ELT Antenna Location

[HighWing]

I spent the bucks for the 406 Mhz ELT and now am trying to find a spot at least 30 inches from the Com antenna to mouint it's antenna and am frankly baffled. My first Model IV had the ELT antenna placed internally at the side and behind the baggage sack. I wonder if the money spent to talk to satellites will be blown if an internal placement reduces signal output significantly. The only other place I can think of is on the turtle deck near the side and immediately aft of the flaperon horn. This would require disconnecting the antenna every time I remove the turtledeck, but not a difficult task as it is within reach of the door. Thoughts would be welcome.
Lowell

[Dave S]

Lowell,

Also got the 406.

In our series 7 - the ELT antenna was placed inside the baggage area on the starboard side. Like in your first IV.

I had the same question you have with proximity to the com antenna; and, my DAR/EAA tech counselor suggested inside the fuselage if at all possible in a fabric covered airplane - logic being if the ELT is ever needed and it is outside on the top or bottom - you have 1/2 a chance it won't work anyway because the plane will be either on its top or bottom with the antenna busted - you can pick the location of the antenna, but not necessarily how an off airport landing will leave one - upside or down side.

Personally I don't believe a person can ever count on 100% functionality of any ELT in the event of an OOPS - it is just a matter of probability, however, I liked the inside the baggage bay location because there is some protection for the antenna no matter which way is up and a fabric airplane with space between the steel tubing so it might work if needed. Also installed an insulating sleeve over the antenna to prevent an accidental shorting out.

Mounting location aside, the theory on the 406 is that no matter what - there is a better chance of getting that line of light necessary for it to work compared to a ground based system.

Empirically, any particular location would have to be tested; and, I do not know of anyone who has done that.

Sincerely,

Dave S

[jrevens]

Lowell,

My buddy Stan has a mod. IV with the antenna located inside the fuselage, along side the baggage area on the pilots side. He doesn't monitor this forum very often, so I'm going to try to describe his experience - I hope he'll add any necessary corrections. He installed a new ACK 406 mhz unit last year. During his trip to OSH, while staying with friends, his airplane was exposed to the worst rain storm & winds while tied down, that he had ever experienced. Long story short, the ELT was somehow triggered when rain got into the cockpit & got the remote indicator/switch unit wet. It worked very well from that point on, as he (or a relative?) got a call from the Air Force in a very short period of time.

I'm installing mine in basically the same position, but on the passengers side, on my mod. 7SS.

3371

[HighWing]

I do appreciate these responses. Actually at this point I am trying to create something that a DAR or the FAA will approve. Both these posts are to that point. I know Stan very well and his experience is worth a lot. It will go inside. I put my first airplane down in a precautionary landing that unfortunately destroyed it and I recall while still at the site a uniformed person asking where the ELT was so he could turn it off - it was screaming at the helicopter overhead. The antenna was inside. That is the way I will go again.
Thanks,
Lowell

[jtpitkin06]

My aircraft has the speed tail so there was room in the vertical stab to install the ELT antenna up through the lightening holes. I made an aluminum plate the same size as the mounting rib as a counterpoise for the antenna.

I mounted the ELT on a cross member and diagonal brace just aft of the baggage sack on my Model 7.

I used the existing holes in the tray and was able to get a good fore and aft alignment using Adel Clamps. The diagonal brace was a bit too high for the ELT so I used some stand offs made with a piece of 3/8 aluminum tube with the mounting bolt down the center of the tube.



It will take more than a few g's to break it loose and that will certainly be enough to set it off. Hard to tell in the picture but there are four bolts holding the tray to the fuselage.


With the tail on the ground I can reach the ELT for battery service or removal. I just unzip the velcro bag sack and it's right there.


John Pitkin

[HighWing]

Thanks again for the posts. As I look at the pictures, mine is now located essentially where jrevens' is. I took it a bit lower and made a mount that clamps between the two tubes seen at the side, but closer to the bottom of the V.

John, it looks like you have lots of extra coax cable. Mine came quite short with the caution to put the antenna as close as possible to the unit. That and the fact I was already covered eliminated many other possibilities. One thought about the mounting, I bought the AmeriKing and as with the one mounted in the first airplane there is a lot said in the manual about a strong G resistant mounting then giving four 4-40 screws to mount it. I suppose that once the inertia switch trips the satellite doesn't really care where the ELT is as long as the antenna remains connected. I also shied away from adel clamps. I mounted mine on a welded up support that clamps to the carry through tube between the lift strut attachments and then went big time to four 6-32 screws. As I was doing this, my rocket scientist friend was here and I mentioned the smaller screws and he rolled his eyes and wanted to see my calculator.
Lowell

[jtpitkin06]

Lowell, I doubled the fudge factor and Finagle's constant (2FF+2Fk) and mounted the ELT with 10-32 hardware. Yeah, 6-32 is a bit small in my book. [rolling eyes in unison with rocket scientist] My tray had #8 size holes.
What the heck, if I hit hard enough to rip the thing loose it probably won't be survivable, anyway.

The extra coax is part of the certification package for the TSO. I must use the factory length coax and the factory antenna for the TSO to be valid. The manufacturer says to simply coil up the excess coax. There's a lot more in the plane with the antenna in the v-stab. The other wire to the ELT is the remote activation to the cockpit wiring. (Also required if not in reach from the pilot seat.).

John

[HighWing]

[rolling eyes in unison with rocket scientist] My tray had #8 size holes.
John

I just reread my post and true I wasn't sufficiently clear. The rocket scientist is back this evening using my hanger to rib stitch his Stearman's aileron that suffered some significant hangar rash that required some rib repair and recovering. Anyway, the reason he wanted to see the calculator was to prove to me that the 4-40 screws in the installation kit were adequate. I suppose from his perspective - extreme engineering and weight saving to the Nth degree - they are, but went to the 6-32 as they are countersunk in the bottom of the tray and larger than that the four heads of the screws would have been the only things contacting the bottom of the ELT.
Lowell

[cainbird]

When running your coax from the elt to the antenna, if you have enough cable, it doesnt hurt to leave exta cable between each cable tie or mounting clamp. This will allow the cable room to stretch instead of breaking if the fuselage were to break apart.

Just my two cents!~Cain B

[RedRooster]

Hi,
I am having false ELT alarms from my new ACK 406 ELT going off when I turn on my Narco Transponder with added UAvionix ADS-B in-out. I built my Kitfox 4 in 1993 and the ELT mount is behind the passenger seat (never had a problem with my old ELT). ELT antenna is behind Pilot on 16" ground plane inside fuselage. Transponder antenna is very close to ELT unit about 12".

The techs at ACK say I need to move transponder antenna at least 3' away from the ELT unit because the new satellite technology is much more sensative to RFI. They also suggested wrapping the ELT unit in tinfoil to protect it from RFI. This worked but not all the time.

Since ADS-B out is pretty new any thoughts? I will post the results of my moving the transponder antenna soon.

Cheers,
Kirby

[Dave S]

Kirby,


I have the same 406 and uavionix units; and, have had zero problems with tripping the ELT; so, I think it is entirely possible to correct what you are experiencing.


Took a while to figure out where all the darn antennas could go considering each manufacturer has a specification for minimum separation from other antennas; and, I didn't want to move the earlier installed antennas if I didn't have to.



It's a little different for a tailwheel and a trigear also - and, what goes in first affects where additional antennas can go in later.


IV is a little narrower than the 7 too.


We have the com mounted on the top of the tailcone immediately behind the turtledeck; and, the Mode C transponder monopole on the starboard side just behind the stick with the 406ELT antenna on the starboard side next to the alieron rod inside the cabin. That provides the radio manufacturer's required spacing for those items.



When it came time to put the uAvionix monopole antenna in, anyplace under the cabin was out for our S7 due to location of the existing antennas and the gear legs.



uAvionics advised that out on the bottom of the tailcone was a good option on a kitfox, particularly a trigear to stay away from the gear legs - the bottom of the tailcone slopes up to the side and back a little; however, the uAvionix people indicated that was not enough to be a problem. Ended up laminating a ground plane against the fabric and the monopole ADS-B antenna through that behind the baggage bay on the port half of the bottom of the tailcone - that gave adequate spacing from the other three antennas - and the test flight for the ADS-B showed zero defects. No problems with the ELT either.



One other item I want to mention is I put a thin, small diameter poly tube over the ELT antenna to prevent any possibility of the antenna shorting out against anything. With an inside mount that is at least a possibility.



This configuration has resulted in all the radios working and no faults showing up with any of them.

[PapuaPilot]

Separate your antennas and other cables too. Get the antenna and ELT interconnect cables as far apart as possible.

My Garmin GTX-23ES was doing the same thing to my ACK-406 ELT and I moved the antenna cables apart. I replaced the ACK interconnecting phone cable with a self made one using a 4 wire shielded cable. It's been over a year now and appears the problem is solved.

[RedRooster]

Update - Jose at ACK sent me a new ELT to try... here is my response to him:

Thanks so much for sending me a new ELT to try!
I got the same false alarm results when ADS-B & transponder were on, so I am sending the new one your sent back today.

I moved my Transponder antenna from a few inches away from the ELT unit to the old mount for my ELT antenna (new antenna mounted inside tail). The new transponder antenna is about 2’ away from the ELT unit and seems to have solved the problem.
I still have the unit wrapped in tinfoil as you suggested to avoid RFI.

I also re-routed the remote switch wire away from most other wires. So far it seems to work. Thanks for the input!

[Lion8]

My aircraft has the speed tail so there was room in the vertical stab to install the ELT antenna up through the lightening holes. I made an aluminum plate the same size as the mounting rib as a counterpoise for the antenna.

I mounted the ELT on a cross member and diagonal brace just aft of the baggage sack on my Model 7.

I used the existing holes in the tray and was able to get a good fore and aft alignment using Adel Clamps. The diagonal brace was a bit too high for the ELT so I used some stand offs made with a piece of 3/8 aluminum tube with the mounting bolt down the center of the tube.



It will take more than a few g's to break it loose and that will certainly be enough to set it off. Hard to tell in the picture but there are four bolts holding the tray to the fuselage.


With the tail on the ground I can reach the ELT for battery service or removal. I just unzip the velcro bag sack and it's right there.


John Pitkin
Hello John. After years of slow restoration of my Model IV, I’m nearing the stage where I’m going to call in the DAR for another inspection. In review. I repowered with a Jabiru, Prince prop, Bush gear and a new tail number.. so far, I installed a King radio, Transponder, ADS-B and now trying to find a location for the ELT antenna. Was considering a dipole antenna but don’t want to affect the function or warranty. Any suggestions?-Tom

[jrevens]

... Was considering a dipole antenna but don’t want to affect the function or warranty. Any suggestions?-Tom

With ELTs, I believe that using any other antenna, other than what was certified for that unit, would not be legal. FWIW. I've seen the antenna mounted inside the fuselage, to the left or right of the baggage compartment, on several Mod. IVs as well as the newer series.

[Eric Page]

Correct. Only the antenna(s) certified with the ELT by the manufacturer are legal to use.

WRT internally mounted antennas, I'm planning to use the ACK E-04. There's some ambiguity in the installation manual about antenna placement, where it says they can be mounted internally in some aircraft, but the details are murky. I've sent two emails to ACK asking for clarification and received zero response. I don't know if it's just bad customer service or their offices have a skeleton crew for COVID, but I guess I'm going to have to pick up the phone to get an answer. I'll post if I learn anything from them.

[Dave S]

Eric,

Give them a call; however, consider you might not get many specifics (although since a call is not in writing you might) the third reason might be that they don't want to stick their necks out on specific locations for an experimental for liability reasons since there are likely variables involved that they can't control - the likely reason for the murky details.

Bottom line is the aircraft manufacturer (you) is considered to be the authorative/responsible person as an experimental builder.

Those unknown variables are taken care of through the type approval process in the case of standard aircraft type certification.

FWIW - I, like many others, have located the ELT antenna inside the fuselage. My DAR (who's day job was approving repairs and modifications for heavy iron) basically said if it's on the outside - top or bottom - you have half a chance the antenna will be buried in the mud if you really need it. Fabric airplanes do not have the shielding to interfere if it is inside. Mine is located on the starboard side behind the co-pilot's seat - I also slipped a thin poly tube over the metal whip antenna to prevent grounding/shorting in case it ends up too close to something else.

[Lion8]

Ji John. I'm placing my ELT antenna on a bracket similar to yours in the photo, however, I have to put it all the way in the back of the fuselage on the bottom just about in the area where the Vert.Stab makes a turn up. The tip of the antenna will be just about where the wing support is for trailering. So if you can see, the bracket will be on the floor with the antenna sticking up into the vert.stab. This is the only place left that will give me some distance from the Comm antenna. 1st one is the ADS-B bottom, 2ns is the Comm, Top, 3rd is the Transponder, Bottom and last is the ELT. My question to you is, how did you resolve the issue of the 'ground plane'? -Tom (Lion8)


Lowell,

My buddy Stan has a mod. IV with the antenna located inside the fuselage, along side the baggage area on the pilots side. He doesn't monitor this forum very often, so I'm going to try to describe his experience - I hope he'll add any necessary corrections. He installed a new ACK 406 mhz unit last year. During his trip to OSH, while staying with friends, his airplane was exposed to the worst rain storm & winds while tied down, that he had ever experienced. Long story short, the ELT was somehow triggered when rain got into the cockpit & got the remote indicator/switch unit wet. It worked very well from that point on, as he (or a relative?) got a call from the Air Force in a very short period of time.

I'm installing mine in basically the same position, but on the passengers side, on my mod. 7SS.

3371

[jrevens]

Ji John. I'm placing my ELT antenna on a bracket similar to yours in the photo, however, I have to put it all the way in the back of the fuselage on the bottom just about in the area where the Vert.Stab makes a turn up. The tip of the antenna will be just about where the wing support is for trailering. So if you can see, the bracket will be on the floor with the antenna sticking up into the vert.stab. This is the only place left that will give me some distance from the Comm antenna. 1st one is the ADS-B bottom, 2ns is the Comm, Top, 3rd is the Transponder, Bottom and last is the ELT. My question to you is, how did you resolve the issue of the 'ground plane'? -Tom (Lion8)

My "ground plane" if you will is the relatively small aluminum mounting plate, which is well grounded to the airframe with a short wire. I have heard that the fuselage tubing may add to the effectiveness of the ground plane. My comm antenna is on top of the fuselage, behind the turtledeck. There don't seem to be any issues with it's proximity to the ELT antenna, that I'm aware of. The radio seems to work very well, and apparently better than some others I've flown with.

[neville]

The ELT works very well in the upper part of the vertical tail. I can tell you that because I accidentally activated it once, in the hangar with door open, and about 10 minutes later got a call from NOAA.

[Steve Sands]

I have a Model 3 I am rebuilding. I note the advice about putting the ELT antennae inside the fuselage. Has there been any concern or discussion about the UV paint with aluminum in it to reduce the effectiveness of the antennae inside? Thanks all.
Steve

[napierm]

I have a Model 3 I am rebuilding. I note the advice about putting the ELT antennae inside the fuselage. Has there been any concern or discussion about the UV paint with aluminum in it to reduce the effectiveness of the antennae inside? Thanks all.
Steve

My KF3 had it inside. Probably does mess up the antenna pattern some. Notice you don't see the COM antenna being placed there.

Better question is whether the ELT has much use at all other than satisfying the regulations.

[efwd]

Many of us have placed our Com antenna beneath the fabric. I didn't and Im pretty sure that some who have, have reported far better reception/xmsn than I. I recall someone who has 50 miles range with his internal mounted antenna.

[109JB]

As far as the real life importance of ELTs in general, I have my opinions.

1. if the ELT is an older 121.5 MHz ELT, it still satisfies the regulations, but in my opinion that is all it does. 121.5 is no longer monitored by satellite and being line of sight, would be like looking for a needle in a haystack to locate you. Airborne aircraft can pick them up but then someone has to figure out where they are using directional antennas and the like to zero in on the location. For this type, I think, do whatever to satisfy the regulation, but if you are really going to be over hostile terrain, buy a personal locator beacon, put a mount on the panel, and if say you lose engine power, push the SOS button. Will be better than that 121.5 ELT (see below)

2. New 406 MHz ELTS - These can actually save your life. The 406 are monitored by satellite and can be connected to a GPS, or have an internal GPS that broadcasts your position if triggered. No direction finding, no fiddling, a Lat-lon is transmitted from the unit to the satellite. The caveat is that it has to activate and it has to not get ripped from the antenna. Definitely better than a 121.5 ELT.

PLBs - Personal locator beacons are sold for outdoor enthusiasts, hikers, climbers, etc. Doesn't mean we can't use them in our airplanes. They don't get activated by a G-switch like an ELT. For the SOS feature you have to push a button, but like the 406 ELT, the PLB broadcasts an alert and your position on 406 MHz to satellites to give instant position. Also, PLBs have a breadcrumb tracking feature where loved ones can track your progress on an online interface even in non-emergency situations. Lets say you are overdue on a flight. Even if you didn't have a chance to push the SOS, the breadcrumbs will get rescuers close and give them a good idea where you might be. This is better than a 121.5 ELT.

So I have 2 projects, one simple, one more complex. The more complex KF4 that has the G5, autopilot, 912, etc. is getting a 406 ELT. The simple KF4 with basic instruments and a 2-stroke 582 is keeping the near useless 121.5 ELT to satisfy the regs, and I'm making a little mount to hold the SPOT PLB that I have. I'll probably put a mount for the PLB in the other airplane too. One factor in that decision is the fact that I live in northern Illinois where it is flat as a table and there aren't many places I can crash that someone would not see and know about it.