ELT Antenna Location

[TXFlyGuy]

Perhaps this has been answered...but does the FAA require the ELT antenna to be installed on an external location, or can I put the antenna inside the fuselage?

[mburch]

My reading of 14 CFR 91.207(d)(1) leads me to believe that "proper installation" means "follow the manufacturer's instructions". The instructions for my ELT say the following:

The antenna may be mounted internally in composite construction, and tubular fabric covered aircraft, as long as the fabric or composite material is of a non conductive nature. The antenna must be mounted externally, on airframes of metallic construction.

With that in mind, plus an undergraduate-level understanding of how radio antennas work, I chose to put the ELT antenna on the aft fuselage of my airplane:



Your ELT, airplane, and opinions may vary.

[RVDan]

If you mount the antenna internally on a metal aircraft, little or no signal will get to the satellite. Some mount the antenna in the baggage area of the -6 or -7, but this is not good either. A study of elt antennas done about 10 yrs ago showed that the metal box formed by the fuselage on the -6 and -7 is just wrong for propogation in the121.5 and 406 mhz reqs. In addition, if the fuselage flips, nothing gets out in the correct direction.

I mounted mine on the aft fuselage where mburch did. On a flip over it is somewhat protected from damge by the vertical. I like this antenna becasue it will likely flex on impact rather than break. I think the recent NASA ELT crash test is proving out this location to be a good one for ELT function.

[RV7A Flyer]

Under the empennage fairing.

[Smilin' Jack]

I like many others mounted mine just behind the roll bar in my 7
why
1. less drag
2. transmitting a 406 Mhz signal through plastic is better then trying to transmit a signal through mud when you flip over
3 Take a field strength meter and trace your antenna pattern
4 50 years of ham radio and I have seen a lot of antennas that should not work that had great impedance,SWR and worked outstanding and in some cases started new antenna designs
5. we get reports all the time from ATC about false ELT signals only to find the
aircraft in a T hanger. talk about shielding a signal. But they work just fine for
airliners to report them
406 mhz signals are very short wave and have good line of sight reception.
they have been a standard for years in survival equipment.
Jack