What is SWR?

Straight from the wiki: In radio engineering and telecommunications, standing wave ratio (SWR) is a measure of impedance matching of loads to the characteristic impedance of a transmission line or waveguide. Impedance mismatches result in standing waves along the transmission line, and SWR is defined as the ratio of the partial standing wave’s amplitude at an antinode (maximum) to the amplitude at a node (minimum) along the line. Data found here.

In normal people speak: When a radio transmits, not all the energy exits the antenna. Depending on how well the antenna works, some energy reflects back to the transmitter. Ultimately we want no RF waves/energy being reflected.

Antenna Tests:

RAK 8dBi
Notes: @ 915Mhz SWR 1.29:1 – 30 day stats up. I seem to have a fair few more invalid-witness than compared to a hotspot of equal height/locality using the RAK 5.8dBi

NEBRA Stock 3dBi Antenna
Notes: @ 915Mhz SWR 1.18:1 – Noticeable changes when the antenna is bent at a right angle.

RAK 5.8dBi Antenna
Notes: @ 915Mhz SWR 1.13:1 – Tested a fair bit better than the 8dBi variant. Will be interesting to see how it performs compared to 8 dBi after 30 days.

Who else is testing antennas?

These guys are! – Helium ACT has tested a bunch of antennas including the McGills 6dBi. Will be interesting to see how my results compare. Of note, they mention the right angle of the smaller 3dBi type antennas. I actually ended up with better results when bent to 90deg! Go figure.

Also, if you want to capture some decent historic stats for your setup. Check this website out! https://helium.hiker.rocks/ I used it to make some correlations between invalid witnesses and the type of antenna used.

Some additional information and handy links:

• VirtualBox Download
• Ubuntu Server Image Download
• Ubuntu Desktop Image Download

TIP 1:

If you intend to use USB 2.0 and USB 3.0 devices with your virtual machine from the host machine then be sure to install the Expansion pack that is separate to VirtualBox. This expansion pack includes tools such as Support to USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards. You can download it here: https://www.virtualbox.org/wiki/Downloads

TIP 2:

After the setup of the image, you can dismount the image file. Virtualbox should un-mount the image automatically, however, if it does not and you end up back at the OS setup, un-mount the image file and reboot the VM.

I’m still a bit trigger happy on the drone, but getting smoother with the controls. It did not help sitting in the passenger seat of the 4wd whilst trying to play pilot.

Kalbarri is located approx 5 hours drive north of Perth.

Saying that, If you were to build your own, these are the two biggest questions I would have you ask yourself. 1. Where will you put them? (If you want to place them in front of a table, do not make them 1 meter high like I did.) 2. Cost of materials – Depending on where you get the MDF, you may actually be better off hiring them. Time vs Materials.

Materials Required

• MDF – Approx 18mm Thick
• Plywood – 3mm or 5mm Ply (3mm Bends easier)
• Small Tacks and Nails (For attaching Ply to the side of MDF)
• Sanding Sheets
• CNC Router or Jigsaw (Jigsaw for Hand cuts)
• White Gloss Paint (Rollers/Brushes etc)
• Fairy light fake bulbs (You can use the lights also)
• OPTIONAL – Pixel Pusher
• OPTIONAL – WS2801 RGB LED strings (If you want to control light)
• OPTIONAL – 5v PSU and travel router to control RGB lights from phone)

Cutting the Letters

Draw up the letters in your favorite CAD/CAM program. I used Aspires Vetric for this. Mostly its a CAM software but still has some good tools for drawings. Another alternative would be to draw it in Adobe Illustrator and convert it to DXF. If you plan to cut the shapes manually, you will need to come up with a template. For smaller letters, this could be achieved in Microsoft word and printing the outlines. However for 1-meter tall lettering, your best off cutting on a CNC router.

Ensure the holes for the lighting are spaced evenly. I used a 150mm gap between each light, however, you can extend this to not use so many lights, or bring them closer together for more lighting.

Bending and Attaching the Ply

It is actually very surprising how flexible Ply is. Especially 3mm thick ply. Obviously the smaller your lettering the tighter the corners will be. You may even have to wet your ply with water to make that bend. However, with these letters, I did not have to wet any of them down. The tightest angle was on the inside of the heart shape and the 5mm ply that I used just made it. I could hear some slight cracks, but nothing visual.

The ply is measured and cut to length, I tried to make the seams join at the apex of the cuts. However, it does not matter too much where the ply joins as you can hide any irregularities prior to painting. Attach the ply with some overhang at the rear of the letters. This will help to hide any unsightly cabling/wiring later.

We used some black tacks to attach the plywood. Every few centimeters I tacked the ply on. This has held well to date. If you use nails, be careful not to split the MDF.

Painting (The Not so fun part!)

What I will say here is that you should really spend some time sanding. As with all wood projects, any imperfections will be seen if you do not deal with them now. However, knowing that these things are always turned in a dimly lit room may entice you to do a half job here. Also, you may want to punch the tacks down below the surface of the wood and use some filler to cover it over. Ok so get painting! we used a gloss, feel free to change it up here.

OPTIONAL – The Electronics

This section is totally optional. I initially used the ‘Christmas’ like lights in the bulbs but found it to be boring. Thus I took it a bit further and installed the WS2801 RGB LED string lights. I acquired these from Aliexpress at a good price. I also used one of the many Pixelpushers I had lying about to drive the RGBs. Using the Pixelpusher for this kind of install is massively overkill however its what I had lying around. The bonus to this is that I could use the LEDlab App and control the lights from my phone. Let me know if you want more info on this setup.