915 MHZ mavlink is degrading GPS signal

#1

I am having trouble with telemetry RF interference. I am using a here+ GPS and it works fine without telemetry.
On the copter: yellow will flash until telemetry is unplugged, then green in a few seconds.
At the RTK base: I notice the loss of GPS if the telemetry radio & GPS are not several meters apart.
My guess is that my radios are cheap & noisy.

My question is are there better or suggested radios that are for the RTK application?

#2

There is no blanket solution that says some devices are cheap and noisy and others are not.
You will find that there are multiple ways to create interference between various devices on your vehicle because everything that you put onto a vehicle will adversely impact every other device on the vehicle.
The essence of developing a good data acquisition system comes down to excellent systems engineering. At least 99% of the time, the way you wire them and the way you install them will outweigh different devices from different manufacturers. The way you wire can create either conducted or radiated interference. The way you locate and wire various devices will determine both the way a device radiates noise and the way it receives noise.
You need to determine the source of the noise, the path of propagation of the noise, and the point of injection of the noise. Once you understand those factors then you can build a defence. It may be one of them, it may be all three that need to be addressed.

1 Like
#3

Craig, Thank you! I am not a developer but I have experimented with this quite a bit. At my base without any copter interference I have tested 2 telemetry links with consistent results. It takes several meters and perpendicular mavlink antenna orientation to get my GNSS rx to perform. With the mavlink turned on the GNSS gets 3 -6 satellites, with it on I get 12-21 satellites.
On my copter I just plugged in to the (gps1 & telem1) ports, put the GPS on top and my mavlink on the bottom, 14 cm vertically apart. I can push my 915mhz out to one of the motors but my test at the base show that’s not enough. I am stuck with RTK GNSS that works best autonomously. I will keep testing and thanks again for the reply.

#4

I’m having the same issue with 3DR 500mW 433Mhz telemetry modules. Looks like these cheap modules don’t come with any filtering at output and can interfere with GPS.
See how sensitive it is:

I tried to use separate power supply for telemetry module, tried using ferrite beads, nothing helped.
Only solution is to position telemetry under multirotor.

Take a look a THIS topic, it contains lot of helpful information about solving this issue.

#5

I saw this. Your build looks pretty good.
I have a rover and a copter that have 100mw telemetry the GPS works good on both. One is a holybro the other came with an APM FC. Neither has the Cube or Here GPS. I will do some testing with these 100mw versions to see if they work with my Here GPS or not.
As far a the topic link goes… I looked through it but there is no acceptable solution there. I already have wrapped the telemetry in foil tape grounded to the antenna with some success but not much. I would never try to isolate the battery powering the telemetry because that’s not how these things were designed to plug in to the FC. Also I don’t have any rf testing equipment or the technical knowledge to not be dangerous diagnosing radio diodes.
My experience is user based and using RTK radios goes back a few decades. I am using 35 watt radios that are 15 years old when they were new GPS & especially GNSS receivers had to be several meters from the tx radio to get a fix. Today with the same old radio I set my 35 watt radio less than 2 feet away from my base on top of my truck. New survey grade GPS receivers are better protected now. I think that is why I am not getting good results or answers with the cheaper ubox M8x stuff.
My experience with other FC’s goes back 10 years and I just looked at one of my first setups:
DJI NAZA v2 with GPS, USB & power module
8 channel Spectrum radio with telemetry RX and a satellite RX
The completed great flying project had:
14 - 3 & 4 wire connections to the FC,
10 - 3 wire connections to the radio,
2 -2 wire connections to telemetry,
12 power wires going to ESC’s &
18 wires ESC to motors.
That is 56 connections & over 100 (mostly plastic insulated) wires that I had to plug in DIY.

Today’s build a quad: motor ESC combos, Cube FC, Here+ GPS, spectrum satellite rx and telemetry. 8 connections to the FC and 8 connections to the power module,
34 wires total including (3-6 wire connectors & 4-2 wire connectors, 8 soldered power wires).
All silicone all built with 10 years of experience.
Now for months looking a my simple quad build?
I would really like a hardware solution at this point. Hence my rant!
Also: I can see the same GNSS loss at the base station. No quad even powered on.

#6

I will not blame HERE2 for this, but poorly designed telemetry modules. I also tried putting my smartphone next to telemetry module to see if there is interference. Detected satellites dropped from 16 to 1.

I fixed my problem by doing following:

  • Shileding telemetry module (both modules)

  • Positioning telemetry module under multirotor (whole frame blocks signal from telemetry)

I’ll also shield bottom side of GPS to reduce interference even more.

After shielding telemetry module I noticed big difference:

How did you make connecting between shielding and ground of telemetry module?

#7

The antenna ground is what you need to insure has contact with your foil. Unscrew the antenna when wrapping and press the foil into the threads.
I also got it to work better but not as good as when it was just unplugged. . At 14cm apart they are still too close. The foil fix was intermittent and GS is still too high to takeoff.

#8

I don’t know what you configuration looks like, but if there is possibility to mount it under multirotor it will be great. Having the whole frame + battery between GPS and telemetry solved my problem.

If there is no possibility to change position of telemetry module you can also try to shield bottom side of GNSS module.

I used aluminium tape to cover bottom part of GNSS. To achieve connection between GNSS ground and aluminium tape I drilled small hole on GNSS and connected wire between GNSS GND and shield.This also improved signal stability.

#9


I had 14cm gps to mav. with the stock antennas I still have interference with theses tall gps mounts and mav under the copter.