ELT antenna in composite planes.

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.

Cy,

That reminds me. I recently built and tried out the MicroTrak 300 APRS
tracker ( .3 watt transmitter) in my aircraft. It managed over 25
miles direct on a ducky. Not bad for transmission. My ducky is about
9" long.

My comparison you quoted was more based on comparing the typical
aircraft radio "transmission" range and the similar range of the APRS
ducky tracker - both are about 5watts, both VHF. It would be
interesting to compare an aircraft tuned ducky reception vs
transmission range. Maybe I'll do that someday. All I need is a second
standard aircraft radio/antenna and a second aircraft to talk to.

On Oct 31, 7:32 pm, "Cy Galley" wrote:
Your reference that your 5 watt will work out 60 miles. Unfortunately the
old style ELT has only a .1 watt transmitter which is 1/50 the output of
your example. I do not have the expertise to tell how this will reduce the
distance, but I will bet it does curtail the range quite a bit.
--
Cy Galley
EAA Safety Programs Editor

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.

wrote:
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.

60 miles coverage on the ground? to what elevation of a receiving
antenna? Details.. details..

As for APRS.. while I applaud it, the "catch" is that you have to have a
HAM radio licence and ham radio equipment to utilize the existing VHF
packet network.

Dave

Dave,

It was about a couple thousand feet above ground - about what I
locally fly. And it was probably more than 60 miles range. Up at 12K
msl above Washington state mountains had one digi got me about 100
miles. My rough comparison is with normal radio aircraft reception at
say 8000 msl - aircraft to aircraft communication fizzles out about
60? miles. So the ducky isn't bad "transmission" range in direct line
of sight situations. But it seems bad in reception.

Yeah the current APRS catch is the HAM license. Wish somehow it was
easier to get a tracker for GA use. APRS tracking can be a great
safety factor.

On Oct 31, 10:32 pm, Dave S wrote:
wrote:


60 miles coverage on the ground? to what elevation of a receiving
antenna? Details.. details..

As for APRS.. while I applaud it, the "catch" is that you have to have a
HAM radio licence and ham radio equipment to utilize the existing VHF
packet network.

Dave

Why not install a "new" ELT that IS satellite tracked? As I stated in
an email way back when on this same topic, what if you are flying in an
area with no APRS coverage? Also, is there just one APRS frequency used
throughout the country? If not, it would require the pilot to change to
an appropriate frequency at the appropriate time, based on his location.

Scott
N0EDV

wrote:
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.


--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

Yeah the current APRS catch is the HAM license. Wish somehow it was
easier to get a tracker for GA use. APRS tracking can be a great
safety factor.


Its not really that difficult, conceptually. Especially when they revise
the bandplan to the next narrowing of the bandwidth. Dedicate an
aviation channel or two nationwide (I'm sure the band planners can spare
ONE or TWO when the next doubling of available frequencies occurs)
packet reception. Digipeaters wouldn't really be needed, provided enough
igates exist on enough tall towers.

If enough aircraft in an area had this, it would also allow tracker
equipped aircraft to see OTHER tracker equipped aircraft as a sort of
poor man's TIS/TCAS, but the beaconing rate would need to be much faster
to support that in real time.

There is no monopoly on using APRS on HAM only, and you can put a TNC on
theoretically any radio, only infrastructure concerns.

Use smart beaconing, so that when traveling straight line, beaconing is
minimized, and use corner-pegging logic so that a beaconed datapoint
defines when a course change occurs. By setting up a system with smart
beaconing you could handle hundreds of beaconing aircraft in an area,
with minimal collisions.

One doesn't crash 1000 feet in the air and line of sight is what really
works. That's why they use a satellite which helps immensely when down in
the trees and valleys


--
Cy Galley
EAA Safety Programs Editor
Always looking for ideas and articles for EAA Sport Pilot
New address -

wrote in message
ups.com...
Dave,

It was about a couple thousand feet above ground - about what I
locally fly. And it was probably more than 60 miles range. Up at 12K
msl above Washington state mountains had one digi got me about 100
miles. My rough comparison is with normal radio aircraft reception at
say 8000 msl - aircraft to aircraft communication fizzles out about
60? miles. So the ducky isn't bad "transmission" range in direct line
of sight situations. But it seems bad in reception.

Yeah the current APRS catch is the HAM license. Wish somehow it was
easier to get a tracker for GA use. APRS tracking can be a great
safety factor.

On Oct 31, 10:32 pm, Dave S wrote:
wrote:


60 miles coverage on the ground? to what elevation of a receiving
antenna? Details.. details..

As for APRS.. while I applaud it, the "catch" is that you have to have a
HAM radio licence and ham radio equipment to utilize the existing VHF
packet network.

Dave

Cy,

That is assuming the ELT will always work. During a crash the ELT may
be destroyed and/or your personal satellite PLB may not go off if you
are injured. According to APOA, ELT failure rate is about 27% - not
too good, not good for Foster, the man with the satellite signal
watch. The 406's failure rate is about 19% - still not too good ( see
http://www.montanapilots.org/ ). At 1000 AGL with a 12/1 glide ratio
the plane is no more than about two miles from the last point - and
you roughly know the direction. But seldom APRS will not get detected
at 500 AGL. The standard ($1000+) 406 ELT accuracy is about two
miles. A $3000+ 406 will transmit your position to the satellite from
your aircraft gps navigation - assuming that your avionics will work
after the crash. Hmmm... $1000, $3000??? An APRS tracker is only
couple hundred bucks - NO subscription fees.

On Nov 5, 9:59 pm, "Cy Galley" wrote:
One doesn't crash 1000 feet in the air and line of sight is what really
works. That's why they use a satellite which helps immensely when down in
the trees and valleys

--
Cy Galley
EAA Safety Programs Editor
Always looking for ideas and articles for EAA Sport Pilot
New address -