ELT antenna in composite planes.

OK. I expected your reply quickly.

On Oct 31, 1:00 pm, "RST Engineering" wrote:
As you say, a ducky is nearly isotropic ... but equally poorly isotropic in all directions.

If the ducky is well tuned it will radiate very well - I measured
pretty low reflection on one I have. The radiation gain in larger
antennas comes from directionality and not from nothing - it does not
radiate more RF energy than the transmitter generates. I have a 5W
APRS (VHF) tracking unit with a ducky in my aircraft and it reaches
about 60 miles direct to my iGate. Not bad.

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.

Yeah, but that is the trick. Nobody knows how the plane will come to
rest. And don't forget even in ideal situation (vertical) most
radiation is against horizontal obstructions and not up - and neither
121.5 nor 243 will get help from repeaters. AND if the plane is
mangled your seat mounted or whatever does not likely have survival
rate as an a small attached ducky. ELT failure rate is about 25%.

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.

The dual freq loss problem is true of any single ELT antenna. You can
tune a ducky to 243, your choice - I understand 121.5 satellite
tracking is being abandoned.

Personally I prefer APRS tracking. You can see my today's track at
http://aprs.he.fi/ - just enter N416 and then again at right in the
box. For those who want more info about APRS see http://www.abri.com/sq2000/GPStrack.html
Its fantastic for GA aircraft tracking.