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Rooftop rnode - under construction, remains to be deployed

Modular build

This is a rnode for a roof top pylon or pole. The rnode is housed in a box, and the box and antenna is attached to an L-shaped extension arm of the pylon. The L-shaped, tubular arm is removable, and bolted to the pylon. Mounting the parts on the roof-top pylon is easier if mounted first on the arm and then the arm is bolted as a single unit in one go to the pylon. Fixing an antenna and rnode box separately and individually on the pylon when accessing the roof-top site is less convenient than mounting a single arm unit to the pylon in one action.

Power

The rnode setup relies on power from a DC mains power supply. The power comes over a long outdoors DC cable from the DC mains power supply output, which is itself housed indoors. The mains power supply used can be set to provide one of several selectable DC voltages to the input of a Buck converter, and provides up to 3 A. The Buck converter is in the box with the rnode, and powers the Raspberry Pi. In this arrangement, the current used in the long wire providing DC can be kept to a reasonable minimum.

The Raspberry Pi is powered by the output of the Buck converter. The output of the Buck converter has to be set manually to the required 5.1 V using trim-pots on the Buck converter, and using the Buck converter’s current and voltage display to set the trim pot screw position to a suitable position.

Peculiarities

The mechanics of the build are governed by the shape of the particular L-shaped tubular arm used, and so other builds will have other constraints. Nevertheless, similar parts will probably be useful for those other builds.

The time taken to build is about 12 hours at my level of competence. Having enough nuts, bolts and washers of various sizes is key. Don’t bother even trying without a good selection.

I made my life hard by trying to use the shortest possible, high quality, shielded rigid coax wire from the antenna to the cavity filter that the build uses. A bit more leeway/compromise on that connection would have made it vastly less fiddly. For some reason, however large a box one buys, it is always a squeeze.

Box should be chosen so as to be able to transmit wifi signals

This build uses wifi from the Raspberry Pi to set up and control the node during setup and placement of the node. If you use a different box, check that sufficient wifi signal reaches your interface device (laptop or mobile phone) that you use to control the rnode via MeshChat on the Raspberry Pi. Ultimately the rooftop rnode will just act as an access point or gateway, and not necessarily need to be connected to by wifi. However in my experience wifi can reach quite a way and it could be that a direct wifi connection can be made with the rooftop rnode from a laptop or other interface in one’s home: which is a very big advantage over bluetooth, whose range I found to be diabolically bad for running nodes on or under the roof.

Parts list:

1. Roof with pylon and L-shaped arm on pylon

2. Radio: RAK4631

3. Antenna: RAK Wireless - 8dBi 868 MHz LoRa fiberglass antenna

4. Adapter: Hailege IPX IPEX-1 U.FL to SMA Female Pigtail Antenna Wi-Fi Coaxial Low Loss Cable 6 Inch (15 cm) for connecting RAK radio to the cavity filter. If you get the IPEX adapter with male SMA connector you can save getting an adapter listed below.

5. Adapter: Greluma SMA male to SMA male for connecting RAK radio’s IPEX cable to the cavity filter. You don't need this if the IPEX adapter above already has a male SMA connector.

6. N type to SMA adapter: to connect the antenna via SMA connector to a coax cable. I used what I happened to have spare, namely TUOLNK N Female to SMA Female 4 Hole Panel Mount 17.5mm SMA Female 4 Hole Panel Mount Housing Type RF Coaxial Adapter but clearly I did not use the flange at all, so you can use the equivalent.

7. Coaxial cable to connect antenna to cavity filter: SMA-male to SMA-male cable, RG402, rigid-flex, coax, 20cm , product number S01SP-S01SP-402-20. This cable has a metal outer sheath and is quite rigid.

8. Adhesive shrink wrap: various diameters from kit to prevent water from getting into adapter and cable.

9. Filter: 868 (863..870) MHz cavity filter, product number cf866.5-kt30. The IN/OUT designation in the image below is not needed, either port can be used on the antenna or radio side.

10. M 2.5 hex risers: to mount Rasperry Pi and RAK radio to perspex, and to provide the M2.5 screws for fixing the cavity filter to the perspex sheet.

11. Box: Therlan Junction Box Black Waterproof Junction Box IP65 160 x 160 x 90 mm

12. Perspex sheet: about 4 mm thick
13. M4 screw kit: provides two M4 10 mm screws and various other nuts, bolts and washers: two 10 mm M4 screws to mount perspex to box.

14. Pole mount adapter: Mast Mount for Security Camera, Universal Vertical 3 Loops Stainless Steel Corner Bracket

15. Aluminium sheet: perforated with circular holes
16. Raspberry Pi 4: various suppliers, more than 2 GB RAM not seemingly needed and high endurance SD card
17. USB-A micro male to USB-C female 180 degree adapter: to link USB-C power from USB-C screw terminal output, to the Raspberry Pi, from a kit of adapters

18. USB-A to USB-C connector: for connecting Raspberry Pi 4 to RAK radio, e.g. 10 cm long, up & down and left & right.

19. USB-C to screw terminal: USB-C Terminal Block Connectors Solderless Pluggable Type C Male/Female to 5-Pin Screw Terminal Block Charging and Data Transfer Adapter Extension Cable

20. Cable tie: thin, for fixing down the USB-C screw terminal to the perspex sheet
21. Wire: e.g. 18 Gauge Copper Clad Aluminium Cable (30 Metres Black/Red) for connecting the Buck converter and the USB-C screw terminal.

22. Cable gland M22: for coaxial cable wire from antenna, and it this big to permit the SMA connector to pass through

23. Cable gland M12: for power cable input to box

24. Buck converter: with display of voltage and current. This is easiest for setting up, if not most energy efficient.

25. Power supply: Zolt 45 W Universal Power Supply AC to DC 5 / 6 / 7.5 / 9 / 12 / 13.5 / 15 V, 3 A Switching Power Supply

26. Hex risers: 3 mm with plastic washers

27. Cable clamps: for providing strain relief for the DC power cable going into the box

28. Aluminium tape: 50 mm wide, for making a heat shield with the furniture pads

29. Furniture pads: made of plastic, self-adhesive, for making a heat shield with the aluminium tape, as they provide spacing

30. Real time clock (RTC) and battery

31. Optionally, sealant to seal the cable glands openings completely.

32. Optionally a desiccant: silica gel to put into the box if the cable glands are sealed with sealant.

Tools and materials:

• Hacksaw for cutting perspex to shape
• Screw drivers
• 3 mm drill for drilling holes in the perspex sheet to mount the risers
• Stufenbohrer: also known as a Christmas tree drill bit or step drill.
• Teflon tape for sealing the cable gland threads
• Heat gun for shrinking the heat shrink tubing
• A file with at least one rounded side to widen the holes for the cable glands
• Optional: screen, keyboard, mouse for ease of setting up the Raspberry Pi
• Multimeter to check the polarity of the power cable
• Soldering iron and solder to tin the ends of wires
• Optionally: hair dryer to dry the box if you intend to seal it completely with desiccant inside

Build steps

Setting up Raspberry Pi and rnode:

1. Flash the RAK radio with rnode firmware.
2. To set up the Raspberry Pi it is easiest to connect Raspberry Pi to a screen, keyboard and mouse, rather than perform the installation in a so-called ‘headless’ manner. In this build, the software used is MeshChat which is installed on a Raspberry Pi.
3. The MeshChat GUI is accessed using a wifi hotspot on the Raspberry Pi.
4. A real time clock (RTC) and battery was installed.

Steps to make the rnode box:

1. Cut the perspex sheet to fit snugly into the base of the box. Drill two 4 mm holes through the sheet in the precise positions needed to fix the sheet to the box’s base’s threaded mounting points when ready.

2. Fix the cavity filter to the perspex sheet at the far top left using four M2.5 screws. Note that the use of a cavity filter is optional. The reason for using one is to avoid the situation that other strong radio signals potentially in the vicinity make the radio fail to work.

3. Attach the coax cable to the antenna using the N type adapter.

4. Using the Stufenbohrer / step drill, drill a hole into the box to mount the M22 cable gland for the antenna cable. The location of the hole must allow for the cable to reach the cavity filter: be careful and double check. I made the gland just fit by filing the hole down to be only just large enough. Use plumber’s PTFE tape to make all joins and threads of the gland as waterproof as possible.

5. Drill 8 3 mm diameter holes for hex risers for Raspberry Pi 4 and the RAK radio. I stacked them over each other. Do one hole, mount the Pi / RAK with the riser. Mark the next hole locatoin. Remove the RAK/Pi. Drill that hole. Repeat for each hole. Doing two at once does not work, it always messes up and results in the holes not being aligned.

6. Attach the IPEX adapter and SMA male-to-male adapter to the RAK.

7. Attach the RAK and Pi to the perspex sheet using the hex risers and screws.

8. Drill four 3 mm holes to fix the Buck converter to the perspex. Use M3 hex risers and screws, with plastic washers, to mount the Buck board to the perspex sheet. See next image below.
9. Cut two wires, and tin the ends, to the right length to connect the +/- output of the Buck converter to the +/- ports of the USB-C screw terminal when the USB-C screw terminal is located, in the box, next to the cavity filter. See next image below.
10. Drill small holes through the perspex sheet, next to the location of the USB-C screw terminal, to take a thin cable tie, to fix down the USC-C screw terminal to the perspex.

11. Attach the DC power plus and minus wires to the Buck output and USB-C screw terminal by screwing in the wires tightly.
12. Drill a hole in the box, at a location of input into the Buck converter, to receive the M12 cable gland, for accepting the DC power cable, as shown below.

13. On the aluminium sheet near the M12 cable gland, fix some of the cable clamps that act as strain relief.

Steps to mount the rnode box and antenna to the L-shaped arm:

1. Using the parts that come with the antenna, fix the antenna to the L-shaped tubular arm at a location (height) where the coax cable from the antenna can still reach into the box via the cable gland and to the cavity filter.

2. Fix the pole mount adapter loosly to the L-shaped tubular support (as shown in the images above) using the long jubilee clips to perform the next steps.
3. Fix the aluminium sheet to the L-shaped tubular support using the pole mount adapter and suitable M4 washers and screws. This can be ultra fiddly because the location of the nuts is hard to access to permit tightening, and I even had to use tweezers to offer the nuts to the screws. The pole mount adapter has viciously sharp edges.

4. Attach the box, using suitable screws, to the metal sheet at a location where the antenna’s cable can still reach the cavity filter inside the box.

Connect parts on the perspex sheet together:

1. Attach the USB power cable arrangement to the Pi: the 180 degree USB-A micro to USB-C female adapter → USB-C plug of USC-C screw terminal.
2. Attach the RAK and connect the USB-A of the Pi to the USB-C port of the RAK using the cable listed above.
3. Check all screws everywhere, on all parts on the perspex sheet are tight.
4. Insert the perspex sheet into the box. The antenna M22 cable gland on the left might make it a bit tricky to insert the perspex sheet, in which case remove it first or fiddle around.
5. Screw the perspex sheet down into the box through the two holes, using the two 10 mm M4 screws and washers if needed for the screw heads to push down onto the perspex. Place sufficient heat shrink tubing around the antenna connector and adapter. I placed different diameters telescopically overlapping along the cable route. Postpone any heat shrinking until 100% sure that the antenna works.
6. Attach the antenna to the cavity filter.
7. Arrange the heat shrink correctly and then screw tight the M22 cable gland that feeds the antenna cable into the box.
8. Test the Pi and radio works when DC power applied.

9. Test with DC power going into the Buck converter. The current trimpot should be turned to the maximum as this only limits the current. The voltage trimpot should be turned to that the voltage reading is 5.1 V. The trimpot can do 12 complete rotations and goes click-click when it has maxed out in one direction.
10. Test that the wifi signal from Pi is received and that the MeshChat GUI can be used.
11. Set the MeshChat settings as (i) transport node (ii) gateway (iii) propagation node etc.. Ensure that the device is set to perform announces every 15 minutes or so.
12. When the antenna is working, and screw connections and adapter checked to be tight, apply the heat-shrink using a heat gun. Telescope the parts so that rain flows over the outside of the joins.
13. Test the node in your attic or somewhere accessible for a longish while to see if it works for a protracted period.

Mounting the rnode on the roof (the planned steps):

1. Connect the DC power supply to the DC cable that is to run to the rnode and select a high voltage e.g. 12 or 15 V because this reduces the current that needs to be carries by the length of power cable running to the rnode.
2. Pack an interface device that can open the MeshChat GUI by wifi e.g. laptop or smartphone.
3. Make sure you remember the wifi password of the Raspberry Pi’s hotspot.
4. Pack some small cable ties.
5. Ensure that you have a second rnode in the vicinity that is working to send a test message to and from the rooftop node.
6. Access the roof and bolt the arm to the pylon.
7. Establish with a multimeter which cable of the power cable is positive and which is negative. If you have the red positive multimeter probe connected to the positive socket of the multimeter, and the black to the negative, then if the red probe is connected to the positive cable and the black to the negative, the display of the multimeter shows a positive non-zero number and the red probe is in contact with the positive cable of the power supply. Label that cable positive.
8. Thread the dome-shaped cover of the M12 cable gland over the DC wires.
9. Connect the DC cables to the Buck converter terminal in the right polarity, running them through the cable gland.
10. Tighten the screw terminal of the Buck converter and tighten the cable gland.
11. Ensure that the cable is sufficiently attached to the metal sheet with the cable holders. Ensure that no part of the DC cable/s can flap in the wind.
12. Check that the voltage and current are sufficient as shown on the display, and if not, tweak the trimpots.
13. Ensure the antenna is vertical and firmly attached.
14. Check the node works via the GUI by accessing the MeshChat GUI using a browser in your interface device, where the interface device is connected to the Raspberry Pi’s hotspot.
15. Seal lid of the box, remembering to use the rubber seal that comes with the box, which may need to be cut to the right length.
16. If the site is accessed by others, put your phone number into and onto the box.
17. If you are concerned about the box getting too hot in the sun, cover the box with metal aluminium tape set off from the box using the furniture pads listed above. This works, because I tested it on a rooftop over many summer months in another build.
18. In my case there was already lightning protection at the site. If there is not, think about that aspect.
19. There is the issue of moisture and sealing the cable glands. One could seal the box more tightly by sealing the cable glands’ holes using some sort of sealant. The antenna cable could be sealed in advance. The power cable is a bit trickier. One could use a second junction box outside of the rnode box to make sure that the rnode box is itself completely sealed and dry at the time of mounting, and use a separate small junction box to connect the power. I would use a hair dryer to dry the rnode box before sealing it with the desiccant inside.

When mounted on roof pylon, more photos and peformance information will follow. For now, this is just a run-down of the build steps thus far.

Last edit 04-17-2025 MMDDYYY 12:00:00 EST