I needed a small-ish collapsible Yagi-Uda antenna for portable use. Naturally I decided that if I was going to build one, I was going to do it right - the coolest Yagi on the block, the envy of the nearest ham-vention if you will

V/UHF Yagi Diplexer

I came across a project that utilised carbon fibre, ( the coolest buzz word since blockchain) as a 2 Metre long lightweight boom - accompanied by 3D printed element holders and RG59 Matchingline ( more on that later )

This project was hosted on Tysonpower.de (https://tysonpower.de/blog/carbon-arrow-yagi-antenna)

The Antenna has enough gain for use with a low power 5w handheld radio and is relatively light. This makes it perfect for my use case

Material list

• 2x 50cm carbon rod - 12mm outer diameter (boom)
• Aluminium clamps for the carbon rods
• some m3 bolts and nuts
• 3D printed parts - https://www.thingiverse.com/thing:3289189
• Aluminium rods with 6mm (~3,5m) and 10mm (~1,5m) diameter (Elements)
• 50Ohm [ RG58/U ] and 75Ohm cable [ RG59 ] (at least two metres of each)
• Cable lugs (for m3 screws)

The parts have to be spaced according to the image below to get the right spacing between the elements. Note that the 2m and 70cm yagi are crossed by 90°.

The Elements need to have the following lengths and need to be mounted centred on the boom.

Note on Matchingline / RF Magic

So you might have noticed I mentioned 75Ohm Cable ( 2 Metres of the stuff )

Your first step is to make a matchingline that is made out of two pieces of RG59 Concatenated and parallel to one another

You will need two of these Cable harnesses -

one for the 2M Triple Element and one for the 70CM Penta-element

The length of the insulated part of the cable for the 2M band is 343mm and 115mm for the 70CM band

I made sure that both stay parallel by using some isolating tape

To finish the cable - solder both the centre conductors together and the outer braiding of both parallel cables so you have one single signal and one single outer sheath connection on both sides.

For the output cable, use regular old RG58/U with your preferred termination (SMA / BNC)

To connect to the elements to the feed point - I used Cable Lugs that get attached to the aluminium with screws.

The PCB

Onto the reason for this post - The kind folks at PCBway reached out to me to help me print my circuit board design. This is a short outline of what it does!

Because I only wanted one output to my radio - I added a diplexer, or otherwise known as RF Magic..for those interested - this is the theory behind diplexers

• Implements frequency-domain multiplexing. Two input ports (2M, 70CM) are multiplexed onto a third port (OUT)
• the signals on 2M and 70CM can coexist on OUT port without interfering with each other.
• the signal on 2M Port will occupy the VHF Band and the signal on the 70CM will occupy the UHF band.
• the diplexer consists of a lowpass filter connecting 70CM Port and OUT
• and a high pass filter connecting 2M Port and OUT.

This PCB can withstand roughly 10W ERP - which is 3 Watts more than any of my HT's can output. Plenty of breathing room + Gain.

Topside

Rearside

Wiring Diagram

Thank you very much for bearing with this. I would like to shout out the team at PCB Way for supporting me in developing and printing my project. If you want to see more :) - https://github.com/AxiomYT/Electronic-Design/tree/70CM%2C-2M-Diplexer

Follow me on Github :) - https://github.com/AxiomYT/

Follow me on LinkedIn :) - https://www.linkedin.com/in/logantarvit/

https://github.com/AxiomYT/Electronic-Design/tree/70CM%2C-2M-Diplexer