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  #1  
Old 11-07-2015, 06:18 AM
rdamazio's Avatar
rdamazio rdamazio is offline
 
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Location: Santa Clara, CA
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Default Feedback on antenna placement?

Hi all.

As I'm about to start building the tailcone, I did some research on all the antennas I may need for my 10 and how to position them (wrt ground planes, interference, etc.).

My plan is to have this or something equivalent to this:
  • IFR+VFR GPS (e.g. G3X+GTN)
  • NAV1/NAV2
  • COM1/COM2
  • Transponder + ADS-B In/Out
  • Stormscope
  • Maybe, just maybe a TAS (since I will fly outside the US)
  • ELT

(I'm still far from buying the actual avionics, so the exact equipment may change over time, but the antennas for them are less likely to change)

I looked at antenna models, and am leaning towards this set:
  • 2 GPS antennas (those don't change much between manufacturers)
  • 2 Delta Pop COM antennas (one top, one bottom)
  • 1 Bob Archer wingtip NAV antenna
  • 1 Delta Pop Transponder
  • 1 ADS-B (e.g. GDL39R)
  • 1 L3 Stormscope (antenna is NY-163)
  • If I get the TAS, 2 directional antennas
  • ELT antenna

To make this a bit harder, I'm also considering adding the MotoPOD hardpoints to have some extra luggage room when needed - but when the pod is on, it takes up most of the belly.

After reading through all the documentation I could find for these types of antennas and the installation restrictions, I made a first CAD draft of what those would look like on the aircraft:







Thoughts? Am I overthinking this? It's obviously impossible to respect all the ground plane sizes (the circles), but I tried to get close (and followed this post about the TAS antenna ground plane specifically). I'm also assuming that it's OK to not have the TAS when the pod is on.

I'm also unsure about all the antennas being laterally aligned with the longitudinal axis - is that the recommended practice? (I suspect that the UAT antenna may be too close to the battery mount and may need to be shifted anyway)

(UWB on there is one of the Delta Pop UWB antennas, which I'm still totally undecided about, but placed anyway - also OK to be unavailable with the pod on)

Any feedback appreciated!
Rodrigo
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Last edited by rdamazio : 11-07-2015 at 06:20 AM. Reason: Adding details
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  #2  
Old 11-07-2015, 09:11 AM
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Carl Froehlich Carl Froehlich is offline
 
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If you are going to mount the XPDR antenna that far aft then recommend selecting a transponder that does not mount in the panel. That way you can mount the transponder itself closer to the antenna.

For the ELT, mount it horizontally under the empennage fairing, the base of the antenna attached to the bulkhead just forward of the fairing.

For the ADS-B receiver antenna, mount it anywhere you want but here again mount the ADS-B receiver with it. Note that there will be minimum spacing requirements between the ADS-B antenna and transponder antenna. There is no concern with proximity to the battery(s). Delta Pop also makes a nice inexpensive ADS-B receive antenna.

The cabin top is problematic for comm antenna mounting. if you go this way, recommend moving it aft to perhaps center the two bulkheads aft of the canopy top. If you leave it on the cabin top, add a ground plane (several small wires glassed into the bottom of the top or a thin aluminum plate). Note also the overhead area aft of the baggage a common area to mount the EFIS ADHARS modules so keep in mind any spacing requirements.

Recommend you consider the mission and decide if you really need the pod or not. As is the RV-10 can hold an amazing amount of stuff - enough to easily hit gross weight limits.

Carl
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  #3  
Old 11-07-2015, 09:50 AM
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Jesse Jesse is offline
 
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I would put the transponder just aft of the firewall in the center tunnel. Then you can put the ADS-B antenna just aft of the rear baggage wall for spacing (wouldn't hurt to mount the ads-b receiver there as well. For now, I wouldn't worry almost at all about antenna placement. That can all be done later when you make your final decisions on the avionics. You actually make end up with a transponder/ads-b receiver in one that may not require 2 antennas, since they are virtually the same antenna anyway.

The NAV antenna can feed 2 NAV radios, so you should be good there.

The ELT antenna under the tail one fairing is my recommdation as well. You can mount the ELT there also.

For now, I would get at least 2 of Van's ELT mount kits for the tailcone side walls to be able to mount an ADS-B receiver and possibly other equipment when you get there.

I have never mounted a COM antenna under the wing, but I don't see any rof Aston why that wouldn't work, except possible the yaw effect of the drag created. A low drag antenna would certainly be the best there. My main concern here would be the chance of hitting something with the antenna when taxiing in tight spaces. Under the fuse has to be clean because of the wheels.
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  #4  
Old 11-07-2015, 06:42 PM
togaflyer togaflyer is offline
 
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For thought, with the G3X you will have the magnetometer. I believe most are mounting that in the tail. Mine will be locatied at the top of the second station aft of the baggage bulk head. You will need to be concernered with magnetic interference. I installed the cat wisker VOR/ILS antenna on the tail, under the horizontal. My GPS antennas, GTN 650 and one G3X same spot as yours, with a third dash mount for the second screen. Transponder and ELT in area that Jesse said, mine is right of the battery on a shelf. Both the Teds transponder and ADSB will be in the tunnel just aft of the battery. I will use the ADSB iIN for weather and TCAS
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  #5  
Old 11-07-2015, 06:51 PM
BobTurner BobTurner is offline
 
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My suggestion: drop the ADSB antenna. Plan to go with a mode S-ES transponder instead. Since you're starting from scratch the cost difference between mode SES and UAT will be minimal. Your GTN can serve as the ADSB nav source for several Garmin and (less expensive) Trig transponders. ADSB-in depends on what panel equipment you want to display it on, but on my GRT HX I use a $550, factory refurbished Sky radar with two small antennas mounted internally, on the door posts. Works fine, brings in lots of ground stations as well as airborn aircraft. You did not say where you are going out of the country, but remember in Europe there is no UAT, just tramsponders with mode S-ES.

I'd also suggest that just one nav receiver is enough, but again that is for the US.
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  #6  
Old 11-07-2015, 07:07 PM
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Bill.Peyton Bill.Peyton is offline
 
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With regard to the archer wingtip antenna. I mounted one in each wingtip. For two years it worked great until one day I was shooting an ils getting vectors to final and lost the GS signal for a few seconds. After doing several flights to determine the issue, I mapped a radiation pattern with my spec analyzer which showed significant notch due to the wing and fuse. I confirmed it in both wing tip antennas..

I now have a cat whisker installed on the belly as far aft as I could. Problem solved.

The other issue I noticed using the wingtip location was a 15 foot offset from the centerline of the runway when shooting the loc/ils.

If you are going to use a panel mount X ponder, I would mount its antenna under the pilots seat to avoide such a long run. If you are going to mount a remote transponder rear of the baggage bulkhead then the position you have selected would work fine.

Leave room for an adsb blade antenna on the belly further forward, or rearward depending on which xponder location u end up using.

I have a com antenna on the top and belly. Mainly driven by ground communications at larger airports.
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  #7  
Old 11-08-2015, 01:49 PM
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rdamazio rdamazio is offline
 
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Thanks for all the replies.

Replies by topic (split due to message size limit):

NAV:

Quote:
Originally Posted by Bill.Peyton View Post
With regard to the archer wingtip antenna. I mounted one in each wingtip. For two years it worked great until one day I was shooting an ils getting vectors to final and lost the GS signal for a few seconds. After doing several flights to determine the issue, I mapped a radiation pattern with my spec analyzer which showed significant notch due to the wing and fuse. I confirmed it in both wing tip antennas..

I now have a cat whisker installed on the belly as far aft as I could. Problem solved.

The other issue I noticed using the wingtip location was a 15 foot offset from the centerline of the runway when shooting the loc/ils.
15' should be OK, it's not like I'm shooting CAT III - even if I break out at 200' minimums I should still have time to correct (not that I routinely shoot approaches to minimums either).

My original thought was to use a whisker-type antenna at the top of the VS, so I did leave a conduit in there, I can easily switch, but a lot of people have had a lot of success with those wingtip antennas. Speaking to Don from Delta Pop at Oshkosh I got the impression that as long as they're installed strictly according to instructions, they should work properly - did you have any deviation from instructions, or did you get the reception gap even with the correct install?

Quote:
Originally Posted by BobTurner View Post
I'd also suggest that just one nav receiver is enough, but again that is for the US.
That's easy to change later, given that a single antenna can be used for multiple receivers. I may as well start with a single NAV.

Transponder and ADS-B:

Quote:
Originally Posted by Carl Froehlich View Post
If you are going to mount the XPDR antenna that far aft then recommend selecting a transponder that does not mount in the panel. That way you can mount the transponder itself closer to the antenna.

...

For the ADS-B receiver antenna, mount it anywhere you want but here again mount the ADS-B receiver with it. Note that there will be minimum spacing requirements between the ADS-B antenna and transponder antenna. There is no concern with proximity to the battery(s). Delta Pop also makes a nice inexpensive ADS-B receive antenna.
Quote:
Originally Posted by Bill.Peyton View Post
If you are going to use a panel mount X ponder, I would mount its antenna under the pilots seat to avoide such a long run. If you are going to mount a remote transponder rear of the baggage bulkhead then the position you have selected would work fine.

Leave room for an adsb blade antenna on the belly further forward, or rearward depending on which xponder location u end up using.
Quote:
Originally Posted by Jesse View Post
I would put the transponder just aft of the firewall in the center tunnel. Then you can put the ADS-B antenna just aft of the rear baggage wall for spacing (wouldn't hurt to mount the ads-b receiver there as well. For now, I wouldn't worry almost at all about antenna placement. That can all be done later when you make your final decisions on the avionics. You actually make end up with a transponder/ads-b receiver in one that may not require 2 antennas, since they are virtually the same antenna anyway.
The issue with the belly below the seats is the MotoPOD - I tried to position all essential antennas away from it (I can't really give up the XPDR if I'm flying with the pod). Maybe if I draw it as its actual shape rather than the box I used, there'll be enough room near the corners for those antennas (but I still worry about them being obfuscated by the pod).

I do plan to use a remote-mount transponder and ADS-B, so I could position those far in the back. Does anyone have experience with having a long run of antenna coax vs having a long run of data cables? Do either of those work well?

Quote:
Originally Posted by Jesse View Post
For now, I would get at least 2 of Van's ELT mount kits for the tailcone side walls to be able to mount an ADS-B receiver and possibly other equipment when you get there.
Do you mean this one? Looking at the plan PDFs, OP-41.pdf mentions F-10112-L, which doesn't match the above part number (also unclear if that mount comes as part of one of the kits, or has to be ordered separately). Also, I don't see dimensions for either of those anywhere - can anyone share those so I can see what would really fit in them?

Quote:
Originally Posted by BobTurner View Post
My suggestion: drop the ADSB antenna. Plan to go with a mode S-ES transponder instead. Since you're starting from scratch the cost difference between mode SES and UAT will be minimal. Your GTN can serve as the ADSB nav source for several Garmin and (less expensive) Trig transponders. ADSB-in depends on what panel equipment you want to display it on, but on my GRT HX I use a $550, factory refurbished Sky radar with two small antennas mounted internally, on the door posts. Works fine, brings in lots of ground stations as well as airborn aircraft. You did not say where you are going out of the country, but remember in Europe there is no UAT, just tramsponders with mode S-ES.
Europe and South America would be my primary long-distance trips (though I admit I dream of joining EarthRounders some day ).
I'm only counting on ADS-B working in the US (hence the TAS).

The reason I'm hesitant to move the ADS-B antennas inside is that I've played with the stratux recently in busy airspace in an aircraft that also had built-in ADS-B, and while I got a lot of the same nearby traffic as the built-in system did, I didn't get it all - there were multiple missing targets (and interesting, a couple that only showed up in the stratux). If I do get the TAS, maybe that won't matter much anyway.

ELT:

Quote:
Originally Posted by Carl Froehlich View Post
For the ELT, mount it horizontally under the empennage fairing, the base of the antenna attached to the bulkhead just forward of the fairing.
Quote:
Originally Posted by Jesse View Post
The ELT antenna under the tail one fairing is my recommdation as well. You can mount the ELT there also.
I like the idea, but I've heard several people recommending against that. The arguments were not enough ground plane, putting your antenna inside a Faraday cage (the fuselage), mounting the antenna horizontally gives the wrong polarization for satellites to pick up the 406MHz signal and increasing the chances of the fuselage bulkhead itself breaking the antenna during a crash.
Thoughts on this? Has anyone tested this beyond the 121.5 signal being picked up by a nearby receiver? I'm interested in any measurements or arguments that indicate the 406MHz would still radiate properly and get you rescue.
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  #8  
Old 11-08-2015, 02:06 PM
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rdamazio rdamazio is offline
 
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COM:

Quote:
Originally Posted by Carl Froehlich View Post
The cabin top is problematic for comm antenna mounting. if you go this way, recommend moving it aft to perhaps center the two bulkheads aft of the canopy top. If you leave it on the cabin top, add a ground plane (several small wires glassed into the bottom of the top or a thin aluminum plate). Note also the overhead area aft of the baggage a common area to mount the EFIS ADHARS modules so keep in mind any spacing requirements.
Quote:
Originally Posted by Jesse View Post
I have never mounted a COM antenna under the wing, but I don't see any rof Aston why that wouldn't work, except possible the yaw effect of the drag created. A low drag antenna would certainly be the best there. My main concern here would be the chance of hitting something with the antenna when taxiing in tight spaces. Under the fuse has to be clean because of the wheels.
Quote:
Originally Posted by Bill.Peyton View Post
I have a com antenna on the top and belly. Mainly driven by ground communications at larger airports.
I've seen a few people mount COMs under the wing, always relatively close to the fuselage, never far out where it might hit something. I do worry about ground reception, which is why I added the second COM to the top.
This is the antenna I'm looking at for the under-wing mounting (the "lower mount" one), but I'm open to any recommendations on low-drag COM antennas. Notice I put mine on the right wing, while I'm assuming NAV and pitot tube will be on the left wing - the thought was to minimize interference and balance the drag somewhat.

Thanks for the hint on the ADHARS - I'll definitely look into the guidelines for that (one more consideration).

I'm aware of the ground plane issues with the cabin top, I just didn't find any other places to put it (given that Stormscope is supposed to be far back and not close to the battery ground current path). If I change the ELT to be inside the empennage fairing I can certainly move both further back, but probably still not all the way onto metal (have to check).

Motopod:

Quote:
Originally Posted by Carl Froehlich View Post
Recommend you consider the mission and decide if you really need the pod or not. As is the RV-10 can hold an amazing amount of stuff - enough to easily hit gross weight limits.
You may be right - I was thinking of the pod more in terms of added volume than weight (e.g. if I go camping, there's all this equipment which is not that heavy but is big). Can anyone who decided in favor of or against using the pod share their decision/rationale?

I guess I'll also run the numbers on a few loading scenarios (with some reasonable assumption of empty weight) and see if the pod really makes sense. If it doesn't, then antenna placement becomes a whole lot easier.

GPS/etc:

Quote:
Originally Posted by togaflyer View Post
I installed the cat wisker VOR/ILS antenna on the tail, under the horizontal. My GPS antennas, GTN 650 and one G3X same spot as yours, with a third dash mount for the second screen.
Did you have a particular reason to have 3 GPS antennas? afaik the screens will communicate GPS data to one another anyway - the odds of two of them failing and a third still working are very slim, so I'm assuming there's an advantage other than reliability?

Quote:
Originally Posted by togaflyer View Post
For thought, with the G3X you will have the magnetometer. I believe most are mounting that in the tail. Mine will be locatied at the top of the second station aft of the baggage bulk head. You will need to be concernered with magnetic interference.
Good point. Yet another consideration.
(still wishing that FOG gyros or carrier-phase-diff GPS were cheap enough to get rid of magnetic sensors altogether in GA)

I'm wondering if anyone has tried mounting it out on the wing, and if that reduces magnetic interference at all (intuitively, it sounds like a much "cleaner" place compared to inside the fuselage close to a lot of antennas).
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  #9  
Old 11-08-2015, 02:44 PM
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Carl Froehlich Carl Froehlich is offline
 
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On the ELT antenna mount. Read any ELT install manual and they tell you to mount it vertically. For 121.5mhz this makes sense IF YOU ASSUME when you need the ELT the plane is sitting upright. For me I figured the odds were I'd be upside down so the ELT antenna on top would be broken off or in the mud. Mounting the antenna horizontally under the eppenage fairing with the base on the last bull bulkead provides more than adequate ground plane, and the structure of the tail will protect the antenna when the plane flips over. Add to that the real benefit is the 406 mhz signal hitting a satellite that has little regard for polarization, the vertical mounting is, in my opinion, a secondary consideration.

On the wingtip, not sure how an antenna in each wing could be phased to use on one VOR receiver. I do know that if one does not carefully install and tune these antennas performace can be questionable. I built my wingtip VOR antenna out of scrap aluminum and used a standard MFJ antenna analyzer to make adjustments. I adjusted the dimensions to take full advantage of the wingtip width. The antenna has performed well for both VOR and ILS reception.
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Old 11-08-2015, 04:16 PM
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rdamazio rdamazio is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
On the ELT antenna mount. Read any ELT install manual and they tell you to mount it vertically. For 121.5mhz this makes sense IF YOU ASSUME when you need the ELT the plane is sitting upright. For me I figured the odds were I'd be upside down so the ELT antenna on top would be broken off or in the mud. Mounting the antenna horizontally under the eppenage fairing with the base on the last bull bulkead provides more than adequate ground plane, and the structure of the tail will protect the antenna when the plane flips over. Add to that the real benefit is the 406 mhz signal hitting a satellite that has little regard for polarization, the vertical mounting is, in my opinion, a secondary consideration.
I understand that the antenna is more protected that way, but will the signal transmitted from it be useful?
From threads like this one it seems that it's a neverending debate (like the primar wars ), so I was hoping anyone would had applied a more scientific method to measuring the antenna patterns when mounted inside.
I'm not an RF engineer, but I'd assume that the vertical mounting recommendation is based on the antenna's gain pattern.

Quote:
Originally Posted by Carl Froehlich View Post
On the wingtip, not sure how an antenna in each wing could be phased to use on one VOR receiver. I do know that if one does not carefully install and tune these antennas performace can be questionable. I built my wingtip VOR antenna out of scrap aluminum and used a standard MFJ antenna analyzer to make adjustments. I adjusted the dimensions to take full advantage of the wingtip width. The antenna has performed well for both VOR and ILS reception.
Can you share what your process for tuning it was?
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