Wireless Tx power and range


#1

Hi,

My research group is using UBNT Rocket M5 on UAVs, to implement communication among UAVs, and between UAV and ground station.

We tested and the range of Wi-Fi can reach about 1 km! (UAVs are flying 100m above clear ground area.) I want to know how could this device realize such long distance communication.

The data sheet shows that this device has 27 dBm Tx-power. UAVs are using 5 dBi antenna, and the ground station is using a huge 17 dBi antenna. So, does any wireless router with 27 dBm Tx-power, equipped with proper antenna, can do such a long-range communication?

I ask this question because the PCB board of UBNT Rocket M5 is a little bit large for our UAV so I'm looking for some alternative to it.


#2

If you're in the United States, you are aware you cannot loose sight of your UAV, correct?

Also, I wouldn't trust WiFi to fly a drone.

You usually have good reception in clear line of sight.


#3

Sounds awesome! Hope you get some good data out of this.

If I’m understanding you right, you’re pulling the circuit board out of the housing , in that case why not look at WiFi repeater devices as they are usually about the size of the plug that goes into the AC outlet https://www.amazon.com/wifi-repeater/s?page=1&rh=i%3Aaps%2Ck%3Awifi%20repeater


#4

I'm not in the US and we do not have such regulation so far.


#5

But how do I offer an AC plug if the UAVs are carrying the repeaters and flying airborne?


#6

I assumed that you were pulling them apart and willing to make substantial modifications.

Are you actually after the smallest device/pcb that will run openwrt? What are all the constriants your working within?


#7

This is exactly what we are working with.
IMG_94E394638B96-1

Now this system just works, but there are some problems we want to fix:

  • The UBNT board is almost twice the size of Raspberry Pi - it is a little bit too large.
  • The UBNT requires 11~24 VDC power, we have to directly use the battery of UAV to drive it.
  • Considering the robust of the system, we want to avoid connectors, including the RJ-45 connector. So I want to integrate all components, including RPi and the router, on on single PCB.
  • All the UBNTs are in the same subnet, and all RPi's are in different subnets. This makes RPi cannot broadcast to other RPi's, and broadcasting is now what we urgently need.

Well, seems this is beyond the `Wireless Tx power and range' topic...


#8

Looks quite interesting :wink:
is there some reason the pi zero W isnt suitable? Sounds like it ticks just about all those boxes. I havent used it myself, but it should be possible to run an x86 openwrt image on a pi.

https://www.raspberrypi.org/products/raspberry-pi-zero-w/


#9

Ubiquity is known for using good radio parts in the RF path. Powerful and clean amplifiers etc.

Try something from GL.iNet. Google for stuff under "travel router" and look for external antennas.


#10

https://openwrt.org/toh/gl.inet/gl.inet_gl-ar300m-lite

PCB is about 50 x 50 mm and trivial to remove from the case.

OEM firmware is OpenWrt ar71xx and I've got it running on the ath79 of master (though need to tweak things a bit more). Four GPIO exposed, two for serial, two for I2C.

You can scroll down to the photos and see that there are on-board antenna connectors. I haven't checked which series they're using.

2.4 GHz, 2x2, 5 V supply, claimed consumption under 2 W, under US$20. Weight with case 36 g (measured), I can weigh it without the case or make other measurements if you need.


#11

But its computing power may not meet my requirement


#12

I need omnidirectional antennas so I must choose the GL-AR300M-Ext version. This will double the price.

I have checked that out UBNT is working at 22 dBm Tx-power 5.8 GHz, rather than its maximal 27 dBm. The GL-AR300M has max 20 dBm Tx-power and only available at 2.4 GHz. So maybe it can reach almost the same range with UBNT?


#13

Not clear how much more gain rubber duckies really have over patch antennas -- and the two on the AR300M are cross-pol, so you'll get polarization diversity. At the price, I'd give it a consideration and maybe a test (I don't know what your budget is).

image

Those RF connectors measure 2.08 mm OD, which seems a tiny bit large for u.FL (2.00 ± 0.050) / IPEX, but who knows.


#14

I would look at USB adapters direct on the Pi, and have the Pi CPU also be your wifi stack.

Also you really should not use 2.4 for this application.


#15

Can You name the UAV you are experimenting ? Or at least it’s payload and frequency used for remote flying ? Just curios as a cat :cat:


#16

why not 2.4 GHz?


#17

Just a plastic model fixed wing plane, for experiment only. We are testing autonomy flight so remote controller is only for emergency.


#18

Those are Murata SWD test points, which are not suitable for permanent connections (no locking mechanism).