REFLECTOR: ELT

[Al Gietzen]

Subject: RE: REFLECTOR: ELT

 

Al-

 

  We are building a XL-FG and I built a Jim Weir antenna on the spar and we
mounted the ELT to the side of the keel as close to the fish fin as
possible.  This puts it under our baggage compartment but not behind the
vanity panel.

 

Craig

 

That seems like a good approach; the dipole eliminating the need for ground
plane.  

 

There may be a question of signal strength distribution.  I'm no expert on
antennas, but I think the dipole on the spar would have good signal strength
in the vertical direction, and horizontally in the direction of the fuselage
axis, but poor horizontally in the direction of the dipole; in fact
essentially zero off the ends of the dipole, especially for the 121.5
frequency as it won't "bounce" very well. For the 243 frequency it is
probably less important.  The signal would be more likely picked up by
satellite, but maybe some blank spots for S & R.

 

Of course we don't know the orientation of the antenna when we need this
thing, but assuming the airplane in basically in a horizontal position, the
monopole (vertical with some sort of perpendicular ground plane) would have
good signal in all horizontal directions, but poor straight up (or down).

 

That's assuming I understand things correctly, of course.

 

Like most things, we take the compromise that is most doable.

 

It does seem that having the transmitter reasonably accessible so it can be
taken out of the airplane with the portable antenna would be a good idea.

 

Al

 

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