Spiderbeam Balun A900 Assembly & Instruction Manual

Parts list Spiderbeam kit SKU A900
SKU QTY
Aluminium 'U'-Rail 15x15mm, length 200mm
PA007 1
PA009 4 M6 x 30 bolt, stainless steel
PA010 2 M6 x 16 bolt, stainless steel
PA012 12 M6 nut, stainless steel
PA013 10 M6 washer, stainless steel (outer diameter 18mm)
PA015 4 M3 slotted head screw, stainless steel, length 10mm
PA016 4 M3 nut, stainless steel
PA115 4 M3 washer, stainless steel
PA017 6 Rubber sealing washer for M6
PA027 4 M6 tubular cable lug, tin plated copper, with 90°angle
PA030 1 Predrilled black plastic enclosure, 120x90x55mm, waterproof, UV-resistant
PA031 1,05m Teflon Coax cable RG142
PA032 1 Ferrit toroid ring FT-240-61
PA033 1 PL Coax socket SO239
PA034 1 Rubber gasket for coax socket
PA035 1 M3 soldering lug
PZ01-1 5 Cable ties, black 200x4,8mm
Technical note for use with Spiderbeam Yagi antennas:
First of all kindly note: Hundreds of hams who have never built a balun before in their life, have successfully
built this easy-to-build Spiderbeam balun. If you follow our instructions, you can too!
The feed point impedance of each driven element is very close to 50 Ω. The short pieces of 100 Ω
transmission line do not have a significant effect on this impedance, so 50 Ω is seen at the balun. Thus,
there is no need for impedance transformation. However, the symmetrical feedlines from the 5 radiators
must be attached to an unsymmetrical 50 Ω coax, thus a 1:1 current balun is necessary to avoid common
All Spiderbeam Yagi antennas use a 1:1 choke-balun with "cross-over" winding, developed by
.
mode current
Joe Reisert, W1JR. It is wound onto the FT-240-61 Toroid, and has 12 complete turns of RG-142, Teflon-
insulated coax, with 6 turns on each side. The crossing to the other side is numbered here as a "turn" for the
sake of understanding, but in fact it is not a turn around the ferrite (see the photo on page 2 with 13 marked
bends). The balun described below (as a coax choke) can be used not only for our antenna, but also in the
entire frequency range from 1.8 - 30 MHz, e.g. for dipoles of all kinds.
Plastic-Enclosure
The plastic box is shown here in light-colored plastic for better visibility.
However, the housing supplied by us is black, as this
makes it more UV-resistant. The box supplied by
Spiderbeam for the kit is complete with seal, pre-
drilled and ready for installation.
Aluminium U-Rail
The aluminum profile is provided with two 6.5 mm
holes for fastening. It serves as a "mounting bracket" for attaching the balun to the
standpipe. Insert two stainless steel M6x16mm bolts through the U-Rail, and then
mount it against the back side of the plastic case, by pushing the two bolts through
the bottom holes of the case. From inside the plastic case, first slide an M6 rubber
washer over each bolt, then an M6 stainless steel washer, and finally an M6
stainless steel nut. Tighten the nuts with an M10 wrench (spanner).
Assembly instructions manual
Spiderbeam Balun (Coax choke)
Description
1