Comment by Jason Wise on April 22, 2012 at 4:19am

Im fussy! when will the air radio be all purple? I want to keep it all the same color! :)

Developer Comment by R_Lefebvre on April 22, 2012 at 4:49am

@Andreas, I would suggest you put the ground side into a little plastic "project box".  That's what I did with my Xbee.  It protects the electronics from static, as well as protects the USB connector.  I now have a USB cable coming out of the box permanently.  It is a great strain-relief for the USB connector.

Developer Comment by Andrew Tridgell on April 22, 2012 at 4:53am

Hi Andrew,

Thanks for the comments! The 900MHz radio was indeed close to other emitters in the plane, in particular it was less than 1m from a 5.8GHz Ubiquity bullet used for digital video. I originally thought that may be the cause of the noise, but I'm not so sure now. The 5.8GHz radio was turned on well before takeoff, but the graph shows the high noise levels started on takeoff.

I also thought it might be the ignition, and we do indeed have an electronic ignition system, but that was also started well before we took off. It may be that it only produces noise in the 900MHz range when running at high revs. That theory is supported by the drop in noise levels as the plane was coming in to land (when the engine was at low revs).

For the flight in the above graph we weren't using the amplifiers, so the LNA wasn't the cause.

We don't know for sure if the noise is radiated or conducted. My guess is radiated as the engines ignition is separately powered from the radios, so the only conduction path would be a very tenuous one via the throttle servo and the APM telemetry port.

It certainly is a puzzle. We'll need to do some more experiments to narrow it down.

Cheers, Tridge

Developer Comment by R_Lefebvre on April 22, 2012 at 4:59am

So do these things radiate less noise than the Xbee does into the airborne electronics?

Developer Comment by Andrew Tridgell on April 22, 2012 at 3:06pm

Hi Robert,

The basic answer is that we don't know for sure. I haven't noticed any difference in APM behaviour between using an Xbee and using a 3DR radio, but that doesn't mean there isn't a noise problem, it just means its small enough that I haven't noticed it.

Seppo did some RF analysis of the 3DR radio prototypes and they were fine, so we were fairly confident they were OK.

One difference with the XBeePro900 is that the 3DR 900 can put out twice the power (100mW versus 50mW). So if you have something sensitive to 900MHz then you could potentially get more interference, but the simple answer to that is to lower the power output of the 3DR radio. The 3DR radio has better receive sensitivity then the XbeePro900 so you should be able to get better range even with lower power. I've done a lot of my testing at very lower power levels (down to below 2mW).

A think a bigger issue is the radio being affected by noise from the rest of the plane, rather than the APM being affected by the radio. See the graph I posted above showing bad noise on our 3m Mugin.

Cheers, Tridge

Comment by John Moore on April 23, 2012 at 8:07am

@Andrew How are you able to extract the RSSI data from the TLOG outside of APM Planner?                                                        

@Robert Could you post a picture of your box?

 

I just did my first flight with the 3DR radios today and at 390m with a clear LOS I was getting a 13dB margin on my ground radio and 17 dB margin on the remote radio with a 60% link quality on the APM HUD. With the XBee I had before I was able to get a 99% link out to 1000m before I ran out of clear LOS room. My first thought is my aerial antenna placement it a little to close to other electronics, the XBee had a little more room.

Comment by Zachary Eldridge on April 23, 2012 at 9:06am

These radios work fawless. I put a bigger antenna on the groundstation and it improved range to a least 3miles I was still geting apm function. I will try 4 miles today.

Developer Comment by Andrew Tridgell on April 23, 2012 at 8:33pm

@John,

With that much margin you should be getting excellent link quality. Can you post a tlog?

My only guess as to what may be wrong is you may be running an older ArduPlane/ArduCopter version that didn't support the flow control that the 3DR radios use. The default settings on the 3DR radios oversubscribe the link, so unless you have a current APM/ACM version then you may get some packet corruption if you try to send more telemetry data than the link can support. With the newer APM firmwares it will auto-adjust the rates to suit the link.

Cheers, Tridge

Comment by John Moore on April 24, 2012 at 3:56am

@ Andrew

Heres a link to the TLOG: https://www.dropbox.com/s/a56mp35fs3r7y2m/2012-04-23%2007-36-03.tlog

Comment by Dennis on April 26, 2012 at 2:04am

Just received two pair of these beauties yesterday, one pair 433 mhz (two air radios, to use one as a ground ftdi style) and one 915 mhz. The problem I have is determining which of the air radios is 433 and which is 915. I've looked the boards over pretty well but can't determine which is which. Any help will be appreciated, and if the answer is just plug them in and see, I would like to be a little more certain before I power mine up. Both pair came in the same box so no help there.

 

Thanks in advance for any help

Dennis

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