As you say, a ducky is nearly isotropic ... but equally poorly isotropic in
all directions. While the radiated signal from an ELT is pretty low to
begin with, you lose about 15 dB on a ducky on the average over a standard
quarter wave whip or dipole.

In a composite airplane you have the luxury of mounting a good dipole ELT
antenna internally on the biggest piece of plastic likely to survive the
incident. If you mount it on the bulkhead behind the pilot or rear
passenger, then the likelihood of both occupants and antenna surviving the
incident is nearly the same. As to the orientation of the dipole, if you
can tell me how the airplane parts are going to come to rest in the
incident, I'll tell you how to mount the antenna.

A tuned ducky for 121.5? Great. How do you radiate the 243.0 component
since the antenna will be nearly anti-resonant at that frequency.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

wrote in message
ups.com...
ELT normally uses an externally mounted antenna. But in composite
planes it may be advantageous to use a ducky.

1. On crash the external antenna may be destroyed - brushing against
trees, whatever. An attached ducky on the ELT will likely stay on.



You can get a 121.5MHZ tuned ducky (low SWR) for only $16 bucks from
http://www.smileyantenna.com/ I don't work for them.