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Thread: TBS Crossfire micro link quality

  1. #1

    TBS Crossfire micro link quality

    The manuals are kinda sparse on the subject below, I am assuming that they are assuming I would just know this stuff. I just dont, please help.
    Ijust had a failsafe and near crash yesterday. I was only 4-500 yards out but was real close to the ground.
    In the first photo you will see the low link quality. The transmitter is at 100Mw, there is an '8' with a % that goes to 0 a few frames later, below that is the -89Dbm I have no idea what this means.
    Before this happens in the second photo I had a 'SNA -3db' pop up and the -102dbm. I am thinking -102dbm is worse than the -89dbm? if so why do I have a 97% 'link quality'?
    In the last photo I am showing my good signal that has 300%? Why 300%? is 100% less good? And I still have -76dbm so this number really means nothing to me.
    please teach meClick image for larger version. 

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  2. #2
    First, a couple of terms explained:

    LQ = Link Quality, goes from 0 to 100%, 100% being best in RF Mode 1. It goes from 180% to 300% in RF Mode 2. The switch between the two can cause short negative spikes in LQ.
    RSSI = Relative Signal Strength Indicator/Index, goes from +10 to -130dB. +10 is when the receiver blows due to the signal being too strong. -130 is the absolute minimum the receiver can "hear".
    SNR = Signal to Noise Ratio, in dBm. Goes from -12dB to 6dB (it can go higher, but we don't show anything above 6 as the measurements become unreliable). SNR is the amount of signal you receive above the noise floor (0dB).

    So, a low RSSI (= good) with a low LQ (= bad) usually means high noise, or it's switching between RF profiles. The handshake between the two RF modes can cause a few very minor dropouts, which results in a low LQ. When the SNR reaches below 0 that means it's going below the noise floor. Crossfire can extract noise from below the noise floor, but it's a shaky situation. So once your SNR goes below 0, it's a good time to turn around. Probably this issue is caused from improper installation, or fresnel zone problem (http://radiomobile.pe1mew.nl/?Calcul...:Fresnel_zones)

    HTH

  3. #3
    Thank you for helping me understand. I do know that between me and the quad there was some power lines. This would contribute to the conditions? I will retest in another location.
    thanks again

  4. #4
    OK, I just had a chance to walk out where I was standing and where the quad was when this happened. What I believe happened is that the quad was flying with the tips of the immortal antenna pointing directly at me (horizontal antenna mounting), flying low to the ground, with 3 or 4 rows of farm irrigation between me and the copter. (after careful review of the DVR.)... I have some thinking to do to figure out some better antenna mounting or go back to the dipole.
    thanks for helping me understand the signal numbers.

  5. #5
    Co-Pilot doobie's Avatar
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    LOL 10' off the ground 500yrds out is asking for failsafes
    flyin HIGH

  6. #6

    Cool

    Quote Originally Posted by doobie View Post
    LOL 10' off the ground 500yrds out is asking for failsafes
    It was more like 2' off the ground, I live on the edge.

  7. #7
    Co-Pilot doobie's Avatar
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    LOL ^^ less damage when it drops!!!! what antenna you using??
    flyin HIGH

  8. #8
    Immortal T.
    Please understand that my post here is in no way critical of the product. Very honestly, I understand that I pushed the limits of the system. My goal here was to have a better understanding of the link quality readout and what I should focus on.

  9. #9
    Co-Pilot doobie's Avatar
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    I hear ya man trappy had to explain the exact same thing to me a couple yrs back. I not familiar with the micro I have a few of the diversity rx's, but I think that antenna is better vertical? like I say I not sure, but you may find an answer in the xfire thread here
    flyin HIGH

  10. #10
    This setup is a 5" alien, T-motor Pro 2 2400, kiss v2, kiss 32 esc, using FPVision vtx/pdb, Crossfire micro setup. Awesome stuff!
    thanks for the help, thanks for the forum, and thanks for the TBS products. Everything I use from them is top knotch quality.
    Last edited by dummel; 6th February 2018 at 11:38 PM.

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