Mounting ELT - Antenna

[LSaupe 123]

My new ELT came with an external antenna (looks like be a standard type VHF about 19" long).

 

Question is:

 

1) Can this be mounted internally or does it actually need to be external?

 

2) Any chance this could be "T" 'd in with the VHF antenna (vice drilling and installing another)?

[EDMO 1078]

If I understand my instructions - the ELT antennae needs to be about 3 feet from the Com antennae -

Don't know why, since you probably wont be using both at the same time, but possible. 

I plan to mount mine under the turttledeck - better to have it under Lexan than broken off outside if you crash. 

Some are talking about mounting it under the plane, but that is almost a sure place to get it broken, and the satellites are above you, not below like VOR - The only time that would help is if you flip the plane over.

I hope someone with more knowledge in this area will post some answers.

I have the new 406 ELT with remote switch, and I think it came with an extra portable antennae.

Hoping I never need any of it.

EdMO

Edited 22 Aug 2015 by Ed In Missouri

[Av8r_Sed 82]

Theory would say that mounting the antenna inside a steel frame would create apertures for the signal to radiate out of. This could create an odd shaped radiation pattern or possibly attenuate the signal to a large degree. Mounting outside with a good ground plane is the safe choice, though many have reported acceptable performance mounted inside. I like Ed's solution, with mounting under a Lexan turtledeck - a good compromise.

While almost anything in radio is possible, I believe it's not a common practice to share an antenna with com and ELT transmitters. You'd have to have some good blocking diodes to prevent blowing the output transistors in the non transmitting radio. Best to plan on two antennas.

As Ed states, it's recommended to separate the antennas by 30" or so assuming you've got a 121.5 unit. I'm not sue about the 406 ones. If they're close together you've got two dipoles that again interfere with each other and produce odd radiation patterns. That said, mine are located about 12" apart and I haven't noted any issues.

[EDMO 1078]

Sed,

     I don't know much about the new units, but I thought maybe they broadcasted on both 406 and 121.5 - but could be wrong on that -  If that is the case, then I can see why they want a separation of this antennae from the com antennae.

     I estimate that if I put the ground plane just under the triangle of tubes coming to the back of the cabin, the antennae will fit just under my turtledeck.   Again, it is a compromise and untried, but my old 121.5 ELTs were mounted behind the seats and just have a short antennae coming out of the top of the transmitter inside the cabin on the Luscomb, J3, and Ercoupe. 

EdMo

Edited 22 Aug 2015 by Ed In Missouri

[Av8r_Sed 82]

Ed,

Yup, you're correct: the new ones broadcast on both frequencies.  Maybe they kept the 121.5 to give the CAP cadets a fun activity to pursue at the big fly-ins.

 

Larry,

Are you going to hook up a GPS to the unit?  If so, what?

[LSaupe 123]

No GPS interface for this unit.  Just need to get something in the bird to pass the DAR inspection.