor of one of the Hamsticks and the other to the passive side of the opposite Hamstick. At this point the balun was mounted to the top of the boom with three large plastic tie wraps and two plastic offsets, raising it by about 2 inches. By connecting only the center of the other two sets of Hamsticks, within their respective termination boxes, the fabrication is completed.
Tuning of the beam. Couple an antenna analyzer to tune the dipole only, adjust for as low an swr as possible (1.6:1 is attainable). Now, drill a hole for mounting to the short mast. Secure the beam in an upright position, away from an conductive material, with the reflector element pointing up. Tune all elements for minumum swr. Tune in very small increments. An overall 1.8:1 swr was achieved. The finished product weighs in at an incredible 13 to 14 lbs, has a very high signal to noise ratio over a full wave 20 meter dipole, has excellent forward gain, easy and inexpensive to make, and as bernie puts it ("A hell of a bang for the buck") A few photographs are shown below. Further information can be obtained from Bernie NP2CB.