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
Replies
Thank you for the news; you're right, we expect a good product to replace these crappy xbees. Keep us updated !
I suggest using a TTL cable instead of putting USB directly on the board. It may well be why SiLabs doesn't put USB on the radio chip even though they could have easily done this. They do have a reference USB radio design. You might check that out to see how this problem was overcome. Also check out the USB power to see how noisy it is. USB power is often so noisy as to be unusable without a lot of filtering.
Baring some easy solution... I suggest using a cable and using the same board for both air and ground. You can then dump all the ground boards at a reduced price on people like me who would remove the USB converter and use their own cable.
Thank you for leting us know about the problem, I hope you can solve the problem fast.
Keep up the good work.
Ah, such is life. Incidentally, this is why hardware (especially radios) ought to be thoroughly tested - to ensure they don't jam other hardware and are themselves as tolerant as possible of outside interference. Sometimes these things aren't discovered early, so we actually got lucky, I think. :)
sounds like you'll have to redo the pcb design completely. not pretty :(
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