Discussions

Developer

delay in shipping 433MHz radios due to USB interference problem

Posted by Andrew Tridgell on April 10, 2012 at 1:49am

Hi All,

I just wanted to give everyone who is waiting for a 3DR 433MHz radio a heads up about a shipping delay. A few days ago I discovered an interference problem with the 3DR 433MHz radios that can cause the range to be much less than expected. We're still investigating the problem, but meanwhile I've suggested to Sam that they delay shipping the 433MHz variant of the radio until we've solved it.

Our current theory is that the 480MHz clock in the USB host controller on some PCs is the source of the noise, and that 480MHz is close enough to the 433 MHz radio band to cause the problem. This theory is supported by testing with the USB host controller forced into USB 1.1 12MBit/s mode ("full speed") instead of the more common "high speed" 480MBit/s mode.

433-scan.pngThe above graph shows a particularly extreme version of the problem on one of my laptops. This graph was produced with a modified firmware that uses the Si1000 as a simple scanner, looking at the background signal level at frequencies from 420MHz up to 950MHz. The graph shows the background noise levels in "433-scan.txt" (the red dots) for a USB version of the 3DR 433 radio. The green dots are for the FTDI version of the radio connected to the same laptop. Those noise levels are far too high, and would severely limit range when connected to this laptop.

We have found some workarounds - in particular running the USB host controller in 'companion' mode, where it forces the controller to run all ports in "full speed" 12MBit/s mode. That helps, but we are not very happy with the solution, and the noise is still higher than we would like.

So we are still investigating the best solution and meanwhile I've suggested to 3DRobotics that they hold off shipping the 433MHz radios until we have properly solved the problem.

The 900MHz radios are unaffected by this and we've got great range on those with lots of different ground station laptops.

I'll keep you all updated via this forum as we make progress on the noise problem. Meanwhile all I can do is apologise for the delay. We thought it was better to ensure the problem is properly fixed rather than having some people disappointed in the range.

Cheers, Tridge

You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –
Follow

Replies

  • Dean April 14, 2013 at 1:51pm
    Thanks, i am having this issue with the 433mhz telemetry. Does this make me alligable for a replacment unit? I have contacted 3DR regarding this and they have done nothing.
  • Dean March 16, 2013 at 12:36am

    anyone able to confirm this?

  • Dean March 14, 2013 at 11:14pm

    Hey guys im not quite as technical as your guys but i know a bit... I just got my 433Mhz 3DRRadio and it appears to be jamming my RX/TX, and the craft just does it own thing. I have no control whatsoever. Im not sure if its just jamming it into a specific PWM which is locking it into a specific flight mode however i cant control the quad, and it just drifts off. I have nearly written this thing off 3 times now.

    When i pull the usb radio out it still does the same thing, so i need to disconnect both radio in order to solve this!

    Could this be related?

    Thanks!

  • marcelo March 11, 2013 at 9:57am

    Hello!!!, I have rctimer's 433Mhz telemetry usb , it is not clear to me how can I fix the problem, I have a very bad range connecting the usb telemetry to my laptop, what can be done?

  • Faraz Ahmad February 4, 2013 at 11:20pm

    Hello,

    If 433mhz Ground Modules are affected  by noise from  FTDI /USB chips and needs some distance between them. this also means the air modules will be affected by presence of any FTDI chip inside the plane electronics. any thoughts ??

    thanks

  • sebiss07 May 1, 2012 at 9:22am

    Hello,

    This problem is it resolved ?


    Seb

  • John Campen April 15, 2012 at 4:53pm

    What are the main pros and cons between the 900 and 433 and how do they compare to the Xbee? I am considering buy either the 900 or 433 and here there are no restrictions so I could use either.

    So firstly (appart from cost) how do they compare to the Xbee for speed and range.

    Which out of the 900 and 433 would be the best choice and why?

  • Tom Worthington April 12, 2012 at 3:13am

    Some thoughts:

    "USB FM Transmitter MAX2606" suggests:

    "A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply."

    Avian’s Blog:

    "The interference from the USB module is mostly gone now that I have a RF shield around that part."

    Note a shield between the USB components and the rest of the circuit board may not be possible if one integrated chip is being used for both functions.

    Another thought might be to build a very large, lightweight antenna into the aircraft, exploiting the fact that the aircraft is mostly dielectric material. The antenna could be some bits of fine wire taped inside or a metal film stuck on.

  • Andre K. April 12, 2012 at 12:42am

    Quality first.

    Ironically , this order also holds my APM2's  - so I am waiting very long now .. and it feels even longer.

  • Chris Gough April 11, 2012 at 4:27pm

    A few comments suggseting this wouldn't be an issue with air modules (UART), only the ground module (with inbuilt USB adapter). Is that right? Or is the interference coming from the Bus, rather than the adapter?

This reply was deleted.

Activity