Hello everyone, this is B3/BG5VAR, currently studying Unmanned Aerial Vehicle Systems Engineering at the Civil Aviation University of China.
Introduction
While at home on vacation, I had a very enjoyable satellite communication experience using the U7V4 antenna.
The distance from Fujian to Tianjin was too great, making it impossible to carry a 1.5m antenna. Therefore, I did not have satellite communication in Tianjin during my first year of university.
In December 2022, during the peak of the pandemic, I suddenly had an idea to build my own UV dual-segment antenna. I found a diagram created by RSJ (a respected figure in the community) for the Moxon + Bakshi design and started building it.
I then bought a piece of PVC pipe, a length of copper wire, and got to work! Because I hadn't fully planned it out, the resonant length was too short (I used a friend's coat hanger), and the hole in the PVC pipe was drilled crookedly (which I later filled in), making it very Syrian-like. I clearly remember that on the evening of December 13th, when I finished it, I got sick!
However, don't think that this Syrian style is actually realistic; it looks quite good.
Once I started using it in the spring semester of 2023, I found that it had satellite communication and cloud map reception capabilities.
However, I still felt that something was missing: the coil was too soft! It was too soft! The vibrations during use would affect the overall efficiency of the antenna, and it also looked unsightly.
I had another sudden inspiration, and in my "Unmanned Aerial Vehicle Control Engineering" course, I drew a completely new eight-pole + Moeken UV dual-segment antenna diagram!
Theoretically feasible; let's get started!
Materials preparation
As shown in the diagram above, we need two PVC pipes of different diameters, but with a relatively small difference between them (each approximately 1 meter). I chose 32mm and 25mm. We also need corresponding pipe caps and adapters for changing the diameter. This cost approximately 7 yuan.
Additionally, I needed the antenna's resonant element. This time, instead of using copper wire, I used a stainless steel rod (4mm diameter). According to the dimensions in the diagram, I asked the shop to cut it roughly to size (my particular shop only did the cutting, not the bending). This cost approximately 12 yuan.
Additionally, I needed four connecting rods (4mm) and one screw (M4*45). This cost approximately 20 yuan.
I used a Syrian version of the 50-2.5 (model RG316) feeder cable, which is quite thin and flexible. This cost me 15 yuan.
Approximately 50 yuan in total.
Manufacturing process
On thicker pipes, cut a length of approximately 20 cm using hand tools, and then drill through it.
Pass through the M4x45 screw, and then attach a coupling to both ends.
Next, we'll be drilling, drilling, and more drilling!
Without specialized tools, creating this hole is extremely difficult; it's either too high or too low, or one side is higher than the other.
Fortunately, the drill bit was 3mm in diameter, and I still had a 1mm margin for adjustment. Based on the horizontal alignment, I expanded the hole slightly in the correct direction, ensuring that all the oscillators were parallel to each other and perpendicular to the main beam.
Next, cut the guide rod approximately 5 cm from the end of the coaxial cable, pointing towards the antenna. Here, a detachable guide rod assembly will be created by connecting a smaller tube to the main rod.
Attach the fine tube, and according to the diagram, calculate the spacing between the two guide tubes that span across the thick and thin tubes. Then drill!
Cut off the last wire that extends from the oscillator to the antenna, approximately 5 cm in the positive direction, and then attach a small tube cap.
At this point, our main beam is complete!
The following instructions will guide you in bending and assembling the MoCox section of the diagram.
This 4mm stainless steel bar is indeed difficult to bend. I obtained a similar-sized aluminum rod and inserted it into the bar to a certain length, then began bending it.
By bending two aluminum strips simultaneously, you can ensure that both of the vibrating elements have the same shape.
The oscillator part is complete.
Here are the feed lines:
First, drill a hole in the main cap and pass the feeder through it.
Remove both the inner and outer shielding layers, along with the gaskets.
Insert the feed line into the thick tube. At the aligned vibration hole, use the screws provided with the coupling to pass through the gasket, from inside the tube to outside, and connect it to the coupling.
I closed the large cap and installed the rough pipe vibrator in its proper position. Due to inaccurate drilling, there was a problem with the vibrator being misaligned. I expanded the hole and then used hot glue to precisely locate the positions of each vibrator.
Measuring standing wave, at 416 MHz, the VSWR is 1.055, perfect!
However! There is a 14mm distance between the two L-shaped oscillators in the diagram, but when I built it, I found that the two oscillators overlapped. After measuring, I discovered that the long side of the L-shape was bent too little, causing the short side to be too long. But since this has already happened, the only solution is to cut out the extra oscillator so that there is a certain distance between them.
To ensure that the thick and thin tube oscillators are aligned on the same plane during assembly, I verified alignment after mounting, and then drilled four holes for later assembly positioning.
The manufacturing process for the Moxon + Yamagiwa dual-segment antenna has now concluded.
Finished product display
First, let's look at the standing wave. Both the UV dual-band antennas have a minimum standing wave point, with the V band at 144 MHz and a VSWR of 1.176, and the U band around 416 MHz with a VSWR of 1.156. This is within the expected range!
Existing issues
① Without a lathe, the hole will be crooked.
② The oscillation does not bend uniformly, resulting in inaccuracy.
③ The oscillator with no coupling is prone to instability and movement.
These were the most challenging issues I encountered, so please share your best solutions in the comments!
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This concludes the entire content of this column. Thank you for reading this far. In the future, I will also use this antenna to conduct some communication activities, and I will release several video episodes then. Please look forward to it!
If you would like to see more detailed images and text, please visit https://www.bilibili.com/read/cv23239516?jump_opus=1
This is B3/BG5VAR, 73.
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