Research: antennas

This is a long delayed post, but only now I got to write it.

Since antennas are not part of the standard kit, I've been researching what antennas I need for the plane and how to position them.

My plan of record is to have the following avionics:
That gives me a pretty good IFR setup and a decent ADS-B setup (1090+UAT In plus 1090 Out).
That means I need the following antennas (confirmed from a Garmin representative about which devices can share antennas):
  • 2 GPS/WAAS/antennas (must be on top, one of them with XM)
  • 2 COM antennas (one on top, one on bottom)
  • 1 NAV antenna (shared between GTN and GNC, on wingtip)
  • 2 transponder antennas (GTX+GDL, on bottom)
  • 1 marker antenna (coax cable)
  • 1 ELT antenna (on top)
  • 1 stormscope antenna (NY-163, included in the WX500)
  • Maybe: 2 TAS antennas (top and bottom)
The tricky part is - all the antennas interfere with one another if they're too close together, so I have to figure out what ground plane clearance I need around each one.  I'm taking the following antennas as reference, and assuming that any other antenna of the same type will be similar - the frequencies are the lowest needed, which thus require the largest ground plane.

Top antennas:
  • Garmin GA57X (G3X GPS+XM) - 1565MHz - 4" ground plane radius
  • Garmin GA35 (GTN GPS) - 1565MHz - 4" ground plane radius
  • Delta Pop Top Mount COM antenna - 118MHz - 23" ground plane radius
  • ELT - 121.5MHz - 10" ground plane radius
Bottom antennas:
Top/bottom antennas:
  • NY-163 Stormscope antenna - 12" ground plane radius, away from skin current, 48" away from Transponder antenna, 12" away from COM antenna, within 6" of ventral fin, etc. etc. etc. (understandably, this one is picky, but can go on top or bottom equally)
  • TAS antennas (top AND bottom) - 6-9" ground plane radius, most forward position, bottom and top aligned
The problems here are:
  • COM antennas require a large ground plane
  • Stormscope antennas appear to be very picky
  • TAS antenna also appears to be very picky (great advice about the GTS800 antenna on VAF)
  • Top TAS antenna needs to be mounted forward where there's no metal, so it'll require me to fabricate a ground plane
Another nice gadget to have is a UWB antenna, which can boost 4G signal to the ground and get good LTE reception. I'm undecided on whether to actually install it, but it's easier to allocate space for it anyway.

In addition to all that, and to that the most complication, I'd like to have room on the bottom of the fuselage for a MotoPOD, which takes away significant belly area that could be used by antennas (I can probably live with not having the TAS, the UWB and maybe one COM when that's installed, but that would be suboptimal).

This was my first attempt at placing all the antennas (I only had overall dimensions for the MotoPOD, not the detailed shape, so I used a box):

(CAD file available here for anyone interested)

I posted this to VAF, and got lots of good pieces of feedback (also, it appears that mounting the ELT antenna inside the empennage fairing vs vertically is one of those endless discussions, like the primer wars). Highlights were:

  • My GPS antennas were too close - fixed.
  • If I want to put transponder and ADS-B antennas in the back, then the respective transmitters should also be back there (doable given they're remote-mounts)
  • Having one COM on top is a good idea
  • Do I really want the MotoPOD? I'd rather leave this one unanswered for now - if I plan for antennas away from the belly, I can decide later when I get to the fuselage.

So I'm sticking to this plan for now, and will plan the tailcone accordingly (a post on that to come later).


These are various sources of information I used for this:

Overall antenna selection and placement:

Bob Archer NAV antennas:

Whisker-type NAV antennas:

ELT placement:

Marker beacon:



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