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Mysterious higher noise levels in air module

Posted by Tobin on December 31, 2013 at 1:13pm

I've been seeing 20 - 30 dB higher noise levels on the air module of my 3DR radio (which is connected to a px4 board), which appears to be severely impacting the range and link reliability. I currently see about 23 - 27 dB of noise in the ground module and 39 - 65 dB in the air module (values based on averages over a 20 second period).

I have tried several steps to identify the source of the additional noise:

- The noise levels are unchanged when the air module is connected with a long enough cable for it to be immediately adjacent to the ground module.

- The noise levels are unchanged when using a super clean power source (which I have scoped to confirm).

- I tried swapping out a different air module. No change.

- The noise levels do not appear to be coupled with throttle.

- I have tried re-flashing both modules and confirming that all settings are consistent.

- Noise levels do not change significantly when using a 12 inch coax cable to connect the antenna to the radio module.

These tests suggest that it's not the power supply, environment, or the individual module that I am using. But that doesn't leave me with much else. I have not been able to identify any pattern to the explain the large range of the noise values.  Any other ideas as to what might be causing the additional remote noise? Anyone else seeing similar behavior?

Thanks for any and all suggestions!

Tobin

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Replies

  • Tobin January 2, 2014 at 9:19am

    Just figured out the problem!

    I had mistakenly presumed that the module required 3.3 V, as the logic was 3.3 V and the VDD for the HopeRF module is 3.3 V. Changing it to 5 V in reduced the noise from 45 to 28. It is still about 9 units (I understand now that the units are not in fact dBm as I previously thought) higher than the ground station, but it's clear that this was a major source of error.

    Many thanks Andke and Mike for the other suggestions which led to me questioning some other assumptions.

  • Stone1295 January 2, 2014 at 8:38am

    Which frequency and what version of firmware are you flashing them to?

    -Mike

  • Andre K. January 1, 2014 at 5:39am

    Try to swap those modules, ond/or antennas ,  maybe one radio is just bad..

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