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  #1  
Old 10-26-2018, 03:08 AM
AGORV AGORV is offline
 
Join Date: Apr 2018
Location: Roma
Posts: 9
Default RV7 transponder antenna location

question I have seen so many sites but I have so much confusion where to install transponder antenna, I have the dynon skywev and many install it to the bow under the foot of the passenger, but say maybe too close to the transponder itself, and then I saw so many behind but I already have two antennas com and it would be too close, and then how long should the wire be?
thank you
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  #2  
Old 10-26-2018, 03:58 AM
Bevan Bevan is offline
 
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Location: BC
Posts: 1,557
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Yes. Antenna placement can be an important thing. Certain spacing should be maintained between potential victims and antagonists. Here is what I have done on my RV7A with good results.

Comm 1 is on the top fuselage behind the sliding canopy when it’s open. This location is optimum in theory when transmitting while on the ground.

Comm 2 it’s on the belly Under the seat pan (far left side). This location is optimum in theory while airborne transmitting to ground stations.

The transponder Antenna is located on the belly one bulkhead after of the aft baggage bulkhead. This should be a little further from the transponder radio and behind the wing to prevent its theoretical shielding effect.

The transponder based traffic receiver antenna [looks Same as transponder Antenna] Is located on the belly just forward of the right main gear leg. THis should be a few feet away from the transponder antenna.

The VOR antenna is located on the top of the vertical stab and should be a few a few antenna lengths away from a comm antenna.

Most of the GPS antennas are on the glareshield in front of the passengers position. One GPS antenna is on a bracket under the fibreglass cowl forward of the firewall, And works well there.

My 406 ELT antenna is located in the Baggage area on a tab riveted to the longeron, The antenna is slightly bent to accommodate the curvature of the canopy. This should be a few feet away from each comm antenna.

These all seem to work well and play nice together in these locations.

Bevan
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Last edited by Bevan : 10-26-2018 at 04:04 AM.
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  #3  
Old 10-26-2018, 06:28 AM
alcladrv alcladrv is offline
 
Join Date: Oct 2006
Location: Southeast
Posts: 455
Default

I solved my transponder antenna placement question when I dropped a bucking bar onto the skin under the baggage floor, about a foot inboard of the right side step on my -7A. It opened a hole like an old metal pointed can opener.

I showed the picture to Tom Green at Vans and he suggested it was a great place for the transponder antenna. Out came the drill to enlarge the hole and in went the antenna. It has worked flawlessly ever since, 13 years ago. He sure was right.

My comm antenna is about 6" aft of the wing spar under the left seat.
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  #4  
Old 10-26-2018, 07:10 AM
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uk_figs uk_figs is offline
 
Join Date: Jan 2005
Location: Tulsa, OK
Posts: 879
Default Fwd of spar

Have the transponder and comm antenna's just fwd of the spar outboard in the foot-well, worked fine for the past 10 years. Comm antenna can get blanked occasionally on the ground when talking to tower.
Figs
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  #5  
Old 10-26-2018, 07:36 AM
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Walt Walt is offline
 
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Xpdr antenna should have approx 10" dia ground plane, 6' of RG400 is generally considered the max.
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Last edited by Walt : 10-26-2018 at 08:27 AM.
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  #6  
Old 10-26-2018, 08:07 AM
BillL BillL is offline
 
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Location: Central IL
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Default Less than ideal so . . .

Quote:
Originally Posted by Walt View Post
Xpdr antenna needs approx 10" dia ground plane, 6' of RG400 is generally considered the max.
I won't disagree with Walt, on the ground plane, but I did locate my transponder antenna where you mention, just behind the FW and outboard of the angle forming the center channel on the 7. That way it was behind the cowling air exit (no drag). It has seems to work well and passed the FAA antenna check nicely and ADSB inflight (if it has anything to do with that)

Sorry no actual data, just anecdotal information. When installed it was a risk (ground plane), and talked to Garmin help line. I was concerned it might interfere with the GPS antenna located under the cowl, but it has not seemed to do so.

Close to the transponder and far away from everything else is hard to do.

Good luck, following Walts suggestions is best.
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  #7  
Old 10-26-2018, 08:19 AM
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N941WR N941WR is offline
 
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Location: SC
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I put my transponder antenna just inboard of the right fuel vent, up against the firewall.

Years later I upgraded the Dynon D100 EFIS / D10 EMS to a SkyView and added ADS-B. I put the ADS-B antenna in the same location on the left side.

Never once have I had a controller say they couldn't pick up my transponder and I have not has issues with the ADSB in the four years it has been installed.

Zoom in on this old picture and you can see the transponder antenna.

(click to enlarge)
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  #8  
Old 10-26-2018, 08:26 AM
Mark33 Mark33 is offline
 
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Location: Baton Rouge, La.
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Hey Walt,
Are you saying that 6 foot of RG-400 is the maximum length of cable that you'd want to run from the transponder to the antenna? With the transponder being mounted in the panel and the antenna being mounted on the belly of the fuselage, it's pretty easy to eat up 6 feet and I don't see how I'll be able to keep my coax run that short. Do you recommend a different kind of coax that could withstand a longer run or would it be better to mount the antenna closer to the front of the fuselage so that the coax run could be kept to that 6 foot maximum length rather than mounting the antenna behind the rear baggage bulkhead?

Thanks,
Mark
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  #9  
Old 10-26-2018, 09:12 AM
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Raymo Raymo is offline
 
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Location: Richmond Hill, GA (KLHW)
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Quote:
Originally Posted by Mark33 View Post
Hey Walt,
Are you saying that 6 foot of RG-400 is the maximum length of cable that you'd want to run from the transponder to the antenna? With the transponder being mounted in the panel and the antenna being mounted on the belly of the fuselage, it's pretty easy to eat up 6 feet and I don't see how I'll be able to keep my coax run that short. Do you recommend a different kind of coax that could withstand a longer run or would it be better to mount the antenna closer to the front of the fuselage so that the coax run could be kept to that 6 foot maximum length rather than mounting the antenna behind the rear baggage bulkhead?

Thanks,
Mark
You'll find that RG-142 is easier to fit the TNC pin on for crimping and, I believe, it works better for longer installations.

My Dynon/Trig XPNDR is installed on the right side sub-panel with antenna mounted under the MLG weldment (for protection from feet). Wire length is may be 4'. You should have no problem doing something similar with the antenna mounted toward the firewall.
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  #10  
Old 10-26-2018, 09:20 AM
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Dan Langhout Dan Langhout is offline
 
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Location: Huntsville, AL USA
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Default Cable Length

Quote:
Originally Posted by Mark33 View Post
Hey Walt,
Are you saying that 6 foot of RG-400 is the maximum length of cable that you'd want to run from the transponder to the antenna? With the transponder being mounted in the panel and the antenna being mounted on the belly of the fuselage, it's pretty easy to eat up 6 feet and I don't see how I'll be able to keep my coax run that short. Do you recommend a different kind of coax that could withstand a longer run or would it be better to mount the antenna closer to the front of the fuselage so that the coax run could be kept to that 6 foot maximum length rather than mounting the antenna behind the rear baggage bulkhead?

Thanks,
Mark

If you read Garmin's installation documentation carefully (GTX-327 for example) it definitely lists maximum cable lengths for different cable types.

I mounted my transponder antenna in the center of the belly about a foot or so aft of the baggage compartment as described here - so my cable length was over the Garmin recommended length for RG-400. I hunted down and bought some of the special ($$) coax cable and BNC ends that Garmin specified for longer lengths (don't recall the # - it's in the install docs. Special # from Vendor ECS). Has worked great. RG-400 might have worked OK, but I didn't really want to take the chance.
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Last edited by Dan Langhout : 10-26-2018 at 09:26 AM.
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