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Thread: Help - EZUHF - RSSI values too low

  1. #1
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    Help - EZUHF - RSSI values too low

    My EzUHF long range system appears to have low RSSI values compared to similar systems and compared with the standard values I read from Sander Sassen in this forum (-57 dBm at 1Km, -63 dBm at 2Km etc.) Consequently the range is poor: 1,5 - 2 Km.

    Here's my configuration:

    EzUHF Tx with Diamond SRH 771
    EzUHF Rx 8 ch diversity receiver
    EzOSD
    Futaba 8FG with 3s
    two Sander style antennas
    Lawmate 2.4Ghz 500mW VTx
    QAV500 with Naza M
    TBS core with tin shield
    4 Tiger motor ESCs 30A 400Hz

    Last release (RX and TX) firmwares (1.43)
    433-435 Mhz

    The RSSI values in function of distance, if the Diamond antenna is vertical are quite constant. I have tested the quad in different places with similar results. LOW mode.
    (In high mode the values differ 4-6dBm.)

    1,5 Km -75dBm
    1 Km -72dBm
    500m -66dBm
    250m -60dbm
    125m -54dbm
    60m -48dbm
    30m -42dB
    15m -36dBm

    The LQ normally is 100 and it starts to drop when the RSSI is less than -85dBm and then I get failsafe.

    The bad packet value is similar to the RSSI values.

    This doesn't seem to be a RF noise problem, with the immersion RC tools spectrum analyzer I have optimized the positions of the core, VTX, EzOSD sensor, Naza bec and wiring. My worst values, with everything on, are now -92dBm in my frequency range (433-435MHz). Not so good but flyable, at lest for a quad, as far as I read.
    I never had failsaves with RSSI values lower than -80/85dBm.

    I don't pretend to fly my quad very far. I'd like to have a reliable link, without the need to have always the TX antenna in a perfect vertical position, of 5Km.
    I have to shoot some aerial videos for a documentary movie in a wild environment.

    I bought my system from Onedrone (Slovenia), and I have already contacted Robert but before sending him back my TX, to be tested and changed or repaired, I post this, just in case there's the possibility to calibrate the TX myself (without loosing the warranty).

    In order to solve the problem I have tried to change all the antennas (RX and TX) and I have performed also ground tests, according to the methodology I found in this forum, only with the RX connected to a laptop (with the quad off). Here the RSSI values

    1m -13dBm
    3m -23dBm
    6m -31dBm
    12m -35dBm

    And here are the values read from Ezosd, with the quad with everything on (low mode), a little better:

    1m -13dBm
    3m -22dBm
    6m -27dBm
    12m -31dBm

    The values in high mode differ 4-6dBm.

    I enclose some pictures of my quad, a rough wiring scheme and a spectrum diagram with everything on, the base noise is -105dBm.

    The values of RSSI of the two RX antennas are equal or differ by 1dBm.

    As a last test I thought to bind another EzUHF TX to my quad but I didn't found any in my zone (I live near Barcelona, Spain).

    Thanks in advance for your help.
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    Last edited by Axel; 8th August 2013 at 10:31 AM.

  2. #2
    Ouwe Zeikerd Carbon's Avatar
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    Your whole layout seems very good, it shouldn't be an interference source on the craft. Just to confirm, your spectrum analysis was done with the craft and GoPro powered up?

  3. #3
    ImmersionRC Support Guru swillhide's Avatar
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    Your reading the RSSI from the OSD? If so then there is a way to adjust the RSSI read value from the OSD. One thing that I didnt see what a reading from where you fly. If your in Europe then you can only use 100mw and that might be a starting issue if you are flying near some other UHF tx spewing garbage on your band. BECAUSE your build looks solid, except you should RF shield your gopro cause it is noisy while recording.
    AMA # 1015480 HAM Callsign # Procrastinating..
    Futaba 9c w/Ezuhf /Skywalker 1880 or anything else that I can Lawn Dart.
    Retired: Disco(Sold), Skywalker 1900(Dirt Nap), Qav540g/Nazav2/Iosd mk2

  4. #4
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    Thanks Carbon, and yes, spectrum analysis with everything powered up (GOPro included, but doesn't change a lot).

  5. #5
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    Swillhide, yes, the first values are from the EzOSD, but the second ones (short distance ground test) are from the laptop, only RX powered up, quite similar to the third ones, from the EzOSD, with craft powered up. I'm not an expert but I believe the RF noise (internal or external) influences above all the LQ, not much the RSSI values.

  6. #6
    ImmersionRC Support Guru swillhide's Avatar
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    Help - EZUHF - RSSI values too low

    No, the RSSI is also noise based. Basically volume and LQ is clarity. So if the noise floor is higher where you fly then you can still hear the tx and can hear it clear.

    Neither hear nor there. When your reading the numbers those are dBM numbers not RSSI.

    Looking at your values, you for sure have an issue but with my knowledge I don't know where to point you to first but I am sure Ssassen will be along shortly to help or maybe a good idea to see if Onedrone will swap the tx.

    Question: in which order do you power up your RC tx and Ezuhf? Do you power on the tx then apply power to the UHF from the 3s or the UHF first?
    AMA # 1015480 HAM Callsign # Procrastinating..
    Futaba 9c w/Ezuhf /Skywalker 1880 or anything else that I can Lawn Dart.
    Retired: Disco(Sold), Skywalker 1900(Dirt Nap), Qav540g/Nazav2/Iosd mk2

  7. #7
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    The ambient noise is about -105-110dBm, and then I tried different places, quite far from the city, with the same results.
    Usually I power on before the Futaba 8FG, that anyway is connected with the EzUHF (power included, not only signal). But I tried to compare the RSSI values powering the TX in two ways: with or without external 3s lipo. The results, in low mode, are similar.

  8. #8
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    Click image for larger version. 

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ID:	30350Here is the ambient RF noise.
    Last edited by Axel; 6th August 2013 at 02:55 PM.

  9. #9
    ImmersionRC Support Guru swillhide's Avatar
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    Ok those numbers look good, I think its time for you to get ahold of Onedrone and see what they can do for you.
    AMA # 1015480 HAM Callsign # Procrastinating..
    Futaba 9c w/Ezuhf /Skywalker 1880 or anything else that I can Lawn Dart.
    Retired: Disco(Sold), Skywalker 1900(Dirt Nap), Qav540g/Nazav2/Iosd mk2

  10. #10
    His Royal Sassiness ssassen's Avatar
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    Axel, it is getting late, and I have had a few long island ice teas too many, but what is your issue exactly? Lack of range? How far out do you get before failsafe kicks in?
    Velvety smooth drone pilot for hire

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