ELT antenna in composite planes.

Ok. I don' t actually use a short "stuby" ducky. There are some 9-12"
long duckys with pretty decent gain which is still small enough to
directly mount on the ELT. Check http://smileyantenna.com/ choices.
The disadvantage of inside mounted ducky depends where it is - the
composite material by itself does not attenuate the signal
significantly. In fact my wing mounted VHF aircraft regular antennas
are mounted "inside" composite winglets ( see http://www.abri.com/sq2000
)

A quarter wave with ground plane has a donut pattern with a hole on
top. Also, my logic tells me (gain reciprocity notwithstanding) that a
ducky radiates better than receives - there is simply not enough
antenna surface to collect signal like in a larger antenna. But for
ELT transmission is what counts.

Paul (KC0WIF)

On Oct 31, 6:19 pm, "Vaughn Simon"
wrote:
wrote in message

ups.com...

The radiation gain in larger
antennas comes from directionality and not from nothing

Yes, but in this case, we are comparing a shortened (ducky) antenna to a 1/4
wave antenna, not a gain antenna. A 1/4 wave antenna has a pretty high angle of
radiation. I raised my eyebrow at Jim's estimate of 15 db, but when you start
adding factors, (eliminate the loss of the stubby antenna, antenna in the clear
outside of airframe, elevated antenna) you could end up with more difference
than you think.

You are correct that a long antenna gets its gain from decreasing the angle of
radiation and concentrating more of the signal at (or even below) the horizon,
but I have never seen a gain antenna used for an ELT, have you?

Vaughn (WB4UHB)

A quarter wave with ground plane has a donut pattern with a hole on
top.

No sir, a vertical dipole has a donut pattern with a hole on the top. A
quarter wave with a ground plane has a donut sliced longitudinally (like
slicing a bagel for cream cheese) with a hole on the top. Practically zero
radiation on the back side of the ground plane.



Also, my logic tells me (gain reciprocity notwithstanding) that a
ducky radiates better than receives - there is simply not enough
antenna surface to collect signal like in a larger antenna. But for
ELT transmission is what counts.


Oh, my dear Lord. First the man cites the reciprocity property of antennas
(which in a hundred years has yet to be disproven) but HIS logic says that a
ducky has to transmit better than it hears.

Sorry, sir, I want nothing more to do with this conversation. You evidently
belong with those geniuses who sell magnets to put in the carburetor to
double the gas mileage.

Jim

On Oct 31, 7:33 pm, "RST Engineering" wrote:
A quarter wave with ground plane has a donut pattern with a hole on
top.

No sir, a vertical dipole has a donut pattern with a hole on the top. A
quarter wave with a ground plane has a donut sliced longitudinally (like
slicing a bagel for cream cheese) with a hole on the top. Practically zero
radiation on the back side of the ground plane.

Aw comon. Now we are nit picking to win an argument. My main intended
point was that it has a hole on top irregardless if its a half or full
donut.


Also, my logic tells me (gain reciprocity notwithstanding) that a

ducky radiates better than receives - there is simply not enough
antenna surface to collect signal like in a larger antenna. But for
ELT transmission is what counts.

Oh, my dear Lord. First the man cites the reciprocity property of antennas
(which in a hundred years has yet to be disproven) but HIS logic says that a
ducky has to transmit better than it hears.

Please take a look at http://en.wikipedia.org/wiki/Radiation_pattern .
Reciprocity refers to radiation/reception "pattern" (geometry) being
the same and not to total radiation/reception efficiency. The second
equation says the total power actually received depends on
A(theta,phi) the "effective area or effective aperture of the antenna"
for a receiving antenna - i.e. the size of the antenna. A small tuned
antenna can send most of its power out (not necessarily directionally)
but will receive much less signal than a large antenna simply because
it has small receiving area. We are confusing directional gain with
RF power transmission efficiency.

Sorry, sir, I want nothing more to do with this conversation. You evidently
belong with those geniuses who sell magnets to put in the carburetor to
double the gas mileage.

Why do you have to use insults? If you really don't want to comment
just don't.

Because, you stupid imbecile, if you don't get answers to your posts, people
might really believe the bull**** that you are passing on as fact. And then
it takes me HUNDREDS of HOURS to tell people why your stuff isn't right.

Don't you understand that? Or pass your credentials on as a professional
antenna designer and we'll carry this discussion on at a whole different
level.


Jim


Why do you have to use insults? If you really don't want to comment
just don't.