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3DR Radio, First Impressions

Posted by Mark Harrison on April 21, 2012 at 5:38pm

P1020223.JPG?width=256

I'm thrilled to report that my radio kit arrived and it works well.  Andreas is likewise happy with his kit.

Writeup here:

http://eastbay-rc.blogspot.com/2012/04/review-3dr-900mhz-radio.html

Fixing the air unit network id:

http://eastbay-rc.blogspot.com/2012/04/setting-network-address-on-3dr-air.html

Thanks 3DR, Tridge, and everybody else that worked in producing this unit!

Tags: 3dr-radio
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Comments

  • Developer
    Michael Oborne April 22, 2012 at 12:33am

    just a fyi,

    in the planner under "Status" and "tunning" you can see all the values tridge included in his graph live.

  • Developer
    Andrew Tridgell April 21, 2012 at 10:59pm

    Hi Andreas,

    The antennas are reasonable, but may benefit from having a ground plane. It would be interesting to do an experiment watching the reported RSSI value with and without an aluminium foil ground plane.

    Regarding range testing, you can extrapolate the range quite well from the RADIO packets in a tlog. What you need to look for is the difference between the RADIO.rssi and RADIO.noise levels at both ends of the link. Convert that difference to dBm and use the rule that each 6dBm doubles the range. The formula for RSSI to dBm is on the 3DR wiki page.

    For example, here is a graph from a flight I did today:

    3692402839?profile=originalThe 'RADIO.rssi' and 'RADIO.noise' graphs show that at a distance of 500m the GCS was getting a RSSI of 66 (which is -92dBm) and a noise level of around 27 (-112dBm). That means we had 20dB margin. If we allow for 6dB of fade margin then that gives us 12dB spare. That corresponds with 4x the range, so it would have gone to 2 km very easily (the 6dB fade margin is generous).

    The radio in the plane is a different story for this flight. It was getting a similar signal level (about -92dBm), but the noise level was very high, sitting around an RSSI level of 60, which is -95dBm. That is only 3dB below the signal. It did keep a solid link, but it was quite marginal. If we had flown any further it would have lost the link.

    So in this case what we need to do is work out why this plane (a 50cc petrol plane) had such a lot of noise in the plane. The same radios when I flew them yesterday in my SkyFun gave much lower noise levels, and extrapolating that result implies a range of about 5km or so for those flights.

    So the range you get very much depends on the noise levels you have. One of the things we aimed for in the design of the radios was to make it easy to log the signal and noise levels so you can work out why a link is poor. With most radios its just guesswork, but with logs like the one graphed above its easy to see what needs fixing.

    Cheers, Tridge

  • Ayush Gupta April 21, 2012 at 10:04pm

    Hi Mark, Could you please do some Range Test and Let the community know what kind of Ground range and In air range one can expect out of this Beauty.

  • Developer
    Andrew Tridgell April 21, 2012 at 9:51pm

    Thanks for the review Mark! I was really looking forward to the first reviews coming out so it's nice to get a positive one first up!

    Cheers, Tridge

  • Developer
    Andrew Tridgell April 21, 2012 at 9:48pm

    Hi Jack,

    It's not closed source - the full schematics of the design are available from Si (it's just the Si1000 reference design), plus all the source code is open. This is the most open telemetry radio I'm aware of.

    Cheers, Tridge

  • Moderator
    Mark Harrison April 21, 2012 at 9:46pm

    Thanks Greg, fixed!

    Jack, all in good time, I'm sure this won't be the last radio system offered.  My perspective on this one: worked painlessly, half the price. Onward and upward!

  • Greg Fletcher April 21, 2012 at 8:07pm

    Error in your review, wt. is 17.5g not 175g.

  • Jack Crossfire April 21, 2012 at 6:44pm

    It's a closed source Hope electronics module soldered to a microcontroller which presumably translates MAVLink.  You'd think 3d robotics could just design the entire radio.

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