Developer

delay in shipping 433MHz radios due to USB interference problem

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.

The 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

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Replies to This Discussion

Permalink Reply by Chris Gough on April 15, 2012 at 5:58pm

433 needs an antenna twice as big as 900 MHz.

433 might perform better with line-of-sight obstructions.

I'll be using 433 in fixed wing platforms and keeping 900 MHz in my multicopter.

Permalink Reply by John Campen on April 16, 2012 at 3:46am

 Chris..your long post  is very informative and love to get this type of information . Thanks !

Permalink Reply by sebiss07 on May 1, 2012 at 9:22am

Hello,

This problem is it resolved ?


Seb

Permalink Reply by Andke on May 1, 2012 at 10:11am

it's worked around by using FTDI cable.

Permalink Reply by olli on November 25, 2012 at 3:00pm

hello,

i have also a groundmodule with usb...  it´s possible to cutt the usb plug + chip and solder some PIN´s for FTDI cable ?

or i must buy a new air-module ?

rg olli


3D RoboticsPermalink Reply by Sam Kelly on November 25, 2012 at 6:44pm

olli, if you have a ground module, it is 915MHz. 3D Robotics has not shipped any 433MHz ground modules. You don't need to do any modifications since the 915MHz ground modules are OK.

Permalink Reply by olli on November 26, 2012 at 1:15am

i have the usb-433 mhz modul.i have buy it as "used" .....  i think it ´s a clone.i am not shure :-(

it´s possible to DEsolder the usb-chip and connector and solter the FDTI cable to the 3DR directly ?

or is the board design completely different to the air-module ?

olli

Permalink Reply by Faraz Ahmad on February 5, 2013 at 12:20am

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

Permalink Reply by Andke on February 5, 2013 at 12:27am

it's not really about FTDI chips, butthe frequency of  USB which you use in only one end.

Permalink Reply by Michael Utz on February 5, 2013 at 1:19am

the air modules can be affected by some camera like gopro see here:

http://www.rcgroups.com/forums/showthread.php?t=1422899

Permalink Reply by marcelo on 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?

Permalink Reply by Faraz Ahmad on March 12, 2013 at 9:27am

hi @ marcelo, just replace the stock antennas with 13.6 inch 18awg wire on both air and ground modules..

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