2021
Copper
Making a helix antenne for 2.4GHz using materials from the workshop. The reflector is a 20cm 4mm thick spare part from Kootwijk Radio. Cleaning the surface and using the turning lathe to adjust the size.
Drilling exact 22mm hole for the LNB
Chaparral
This Chaparral C Band Feedhorn was used in combination with my prime focus 3m dish. I want to re-use the the fastening parts and therefore the insert is modified.
A seperate inlay is made from a bronze bearing using the lathe.
Finishing
4x M16 A2 wire-ends will keep the center point in place. wire is tapped into the housing.
After choosing the 7/15 chasis adapter, the desired position is marked onto the reflector.
Fitting
First drilling the outer diameter of the 7/16 in the reflector and finally 4x 3.1mm holes threathing the connector. John Kraus, W8JK, is the originator of the helical-beam antenna; as he puts it, “which I devised in 1946”. His 1950 book, Antennas, is the classic source of information. The radiating
element is a helix of wire, driven at one end and radiating along the axis of
the helix. A ground plane at the driven end makes the radiation
unidirectional from the far (open) end.
Helix
where s is the spacing from turn to turn and D is the diameter, the circumference divided by π.
@PA1A:
α = Pitch Angle = 11.8deg
S = Turn Spacing 28mm
D
=42mm and L= 134mm
The gain of the helical antenna is also proportional to the number of turns.
Typical helix dimensions for an axial-mode helical antenna have a helix circumference of one wavelength at the center frequency, with a helix pitch of 12 to 14 degrees.The ground plane diameter is typically 0.94λ diameter using 16mm2 solid copper wire which is bend using very careful turning the lathe.
Socket
Extra impact resistant sheets made of extruded PLEXIGLAS® (from an old table) is used to make the helix socket.
Drilling @ 12 degrees 9mm holes at 28mm distance.
Impedance matching
Finalyzing a typical short helix, 4 turns with a 11.8 deg pitch and a ground plane of approx 0.94λ diameter. Using a 5mm copper strip plate for adjustment.
