This is a guide to build Helical UHF Antenna v4. The central frequency is 434Mhz, and the antenna is can be Left-Hand or Right-Hand Polarized.
During all steps make sure to check with the Dimensions Table file; precise dimensions can be found here.
All calculations are on axial mode.
Any change of the pipes diameter must take into consideration the fact that they are attached on constant diameter of 220mm.
The three PVC pipes are marked A, B and C. The RHCP design uses a Β-Α-C arrangement, and the LHCP a C-A-B arrangement.
A note on cost and alternative materials:
In the EU, the cost is estimated around 60 euros.
Instead of plexiglass, polycarbonate sheet can be used.
Instead of PVC pipes, polypropylene pipes can be used.
Brass is used since it’s more rigid than copper and able to maintain its form. However, copper is still a good alternative.
Position and secure the printout of the base on your workbench.
Position the reflector grid axially, and mark a perimeter of 552mm to cut.
Cut the the perimeter and put adhesive tape around it to avoid cutting yourself. After finishing up and positioning the antenna on a rotator, the tape can be removed.
Position the plexiglass 6 radial base on the corresponding mark on the printout. In the case of a LHCP antenna, follow the picture provided; for a RHCP antenna it should be vice-versa.
Stabilize the plexiglass on the printout using adhesive tape. Position the reflector on the plexiglass and use tie-ups and small wires to tie-up the six small peripheral holes and the 3 inner holes that will not be used to place PVC pipes through them.
Cut the grid at the positions where the pipes and the N-type connector will be placed.
Cut 3 PVC pipes 1430mm long.
Connect them in parallel and mark a straight line through all three of them. This line will be used for the horizontal positioning of the contacts with the helical antenna and the triangular plexiglass supports.
Mark the bottom of your pipes as A, B and C.
Mark the positions of the helical antenna and the plexiglass supports on each pipe using the provided dimensions table, starting 40mm from the end of the pipe.
Use a small file to create a small cavity, angled about 15 degrees, at the contact spots of the PVC pipes and the helical antenna. Warning: Don't create a hole! The direction of the cavity depends on the orientation of the antenna; the photo shows the direction for an LHCP antenna.
Using the printout, mark the triangular stabilizer at the alignment of the tube center as shown.
Position the tubes on the plexiglass base, then place the triangular stabilizers on the tubes
Turn the pipes so that the center line created in Step 4 aligns with the marks on the triangular stabilizers.
Apply PVC-plexiglass glue and stabilize the second triangular stabilizer first.
Don’t apply glue to the first stabilizer yet! It will be fixed on the final antenna application on the ground station.
Glue the basis and the third triangular stabilizer. Apply glue to both sides, and let it dry.
In our example we're using 1.5mm-wide brass wire. Our final length will be 5696mm, so we cut 6 metres to have a bit extra.
The antenna will have 8 turns, which means that one turn will be 5696/8 = 712mm long. The diameter of our form needs to be 712/π = approximately 226mm.
Winding must be clockwise or counter-clockwise, depending whether it’s a RHCP or a LHCP antenna.
Use any cylindrical object with the correct diameter as a form; in our case, we found kitchen ware with a diameter of 23-24cm perimeter.
Position the wire around the three PVC pipes. The wire must go clockwise or counterclockwise, depending on whether you're building a LHCP or RHCP antenna. The picture shows an LHCP antenna.
At the base of the wire we mark the PVC-wire contact positions, according to the provided dimension table.
The first mark from the base is at 178mm, from N-type connector to position B. Next, make 23 marks every 237,3mm (712mm / 3); this will leave 59mm free hanging wire in the end. To make this easier, we used plastic ABS filament marked every 237mm.
As soon as the positions of the wire are marked on the PVC pipes, tie-ups or zip ties should be used to initially attach the wire to the PVC pipes (except at position B). You should constantly check the geometry and the proper positioning of the antenna.
Using hot glue, attach the wire to the PVC pipes at the cavities we created using the file in Step 5. Let the glue dry.
Using zip ties over and under the wire will provide even greater rigidity.
Place the N-Type connector in place without screwing it in.
Cut, perforate and bend the triangular copper sheet according to the design file. File the tip so that it can be inserted into the N-type connector.
Attach the brass helical wire to the triangular copper sheet using small wires, and solder it in place.
Insert the small tip of the triangular copper sheet into the N-type connector and solder it in place.
Screw the N-type connector into its final position.
Use a multimeter to ensure that there is no short between the reflector grid and the helical wire.
Trim the helical wire to a length of 5696mm.
Drill holes in the PVC pipe boom. Use zip ties to clamp the two plexiglass stabilizers to the boom.
Connect the co-axial cable to the N-type connector.
These pictures show a finished RHCP antenna attached to a rotator. Note that polypropylene pipes were used here instead of PVC.