Welcome to PhantomPilots.com

Sign up for a weekly email of the latest drone news & information

90 Antenna Elbow To Change Antenna Position

Discussion in 'Phantom 2 Mods' started by Buzz313th, Apr 22, 2015.

  1. Buzz313th

    Joined:
    Apr 18, 2015
    Messages:
    277
    Likes Received:
    103
    My IRC600mw Vid TX is mounted underneath on the belly of the phantom with the cloverleaf fatshark sticking straight out the back. I was bending it 90 degrees to get it to point straight down for better transmission coverage. I want to position the antenna lower, but I like the balance of the phantom and don't want to mount the TX on the leg.

    I was thinking of getting a 90 degree antenna elbow adapter so the cloverleaf will point straight down from the TX's current position. Such as this one...
    http://www.hobbyking.com/hobbyking/store/catalog/FR90DEGA.jpg

    Here's my question...

    By adding another connection between the TX and the cloverleaf, is it possible that I might be sacrificing a small bit of transmission power? as compared to just remounting the TX on the leg and not using a 90 degree connector?

    Thank you

    JB
     
  2. SteveMann

    Joined:
    Aug 27, 2014
    Messages:
    1,977
    Likes Received:
    652
    Location:
    Westford, MA
    Typically, every connector in a transmission line adds 3dB of loss.
     
  3. N017RW

    Joined:
    May 2, 2014
    Messages:
    6,236
    Likes Received:
    1,606
    Location:
    Palm Beach Co.- FL
    Anytime you insert something in the path there will be 'insertion losses' primarily due to power reflections back to the Tx..
    These will generally be about a dB or two for good quality connectors however the improved performance by optimizing your antenna's position or alignment may actually overcome any loss(es).
     
  4. Buzz313th

    Joined:
    Apr 18, 2015
    Messages:
    277
    Likes Received:
    103
    Thank you guys for the info...

    So really my next question is... Do I give up 1-3 db in power and add the adapter, or do I just reposition the TX on one of the legs with the cloverleaf pointed straight down..

    Anyone have a link to a really good quality adapter?
     
  5. jason

    Joined:
    Oct 12, 2014
    Messages:
    4,099
    Likes Received:
    404
    Location:
    Commerce Twp,MI
    Are you forgetting a decimal point there Steve? The estimated loss for a SMA connector is 0.5db.
     
  6. antares

    Joined:
    Oct 28, 2014
    Messages:
    57
    Likes Received:
    8
    Location:
    Philippines
    I have inserted a 90 degree SMA adapter to get my cloverleaf antenna pointing straight downwards. I did not notice any effect on the fpv range. For me, the purpose of the adaptor was to have less vibration on the antenna, and from the antenna into the transmitter. Solder joints do not like vibrations so i was expecting problems in the transmitter.
     
  7. jason

    Joined:
    Oct 12, 2014
    Messages:
    4,099
    Likes Received:
    404
    Location:
    Commerce Twp,MI
    I had done the same thing with my TX and a 0.5db loss in signal isn't noticeable.
    IMG_1554.jpg
     
  8. gazza0315

    Joined:
    Apr 25, 2015
    Messages:
    7
    Likes Received:
    1
    I was encountering an issue similar to the one you have. When I had the phantom flying away (the antenna pointing towards me) the FPV signal range was very good, when I turned the copter, to return home (the antenna now facing away from me) I lost fpv signal altogether. I fitted a 90 deg elbow and had the antenna pointing straight down, this gave me the desired result where I had more fpv from the phantom regardless of its position relative to where I was.
     
    Buzz313th likes this.
  9. noiseboy72

    Joined:
    Jul 13, 2014
    Messages:
    575
    Likes Received:
    17
    Location:
    Lincs, UK
    Typical losses on a 90 degree SMA through adapter @ 5.8GHz are 1.5-3 db. You also need to consider the VSWR as well.

    That being said, compared to over-bending the coax, these loses are quite acceptable. the lowest loss solution would be to fit a 90 degree plug, as the losses on this will be around half those of an adapter and with better VSWR performance as well.
     
  10. vk3bq

    Joined:
    Feb 13, 2015
    Messages:
    21
    Likes Received:
    5
    Location:
    Melbourne - Australia
  11. noiseboy72

    Joined:
    Jul 13, 2014
    Messages:
    575
    Likes Received:
    17
    Location:
    Lincs, UK
    We could argue this all day, but 90 degree adapters have a higher VSWR according to their spec sheets. You need to consider the whole length of the transmission line, as you are in effect, altering the impedance "seen" by the transmitter. This can reduce the total available power at the antenna.

    The insertion loss is directly proportional to the frequency. It also assumes a perfect environment, so any contamination or moisture will affect things as well.

    As I originally said, bending a piece of coax beyond its minimum radius to get a cloverleaf pointing down is more harmful, as this will also have a detrimental effect on the performance of the transmission line as a whole.
     
  12. rrmccabe

    Joined:
    Jul 2, 2014
    Messages:
    1,647
    Likes Received:
    358
    Location:
    Ankeny, Iowa
    I don't know what the antenna in question is but the characteristic impedance of the feed line must be different than the antenna impedance? Otherwise the length of transmission line would not matter as far as SWR. Have more info on the antenna and coax?
     
  13. jason

    Joined:
    Oct 12, 2014
    Messages:
    4,099
    Likes Received:
    404
    Location:
    Commerce Twp,MI
    I don't know where you got those losses for SMA 90° elbow connector but I got mine from the manufacture. As far as VSWR the wattage and length of that antenna are so minute it couldn't be measured on an SWR meter.
     
  14. Buzz313th

    Joined:
    Apr 18, 2015
    Messages:
    277
    Likes Received:
    103
    So I finally had some time and picked up a high quality 90 degree adapter..

    I am consistently getting a much cleaner signal all the way around. Regardless of phantom attitude and yaw angle to the transmitter, the video signal is clean with no hickups or dropouts. I have tested out to a clean line of sight at 2000 meters and the signal is much more consistent than before..

    I am going to take a guess that a good antenna position (as far away from any objects on the phantom) is a key point here.

    The current antenna position is pointing straight down off the back of the phantom and is currently lower than the skids. I use my pelican case to launch it with the phantom backed up to the edge of the case so it sits on the skids without the antenna getting in the way.. I always hand recover it as it wont sit flush on the ground.
     
  15. vk3bq

    Joined:
    Feb 13, 2015
    Messages:
    21
    Likes Received:
    5
    Location:
    Melbourne - Australia

    It's not a CB big buddy. 10-4. How's your swer...

    Happily use 90 degree SMA adaptors. On high power microwave gear Ham radio gear.

    If your elbow changes the impedance or vswr teen you need a better connector. The losses. From the spec sheet I provided above.

    SMA SPECIFICATIONS
    Electrical
    Impedance 50 Ohm
    Frequency Range
    .141" & .085" O.D. Copper Jacket Semi-Rigid Cable 0-18 GHz
    Flexible Cables 0-12.4 GHz
    Voltage Rating
    RG-55, 58, 141, 142, 223, 303 500 volts peak
    RG-122, 174, 188, 316 375 volts peak
    Dielectric Withstanding Voltage (max.)
    .141" & RG-58 Group 1000 VRMS
    .085" & RG-316 Group 750 VRMS
    VSWR for Straight Connectors
    .141" O.D. Copper Jacket Cable 1.05 + .005 f (GHz)
    RG-55 Group 1.15 + .011 f (GHz)
    RG-122 Group 1.15 + .02 f (GHz)
    RG-178 Group 1.20 + .025 f (GHz)
    VSWR for Angle Connectors
    .141" O.D. Copper Jacket Cable 1.10 + .01 f (GHz)
    RG-55 Group 1.15 + .02 f (GHz)
    RG-122 Group 1.15 + .03 f (GHz)
    RG-178 Group 1.20 + .03 f (GHz)
    Insulation Resistance 5000 MΩ
    Contact Resistance
    Center Conductor 2.0 mΩ
    Body 2.0 mΩ
    Braid to Body 0.5 mΩ
    RF Leakage -60 dB min
    Insertion Loss .03 sqrt(f(GHz)) dB max


    ImageUploadedByTapatalk1430131231.509945.jpg


    Sent from my iPhone using Tapatalk
     
    rrmccabe likes this.
  16. rrmccabe

    Joined:
    Jul 2, 2014
    Messages:
    1,647
    Likes Received:
    358
    Location:
    Ankeny, Iowa
    Greetings vk3bq de kd0zv

    73
     
  17. jason

    Joined:
    Oct 12, 2014
    Messages:
    4,099
    Likes Received:
    404
    Location:
    Commerce Twp,MI
    Do you think he got the message in the UK.