4/13/2007

Folding 3band Hamstick Dipole (F3BHSD)

| Bill of Materials | Drawings | Photos |
  • OVERVIEW:
    • I had seen articles about using two Hamsticks as a dipole, and I had seen multiple Hamsticks mounted to a common base to use as multi-band. So, I thought I would combine those thoughts and create a multi-band Hamstick Dipole.
    • In the process of designing the mount, I came up with the idea to make the assembly foldable for easy transport. That way, it would be an easy unit for field day or emergency use. I am sure the idea could be carried to extremes, but I decided on a tri-bander: 20m, 40m, and 75m.
    • All parts are aluminum, stainless steel, nickel-plated or bare brass, or plastic or fiberglass. I expect no corrosion problems with these materials.
    • For economy, I have chosen Workman antennas from WBØW. If they prove unreliable, I can easily change to real Hamstick units.
  • DESIGN:
    • The original design was sketched 3/29/07 in a spiral notebook while lying around watching television. The next day, I drafted the design using AutoSketch on my laptop computer. The general design never changed, although several variations were tried to optimize material usage and durability.
    • A few items were designed on-the-fly while building the first unit. The droop of the elements necessitated the addition of acrylic spacers at the ends of the fiberglass base sections. These will be changed to a more suitable material as time permits. Acrylic is just too brittle for the continuous flexing and wide temperature variations that these spacers will see. I suspect that UV-resistant nylon or UHMW may be the material of choice.
    • Since both the base and the angles are made of 6061-T6 aluminum, they would gall and bind if permitted to rub against each other (like when folding and unfolding). Therefore, I added a layer of .005" adhesive-backed UHMW polyethylene tape to the backs of the angles. This will provide a slick surface for easy movement plus avoid any chance of galling.
    • The aluminum is unfinished to allow good conductivity between the parts. If corrosion becomes a problem, I would recommend a conductive coating such as "Alodine 1201".
      Alodine 1201 MSDS - READ THIS CAREFULLY BEFORE ATTEMPTING TO USE!
      Anodizing or paints are not conductive and cannot be used.
    • 4/23/07 Problems Encountered... Redesign time!
      The 3/8-24-to-SO239 adapter proved to be "a piece of junk". It was fair in design, but so poorly manufactured that it was unusable. The center socket contact was bored too small, plus being only partly slotted, preventing insertion of a standard plug. There was also no notches in the rim for the teeth of a standard plug. I don't know who made this adapter, so I can't offer any advice to others. Just be aware that there are less-than-perfect products out there.
      Also, I had intended to use a UHF elbow to route the coax down from that adapter. The elbow that I had was better, but still not acceptable.
      So... I added another part made from the same 1" aluminum angle used for the element mounts. On it, I mounted a standard SO239 receptacle and a lead of 12AWG stranded building wire and a soldered lug. This is intended to be just long enough to allow the antenna to fold for transport.
  • PROCUREMENT:
    • Antennas were ordered from WBØW.com via the internet.
    • Aluminum plate and angles, UHMW tape, brass sheet, and stainless U-bolts were ordered from McMaster-Carr.
    • Stainless bolts and washers and acrylic sheet were purchased at a local hardware store.
    • Stainless ESNA nuts were from my personal stock but could also come from a local hardware store.
    • Mast and rotor are just things I had lying around (plus some fresh paint).
  • CONSTRUCTION:
    • Gather all parts and materials
    • Layout and cut 1/4" plate and angles to size
    • Layout, drill, radius corners, and debur plate and angles
    • Lightly sand and thoroughly clean plate and angles
    • Cut and fit UHMW tape to angles
    • Assemble angles to plate using (4) 1/4-20x1" SS hex bolts, flat washers, and ESNA nuts
    • Loosely assemble U-bolts, flat washers and ESNA nuts to plate, including the connector bracket
    • Assemble (3) grounded antenna studs to the grounded angle
    • Assemble (3) insulated antenna studs, connector lead, and busbar to the hot angle
    • Mount assembly to the mast
  • DEPLOYMENT/INSTALLATION:
    • Tools:
      • Ratchet handle
      • 7/16" socket
      • 9/16" socket
      • 7/16" box or combo wrench
      • 1/2" box or combo wrench
      • Adjustable wrench
      • Allen wrench (comes with antennas)
      • Spare bolts, nuts, washers (just in case)
      • Spare hose clamps
      • Roll of electrical tape
      • Small tool box to keep all this small stuff in
      • Fence post driver
      • Fence post puller
    • Find a location where an 8-foot radius is clear for antenna rotation.
    • Drive a steel fence post at least 18" into the ground, making sure that it is true vertical
    • Place a scrap of lumber or a rock as a base on which to rest the mast.
    • Lay out the antenna on the ground and raise and secure the folding elements into position.
    • Stand up the antenna assembly and secure it to the fence post with two stainless hose clamps.
    • Orient the antenna in the desired direction before tightening the clamps.
    • Connect the coax and rotor control (if provided).
    • Operate!
    • When reversing this process, be sure to secure the bolts back into their holes so they don't get lost.
    • When elements are folded down, use electrical tape to secure them to the mast.