Long Range on 433 Mhz SiK Telemetry

Hi,

For my custom built F450 Pixhawk, I wanted to get very long range on telemetry (to send in autonomous missions and in the mean time know what is going on), so I have searched for the best (at a reasonable price) 433 Mhz antennas.

After reading on forums, etc, I have come up to buying these 2 antennas:

For Tx:

http://www.hobbyking.com/hobbyking/store/__25646__RMILEC_433MHz_SRC771_1_2_Wave_Length_UHF_Antenna_FPV.html

For Rx:

http://www.hobbyking.com/hobbyking/store/__63105__ImmersionRC_433MHz_34_Sander_34_Antenna_Replacement_or_Telemetry_Radio_Upgrade_.html

I heard I should be getting a few kilometers (3 - 4) at least easily with this combo, but I have situations when after even less than 1 km I lose signal and Tower disconnects. I saw some youtube videos with more than 10km range even!

Anyone else tried this exact combo and got great range? Or maybe the SiK radios are the problem? Or can you recommend me anything better?

Thanks

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Replies

  • Your antennas need to be either both vertical or horizontal, any misalignment drastically reduces the range. also note that if they were to be both at, say,  75 degrees, this only works outbound as when the vehicle turns 180, there is now a 30 degree misalignment.

    I couldn't remember the exact losses so googling turned up this.

    "On line-of-sight (LOS) paths, it is most important that the polarization of the antennas at both ends of the path use the same polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20 dB or more. Likewise, in a circular polarized system, both antennas must have the same sense. If not, an additional loss of 20 dB or more will be incurred."

    Every 3db loss is the equivalent of halving the power. Power and range are not directly related, it takes 4 times as much power to get twice the range, try to think of this in reverse to get an idea of the loss in range. Lets look at the part that says 90 degrees misalignment can be 20db or more loss. Lets make it easier and round to 18db, this is the same as halving the power 6 times.

    The maths is 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 = 1/64. Now think what that does to the range. And that is in ideal conditions.

    I hope this is helpful.

  • bump

  • Hi Rrayden

    With the RMILEC on the ground control station side and the standard antenna that comes with the radios, I achieve good comms to 20km and occasional/bad comms up to 30km. (LOS obviously) 

    I would expect the immersion antenna should be better than the std antenna's, I actually have some of those and my next test would be to use the immersionRC antenna, I will let you know the results when done.

    Cheers

     

    • Have you managed to test the immersionRC antenna with the RMILEC?

      Thanks

    • Ok, thanks, this is very weird then!

      How are your antennas oriented? Maybe mine are not in the optimum position, but this cannot make such a big difference to have less than 5km, no? I mean the Rx one is oriented down but not quite vertical because it is longer than my landing gear, so it's like 75 degrees instead of 90, and the Tx one I admit it is more horizontal than vertical, but I will fix that and test again.

      Maybe I should try again with the stock one instead of the ImmersionRC, maybe I just got a faulty one... if you say that RMILEC alone is so amazing...

      On another note, since you seem to know much more than me regarding these long range flights... can you please recommend me a good Rx (or pair with Tx) antenna for getting a few km of FPV also? I am using a pair of 3 and 4 lobes standard mushroom type 5.8 Ghz antennas and again I get less than 1km... I think a helical one for ground, and the mushroom is ok for drone?

      Thanks

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