Project Dashboard Hardware UHF Helical 8 Turn Antenna Workflow

1 Basic characteristics of the antenna

Characteristics

  • Frequency 435 MHz
  • Turns 8
  • Circumference/Wavelength (0.75 - 1.33) = 1
  • Reflector Diameter/Wavelength (0.8 - 1.1)= 1
  • Turn Pitch/Wavelength (0.2126 - 0.2867) = 0,25
  • Wavelength (Λ) 689 mm
  • Winding Diameter 219 mm
  • Winding Circumference 689 mm
  • Winding Spacing 172,3 mm
  • Winding Length 5683 mm
  • Reflector Diameter 689 mm
  • Boom Length: 1.378 m
  • Gain: 12 dBi
  • Half-Power Beamwidth: 36.770 deg

Characteristics calculation site. http://www.vk2zay.net/calculators/helical.php

All calculations are on axial mode

Basic geometry

  • The upper surface of the Grid-Reflactor is ±0
  • The support arms are at -2mm
  • In between the N-type is positioned and the start of the Winding at +9mm
  • The first support connection is after ¼ of the Winding Spacing so. (172,3/ 4)+9 = +52
  • Next support connections are at ¾ of the winding spacing so. 129.2mm
  • Thus the we have the following sequence +52 +181 +311 +440 etc

2 Design files, materials and cost

All design files needed are available in the following link

https://github.com/satnogs/satnogs-antennas/tree/master/Helical/UHF-435-8

Overview in stl format for RHCP

Helical-435-8-RHCP.stl

3 pdf files with antennae presentations

Helical-435-8-RHCP-View_1.pdf Helical-435-8-RHCP-View_2.pdf Helical-435-8-RHCP-View_top_A&B.pdf

3 pdf files with all needed dimensions

Helical-435-8-RHCP-Boom.pdf Helical-435-8-RHCP-Side_A.pdf Helical-435-8-RHCP-Side_B.pdf

Brass triangle to match resistance (Matching)

Helical-435-8-RHCP-Triangle_Brass.pdf

Pattern to print for RHCP top in pdf Helical-435-8-RHCP-Top_pattern.pdf

Materials and cost

  • 1 Pcs Aluminium (Square tubes profile 20x20mm) = 1600mm
  • 2 Pcs Aluminium (Symmetrical L profiles 15x15mm or 20x20mm) = 680mm
  • 2 Pcs Aluminium (Symmetrical L profiles 15x15mm or 20x20mm) = 420mm
  • 1 pc at least of 70Χ70cm good quality grid mesh of 2mm with at 1in (25,4 mm) spaces.
  • 11 pcs Acetal rods 8mm wide and 140mm long
  • 22 Nylon nuts Μ8
  • 1 N-Type connector
  • Brass wire 3mm approx. 6 m
  • Brass sheet 0.3 mm thick approx 20Χ10cm

In EU cost is calculated around 35-50 euros

3 Cutting and drilling aluminum

  • 1 Pcs (Square tubes profile 20x20mm) = 1600mm
  • 2 Pcs (Symmetrical L profiles 15x15mm or 20x20mm) =680mm
  • 2 Pcs (Symmetrical L profiles 15x15mm

Boom drilling

Mark perimetrically the boom in the ±0 position and in 240 mm distance from the base leaving a 1360 mm remainder Mark one side as side A and the other one as side B.

Using Helical-435-8-RHCP-Side_A.pdf start drilling side Α . The hole at -229 is for the 420mm struts all else are for Acetal

Β side uses Helical-435-8-RHCP-Side_B.pdf

All holes with a positive sign in side B are for Acetal and the to in -109 and -161 for the final attachment system (in our example a U-bolt) If a different support system is chosen adjustments might be required The 2 smaller diameter holes in -8 and -13 are use for the final attachment profiles of 680mm and must be 5mm

drilling

4 Acetal Elements

Creating elements using 11 rods of Acetal 8mm wide 140mm long

Drill 3,5 mm in 9 mm distance from one edge. On the other edge create an M8 coil using a spinnerette at least 40mm long

Note

Nylon Threaded Rods can be used instead of Acetal rods, but it can be more expensive

drilling an Acetal element
coil making using a spinnerette

5 Preparing Acetal Elements for placement

Preparing Acetal elements for final placing.

  • 11 Acetal Elements
  • 22 Nylon nuts

Screw the nylon nuts so there is a 100mm distance from the hole center to the edge of the nylon nut, that the boom will will touch

Use plastic glue to secure in place.

measuring 100mm distance
Gluing a Nylon nut

6 Preparing the 690mm reflector.

Print on a 1:1 scale Helical-435-8-RHCP-Top_pattern.pdf and place firmly on our work area. We use a 2mm 1inch (25.4mm) spaced grid mesh if it’s rolled we try to make it as flat as it gets without distorting its linear alignment.

We place the grid piece so that the boom mesh (20x20mm) trace on our print is surrounded equally by the central mesh grid space. (25.4x25.4mm) Also the linear alignment should not be identical to alignment A since it corresponds to the N-type. The reason is that the abnormal alignment will be forced during forced during the assembly

We point using a marker at the 690mm diameter. We cut the excess mesh grid and cover it with insulating film tape, to avoid hurting when handling. After the antenna placement we can remove the tape.

Grid piece placement
Excess mesh grid removed

7 Wooden drum construction

A construction that will assist in the configuration of the 3mm thick winding

The diameter must be strictly 225mm. This arises from the fact that the final helix diameter will be 219mm when the winding spacing is 172mm

Calculation of the 225mm

  • Winding Length 1Turn=710mm
  • ½ of the Winding of 3mm thickness = 1,5mm
  • Wood diameter=(710/3,14)-1,5=225mm

Use two chipboard pieces 20mm thick. We bonded them in one piece as pictured. Mark the perimeter with slots in it’s quadrants, preferably not in the direction of the arm.

The construction should look like a 40mm “banjo”

Cutting wood 225mm diameter
Finished "banjo" (let's rock)

8 Cutting the winding

Cutting Winding 3mm thick. Brass material.

Used a 60cm diameter.

We cut it in 3.5 diameters since we need it for winding length.

Winding Length 5683 mm (600Χ3,14)Χ3,5>5683

60cm diameter wire
5683mm cut

9 Configuring the winding

These instructions regard a RHCP configuration

Secure the edge of the 3mm thick brass wire together with the wood using a vise to start winding.

Winding must be performed counterclockwise as we see it so it would be clockwise from the vise to us so RHCP,

Procedure must me tight without kinks.

secure the brass wire with the wood
winding configuring for RHCP

10 Marking the winding

We keep in place the wire in place with tape and mark it up with black or blue permanent markers on it's outer surface.

On the wood quadrants marked with cutouts.

taping the wire around the wire
marking

11 Reflector support bars

Mark the middle of the 680mm, and mark 10mm to the left and 10mm to the right (also helpful with the boom connection)

Drill 4mm holes at a 110mm distance from the center as pictured.

Remove part of the vertical side of the L profile from 90mm to 130mm from the central line. The cuts of the two rods must be facing each other.

cutting
drilling

12 Boom angling

Angle the boom and one of the L-profiles at a -2mm distance from the 0mm of the boom in their final position.

Mark using a long and thin mechanical pencil tip the drilling points on the L profile

Repeat the process on B with the other L-profile and drill 4mm.

The result must be symmetrical as in the provided photo.

angling
marking
symmetrical result

13 Testing boom and L-elements connection

We will test the boom and L-elements connection using M4 screws by checking the proper angle.

We disassemble and test the N-type connector positioning. Subsequently we temporarily remove it.

boom to L-elements connection testing
testing the N-type connector positioning
testing the N-type connector positioning
testing the N-type connector positioning

14 Final Assembly of L-elements on boom

Place the L-elements and boom on a vice and above them the mesh grid (on a probably non linear alignment) in parallel with the L-elements.

Mark upon the L-elements on both sides of the wire on at least three distances.

Overall drill at least 24 3mm holes.

Cut and remove part of the mesh grid in place for the N-type connector.

placing on a vice
removing part of the mesh grid for the N-type

15 Placing the reflector

We firmly secure the reflector using small wires.

I should be a plane level since it is retained by the L-elements.

We cut away the grid in place of the N-type connector and slightly crook it in order to screw in the N-type.

reflector final installation
N-type connector final installation

16 Triangle Construction

Cut the triangle out of a brass sheet of 0.3mm thickness (or slightly thicker)

Keep in mind that during cutting scale must be preserved and the extension to connect the N-type connector must be preserved.

The other protrusions are in place in order to embrace the wire.

We adapt the curvature and orientation using the "banjo"-like structure we made on a previous step.

cut brass sheet triangle
curving using the "banjo" structure
curved brass triangle

17 Connecting the wire to the triangle

Adjust the triangle by starting on the first mark of the wire and an orientation that conforms to Right Hand Circular Polarization (RHCP).

Stabilize the wire on the triangle by tightening the protrusions and use a torch to secure.

Remove and cut ONLY excessive part on the start of the wire based on the markings done on a previous step.

tightening the protrusions
torch to secure in place

18 Struts placement

Cut in angle the edges of the 420mm L-elements and drill, as pictured.

Keep in mind that cutting must symmetrical.

Screw symmetrically the last hole under the boom with at least an M5 screw.

Tie up the two quadrants of the reflector on the edges of the struts.

L-element edge cut
tightening up the struts to the reflector

19 Spacing out the winding

Space out the winding on a small rod or stick (whatever is handy)

Cautiously place through the 11 acetal elements evenly.

This step will facilitate an easier final installation.

spacing out the winding

20 Placing the winding

Having the boom stable gradually place the acetal elements starting from the closest to the reflector using the nylon nuts.

The placement should be every three on the top corner of the triangle.

Be cautious not to bend the wire This is probably the most difficult step, every time you screw one of the acetal elements must fix the wire on the rest.

screwing the Acetal elements
try not bending the wire

21 Acetal Element placing

Keep in mind that the marks must be covered in the spacer hole.

In the photo it is just before being covered by the spacer hole.

Subsequently marking with a red marker should be used for marking the final position

The remaining markers would assist in proper alignment

Checking them from the sides would place the boom exactly behind them.

before being covered by the spacer hole
marking

22 Alignment control

Control alignment and temporary stabilize using tape is applied.

Using glue on both sides we could secure the alignment

Same for nylon nuts.

alignment control
glue application
glue application

23 N-type triangle connection

Finally solder the the winding-triangle to the N-type.

A conductivity control should be performed.

Brass triangle to N-type connection
Brass triangle to N-type connection

24 Rotator installation

Final installation on an Az/El rotator's horizontal pipe.

Final installation on an Az/El rotator's horizontal pipe.
Final installation on an Az/El rotator's horizontal pipe.
Final installation on an Az/El rotator's horizontal pipe.
Done! Take me home