Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: Top Antenna Question with Rearward Performance

  1. #1
    Senior Member LSaupe's Avatar
    Join Date
    May 2014
    Location
    Galway, NY
    Posts
    217

    Default Top Antenna Question with Rearward Performance

    I have an odd one here, and I know next to nothing when it comes to radio's. I have a top mounted antenna (grounded to the fuselage) at the standard Kitfox III antenna location.

    Radio performs strong in the air and on the ground (often over a 50 mile range).

    However, on the way home from a fly in yesterday a Champ was flying loose formation to my side and rear. When he was anywhere behind me, I could barely make out him and he could barely make out me. He was at my altitude or slightly lower. If he was well above me or in front things were strong as usual.

    Question is, could my tail feathers or fuselage be hindering transmissions to the rear? Anyone run across this before?

    Larry

  2. #2
    Senior Member Av8r_Sed's Avatar
    Join Date
    Feb 2010
    Location
    10C Greenwood, IL
    Posts
    671

    Default Re: Top Antenna Question with Rearward Performance

    Hard to say based on one observation. It's equally likely the champ has a problem. Besides having your antenna grounded, does it have a ground plane? It doesn't have to be a continous disk of conductive material under the antenna but should be more than just a fuselage tube. There are numerous ways to acheive this. The simplest consists of using conductive copper tape on the back side of the fabric to create a well grounded asterisk, if you will.

    If it were me, I'd gather more data by flying outbound from a known good ground station (FBO) and get some radio checks. When the signals get weak you could orbit and see how it is from different angles.
    -- Paul S
    Model III SN910
    582 IVO Med

  3. #3
    Administrator DesertFox4's Avatar
    Join Date
    Aug 2008
    Location
    Arizona
    Posts
    3,563

    Default Re: Top Antenna Question with Rearward Performance

    Larry, I've had this happen many times when flying with other Kitfox either in close formation or cross country loose formation. Otherwise perfect working radios get garbled when too close to each other. Also noticed depending on indiviidual aircraft that it can be very directional.
    If you are able to transmit and receive 50 miles there is likely nothing much wrong with your setup. Most of my close group I fly with are running the Garmin SL40 radios. When they get too close to my Micro-Air they can "overpower" it, for lack of a more scientific term.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  4. #4
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,833

    Default Re: Top Antenna Question with Rearward Performance

    Larry,

    I have always considered radio technology a form of voodoo....; However, there can be more than one cause for the observation.

    Airframe shadowing (Transmission or receiving) probably can happen; but, it is probably not always be as big an issue as we might think it to be. As DF4 indicated - distance can be a factor too.

    Another issue is Antenna null zones on transmission. This is dependent on the antenna design and installation and is one of the reasons I think of radio work as voodoo.........given the design and configuration differences out there; and, the mix of new and old systems; I am more suprised by the fact our radios work more often than not.

    The fact that the observation included affects on transmissions both ways might inspire a person to try the same experiment with a different aircraft in the positions around you - Maybe the champ guy, if he is interested could experiment with different aircraft in front and behind his plane.

    I don't think this has a solution other than pinning down the knowledge of the conditions under which it happens. That's good to know.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  5. #5
    Senior Member LSaupe's Avatar
    Join Date
    May 2014
    Location
    Galway, NY
    Posts
    217

    Default Re: Top Antenna Question with Rearward Performance

    Quote Originally Posted by Av8r_Sed View Post
    Hard to say based on one observation. It's equally likely the champ has a problem. Besides having your antenna grounded, does it have a ground plane? It doesn't have to be a continous disk of conductive material under the antenna but should be more than just a fuselage tube. There are numerous ways to acheive this. The simplest consists of using conductive copper tape on the back side of the fabric to create a well grounded asterisk, if you will.

    If it were me, I'd gather more data by flying outbound from a known good ground station (FBO) and get some radio checks. When the signals get weak you could orbit and see how it is from different angles.
    I am not sure what a ground plane is other that is it bolted through and grounded to the upper Kitfox antenna plate just aft of the turtle deck. Does that count?

  6. #6
    Senior Member Av8r_Sed's Avatar
    Join Date
    Feb 2010
    Location
    10C Greenwood, IL
    Posts
    671

    Default Re: Top Antenna Question with Rearward Performance

    Probably sufficient. I like the theory of overloading the radio due to the close proximity of the transmission.
    -- Paul S
    Model III SN910
    582 IVO Med

  7. #7

    Join Date
    Jan 2014
    Location
    Australia
    Posts
    93

    Default Re: Top Antenna Question with Rearward Performance

    I fly gliders and tow planes, we often find that a glider on tow (behind and just lower/higher) can be hard to hear on the radio.

    I believe it is simply because of the radiation pattern of the antennas.

    It sounds like the champ was in a similar position?

  8. #8
    Senior Member LSaupe's Avatar
    Join Date
    May 2014
    Location
    Galway, NY
    Posts
    217

    Default Re: Top Antenna Question with Rearward Performance

    Yep, Champ problem was between 4:00 and 8:00 when at, or slightly below, my altitude.

  9. #9
    Senior Member Dusty's Avatar
    Join Date
    Dec 2012
    Location
    Christchurch, New Zealand
    Posts
    378

    Default Re: Top Antenna Question with Rearward Performance

    AM or PM

  10. #10
    Senior Member jmodguy's Avatar
    Join Date
    Jul 2014
    Location
    Carmel, IN
    Posts
    744

    Default Re: Top Antenna Question with Rearward Performance

    The antennas we use are typically vertically polarized 1/4 wave monopole "whip" style antennas that put out an omni directional radiation pattern. The radiation pattern typically resembles a doughnut (mmmmmm)
    Omni directional means basically "every direction" around the antenna. In a perfect world the transmit and receive antennas are perfectly parallel to each other. Any offset in the alignment of the 2 antennas results in a signal loss. The closer they get to 90 degrees to each other, the greater the signal loss.
    Ground planes are important for antennas. The antennas we use are ground plane or monopole antennas that are basically half of a di-pole antenna. The active part of the antenna is the whip you see, and the ground part you don't see is the "ground plane".
    Here is a website to peruse at your leisure...
    http://electronicdesign.com/wireless...-plane-antenna
    Here is a site that can help you figure the minimum size of your ground plane. Ground planes should NOT BE ROUND. Ground planes do not have to be thick. Aluminum foil will work as long as you can make a good bonded connection to the antenna base.
    http://www.buxcomm.com/ground_plane_calculator.htm
    Jeff
    KF 5
    340KF

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •