915MHz Telemetry cuts out... any ideas?

Hi everyone,

I have a Bixler 2 with APM 2.5 and 915MHz telemetry. It flies really well and I've never had any problems with it. However, I've never flown it particularly far away from me. I have tried to do a few surveys on auto mode recently, and the telemetry cuts out at about 300m away from me. I then ran over to the plane in the air (on auto) and it didn't regain signal. Later on it did once it was coming in for landing.

The telemetry logs (attached) show that the noise is always fairly low, and it's the rssi - both air and ground module - that drop sharply, not related to distance.

Any ideas?


2014-12-17 13-10-18.rlog

2014-12-17 13-10-18.tlog

2014-12-17 13-10-18.tlog.jpg

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  • Ok, let's try this again. What is the difference between the above picture and these two? The one with the red dot is the 3DR antenna. The other is one I bought last year. I freely admit radio electronics is not my forte'


    • And I found the other one, which has a male pin. I was thinking both had to be the same antenna so I didn't use the other one, didn't notice there was one without the male pin. For fun, tonight I used the large antenna in the other picture without the male pin, attached to my phone using Droid Planner.

      I walked to the other end of my house and the signal never dropped below 100%.

      With the 3DR antenna, it wanders all over the place, from 50% to 75-80%.....much like it does in the air. Bottom line: the 3DR antenna is horrible.

      Now I'm wondering if that other antenna could have been used all this time!

      I read this at RCG, but never did the mod:

      See Pattaya01's posts, and jump back to pg 7 & 12 to see the mod.



      • Huh I just looked at the specifications of that antenna and not at the picture. The specs say SMA plug, but the picture is clearly RP-SMA, which would indeed fit your radio. Sloppy work, jDrones.

        Thanks for bringing my attention to that other thread. A few months ago I lost my radio antenna and wondered if I could use a spare 2.4GHz antenna I had from a Turnigy RC radio because they look exactly the same. I ended up buying another one to play it safe, but now I'm annoyed because now I know it is exactly the same - the wrong one!

        In light of this new information, your new antenna is better because it's a 3dB antenna, but MUCH better because it's actually a 915MHz antenna!

        It looks like you answered your own question, but just in case you missed it - the two antennae you're holding are both RP-SMA connections. I can't see the lengths, but if one is longer, it is probably a 915MHz antenna, while the 3DR one is 2.4GHz. The one you're holding in the bottom picture has an SMA connector

  • 3FIJAv8.png

    It sure looks female to me. My 3dr radio has a male pin. Am I missing something?

    Several months back I ordered two antenna with a male pin. Doh!

  • Moderator

    RSSI is reported signal strength so if they drop sharply it's clear what's happening. Why is another story.

    What antennas are you using? What power are your radio's set at? Are you using ECC?

    • Thanks for the quick response!
      I'm using the stock antennae (which look exactly the same as my 2.4GHz radio and my 5.8GHz FPV antennae...?). How do you set the radio power? What is ECC?

      FPV system is not on the aircraft btw

      • Moderator

        Have a read through here: http://copter.ardupilot.com/wiki/3dradio/

        • Looks like they're set at power level 20 (full) and ECC is turned on...
          I did notice a few weeks ago (before I had the courage to fly far away) that when the aircraft came back with a loose antenna. I know they don't like to transmit without an antenna attached, but if it were damaged it would be completely shot, right?

          • Moderator

            Normally yes, but as they overheat without an antenna that can cause other issues too. The stock antennas are usually not great with range and better ones can make a large difference.

            It doesn't help too that the antennas all look alike and some radios have even been known to ship with the incorrect antennas. It may be worth trying any other antennas you have to see if there's a difference in the RSSI values.

            Also check the antenna connecter to see if it matches the radio, ie SMA or RP-SMA.

            • Ha got it!
              The air module had two females! Interesting that it actually worked for a bit...

              Thanks heaps for your help Graham :)

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