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Amplification warning

Discussion in 'Phantom 2 Vision Discussion' started by themosttoys, Jan 29, 2014.

  1. themosttoys

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    Word to the wise to those adding amplifiers to the TX (controller 5.8ghz) or wifi (2.4ghz repeater and camera). Be aware of the maximum input of the amplifier. Most amplifiers can only handle 20dbm (100mw) maximum input (many much less).

    It is well known that the controller has two modes CE = 25mw (14dbm) and FCC = 126mw (21dbm). I just finished testing using an RF Power Meter and these power levels are accurate.

    The published power level for the repeater is 17dbm (50mw). My testing with the RF Power Meter is showing 21dbm (126mw).
    There is no published power level for the camera. My testing with the RF Power Meter is showing 21dbm (126mw).

    The word to the wise, for best results and the life of your amplifier, be sure you use an attenuator to lower the power level before input into your amplifier.

    Happy flying.
     
  2. PVFlyer

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    Thanks a lot themosttoys for sharing this valuable information. I initially thought both DJI repeater and camera are 17 dBm, but your testing shows 21 dBm on both. Such 4 dBm discrepancy (50mw vs. 126mw) is talking about 150% higher than DJI advertised. How can DJI provide such misleading information? As a long range flyer, I prefer higher TX power from the camera for sure.

    Are you able to verify your testing on TX power of the camera? I don't really care about the repeater TX power, though I only use it for short range <300 meters flight. How did you test the TX power?

    I think modern 2.4G Wifi boosters are built-in AGC (automatic gain control), which should take care of exceeding input power.
     
  3. themosttoys

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    I too was surprised in the power levels vs DJI's claims. I can't explain it, but since they are closed units (not expected to be opened by the consumer) the added power does not break any regulations and adds reliability and range, I guess DJI figured no harm.

    I tested the power of the camera by connecting the RF Power Meter directly to right (as seen looking from the bottom of the camera) U.fl antenna connector inside the camera.

    I tested the TX power by connecting the RF Power Meter directly to the U.fl antenna connector (there is only one) inside the transmitter (controller).

    True, many (most) commercial 2.4ghz wifi boosters have AGC, but not all, especially DIY or very small (light weight) amps that are best options to mount on the P2V (connected to camera).
     
  4. PVFlyer

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    Thanks again for the details. I'm unsure whether that's the proper way to test MIMO TX power though.
     
  5. themosttoys

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    Happy to provide the data.

    The testing is consistent with MIMO / diversity Power Measurement (the meter showed the variation.) That being said, while it is clear that some type of diversity is being used, it is unclear which type. How did you determine that MIMO is in use and not something more simple like switching or combining?
     
  6. PVFlyer

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    Just curious, no offence. You indicated "connecting the RF Power Meter directly to right (as seen looking from the bottom of the camera) U.fl antenna connector inside the camera". Did you keep the left U.FL connector on the left antenna?

    Just don't quite understand how this "MIMO / diversity Power Measurement" works.
     
  7. themosttoys

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    No offence taken. MIMO (for sure) and many (the most common) diversity configurations depend on the spreading the same total transmit power across all antennas to achieve array / diversity gain. So while it will work, the best results are achieved by using very similar antennas. Of course it will work without similar antennas, just will not be optimal. I have been planning on replacing my linear whip (I added to the P2V camera) antenna with a skew planar (circ pol) antenna (of course with a matching helical on the repeater), but if this is a MIMO setup, I'm not sure I'd gain as much. Of course I also have an 800mw amplifier that I plan to mount to the P2V but I don't want to do two amps. Lots of testing to do, and now that I have an accurate power measurement I can do a better configuration. BTW, adding the amp is not necessarily for added range (that is a nice side effect for me) it's more for penetration. Today I have plenty of range, but fly behind anything and things go bad quick.

    Bottom line is that if it is true MIMO, that is good, just not necessarily great for what I have been planning. We shall see.

    Good times.
     
  8. PVFlyer

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    Glad to know you plan to boost your P2V. If it can fly behind obstacle, it will increase the range as well for sure. AFAIK, the stock camera antenna is circular polarization, which is similar to cloverleaf or skew planar wheel. It may not help much by replacing SPW that is about 0.9 dB gain only.

    I also planned to boost my P2V a few weeks ago. I tested it with a 2.5W booster (that used to reside in my AR.Drone), but I did not see significant gain from WiFi Analyzer comparing to the experience on AR.Drone. I'm unsure whether I missed or misunderstood something about MIMO.

    Please share with us of your boosting P2V result.
     
  9. themosttoys

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    Plan to use Circular Wireless SPW24 (nominal gain of 2.3db). viewtopic.php?f=7&t=3880&start=700#p54819

    Hmmm, tonight I'll take the camera apart and look again, but I don't remember the antennas being Circ Pol. Could have just been that everyone had been saying that they were vertical polarized, so I didn't even bother to look more closely. Are you sure they are circ pol? Are they right hand or left hand?

    Thanks
     
  10. PVFlyer

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    The camera antenna is LHCP, which is called Truncated Corner Microstrip Patch.

    I took a picture (right-hand side only) of the antenna when I opened the camera cover a few weeks ago. Both antennas are with the same part# as I recalled, thus I believe both antennas are LHCP with different phasing.
     
  11. themosttoys

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    That is VERY interesting, I'm embarrassed to have not looked more closely at the antennas myself. I am very familiar with Microstrip Patch antennas, for anyone interested in learning more, this is a great paper: http://ethesis.nitrkl.ac.in/992/1/Complete_Thesis.pdf

    Well, that explains a lot, most of all why your Left-handed helicals (btw, good job on the home made) produced the results they did. I'll need to give this a little more thought, but the good news is that since they are LHCP and the antenna I bought is RHCP, I should still be able to run some tests without cancellation.

    Thank you.

    hmmm, good times.
     
  12. PVFlyer

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    Can you post a picture of BOTH left/right antenna of the camera? I want to make sure my assumption (left/right antennas are the same with the same part#) is correct, while I don't have my P2V wtih me right now.
     
  13. themosttoys

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    Part numbers are the same.
     

    Attached Files:

  14. themosttoys

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    More inside pics:
     

    Attached Files:

  15. PVFlyer

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    Thanks a lot for the pictures. I believe both left/right antennas are LHCP.

    If you use RHCP helical alone connecting to repeater, there will be max. 30 dB (1000X) lost due to LHCP vs. RHCP rejection (similar to multipath rejection). I'm afraid your FPV range may drop under 300 meters. Anyway, test it out and share with us your result.
     
  16. themosttoys

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    I'm also using spw24 RHCP Skew planar on the P2V. You are absolutely correct, never mix handedness.

    Sent from my Note 3 using Tapatalk 4
     
  17. oukenfold

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    well one question, i am not a master antenna dud, but knowing this what you recomend, to put in to the camara antennas? LHCP, RHCP, directional, helical, circular, or what? i just wanna have that most range that this setup can give me. thanks.

    whats the best setup so far, with repeater and camara antenna? whats the perfect match.
     
  18. helixaviator

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    Yes I am a bit confused as well. So if the camera has circular polarized antennas I am assuming the repeater has circular polarized as well since they appear to be the same. Is it best to match LHCP in transmitter with LHCP in receiver or do you want LHCP in one and RHCP in the other? If the cam is using LHCP does this mean its not wise to be using the linear polarized 8dbi tp link omni antenna since you dont want to mix linear with circular polarized?
     
  19. themosttoys

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    There are many possible solutions, each with their own pro's and con's.

    My recommendations are:
    For the camera:
    a) GOOD - Add either a 5dbi whip or a 2.3dbi Skew Planar. Change one or both, theoretically, changing both will have better results, but it won't be a big difference.
    b) BETTER / BEST - For more penetration (and range) add in a 2.4ghz amplifier, use the smallest and lightest you can find and don't bother with max power, 600mw to 800mw is more than enough for the maximum flight time of the P2V. What's the point in being able to go 10km if you can't get back. Airplanes have glide slopes, the P2V does not.

    For the Repeater:
    a) GOOD - Add one or two antennas to the stock repeater. If you go with circular polarization you MUST match right-handed or left-handed. So if you use a RHCP (right-handed) antenna on the camera, you MUST use a RHCP on the repeater. You can go with a omni (like a skew planar), but better results will be had with a patch or a helical. Linear antennas work with circ pol antennas, you just lose 3dbi of gain (Ex: if you use an 8dbi linear whip it will perform like a 5dbi (8 - 3 = 5).
    b) BETTER - Add an amplifier to the repeater. Since you are not flying this amplifier you can use whatever you like, but again, there will be little difference in returns between 800mw and 3w.
    c) BEST - Use a separate repeater (Ex: Docooler, Amped, ...), using a ground station will make using larger antennas easier and will produce the absolute best results, but is not as convenient / portable.

    For the controller / transmitter:
    a) GOOD - Change the little white whip for a larger (5.8ghz) whip (ex: 5dbi or 7dbi) or a patch (ex: 11dbi). Remember, as with all antennas, the higher the dbi, the more precises you must orient.
    b) BETTER / BEST - Add a 5.8ghz amplifier.

    Hope this helps.
     
  20. themosttoys

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    Always best to use matching antennas. Especially with circular polarization, you MUST match, so if you use RHCP on the camera, you must use RHCP on the repeater (ore vise versa). Linear antennas work with circ pol but you lose 3dbi of gain. Ex: if you have a circ pol on the camera (like stock) and you use a 8dbi whip on the repeater, the 8dbi whip will perform like a 5dbi.