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Artex 345 Antenna Location

majuro15

Well Known Member
I'm interested in hearing (or preferably seeing) the location where folks are mounting the ELT anteanna from their Artex 345 ELT on their 10s. It's a pretty long whip antenna and after doing so much hard work to keep antennas clean and off the top of the plane, I'm not seeing many alternatives.

Vic had a good idea of putting it inside the cabin on the rear seat back support cross bar but I have the Aerosport headliner and am not crazy about that idea.

I know some have burried it in the vertical stabilizer fairing but that's not going to pass muster with the final inspection for airworthyness.

Any other ideas before I accept fate and put a fishing rod on my tail cone?

Thanks!
 
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I drilled two 2" holes in the bulkhead for air feeds into the o/h console. I only ended up doing one NACA vent. So, I made a plate to cover one of them and used it to mount the artex antenna facing inside the o/h console. While it is horizontal, that doesn't matter for the 406 signal and the 151 signal, that needs the vertical orientation, isn't really used anymore.

Larry
 
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SNIP

I know so have burried it in the vertical stabilizer fairing but that's not going to pass muster with the final inspection for airworthyness.

Says who? The local FAA FSDO office did my first two RVs, both have the ELT antenna under the empennage fairing. The new RV-8 will as well.

I consider this a very survivable location for the antenna - so for me that sets the priority.

Carl
 
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Larry, interesting idea, I haven't thought of that. I'm running aircon up there, but could still fit it in. Does the cabin top interfere with signal at all? That's some pretty thick fiberglass and then will have carbon surrounding it. Are you getting good tests on it?
 
Each FSDO is a bit different. I'm going off the advice of mine so want to comply with their proven practices. I'm no expert, so can't defend/argue either view!
 
Larry, interesting idea, I haven't thought of that. I'm running aircon up there, but could still fit it in. Does the cabin top interfere with signal at all? That's some pretty thick fiberglass and then will have carbon surrounding it. Are you getting good tests on it?

While not an expert, I am told that std fiberglass will pass signals with no degradation, regardless of thickness. A/C shouldn't matter, as long as you seal the plate against the bulkhead. My install is air tight. Carbon is only on the inside and you don't need the signal to pass into the cabin, only out of the cabin and no carbon to block that. I have not tested it yet. Numerous folks receive GPS signals through f/g cowls and parts.

Larry
 
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Antenna interference

While mounting the antenna internally might make it a low-drag, and out of the way, the Artex installation instructions are pretty clear that it is to be installed vertically and with a minimum of 32? clearance from other antennas.

While inspectors may accept the installation, not installing it per the instructions violates the TSO and therefore not a legal or valid installation. Keep in mind that ELT?s are one of the few components installed in experimental airplanes that require compliance with TSO installation and ongoing testing compliance.
 
While mounting the antenna internally might make it a low-drag, and out of the way, the Artex installation instructions are pretty clear that it is to be installed vertically and with a minimum of 32? clearance from other antennas.

While inspectors may accept the installation, not installing it per the instructions violates the TSO and therefore not a legal or valid installation. Keep in mind that ELT?s are one of the few components installed in experimental airplanes that require compliance with TSO installation and ongoing testing compliance.


This is exactly why the DAR in my area won?t let me install it internally. He said that it needs to be installed per the instructions that come with the ELT.
 
ELT

If the DAR insists on it being mounted externally, then on the RV8 it would need to be mounted underneath. I don?t think that the vertical stab or rudder would be acceptable due to the lack of required ground plane. I intend to mount mine between the front and rear seats on a suitable mount.with ground plane. I can mount it almost vertically with a tether to bend it clear of the canopy.

Bearing in mind that if the aircraft turns over during a forced landing, mounting it externally on top doesn?t make a great deal of sense does it. If the aircraft remains upright, then presumably the pilot will be in a position to activate it himself, and can either open or jettison the canopy.
 
the 151 signal, that needs the vertical orientation, isn't really used anymore.
Larry

Larry - I believe your post was intended to state the 121.5MHz signal is not used any more. Please allow me to correct this mistaken belief.

While it is absolutely correct that the 121.5MHz signal is no longer being monitored by satellites, it IS being monitored by many aircraft. More importantly it is also WIDELY used for the "last mile" efforts of ground search parties. I learned of a rescue last week that was successful only because the ground search party was able to home on the crashed aircraft stuck on the side of a mountain in a blinding snowstorm. The searchers homed using the 121.5MHz signal.

OK, back to our regular programming now... :)
 
If the DAR insists on it being mounted externally, then on the RV8 it would need to be mounted underneath. I don?t think that the vertical stab or rudder would be acceptable due to the lack of required ground plane. I intend to mount mine between the front and rear seats on a suitable mount.with ground plane. I can mount it almost vertically with a tether to bend it clear of the canopy.

Bearing in mind that if the aircraft turns over during a forced landing, mounting it externally on top doesn?t make a great deal of sense does it. If the aircraft remains upright, then presumably the pilot will be in a position to activate it himself, and can either open or jettison the canopy.

The RV8 empennage is metal airframe, so if you just get a good ground for the antenna to the airframe, it will be your ground plane. A good reference is AC 43.13-2B, section 3.

Generally, the safest place to install your ELT, hence antenna, is the empennage - which tends to be the most survivable portion of a crashed airframe. AC 91-44A is an excellent resource (with many referenced resources as well) for ELT installation.

While you can install an antenna internally, if it?s an Artex or ACK, it needs to be installed vertically; I suspect that is true for any other brand as well to ensure the best signal transmission.
 
That?s where mine is located and tested out fine.

If you mounted it horizontally...well, I?m going to sound like broken record...it?s contrary to the installation instructions.

If it tested successfully via SARSAT, then you?re fortunate, however a local test with a transceiver won?t ensure the unit communicates with the satellite successfully.

To test and ensure your ELT communicates with the satellites, here?s the ELT test website and the test form to submit for SARSAT: https://www.sarsat.noaa.gov/Beacon Testing Policy.html
 
Larry - I believe your post was intended to state the 121.5MHz signal is not used any more. Please allow me to correct this mistaken belief.

While it is absolutely correct that the 121.5MHz signal is no longer being monitored by satellites, it IS being monitored by many aircraft. More importantly it is also WIDELY used for the "last mile" efforts of ground search parties. I learned of a rescue last week that was successful only because the ground search party was able to home on the crashed aircraft stuck on the side of a mountain in a blinding snowstorm. The searchers homed using the 121.5MHz signal.

OK, back to our regular programming now... :)

Thanks for correcting; I was rushed. I am aware of the last mile usage. However, I don't believe that orientation of the antenna will make much difference at a one mile range. If that were the case, they would only find planes that land upright after the crash. That unit has enough power to send that signal up to satellites (several miles).

Larry
 
Larry - the 121.5MHz signal can be as small as 50mW... it's actually very little signal. Toss in some wet evergreen branches or some active precipitation and it becomes a challenge to receive it even at relatively short distances on the ground. While I agree that our aircraft are not guaranteed to crash "right side up", I also feel there is no sense in hampering the probability of an ELT performing by intentionally installing the antenna in a less-than-optimal fashion.
 
This is exactly why the DAR in my area won?t let me install it internally. He said that it needs to be installed per the instructions that come with the ELT.

Find a new DAR that has a clue on how antennas work - and how you match the antennas to the need. How many of you walk around with a full size antenna connected to your handheld radio because ?it works better??

Reviewing such ?TSO installation requirements? I find great strides taken so that no matter what the circumstances the company paying the money to get a TSO cert can always point to their install instructions as proof ?it was not our fault?.

You want a survivable install. It may not be the most perfect in terms of the last fraction of a dB of signal strength, but at least you will have a signal. And shoot fire - just go test whatever you end up with and show the results to the DAR.

Carl
 
No need to hit against the DAR. The experience they have and the been there done that can help all of us out.

I've done EPRB searches on 121.5 back in my days of CAP and yes the signal can be weak even on a good day. Planes don't always crash upright. It's all about mitigating risks and accepting levels comfortable and within the guidelines.

I am set on the DAR I'm using, so that identifies my limfacs as well as guidance from others. I'll put it in the overhead and if I don't get good test results (both 406 and 121) then I can easily mount it on the tail cone. I'll try and remember to update folks on my results.

Thanks!
 
keeping the coax intact between the ELT and the antenna is much more important than antenna location. The NASA crash tests showed COSPAS/SARSAT 406MHz reception from the antenna in the dirt. The ELTs with a broken cable?...nope.

https://www.youtube.com/watch?v=FsRwlr7RDkk

FYI, ED-62B adds firesleeve on the coax and includes the cable in the flame test. This is to help ensure that at least the first couple full 406 messages make it out.
 
keeping the coax intact between the ELT and the antenna is much more important than antenna location. The NASA crash tests showed COSPAS/SARSAT 406MHz reception from the antenna in the dirt. The ELTs with a broken cable?...nope.

https://www.youtube.com/watch?v=FsRwlr7RDkk

FYI, ED-62B adds firesleeve on the coax and includes the cable in the flame test. This is to help ensure that at least the first couple full 406 messages make it out.

A most excellent point! We've seen too many ELT's fail where the ELT broke free from its mount and sheered its coax cable, or the coax cable was poorly installed and sheered under crash forces. The ELT coax should be secured as though it were a fragile aluminum fuel line, with Adel clamps and grommets where necessary and with caterpillar grommet on the edges of lightening holes through which the coax passes plus standoffs to hold the coax away from structure. If you treat the coax like it was a fuel line it will most likely produce a much more crash-survivable installation.

Since the first valid 406MHz distress signal is only sent 50 seconds after ELT activation, the point on adding fire sleeve to the coax is definitely worthy of consideration.
 
For anyone following, I'm going to experiment (shocking, I know) and mount it vertically, but upside down from my ADAHRS tray. It's in the center of the tail cone and allows the antenna adequate clearance while keeping it from being directly up against a lot of metal. I'm going to use 406test.com to see if I get a good signal on it before finalizing the wiring, etc. If it works, great, if not then I'll just mount it vertically on the upper side of the tail cone exterior.

Has anyone ever used 406test? Just curious, not finding much on a search here.

Tim
 
Chuckle

I have to chuckle at some of these posts.

If you follow all of the "advice" and the installation manuals, the best place to locate the ELT antenna is with the magnetometer...10 feet from the external surface of the aircraft flying in close formation...

...but wait, then the ELT antenna would be too close to the magnetometer!

:rolleyes::rolleyes::rolleyes::D
 
For anyone following, I'm going to experiment (shocking, I know) and mount it vertically, but upside down from my ADAHRS tray. It's in the center of the tail cone and allows the antenna adequate clearance while keeping it from being directly up against a lot of metal. I'm going to use 406test.com to see if I get a good signal on it before finalizing the wiring, etc. If it works, great, if not then I'll just mount it vertically on the upper side of the tail cone exterior.

Has anyone ever used 406test? Just curious, not finding much on a search here.

Tim

Tim - I wish you good luck with this approach. The tailcone is effectively a big "tin can" or faraday cage. It will most likely be very effective in containing the ELT signal within its confines rather than letting the signal radiate into free space. An installation of this nature might work under perfect circumstances but would be considered to be poor design practice, at best and potentially criminally negligent at worst. Yeah, lawyers can be pretty good at picking up on stuff that's not installed in accordance with manufacturer's instructions. Especially life-saving equipment.

While your pursuit of an invisible ELT antenna is laudable, it's worthwhile to step back and perform a harsh cost/benefit analysis of this as a design goal. I think an honest evaluation will result in understanding the potential down-side of a non-functional ELT outweighs the potential up-side of a smoother airframe.

I know of one builder (of a different aircraft type) who performed an analysis of all available crash records for that type. In the end the analysis showed the huge majority of those aircraft ended up upside-down when they crashed. He used this data to substantiate installing the ELT antenna on the belly of the aircraft - a substantiation the inspector accepted once he saw the supporting data.
 
I've built three airplanes and working on a fourth...a 10, and I've mounted my ELT antenna vertically, on top of the tailcone, generally at a rib forward of the vertical stabilizer.

It works very well in this location. I have tested mine recently on my RV12 using http://www.406test.com with excellent results. Knowing that the ELT is ready to do it's intended purpose is a good thing.

I personally do not understand the apprehension to mounting it in this very traditional location; it has excellent sky reception, and in the unlikely roll-over of the airframe, the vertical stabilizer does provide some protection for it.

The only negative I think of is drag, which is .66 pounds of drag at 600 KT for my whip antenna, according to the manual, but that's very insignificant if you compare that to the whole drag value of your airframe. Especially for my humble RV-12...

" The tailcone is effectively a big "tin can" or faraday cage." ...nice
 
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Ron - you and I share common thinking in this regard. Folks want to go nuts to hide antennas when, in reality, there is very little penalty associated with an externally-mounted antenna if done properly.


What Tim implied (and please, please correct me if I have misinterpreted your statement, Tim) is that he would mount the ELT antenna upside down INSIDE the tail cone, hanging it from the AHARS mounting bracket which is at the top of the tail cone structure.

Under this interpretation the antenna would be both upside down (not the best if the airplane is right side up and we're expecting satellites above us to monitor our ELT transmission) and inside the aluminum structure of the tail. This ultimately is a situation where two wrongs don't make a right...

Again, Tim, please correct me if I mis-read your intentions with respect to this trial ELT antenna mounting location and orientation.
 
thoughts

While I agree with the comments about internally mounting the antenna, some of the comments here propose a top mounted antenna.

It would be interesting to look at the data to discover how many emergency activations occurred when the aircraft was upside down. In this case, there is a strong possibility that the antenna would be damaged in the roll over and likely shadowed in it's final position. If the data suggested that a higher percentage of incidents end upside down, it would make more sense to put the antenna on the bottom...

Seems to me, either way, you are playing the odds of being right side up or upside down...as is true in every facet of aviation, it is a compromise either way...
 
Inadvertent ELT operational test

As a data point for an ELT antenna mounted under the empennage fairing. An RV flying with this set up did an inadvertent ELT activation while flying. The ELT was on for perhaps 15 seconds. This prompted calls to the home and such (even though the plane was on a IFR flight plane talking to controllers).

Carl
 
Yes, CJoy, you're correct that I am going to test it hanging from the tray inside the tail cone. It may not work. That's why I'm going to test it.

I agree that it is playing a chance game with how a crash will happen and the final resting position of the airframe vs the antenna. I've seen quite a few wadded up aircraft in person from C.A.P. days and have personnally seen ELT antenni ripped off and others that looked like they should have been but remained fully intact. I've also seen a handful of wrecks where nothing survived.

In the end folks, I may wind up putting it up top, but I think it's ugly and yes, there is a bit of drag penalty. If I can get good performance and adequate test results with an internal mount, great! If not, she'll go up top and I'll build on.

This is what building is all about, education and recreation. I'm educating myself on where it will work and where it won't! Others don't agree, I respect that, build what and how you want to build!

Fingers crossed that if I do mount it inside, my aircraft won't instantly burst into a fireball of flames and destruction killing thousands of innocent puppies on my first flight :D
 
Tim - I'm curious about how you will test this and assess pass/fail. Please share your test plan. If your test plan relies solely on passing the self-test, please reconsider as the self-test is a far cry from an end-to-end communications test.

If you're open to suggestions, it would be worthwhile to subscribe to ACR's 406 test to get a read on the 406 beacon, and conduct a test using a VHF handheld on the far side of the airport to see if the 121.5MHz homing signal is being radiated from the aircraft effectively.

Ask yourself if you would install your primary VHF comm antenna in this same location.

I wish you success in your endeavor. Please do report your findings.
 
Yes I’m going to use 406test and a handheld about 1000’ away through woods as a starting point for the 121.
 
It would be interesting to look at the data to discover how many emergency activations occurred when the aircraft was upside down. In this case, there is a strong possibility that the antenna would be damaged in the roll over and likely shadowed in it's final position. If the data suggested that a higher percentage of incidents end upside down, it would make more sense to put the antenna on the bottom...

Seems to me, either way, you are playing the odds of being right side up or upside down...as is true in every facet of aviation, it is a compromise either way...

The data would be interesting to know and I understand your position, but it's very odd to me that you would even considering mounting your ELT antenna on the bottom expecting you're going to landing on the top. If you look at most certified aircraft, the ELT antenna is mounted on the top of the airplane vertically facing. What drove that decision? {rhetorical question}

I honestly don't know what the odds of landing upside down in a crash, but the odds are probably not as bad as the buttered side of bread doing the same.

I just can't imagine making a critical component location decision based on the odd chance you might land upside down - what about all the other times? You'd be on top of the antenna :confused:
 
Comment

My comment was hypothetical. I have not mounted my elt antenna as of yet.

My point was that of the buttered bread. You really don?t know which side will be up. Same goes for an incident. That is why I said looking at the data would be interesting. Mainly because unlike the bread, we have some control of the descent and ?landing?. That may make a statistical difference.

As far as following the lead of the certified fleet, I would venture a guess that the reason the antenna is mounted on the top is that it is accessible, convenient, and probably most import, easy. I would be surprised if anyone even considered another location. Heck, a bunch of cessnas that I have flown had the elt mounted in the baggage compartment, antenna and all. That would really be no different than mounting it in the tailcone...
 
As far as following the lead of the certified fleet, I would venture a guess that the reason the antenna is mounted on the top is that it is accessible, convenient, and probably most import, easy. I would be surprised if anyone even considered another location. Heck, a bunch of cessnas that I have flown had the elt mounted in the baggage compartment, antenna and all. That would really be no different than mounting it in the tailcone...

The easy answer is often the best one (KISS principle). Installing it in the practical location, that also happens to be the easy location (on top), also matches the instructions and just happens work with TSO'd...those crazy engineers bringing it all together :cool:

It just seems like a lot of work finding alternate locations to mount an antenna just to avoid the obvious one on top. Especially for a device intended to save your hide.
 
As far as following the lead of the certified fleet, I would venture a guess that the reason the antenna is mounted on the top is that it is accessible, convenient, and probably most import, easy. I would be surprised if anyone even considered another location. Heck, a bunch of cessnas that I have flown had the elt mounted in the baggage compartment, antenna and all. That would really be no different than mounting it in the tailcone...

A couple of comments, if I may?

1) Mounting an antenna in a baggage compartment in a Cessna was likely a retrofit installation; standard Cessna mounting puts the ELT behind the baggage compartment in the top right corner of the tail cone with the external antenna almost directly above it on the outside of the tail cone. Keep in mind, many Cessna's left Wichita before ELTs were first mandated so there are many field retrofits out there.

2) Installation of an ELT antenna inside the cockpit area has a significant benefit over installing one inside the tailboom. That advantage is... WINDOWS. Back in the tail boom there are no windows to let RF energy escape. My earlier comment about the tail boom being a tin can or Faraday cage hold. Installing inside the tail boom of an aluminum or carbon fiber aircraft is putting the installation at a severe disadvantage.

3) The outside of the tail boom is a good location for a number of reasons.
a) the tail boom acts as a ground plain for the antenna - these 1/4 wave antennas require a ground plain that functions as the "other half" of a half-wave dipole antenna. The aluminum tail boom does this job well.
b) in a conventional aircraft, the vertical stabilizer / rudder assembly tend to protect the top of the tail boom in a flip over event, thus preserving the integrity of the ELT antenna


I'm the first one to acknowledge the vulnerability of any externally-mounted ELT antenna. That's why I have an ELT which includes an internal 406MHz antenna as a backup, AND my primary ELT antenna is mounted inside the fiberglass tail cone of our Glasair Sportsman. I see this as the most robust solution possible - inside an RF-transparent structure, protected from being swept off the fuselage or crushed, with a backup antenna in case either the primary antenna or the interconnecting coax cable should fail. This represents, I believe, an honest attempt at engineering an installation that provides maximum possible up-side in an impact event.
 
With respect to getting detailed data on ELT installation methods, antenna locations etc when sifting through accident data, I hate to say it, but "good luck". We're fortunate if even the barest minimum of info related to the ELT is captured in accident reports. This paucity of data is truly unfortunate because it robs us of the ability to truly analyze any installation-related factors. It also robs us of the ability to specify changes in new ELTs such that we truly improve their overall performance.

In case you can't tell, I'm a realist when it comes to ELTs. No, they are not the ultimate solution, but they are far better than nothing and they are what's legally mandated to be installed in our airplanes. As such I'm a huge proponent of maximizing the potential for an ELT to save my bacon should I ever have an unplanned landing. I really wish others would take this same approach, rather than the dangerous mentality of, "I have to install this darned thing, but it will never work so I don't care how well it's installed." A poor installation makes sub-optimal ELT performance a foregone conclusion. Why on earth would any sane person stack the deck of survival against themselves? I just don't understand that way of thinking.

OK, I'll shut up now. Fly safe out there!
 
I may even use this airplane to fly over mountains at night with one engine! Dear God!!!!

I’ll post test results. Maybe even get to it this weekend if I can get out of helping the wife in the yard!
 
Location, Location, Location

If I am not mistaken, most if not all 406 ELTs have a 50 second time lapse from the moment the G switch is tripped (or the on switch) until the first broadcast pulse on 406.

For aircraft that fly into cumulus granite, lumber maximus, or terra firma with any velocity , the wire between the ELT and the ant. or the antenna itself might be compromised / destroyed before the 50 second count.

Not too many pilots will have the knowledge or foresight to hit the on button 1 minute before impact.

In all the images I can recall of airframe wreck site photos, the one piece of airframes most often remaining are the tail feathers- albeit in a lot of different attitudes.

I think I prefer inside the cockpit for reasons provided in post #34- canopy, windows and perhaps a fibreglass roof section all allow signal Tx from an antenna mounted on the ELT itself or the legally required whip /base mount ant. also mounted inside.


With respect to getting detailed data on ELT installation methods, antenna locations etc when sifting through accident data, I hate to say it, but "good luck". We're fortunate if even the barest minimum of info related to the ELT is captured in accident reports. This paucity of data is truly unfortunate because it robs us of the ability to truly analyze any installation-related factors. It also robs us of the ability to specify changes in new ELTs such that we truly improve their overall performance.

In case you can't tell, I'm a realist when it comes to ELTs. No, they are not the ultimate solution, but they are far better than nothing and they are what's legally mandated to be installed in our airplanes. As such I'm a huge proponent of maximizing the potential for an ELT to save my bacon should I ever have an unplanned landing. I really wish others would take this same approach, rather than the dangerous mentality of, "I have to install this darned thing, but it will never work so I don't care how well it's installed." A poor installation makes sub-optimal ELT performance a foregone conclusion. Why on earth would any sane person stack the deck of survival against themselves? I just don't understand that way of thinking.

OK, I'll shut up now. Fly safe out there!
 
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Tim

OMG. Single engine over mountains at night...what are you thinking? That is WAY too dangerous! Next you will say you have an electrically dependent engine! Oh, the horror!:rolleyes:
 
So I primed the ELT today and decided I don’t even need an antenna!

But seriously, I just got lazy today and mounted the antenna on the top of the tail cone. Hope everyone sleeps better tonight.
 
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