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antenna locations

T

togaflyer

Well Known Member
I plan to have all my antennas externally mounted, no Archer antennas in the wing tips. The plan is for two comms, one loc/gs, two gps antennas, one marker, and one transponder. Just configuring the location for each.

The VOR/GS will be a Comant CI 157P antenna. I have seen some installed under the tail below the horizontal stabilizer. Question, can you access the inside of the tail in that location for install and removal or would it require my two year old grandson to be required to crawl all the way back in the tail to access the nuts once the tail is completed.

Second
Has anyone mounted an antenna under the tail, aft of the bulkhead. I have seen some mounted under the cabin.

Third
GPS antenna. Is it ok to mount one on the top of the cockpit between the doors. Any issues with it.

Thanks, Rich
 
Lets see:

- I have the bottom tailcone mounted VOR antenna -- you can access it from the outside but it helps to have skinny arms.

- I have a topside COM antenna mounted right behind the seam of the cabin top and tailcone on the tailcone top skin. I did extend a ground-plane onto the cabin top using 3 strips of copper foil.

- My transponder antenna is right behind the baggage bulkhead on the bottom of the tailcone (my transponder (a GTX 23ES) is back there too)

- I have my GTN 650 and one of the G3X GPS antennas mounted between the doors on the cabin top. The coax runs through my overhead console.

All of my antennas seem to work just fine, but truth in lending I only have 3 hrs on them in the air right now.
 
togaflyer said:
I plan to have all my antennas externally mounted, no Archer antennas in the wing tips. The plan is for two comms, one loc/gs, two gps antennas, one marker, and one transponder. Just configuring the location for each.

The VOR/GS will be a Comant CI 157P antenna. I have seen some installed under the tail below the horizontal stabilizer. Question, can you access the inside of the tail in that location for install and removal or would it require my two year old grandson to be required to crawl all the way back in the tail to access the nuts once the tail is completed.
Click to expand...

I had absolutely no issues installing mine under the horizontal before I had the vertical and horizontal installed on the empennage. I installed the doubler, along with nutplates for the antenna mount. I was also able to reach through one of the round holes with the horizontal and vertical installed to remove the BNC connector to remove the antenna recently. I don't think I could have done the initial install with them on, at least not with the size of my arms.


QUOTE=togaflyer;982606]Second
Has anyone mounted an antenna under the tail, aft of the bulkhead. I have seen some mounted under the cabin. [/QUOTE]

Yes, I have an ADSB antenna in the back of the first bay behind the baggage bulkhead.


QUOTE=togaflyer;982606]Third
GPS antenna. Is it ok to mount one on the top of the cockpit between the doors. Any issues with it.[/QUOTE]

My only concern would be ground plane and there are others here that know more than I do on that subject. I have two GPS antennas on the top right behind the transition from the cabin cover.


Btw, I have all the antennas you do, but I have two more GPS antenna, APRS antenna, and an ADSB antenna.
 
I mounted my Comant fiberglass VOR antenna on the VS tip. ELT whip on the top of the tailcone forward of the VS. Two comms: one Comant bent whip on the belly and one Comant swept fiberglass on the cabin top near the tailcone junction. Garmin 650 antenna on the cabin top. Had to add a ground plane for that. The G3X pucks are on a shelf mounted on the firewall under top the cowling along with GDL-39 GPS puck antenna. The transponder blade and ADS-B blade antennas on the bottom. Both bottom blade antennas are from Deltapop Aviation. I was more concerned with antenna performance rather than drag.
 
#2. If you mount an antenna on the belly aft of the main gear, make sure it cannot hit the ground if you over-rotate, over-flare, have 2 people on the steps at the same time, need to tie down the tail to do maintenance work on the nose gear, etc. I put a bent whip under the rear passenger seat (plan ahead!). Works okay except once in a while I have to re-orient the plane to talk to ground control (or use #2 com whose antenna is in the wingtip).

#3. A number of people have put gps antennas between the doors. Note that Vans does not approve of any holes drilled into the honeycomb; you're on your own there. Mine is just aft of the baggage area bulkhead, on the metal (with a doubler), works fine.
 
rleffler said:
I had absolutely no issues installing mine under the horizontal before I had the vertical and horizontal installed on the empennage. I installed the doubler, along with nutplates for the antenna mount. I was also able to reach through one of the round holes with the horizontal and vertical installed to remove the BNC connector to remove the antenna recently. I don't think I could have done the initial install with them on, at least not with the size of my arms.
Click to expand...

Bob makes a great point. I installed my VOR doubler when I was building my tailcone. It would be a real bear if not just about impossible once the tailcone is finished unless you used blind rivets. Way easier to think ahead a bit -- I just wish I had thought about installing nutplates, but my failure to do so just shows that you can install the antenna with the original washers and nuts.
 
Great input. Im in the process of assembling the tailcone and thought this would be the time for some doubles. I will be on that tomorrow for the tail cone. Much thanks!
 
Has anyone installed the comm gps combo antenna

CI-2480-201 ComDat VHF/GPS
Comant’s ComDat dual function single engine antenna for VHF/GPS. Our patented technol- ogy provides 80 dB of VHF harmonic suppres- sion allowing Comant to offer VHF and GPS in one radome without in-line filters.
Designed as a “drop-in” replacement for com- mon single engine teardrop footprint.
Compatible with Garmin 17 dB GPS panel mount receiver systems.
Not compatible with most portable GPS receivers systems.
 
I have one of those, but am still a few months (?) away from flying so I can't provide a review. That will be the G3X/comm 2 antenna; GTN 650 is not compatible so it gets its own antenna (cabin top) and the comm is bent whip on the bottom.

==dave==
 
Hey Big D got this from Garmin re the combo antenna. I check and the G3X has WAAS.

The CI antenna you listed does not meet the dB gain required for the GTN 7XX or the 6XX WAAS requirements of 25dB. It does meet the requirements for the non WAAS GPS system. As an experimental you can use what you think will work, but I would go with what the STC install manual recommends as that is a proven system.

Cessna had been using the combo antenna, but seem to be going away from that on their newer aircraft. I would use the GA 35 GPS antenna and a standalone Com. I think you would be happier in the long run as the separate antennas would be cheaper to replace if one section goes bad.
 
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Just another data point. I have the bent COMMs on the belly between the steps and main gear. The transponder is on the belly in the tunnel just forward of the tail cone joint. The marker beacon is on the belly just right of the tunnel where the controls run to the wings. The ELT antenna is aft the second tailcone bulkhead on top. The GPS antenna and the combo GPS/SAT are both on the cabin top staggered left/right. To get the required distances, including from the ELT, one is just aft the rear door hinges and the other back on the cabin top. No ground plane required for the GPS antennae, according to Garmin, though they recommend it as it may increase performance. While testing the panel before they were mounted, they were just lying free on a blanket on the engine mount and worked great. And, finally, I considered mounting the NAV under the tail cone or buried so it was under the horizontal stab. The latter would have been difficult and left part of the antenna buried inside the tail cone. The former would have been easier but would have still needed some work to mount the flat puck to the curved bottom and also left the tips at eye-poking height for the small children and animals that inevitably appear on the ramp when you least expect it. In the end, I put mine at the top of the vertical stab just behind the fairing. Mounted directly to the top rib, the puck is flush with the skins and clears the rudder counterbalance perfectly.

Other considerations: I considered long about leaving the marker beacon antenna off entirely. Alternatives are to use an Archer antenna in the wing tip or cowl but I didn't want to do those wiring runs. While I'll probably never use it, it was part of the G900X package so I caved and installed it. I can always remove it with little difficulty and little to indicate it was ever there. Likewise the NAV whiskers, though I hope they retain VOR as a backup at least, for the foreseeable future. According to local ATC, the outlook for VOR is grim due to maintenance costs. In any case, I tried to make sure my installations had minimal impact on the structure because the only constant in life is change...
 
The combo antenna is an approved non-garmin solution, see table 17-1 in the G3X installation manual. For the GTN 650 I will be using the Garnin antenna, mounted to the cabin top. My goal was to have all GPS antennas on the upper exterior and to have an upper and lower comm antenna, and the Comant looked like it would help do that with one less mounting point.

==dave==
 
Im doing the VOR/GS the way Bob did. Doubler with nut plates. Our airport, KPGD, is installing an ILS system to accommodate Alegent Air ( the airport already has WAAS approaches that are down to 200 ft). Figure since the airport is spending the money for the system, might as well add the antennas. I like the comms on the bottom, but some of the airports we go to use the RCO for the clearance. Thats why Im probably going to keep one on top. Could use DME instead of a marker beacon, but then whats one more antenna.
 
On the bottom centerline, measured from the firewall, transponder 2' 2", ADS-B receiver at 5', straight com at 7' 4", bent com at 12' 8". ELT is inside the baggage at the top. GPS on the cabin top.

The bent com will bend slightly more if the rear tie down ring ever hits the ground. (It does not come off, protects the bottom rudder fairing.)
 
When to install Antennas

When in the build process is a good time to install antennas? I've started basic wiring now. Seems like a good time, but I haven't bought any avionics yet, but am pretty settled on what components I'll be installing.
 
When you still have access. I installed the underbody antennae while I still had the floorboards off so I could install doublers, plate nuts, etc. Similarly, I installed the ELT antenna when I installed the top aft skin, and the NAV whiskers when I installed the tail. I'm doing the GPS now so I can install the overhead console before permanently installing the cabin top.
 
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