Garmin GA35 GPS Antenna Location

[12vaitor]

I am waiting to know if anyone might have some experience or advice on an alternate mounting location for a Garmin GA35 GPS antenna. I have come up with two, just in front of the canopy or just aft of the window on the turtle-deck. I already have the Dynon GPS antenna under the cowl, so the concern with the front location is two GPS antenna within 12" of each other. The turtle deck location has a COM2 antenna about 24" forward of the VS. The top of the VS is already taken by a NAV/LOC antenna. Suggestions welcome.

Thanks.

John Salak
RV-12 #120116

 

[Dave12]

I would like to see your panel when it's done. Sounds interesting.

 

[Mich48041]

According to the discussion on this forum,
http://www.thehulltruth.com/marine-electronics-forum/308495-minimum-distance-between-gps-antennaes.html#b
the NMEA standard recommends 6" minimum separation between GPS antennas. However, it is debatable what minimum distance would actually cause interference between two GPS receiving antennas. On the D-180 versions of the RV-12, the GPS and XM weather antennas are mounted adjacent to each other on the antenna shelf.
Com antennas are routinely mounted less than 1 wavelength from each other. If the same reasoning is applied to GPS with a wavelength of 20mm, then very little separation is required. But who knows without testing.
I think it is worth a try to mount both GPS antennas on the same firewall antenna shelf. If it doesn't work out, one antenna could be moved later.
Maybe someone with more experience or knowledge will chime in.
Joe Gores

 

[Taildrgr]

Both my Dynon and Garmin GPS antennas are mounted on the glareshield under the tipup canopy. They are on a relatively flat surface and are 9 inches apart.
I have not flown yet, but I have seen several pictures of RV's with the antennas in this location.

I have 2 Garmin gps antennas in my Cessna on the glareshield and they work fine.

 

[Dvalcik]

My GPS farm - LOL

Modified the shelf under the cowl.

No issues with them close to each other.

 

[12vaitor]

Dave12,

You can find a photo of my 2nd Gen prototype panel at the link below. Typical RV-12 type Skyview (SVD1000, Dynon GPS, ADAHRS, EMS-220) with ADS-B and -261 XPNDR. The COM2 radio is a Garmin GTX-200 that was just installed last weekend (connected to a SV serial port). The rack in the big hole is a GNS530 rack that is waiting for an Avidyne IFD-540 WAAS GPS/COM/NAV to be delivered when certification is done (soon, they tell me). The -540 GPS is wired to the -261 XPNDR for compliant GPS OUT. I also installed the Dynon ARINC-429 module to connect the -540 to the Skyview for all the NAV output goodies. Using a PM3000 intercom with a manual COM1/COM2/NAV audio switch. Would have been a lot happier if Garmin had included an input for a second COM in the GTX-200 audio section (they included a TX interlock, so someone was thinking of a 2nd COM). The blank panel area is for my RAM iPAD 3 mount.

https://www.dropbox.com/s/wm8afkitead5776/RV12 Prototype Panel #2.JPG

Six antennas makes for a lot RG-143 to run in a tunnel run designed for only two. Next time I will make sure to run some conduit for extra wiring. All of the wiring is 100% custom, including a dual battery, A/B electric system with Shorai LFX batteries to keep the weight down.

Goal is a IFR trainer/light IFR if (when) the WX goes overcast on a typical Florida afternoon in summer. Regarding another thread on building a low cost -12, I took all the money I saved from buying a Viking engine FWF package and spent it on avionics!

John Salak
RV-12 # 120116