ELT Antenna Location

[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.

Attachment 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.