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Antenna Locations

S

sjjonesnz

Well Known Member
Rather than stand back and just throw antenna (metaphorically speaking) at my RV, I'm wondering the best place to put those causes of drag. The installation guides say at least 36" between antenna with the ELT as far away as practical. I was thinking...

GPS hockey puck - topside of fuselage, behind canopy
ELT - topside of fuselage, next to tail
VOR/GS (CI-215) - top of tail
Transponder (CI-105) - underside of fuselage, middle but slightly rearward to keep away from exhaust if possible
Com 1 & 2 (both CI-122) - underside of fuselage, left & right of exhaust

Thoughts??
 
my plan

rami bent com, mounted under pilot gear weldment, so its protected but maybe so cable can be unscrewed if needed to screw into portable as backup, trans at front pass side firewall beside fuel vent. NAV, in ray allen wingtip, and GPS under cowl.
Thats my thoughts. Just there now doing my research, be interested in what others say.
 
Garmin

RickWoodall said:
rami bent com, mounted under pilot gear weldment, so its protected but maybe so cable can be unscrewed if needed to screw into portable as backup, trans at front pass side firewall beside fuel vent. NAV, in ray allen wingtip, and GPS under cowl.
Thats my thoughts. Just there now doing my research, be interested in what others say.
Click to expand...

Rick... Garmin transponders call for a 36 inch straight line distance from the antenna to the physical unit.

This is separate from any cable measurements.

gil A
 
Bob Archer

.....VOR/LOC antenna in the wingtip works well. A length of stripped coax in the other for marker beacon works great..no drag. XPDR ahead of spar in turbulent exiting engine air...little/no drag. Comm under baggage area won't even cost you 1 MPH. We decided to not compromise our communication clarity or reception, so we went outside with those.

Regards,
 
Gil - not sure where you're seeing the 36" requirement you've referenced. Could you please provide additional details/references from the installation manual? The only thing I've seen that's concretely stated in the manual is a requirement for maximum cable loss of 1.5dB @1090MHz. This kind of spec is common to most transponder installations, while an absolute distance separation spec is something which I can't recall ever having seen before.
 
Three feet

Canadian_JOY said:
Gil - not sure where you're seeing the 36" requirement you've referenced. Could you please provide additional details/references from the installation manual? The only thing I've seen that's concretely stated in the manual is a requirement for maximum cable loss of 1.5dB @1090MHz. This kind of spec is common to most transponder installations, while an absolute distance separation spec is something which I can't recall ever having seen before.
Click to expand...

Gil is right ...




From GTX-327 installation manual, Section 2.3.1 D (p.5):
"To prevent RF interference, the antenna must be physically mounted a minimum distance of three feet from the GTX 327."​
 
In the manual....

Lycosaurus said:
Gil is right ...




From GTX-327 installation manual, Section 2.3.1 D (p.5):
"To prevent RF interference, the antenna must be physically mounted a minimum distance of three feet from the GTX 327."​
Click to expand...

Thanks Alfio... that is the wording.....:)

It's also the same in the GTX-320(A) manual.... which makes it a part of the TSO requirements.

gil A
 
This is unconventional, but if you want good comm coverage, mount one antenna under each wing about a third of the way out, just beyond the tank! Antennas on top of the fuselage have poor lateral coverage, but in the case of GPS, that's the way to go. As far as the ELT, that depends on whether you end up right side up or upside down.
 
Lycosaurus said:
Gil is right ...





From GTX-327 installation manual, Section 2.3.1 D (p.5):
"To prevent RF interference, the antenna must be physically mounted a minimum distance of three feet from the GTX 327."​
Click to expand...


Minimum.
The longest run of RG-400 I could come up with was 6 ft for the transponder ant. I went with just barely forward of the spar on the right side.
 
AltonD said:
I went with just barely forward of the spar on the right side.
Click to expand...
Your probably pushing the minimum distance rule.
It's my understanding that this rule is to keep the transponder from interrogating itself. We had a big problem with this on a Pitts a while back. In this case the antenna was about 8" from the transponder. Once we moved the antenna farther away the problem was solved.
 
Here is where I put mine:

GPS hockey puck - Velcro'ed to the top of the glairshield
ELT - Inside the canopy, attached to the back of the tip-up roll bar
VOR/GS (CI-215) - Don't have one
Transponder (CI-105) - On the right side, just to the left of the fuel vent (works fine, even though it is right next to the gear leg.
Com 1 - Under the pilot's left knee w/ the aft two bolts passing through the spar flange (I only have one com)

One thing to think about...

My airport is 10 miles from CLT and I have to get to about 2,500 to 3000 feet before CLT can hear me clearly. At altitude (8.5K feet), I have spoken to people 150 more miles away so I know the radio is good. This makes me think that if I had two radios, I might like to mount one antenna on the top of the fuselage, as ugly as that might be.
 
sjjonesnz said:
Rather than stand back and just throw antenna (metaphorically speaking) at my RV, I'm wondering the best place to put those causes of drag. The installation guides say at least 36" between antenna with the ELT as far away as practical. I was thinking...Thoughts??
Click to expand...

GPS hockey puck - topside of fuselage, behind canopy
Yea sure. What kind of GPS antenna do you have, a real GPS antenna for external with a panel mount GPS or a little black hockey puck for a handheld?**

ELT - topside of fuselage, next to tail
Good on you mate, that is the way to do it

VOR/GS (CI-215) - top of tail
I like under the tail on the bottom of the fuselage on a taildragger. These antennas will put an eye out. click me


Transponder (CI-105) - underside of fuselage, middle but slightly rearward to keep away from exhaust if possible,
Yep

Com 1 & 2 (both CI-122) - underside of fuselage, left & right of exhaust
Yep

Here is the truth on the drag, about 1 mph max total at top speed for all you Ant's mentioned. That is it.


** Consider GPS inside, under the canopy somewhere, especially if its for a handheld for VFR. If IFR and flying GPS WAAS approaches with a panel mount, than yes put it outside as you say. You could put it just forward of the windscreen (out side). Wire run will be shorter, however that is a high pressure area and might be a little more drag. Also putting the antenna in an electrically quite place might be best. I have run handheld GPS in RV cockpits with great success in North America.
 
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Tom Clark slider on RV-8

I haven't considered any other antenna than the ELT one at the moment, but I have to admit one of the reasons I went with a fastback kit is to give me space for the ELT antenna in front of the VS. I went with the TC kit because it retains the slider and, being shorter than the Vans capopy, should still leave me a gap for the ELT antenna. I hope!
 
AntiGravity said:
I haven't considered any other antenna than the ELT one at the moment, but I have to admit one of the reasons I went with a fastback kit is to give me space for the ELT antenna in front of the VS...
Click to expand...
Jeff,

Make sure you mount it far enough forward that when bent over it doesn't contact the VS. I've seen one -8 where the VS was beat up from the the ELT antenna hitting it in flight. :(
 
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Thanks Bill

...I'm hoping the Tom Clark fastback provides enough gap to prevent this. It wasn't something I'd thought much about. I shall mount it as far forwards as I can get away with. Thanks for the heads up.
 
Got a couple of questions regarding Ant:

1. What are you guys using for a marker beacon ant and where are you mounting it?

2. I have a GNS 430W and would prefer not to have to use a CI-215. Is there another option (preferably wingtip) that is reliable for IFR flights?

3. I'm aware of the 36" placement requirement for the transponder ant, but is there any other limitations regarding placement of com, trans, marker beacon next to each other?

Thanks,
Kevin
 
My MB antenna

...is located on the belly, abeam the elevator bellcrank, just left of it.

11.jpg


I'm not flying yet, so I can't tell you how well it works. But at 75 MHz, just about anything should work!

Martin
 
Com Antenna Spacing

Alrighty, so I'm looking to have my Com1 and Com 2 antenna (both CI-122s) in the same place that Martin's put his, ie forward left and right either side of the exhaust, they're about 28" apart or there abouts. The Comant antenna install guide states "keep antennas at least 36? from any other antenna" while the GNS430W install manual states the COM antenna "should be mounted a minimum of six feet from any DME or other COM antennas".

I could move one back under the copilots seat giving a bit more separation, but nothing like the 6' Garmin are wanting and that would also ruin the aesthetics ;-)

Am I really going to have any problems (Com1 = SL30, Com2 = GNS430W) with cross chatter, etc, or is this a real case of the maufacturer playing it safe?????
 
Mine are 36" apart

I just measured my comm antennas. They're 36" apart...so I'm at least somewhat compliant! In case it's not obvious from the photos, I put them in the most outboard bay under the seats.

Cheers,
Martin
 
Don't sweet it

The engineers that write the manuals right what the dream of. Spacing, location other structures all affect the performance of the antenna, but as long as you are reasonable it will will WORK! Keep the antenna's close, for short coax, ie not in the wing tips or tail if you can help it (especially for transmitting antennas). VOR the tail is ideal despite the long coax. It is only reception so that is fine. The Transponder is up in the Gigahertz freqs and the COM and VOR are in VHF. Don't worry about it. Use the Kiss method.

The biggest challange for and antenna is one most don't need and that is the ADF. The best ADF antenna is over 400 feet long! Of course that is why they use loops.
 
Why not put one on the top of the fuselage and the other on the bottom. This will give you great isolation and next to no cross talk if any.
 
On top's certainly an option, unfortunately I can't remember the actual distances off the top of my head, but forward of the tail I've got the ELT antenna (which needs to be far enough forward of the tail so it doesn't give it a nice golf ball finish) and the GPS antenna which is as far fwd as I can put it.

Putting a com antenna in the middle of these two goes against other statements in the GNS430W installation guide - "The GPS Antenna should be no closer than two feet from any VHF COM antenna....or any antenna emitting more than 25W of power" (the CI-122 emits 50W), and "the COM antenna should also be mounted as far apart as practical from the ELT antenna". I know "as far apart as practical" is open for interpretation, however....

Appreciate there're always compromises, I'm just trying to figure out the best one without turning my nice RV into swiss cheese trying to fix a bunch of harmonic problems :eek:
 
Um, don't want to nitpick, but the CI-122 antenna emits what it's being fed. It's rated for a max of 50W, but in reality it's only emitting as much power as the transmitter in your VHF comm is capable of feeding it, likely 10W or less.

As for separation from the ELT antenna, 2 antenna lengths between them is about as much as you can get on any airplane the size of an RV and it works OK. More is always better, but there are practical limits given the space available.

Of course you could alway stick a nice blade antenna on each wingtip and call them winglets! ;-)
 
Norman CYYJ said:
Why not put one on the top of the fuselage and the other on the bottom. This will give you great isolation and next to no cross talk if any.
Click to expand...

That's exactly what I'm planning to do - one CI-119 on top for the secondary comm, and one CI-119 on the bottom for primary comm.
 
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