~ 450MHz Yagi Antenna

The goal of this instructable is to make a cost effective ~450MHz Yagi Antenna for Radio Direction Finding or other uses in the most resourceful ways I can find, while still providing a standardized antenna build for use with comparing results using the same analysis software and/or methods.

I'll demonstrate a method to; make the antenna using common materials that can be found locally, where to find the materials and using a 3D printer to make the parts used to mount the antenna elements to the boom for a more expert look if you have access to a 3D printer.

Keep in mind, different materials can be used to a certain extent where the main focus and attention required will be on the dimensions and the specifications for best performance. I'll note ideas for different methods to make in each step.

1. ~48" of 1cm or 3/8" diameter Aluminum, Copper or Brass Tubing (wooden dowel covered with aluminum duct tape or tin copper braid will work too. 12 or 14 gauge solid copper wire can be use also.)

2. ~36" of 1cm or 3/8" Copper Tubing (old free or salvage yard water or refrigerant pipe since the thinner wall bends easier. 9.5mm x 1.5mm thick aluminum or copper can be used also or you can try using 12 or 14 gauge solid copper wire.)

3. ~30" of 1" or 2.5cm Square Aluminum Tubing (old free or salvage yard truck cap frame. Technically you can even use a tree limb or piece of wood that's dry and straight so long as the elements are on the same plane)

4. 6 Plastic or Paper Straws (restaurants)

5. 5 Screws (optional and see Hot Glue Gun and Hot Glue)

6. ~ 30cm of RG6 75ohm Coax Cable (old free satellites are a great source)

7. ~ 40" of RG58 or other 50ohm Coax Cable

8. RG58 or whatever 50ohm Coax Cable is used Male Connector (SMA, BNC or whatever your input receiver)

9. Soldering Iron and Solder (flux if solder is not flux core)

10. Wire Cutters (optional since knife or other cutter can be used)

11. Wire Strippers (optional since knife or other cutter can be used if careful not to cut wires)

12. Saw to cut the tubing and boom

13. Mini Copper Tube cutter (optional, though is nice to have)

14. Hot Glue Gun and High Temp Hot Glue (optional since super glue, epoxy, 3D printer pen or screws can be used. If screws are used a drill will be required to drill the holes in the boom for the screws)

Once you've determined what materials are going to be used for the antenna elements (aluminum tubing, wooden dowels covered with aluminum tape or tinned copper braid, copper pipe, brass tubing, copper house wire, etc.), you can measure and mark where to cut. Keep in mind to error on cutting a little longer than shorter so if later you want to try to tune the antenna more... you can trim down the length. This is good practice to keep in mind for future antenna builds. Best is to try to keep the cuts per the specified noted length for consistency.

The specifications for the following are as follows:

Directing Element 1 - 25cm

Directing Element 2 - 26cm

Directing Element 3 - 26cm

Driven Element - 68.7cm (this can be measured and cut longer since some may be trimmed later based on the radius bend quality and for the ~2cm gap)

Reflecting Element - 36cm

Boom - 74.5cm

Balun RG6 Coax Cable - 25.1cm

Feedline RG58 Coax Cable - I used 38" though technically the feedline can be tuned for optimal wavelength SWR length

Bending the Driven Element:

Bend the 2.5cm radius on each end, using a 5cm diameter round dowel or form depending on what you have available, carefully measuring so the Driven Antenna Elements width is 30cm. You can bend by eyeballing carefully and measuring as you bend. You can also bend using the filling with sand method like in this instructable or filling with salt method like in this instructable or a tubing bender or a spring bending method.

Cutting and Stripping the RG6 Balun:
λ/2@435MHz = 300,000/435 x 2 = 345mm (air)
Coax Velocity Factor (v)

In URM111: 16mm of stripped end (v=0.9) = 18mm (electrical)

Cutting Length = 345mm-18mm

For PE cable v = 0.66,

345mm - 18mm x 0.66 = 215.82mm unstripped and add 1cm PE unstripped and ~6mm stripped for 231.82 total length

PTFE cable v = 0.72,

345mm - 18mm x 0.72 = 235.44mm unstripped and add 1cm PE unstripped and ~6mm stripped for 251.44 total length

Cutting and Stripping the RG58 feedline:
Strip approximately 3cm of the outer insulation from the end of the RG58 and 1cm from the PE/PTFE inner insulation.

If you don't have access to a 3D printer locally or through the mail, this step can be creatively modified to make sure the antenna elements are mounted ~5/32" (4mm) above the surface of the boom using an electrically insulating material like whatever plastic, or even wood, you can find to use.

If you have access to a 3D printer whether your own, at a Maker Space or online, an excellent STL model (STL is the file format the 3D printer uses) and file I've found already made is here at the following site: https://remoteqth.com/3d-vhf-ant-insulator.php

Just save a copy of the .STL file of your choice, copy to a thumbdrive or however you need to transfer the file to the 3D printer (email, shared drive, etc.). Ask whomever has the 3D Printer what to do if you don't know.

Keep in mind the above link Revision 0.2 version is 12mm and is for 12mm diameter elements, though the straws can be used as shims to fill in the space by cutting the straws to the length of the width of the 3D print and then slit down the length to open up for wrapping as many layers as you need to shim for a not loose fit.

The above link Revision 0.1 version is really obvious in regards to the element diameter, though I'd print out a size 1mm larger than your element material plus considering shrinkage of the 3D printer material so you don't have to drill the mount print out later if you need to make the hole larger. I used the 12mm version to be safe.

I found the Revision 0.1 12mm version works best for the Driven Element (that's the copper element where the coax cable (feedline) is connected), since you can move the mount around corners without getting stuck.

Don't get carried away printing to much at one time on the base since some printers behave differently and if you noticed in the image with the gray Revision 0.1 prints, another discone antenna prints didn't turn out correct.

Note: You can use Primer to seal the 3D Print so the print last longer. This is good advice in general if you've never 3D printed before since some materials are biodegradable and will break down over time.

Layout the antenna elements after inserting and centering the elements using the plastic straw, or other non-conductive, material shims. Keep in mind if your boom isn't 3cm square like the 3D Print mounts mount point is, just use the smooth side of the mount print to align with. Also, keep in mind to adjust for the center of the boom and the center of the elements for even symmetrical top view spacing.

Measure each antenna element spacing starting from one end of the boom and working to the other end of the boom. I started from the Reflecting Element side of the boom. The distances are noted in the first image keeping in mind the distances are not "On center" in the image. You can use those dimensions or the listed "On Center" distances if you're using another material like 14 or 12 gauge solid core copper wiring.

The "On Center" distances between the elements are noted as follows:

Reflecting Element to Driven Element (closest side to Reflecting Element) - 13cm

Driven Element (closest side to 1st Directing Elements) to 1st Directing Element - 3.5cm

1st Directing Element to 2nd Directing Element - 14cm

2nd Directing Element to 3rd Directing Element - 14cm

I used rubber bands to hold the mounted elements temporarily in place while I performed the next step to make sure the spacing was correct when tuning using a NanoVNA.

Soldering the Balun and Feedline to the Driven Element:

Sand the Driven Element where the balun and feedline will be soldered, making sure to clean thoroughly. You can apply flux also if the solder you're using isn't flux core.

Twist the ground (outer) wires on each end of the RG6 balun cable into one wire so easier to solder later and do the same for the conductive wires since is a stranded wire most likely. Do the same for the one end of the RG58 cable.

Bend the RG6 balun cable and RG58 cable and position the ground wires as shown in the images and solder together.

Then position the center conductive wires of the RG6 balun as shown in the images and solder to the Driven Element.

Solder the center conductor of the RG58 to the right side of the Driven Element as shown in the images.

Solder the SMA, BNC or whatever connector you decided to use on the RG58.

Connect the Element Mounts to the Boom and Tune Antenna:

As noted in the previous step, I used rubber bands to hold temporarily in place each mounted element before I Hot Glued in place since I wanted to verify the performance with the NanoVNA. This step is optional, though recommended to be performed to ensure antenna integrity and to learn how to tune antennas and other radio related parts.

The NanoVNA is a really cost effective Vector Network Analyzer (VNA) that theoretically can perform phase related tests along with the amplitude related tests a Scalar Network Analyzer performs.

The two main tests that can more easily and cost effectively performed with the NanoVNA are:

Impedance - For making sure the impedance matches the receiver we're using in the frequency range

Reflected Loss - Re-arranged in a different way we can also calculate the Standing Wave Ratio (VSWR)

There are tutorials online that show how to use the NanoVNA if you have one. I recommend investing in a NanoVNA if you plan to get into radio more. Further measurements can be performed also as shown in this article.

There are also other ways to tune the antenna that are cost effective that were used before the NanoVNA came out such as using a cheap RTL-SDR and a Wideband Noise Source to determine the optimal Reflected Loss and VSWR.

Secure Element Mounts:

Hot Glue, 3D Pinter Pen, Super Glue, Epoxy or Drill and Screw the Mounts to the Boom once spaced to the above or finer tuned dimensions. I used Hot Glue on the high temperature setting for the elements to the mount and the mount to the boom since the first build I'm only using inside since I made the elements from wood dowels wrapped in aluminum duct tape.

You can apply a light coat of Krylon to seal the Antenna Elements, Boom and Mounts to prevent corrosion later on that might adversely effect the antenna performance.

You can also make a hand grip out of silicone tape, an old grip or whatever non-conductive material you want.

You can also make a mount for the antenna to mount to a tripod or other location like a fixed mast or a mast with a rotator.

There are other awesome yagi antenna designs you can find online, in ARRL Books or in other Books.

There are also other ready designed 3D Printer mount STL files for Yagi and other Antennas you can find on Thingiverse.

If you enjoy antenna making, you can invest in a SWR Meter or build your own. There are plenty of great online projects to help better understand your antenna's performance and learn electronics at the same time.

Enjoy using your antenna!