TPAS and Transponder - Blind Spot

[jcarlyle]

A few days ago, Bumper mentioned his TPAS "went deaf" in his
transponder equipped glider while flying near other transponders. Jim
S asked about the blanking distance, and Eric Greenwell found in the
manual for the Zaon MRX that this was about 0.4 miles.

But the shape of the dead zone is very important, and we must consider
it. Because of the time difference in the way the ATC radar pulse hits
both transponders, the propagation times of your transponder's pulse
and the other transponder's pulse, the length of the transponder
pulses, the saturation dead time of the ZAON, and the signal
recognition time of the ZAON, there is a funny looking dead zone
around your aircraft where planes can be coming straight at you
without you ever detecting them!

Consider first your glider and the other transponder ship being equal
distances away from the ATC radar. Both transponders fire at the same
time, the ZAON overloads and blanks off for a certain time, then wakes
up. If the other transponder is far enough away from you that the
propagation time for his pulse (plus a little more time for the ZAON
receiver to recognize that it sees a pulse) is greater than the ZAON
blanking time, then you'll detect him. I think this is the 0.4 nm
distance that Eric found in the manual.

Now consider the other transponder being farther away from ATC than
you, on the line that connects you and ATC. Your transponder fires
first and blanks the ZAON. The ATC pulse has to propagate to him for
his transponder to fire, then his transponder pulse has to propagate
back to you to be detected by the ZAON. The net result is that he can
be as close as 0.2 nm for you to detect him.

Now suppose the other transponder is between you and ATC, on the line
that connects you and ATC. Guess what? You'll never detect him! The
ATC pulse reaches him first, firing his transponder, and both pulses
reach your ship at essentially the same time. Your transponder then
fires, blanking the ZAON. By the time it unblanks, his pulse and your
pulse have propagated far beyond the ZAON antenna - they aren't around
for detection.

All this suggests the shape of the dead zone - it consists of a
flattened hemisphere sitting on a paraboloid. Your glider is at the
center of the flattened hemisphere, with the larger radius
perpendicular to the line connecting you and ATC, and the smaller
radius heading away from ATC and parallel to the line connecting you
and ATC. The curving end of the paraboloid sits right on ATC, while
the open end of the paraboloid connects to the flattened hemisphere.
(For ease of thinking, you can replace the paraboloid with a cylinder
of radius 0.2 nm - it extends from you to ATC.)

So, if you fly with a TPAS in a glider equipped with a transponder,
keep an especially careful lookout for planes coming at you from the
direction of ATC, . They will NOT be detected by your TPAS, unless you
periodically turn your transponder off! Then you'll detect everything
right up to oh too close...

-John

Note: the 0.4 and 0.2 nnm distances are for a ZAON MRX. These
distances could very well be different for other manufacturers and
models of TPAS devices.

[jcarlyle]

Darn! The cylinder radius should have been 0.4 nm, not 0.2 nm. It's a
pretty big thing...

-John

On Mar 10, 9:34 am, "jcarlyle" > wrote:
> (For ease of thinking, you can replace the paraboloid with a cylinder
> of radius 0.2 nm - it extends from you to ATC.)

[Eric Greenwell]

jcarlyle wrote:

> Now suppose the other transponder is between you and ATC, on the line
> that connects you and ATC. Guess what? You'll never detect him! The
> ATC pulse reaches him first, firing his transponder, and both pulses
> reach your ship at essentially the same time. Your transponder then
> fires, blanking the ZAON. By the time it unblanks, his pulse and your
> pulse have propagated far beyond the ZAON antenna - they aren't around
> for detection.
>
> All this suggests the shape of the dead zone - it consists of a
> flattened hemisphere sitting on a paraboloid. Your glider is at the
> center of the flattened hemisphere, with the larger radius
> perpendicular to the line connecting you and ATC, and the smaller
> radius heading away from ATC and parallel to the line connecting you
> and ATC. The curving end of the paraboloid sits right on ATC, while
> the open end of the paraboloid connects to the flattened hemisphere.
> (For ease of thinking, you can replace the paraboloid with a cylinder
> of radius 0.2 nm - it extends from you to ATC.)
>
> So, if you fly with a TPAS in a glider equipped with a transponder,
> keep an especially careful lookout for planes coming at you from the
> direction of ATC, . They will NOT be detected by your TPAS, unless you
> periodically turn your transponder off! Then you'll detect everything
> right up to oh too close...

This seems like a plausible analysis, but it's not what Zaon shows in
their manual; instead, they talk about a "bubble of detection" around
your aircraft. A query to Zaon should be the next step, as it might get
an explanation of how their units deal with this situation.

There is a situation that elimanates this problem: multiple radars. This
could be a TCAS equipped airplane or another ATC ground radar.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[jcarlyle]

The key lies in how they blank the receiver. Since there is no
connection to your own transponder, I think they simply blank for time
X when they get a signal of over Y watts. If they do, that will
produce the situation I described above.

Multiple radars will change the situation, but I believe there will be
blind spots there, too. I think you'll have multiple blind cylinders,
each pointing at the various radar sources.

And you're correct, it isn't what Zaon shows in the manual. It would
definitely be best to talk with them directly about happens in this
situation.

Eroc, I know I won't get any time this week to call them. Could you do
it, and post the results?

-John

On Mar 10, 10:24 am, Eric Greenwell > wrote:
> This seems like a plausible analysis, but it's not what Zaon shows in
> their manual; instead, they talk about a "bubble of detection" around
> your aircraft. A query to Zaon should be the next step, as it might get
> an explanation of how their units deal with this situation.
>
> There is a situation that elimanates this problem: multiple radars. This
> could be a TCAS equipped airplane or another ATC ground radar.

[Eric Greenwell]

jcarlyle wrote:
> The key lies in how they blank the receiver. Since there is no
> connection to your own transponder, I think they simply blank for time
> X when they get a signal of over Y watts. If they do, that will
> produce the situation I described above.
>
> Multiple radars will change the situation, but I believe there will be
> blind spots there, too. I think you'll have multiple blind cylinders,
> each pointing at the various radar sources.

As long as they don't overlap, then maybe the unit can still pick out a
potential threat.
>
> And you're correct, it isn't what Zaon shows in the manual. It would
> definitely be best to talk with them directly about happens in this
> situation.
>
> Eroc, I know I won't get any time this week to call them. Could you do
> it, and post the results?

Sure, I'll try to contact them Monday.

>
> -John
>
> On Mar 10, 10:24 am, Eric Greenwell > wrote:
>> This seems like a plausible analysis, but it's not what Zaon shows in
>> their manual; instead, they talk about a "bubble of detection" around
>> your aircraft. A query to Zaon should be the next step, as it might get
>> an explanation of how their units deal with this situation.
>>
>> There is a situation that elimanates this problem: multiple radars. This
>> could be a TCAS equipped airplane or another ATC ground radar.
>
>
>


--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[jcarlyle]

Eric, sorry about the typo in your name in the message above.

Figuring out the geometry is involved, but some signal overlap is OK.
Explaining it in text is hard, but if you make timing diagrams on a
sheet of paper and translate that to geometry, you'll see the
solution. I think that if someone is in your ATC blind zone, and a
TPAS interrogates your transponder and his, and he's outside of the
TPAS blind zone, you'll see him.

Glad you'll try to call Zaon; this coming week is one I want to forget
before it even gets here!

-John

On Mar 10, 11:29 am, Eric Greenwell > wrote:
> As long as they don't overlap, then maybe the unit can still pick out a
> potential threat.
>
> Sure, I'll try to contact them Monday.

[ZL]

jcarlyle wrote:
> Eric, sorry about the typo in your name in the message above.
>
> Figuring out the geometry is involved, but some signal overlap is OK.
> Explaining it in text is hard, but if you make timing diagrams on a
> sheet of paper and translate that to geometry, you'll see the
> solution. I think that if someone is in your ATC blind zone, and a
> TPAS interrogates your transponder and his, and he's outside of the
> TPAS blind zone, you'll see him.
>
> Glad you'll try to call Zaon; this coming week is one I want to forget
> before it even gets here!
>
> -John
>
> On Mar 10, 11:29 am, Eric Greenwell > wrote:
>> As long as they don't overlap, then maybe the unit can still pick out a
>> potential threat.
>>
>> Sure, I'll try to contact them Monday.
>
Don't forget, there is a finite delay in the transponder (3.0
microseconds by spec) between receiving the pulse from ATC and replying.
You're not looking for echoes here.

-Dave

[ZL]

ZL wrote:
> jcarlyle wrote:
>> Eric, sorry about the typo in your name in the message above.
>>
>> Figuring out the geometry is involved, but some signal overlap is OK.
>> Explaining it in text is hard, but if you make timing diagrams on a
>> sheet of paper and translate that to geometry, you'll see the
>> solution. I think that if someone is in your ATC blind zone, and a
>> TPAS interrogates your transponder and his, and he's outside of the
>> TPAS blind zone, you'll see him.
>>
>> Glad you'll try to call Zaon; this coming week is one I want to forget
>> before it even gets here!
>>
>> -John
>>
>> On Mar 10, 11:29 am, Eric Greenwell > wrote:
>>> As long as they don't overlap, then maybe the unit can still pick out a
>>> potential threat.
>>>
>>> Sure, I'll try to contact them Monday.
>>
> Don't forget, there is a finite delay in the transponder (3.0
> microseconds by spec) between receiving the pulse from ATC and replying.
> You're not looking for echoes here.
>
> -Dave

never mind, doesn't matter...

[[email protected]]

Eric what are you reading in the manual that says 0.4 nm? The only
reference I saw to 0.4 nm is the discusison that if you see false
targets of less than 0.4 nm range then you may need to clean the
transponder antenna, etc.

Also it is worth remembering the Zaon PCAs devices are not just
"blanking" the receiver during the local transponder reply. The Zaons
are reading and doing an altitude decode of the local transponder
signal and using that if possible for the altitude reference rather
than the built in altimeter. How good their RF front end and post RF
digital processing is will determine how well they can differentiate
partially overlapping pulse trains from the local and other
transponders. And you better believe they have to do this since the
most nieve approach of "blanking" during the entire ~20us transponder
pulse train (ignoring the ident pulse) would give a dead zone of
~6km. I'd love to see a schematic.. :-)

Like other posters I suspect this not much of an issue in practice
because of multipe illuminations from SSR, TCAS etc. However one thing
with some of the funkier glider tranponder antenna installs is that
the PCAS may be seeing much more RF power from the local transponder
than the designer expected, especially for situations like with RF
transparent fiberglass fueslages and maybe a less than great ground
plane betwen the PCAS and antenna, tranponder antennas mounted in the
cockpit etc. In which case maybe the dead zone is larger because of
the Zaon's reduced ability to detect overlapping pulse trains.

---

The Zaon MRX works amazingly well in my experience and is a great
suppliment for transponders in gliders, but especially for seperation
from heavy iron lets keep the focus on getting transponders in gliders
in heavy traffic areas. Transponders absolutely work -- with no effort
from me except turning on my transponder I often notice traffic
vectored around my glider when flying near Reno (I hear Reno arivals/
departures telling traffic I'm there).

Darryl

On Mar 10, 8:29 am, Eric Greenwell > wrote:
> jcarlyle wrote:
> > The key lies in how they blank the receiver. Since there is no
> > connection to your own transponder, I think they simply blank for time
> > X when they get a signal of over Y watts. If they do, that will
> > produce the situation I described above.
>
> > Multiple radars will change the situation, but I believe there will be
> > blind spots there, too. I think you'll have multiple blind cylinders,
> > each pointing at the various radar sources.
>
> As long as they don't overlap, then maybe the unit can still pick out a
> potential threat.
>
>
>
> > And you're correct, it isn't what Zaon shows in the manual. It would
> > definitely be best to talk with them directly about happens in this
> > situation.
>
> > Eroc, I know I won't get any time this week to call them. Could you do
> > it, and post the results?
>
> Sure, I'll try to contact them Monday.
>
>
>
> > -John
>
> > On Mar 10, 10:24 am, Eric Greenwell > wrote:
> >> This seems like a plausible analysis, but it's not what Zaon shows in
> >> their manual; instead, they talk about a "bubble of detection" around
> >> your aircraft. A query to Zaon should be the next step, as it might get
> >> an explanation of how their units deal with this situation.
>
> >> There is a situation that elimanates this problem: multiple radars. This
> >> could be a TCAS equipped airplane or another ATC ground radar.
>
> --
> Eric Greenwell - Washington State, USA
> * Change "netto" to "net" to email me directly
> * "Transponders in Sailplanes"http://tinyurl.com/y739x4
> * "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

[Eric Greenwell]

wrote:
> Eric what are you reading in the manual that says 0.4 nm? The only
> reference I saw to 0.4 nm is the discusison that if you see false
> targets of less than 0.4 nm range then you may need to clean the
> transponder antenna, etc.

The remark was in a different thread, and it was based page 10,
"Resolution and Accuracy". The remark was...

"My MRX manual doesn't directly answer this question, but my reading is
you have range down to at least 0.4 nm, which is 2400'. It's been giving
you advisories and alerts from 5 nm, so you should have spotted the
threat by the time it's that close."

I'm sure the situation is more complicated than John Carlyle's analysis
suggests, as you point out below (and there must be other things we
haven't thought of), and that's why Zaon should have the chance to
answer the question about a dead zone.


> Also it is worth remembering the Zaon PCAs devices are not just
> "blanking" the receiver during the local transponder reply. The Zaons
> are reading and doing an altitude decode of the local transponder
> signal and using that if possible for the altitude reference rather
> than the built in altimeter. How good their RF front end and post RF
> digital processing is will determine how well they can differentiate
> partially overlapping pulse trains from the local and other
> transponders. And you better believe they have to do this since the
> most nieve approach of "blanking" during the entire ~20us transponder
> pulse train (ignoring the ident pulse) would give a dead zone of
> ~6km. I'd love to see a schematic.. :-)
>
> Like other posters I suspect this not much of an issue in practice
> because of multipe illuminations from SSR, TCAS etc. However one thing
> with some of the funkier glider tranponder antenna installs is that
> the PCAS may be seeing much more RF power from the local transponder
> than the designer expected, especially for situations like with RF
> transparent fiberglass fueslages and maybe a less than great ground
> plane betwen the PCAS and antenna, tranponder antennas mounted in the
> cockpit etc. In which case maybe the dead zone is larger because of
> the Zaon's reduced ability to detect overlapping pulse trains.
>
> ---
>
> The Zaon MRX works amazingly well in my experience and is a great
> suppliment for transponders in gliders, but especially for seperation
> from heavy iron lets keep the focus on getting transponders in gliders
> in heavy traffic areas. Transponders absolutely work -- with no effort
> from me except turning on my transponder I often notice traffic
> vectored around my glider when flying near Reno (I hear Reno arivals/
> departures telling traffic I'm there).


--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[jcarlyle]

Darryl, I admit I oversimplified things. One of the reasons was that I
deal with analog ultrasonic signals produced by nature, not digital
pulse trains from transponders, so it made a first cut analysis easier
for me.

Hopefully Zaon will be willing to tell Eric what they're really doing
inside the box. Since I own a MRX and am planning on installing a
transponder, I'd be more than happy if my analysis at the start of
this thread is wrong!

Meanwhile, it sounds like you understand transponders, RF and digital
processing. Can you refer me to something on the web that would
explain the basics of how partially overlapped pulse trains are
differentiated? Using a stand-alone detector on analog signals of
similar frequency and fairly similar shape, I know I can't detect a
second signal 20-30 dB below an overlapping signal - so the
possibility you hint of for digital signals is outside of my
knowledge. Thanks!

-John

On Mar 10, 1:34 pm, " >
wrote:
> Also it is worth remembering the Zaon PCAs devices are not just
> "blanking" the receiver during the local transponder reply. The Zaons
> are reading and doing an altitude decode of the local transponder
> signal and using that if possible for the altitude reference rather
> than the built in altimeter. How good their RF front end and post RF
> digital processing is will determine how well they can differentiate
> partially overlapping pulse trains from the local and other
> transponders. And you better believe they have to do this since the
> most nieve approach of "blanking" during the entire ~20us transponder
> pulse train (ignoring the ident pulse) would give a dead zone of
> ~6km. I'd love to see a schematic.. :-)
>
> Like other posters I suspect this not much of an issue in practice
> because of multipe illuminations from SSR, TCAS etc. However one thing
> with some of the funkier glider tranponder antenna installs is that
> the PCAS may be seeing much more RF power from the local transponder
> than the designer expected, especially for situations like with RF
> transparent fiberglass fueslages and maybe a less than great ground
> plane betwen the PCAS and antenna, tranponder antennas mounted in the
> cockpit etc. In which case maybe the dead zone is larger because of
> the Zaon's reduced ability to detect overlapping pulse trains.
>
> Darryl

[[email protected]]

John

If you are realy interested I hope this gives you a few key words to
look up if nothing else: Overlapping pulse trains in SSR/transponders
is called garbling, and systems to handle that perform de-garbling.
Specifically you are discussing syncronous garbling where the garbling
is syncronised by the radar interrogation. Systems like TCAS that are
more unidirectional than SSR radar use techniques including wisper-
shout and directional antenas to try to de-garble their signals. A
funky little summary on this stuff is at http://www.radartutorial.eu/13.ssr/sr01.en.html
(see brief mention at http://www.radartutorial.eu/13.ssr/sr15.en.html
for a de-garbling algorithm). If you have access to IEEE there are
papers available there on SSR, collision avoidance etc.

As for general UHF/microwave signal processing, you can do pretty
amazing stuff with very low noise / high dynamic range front-ends,
possibly more than you would expect if your background is ultrasonic
signal processing. And in the case being dicussed the closer the
target gets you have less of a signal dynamic range problem.

But who knows exactly what Zaon does. I'd be suprised if they ever got
into details. Again all I was doing was cautioning is it probably
won't be signal blanking, not at least as initilaly described. None of
this stuff is my area/background, A very long time ago I did research
on ultra-low phase noise microwave sources and some exotic
applciations of those and have just been curious in the past about how
SSR worked.

---

BTW I had not poked around the Zaon website in a while and I now
noticed that they have an installation guide what talks about a panel
install kit and "audio enabled" MRX modules that give audio out. Also
they talk about multi-antenna installs. They definitly are not afraid
of getting the MRX antenna too close to the transponder antenna, they
spec only a few feet minimum distance between externally mounted MRX
and tranponder antennas. So I might have to take back my previous
concern about transponder antennas being really close to the MRX
antenna.

See http://www.zaonflight.com/component/option,com_docman/task,cat_view/gid,8/Itemid,43

Cheers


Darryl

On Mar 10, 5:37 pm, "jcarlyle" > wrote:
> Darryl, I admit I oversimplified things. One of the reasons was that I
> deal with analog ultrasonic signals produced by nature, not digital
> pulse trains from transponders, so it made a first cut analysis easier
> for me.
>
> Hopefully Zaon will be willing to tell Eric what they're really doing
> inside the box. Since I own a MRX and am planning on installing a
> transponder, I'd be more than happy if my analysis at the start of
> this thread is wrong!
>
> Meanwhile, it sounds like you understand transponders, RF and digital
> processing. Can you refer me to something on the web that would
> explain the basics of how partially overlapped pulse trains are
> differentiated? Using a stand-alone detector on analog signals of
> similar frequency and fairly similar shape, I know I can't detect a
> second signal 20-30 dB below an overlapping signal - so the
> possibility you hint of for digital signals is outside of my
> knowledge. Thanks!
>
> -John
>
> On Mar 10, 1:34 pm, " >
> wrote:
>
> > Also it is worth remembering the Zaon PCAs devices are not just
> > "blanking" the receiver during the local transponder reply. The Zaons
> > are reading and doing an altitude decode of the local transponder
> > signal and using that if possible for the altitude reference rather
> > than the built in altimeter. How good their RF front end and post RF
> > digital processing is will determine how well they can differentiate
> > partially overlapping pulse trains from the local and other
> > transponders. And you better believe they have to do this since the
> > most nieve approach of "blanking" during the entire ~20us transponder
> > pulse train (ignoring the ident pulse) would give a dead zone of
> > ~6km. I'd love to see a schematic.. :-)
>
> > Like other posters I suspect this not much of an issue in practice
> > because of multipe illuminations from SSR, TCAS etc. However one thing
> > with some of the funkier glider tranponder antenna installs is that
> > the PCAS may be seeing much more RF power from the local transponder
> > than the designer expected, especially for situations like with RF
> > transparent fiberglass fueslages and maybe a less than great ground
> > plane betwen the PCAS and antenna, tranponder antennas mounted in the
> > cockpit etc. In which case maybe the dead zone is larger because of
> > the Zaon's reduced ability to detect overlapping pulse trains.
>
> > Darryl

[jcarlyle]

Darryl, thanks very much! The links were exactly what I was hoping
for; there's good stuff in there.

This is a bear of a week for me, and I don't have time to dig into the
ramifications of what you've provided.. But I see what you're driving
at, now, and it's clear that I let my ultrasonic work color my
analysis.

Funny thing, I was thinking before you replied about using correlation
on overlapping signals, and sure enough, that's what they're using for
the de-garbling. Don't think I ever saw a hardware correlator,
although I did see a hardware device to do the FFT butterfly once. Do
they still use such things in this computer age?

-John

On Mar 12, 5:53 pm, " >
wrote:
> John
>
> If you are realy interested I hope this gives you a few key words to
> look up if nothing else: Overlapping pulse trains in SSR/transponders
> is called garbling, and systems to handle that perform de-garbling.
> Specifically you are discussing syncronous garbling where the garbling
> is syncronised by the radar interrogation. Systems like TCAS that are
> more unidirectional than SSR radar use techniques including wisper-
> shout and directional antenas to try to de-garble their signals. A
> funky little summary on this stuff is athttp://www.radartutorial.eu/13.ssr/sr01.en.html
> (see brief mention athttp://www.radartutorial.eu/13.ssr/sr15.en.html
> for a de-garbling algorithm). If you have access to IEEE there are
> papers available there on SSR, collision avoidance etc.
>
> As for general UHF/microwave signal processing, you can do pretty
> amazing stuff with very low noise / high dynamic range front-ends,
> possibly more than you would expect if your background is ultrasonic
> signal processing. And in the case being dicussed the closer the
> target gets you have less of a signal dynamic range problem.
>
> But who knows exactly what Zaon does. I'd be suprised if they ever got
> into details. Again all I was doing was cautioning is it probably
> won't be signal blanking, not at least as initilaly described. None of
> this stuff is my area/background, A very long time ago I did research
> on ultra-low phase noise microwave sources and some exotic
> applciations of those and have just been curious in the past about how
> SSR worked.
>
> ---
>
> BTW I had not poked around the Zaon website in a while and I now
> noticed that they have an installation guide what talks about a panel
> install kit and "audio enabled" MRX modules that give audio out. Also
> they talk about multi-antenna installs. They definitly are not afraid
> of getting the MRX antenna too close to the transponder antenna, they
> spec only a few feet minimum distance between externally mounted MRX
> and tranponder antennas. So I might have to take back my previous
> concern about transponder antennas being really close to the MRX
> antenna.
>
> Seehttp://www.zaonflight.com/component/option,com_docman/task,cat_view/g...

[Tim Mara]

FYI, all MRX units have an audio for alert, the new units have an audio
output for use with headsets or intercoms added (optional)
tim
Please visit the Wings & Wheels website at www.wingsandwheels.com

> wrote in message
oups.com...
> BTW I had not poked around the Zaon website in a while and I now
> noticed that they have an installation guide what talks about a panel
> install kit and "audio enabled" MRX modules that give audio out. Also
> they talk about multi-antenna installs. They definitly are not afraid
> of getting the MRX antenna too close to the transponder antenna, they
> spec only a few feet minimum distance between externally mounted MRX
> and tranponder antennas. So I might have to take back my previous
> concern about transponder antennas being really close to the MRX
> antenna.
>
> See
> http://www.zaonflight.com/component/option,com_docman/task,cat_view/gid,8/Itemid,43
>
> Cheers
>
>
> Darryl
>
> On Mar 10, 5:37 pm, "jcarlyle" > wrote:
>> Darryl, I admit I oversimplified things. One of the reasons was that I
>> deal with analog ultrasonic signals produced by nature, not digital
>> pulse trains from transponders, so it made a first cut analysis easier
>> for me.
>>
>> Hopefully Zaon will be willing to tell Eric what they're really doing
>> inside the box. Since I own a MRX and am planning on installing a
>> transponder, I'd be more than happy if my analysis at the start of
>> this thread is wrong!
>>
>> Meanwhile, it sounds like you understand transponders, RF and digital
>> processing. Can you refer me to something on the web that would
>> explain the basics of how partially overlapped pulse trains are
>> differentiated? Using a stand-alone detector on analog signals of
>> similar frequency and fairly similar shape, I know I can't detect a
>> second signal 20-30 dB below an overlapping signal - so the
>> possibility you hint of for digital signals is outside of my
>> knowledge. Thanks!
>>
>> -John
>>
>> On Mar 10, 1:34 pm, " >
>> wrote:
>>
>> > Also it is worth remembering the Zaon PCAs devices are not just
>> > "blanking" the receiver during the local transponder reply. The Zaons
>> > are reading and doing an altitude decode of the local transponder
>> > signal and using that if possible for the altitude reference rather
>> > than the built in altimeter. How good their RF front end and post RF
>> > digital processing is will determine how well they can differentiate
>> > partially overlapping pulse trains from the local and other
>> > transponders. And you better believe they have to do this since the
>> > most nieve approach of "blanking" during the entire ~20us transponder
>> > pulse train (ignoring the ident pulse) would give a dead zone of
>> > ~6km. I'd love to see a schematic.. :-)
>>
>> > Like other posters I suspect this not much of an issue in practice
>> > because of multipe illuminations from SSR, TCAS etc. However one thing
>> > with some of the funkier glider tranponder antenna installs is that
>> > the PCAS may be seeing much more RF power from the local transponder
>> > than the designer expected, especially for situations like with RF
>> > transparent fiberglass fueslages and maybe a less than great ground
>> > plane betwen the PCAS and antenna, tranponder antennas mounted in the
>> > cockpit etc. In which case maybe the dead zone is larger because of
>> > the Zaon's reduced ability to detect overlapping pulse trains.
>>
>> > Darryl
>
>

[[email protected]]

Tim

Your back - you must have finished throwing out all those transponders
you are not going to sell :-)

Thanks for degarbling my post, yes I meant an electrical audio out for
an headset/audio panel

Do you know if current Zaon MRX systems (few months old) can be
upgraded to have the headset/audio panel audio out? Is the volume of
that output independently adjustable?

Thanks


Darryl

--

BTW I also misstyped unidirectional when I meant omnidirectional when
talking about TCAS.


On Mar 13, 9:00 am, "Tim Mara" > wrote:
> FYI, all MRX units have an audio for alert, the new units have an audio
> output for use with headsets or intercoms added (optional)
> tim
> Please visit the Wings & Wheels website atwww.wingsandwheels.com
>
> > wrote in message
>
> oups.com...
>
> > BTW I had not poked around the Zaon website in a while and I now
> > noticed that they have an installation guide what talks about a panel
> > install kit and "audio enabled" MRX modules that give audio out. Also
> > they talk about multi-antenna installs. They definitly are not afraid
> > of getting the MRX antenna too close to the transponder antenna, they
> > spec only a few feet minimum distance between externally mounted MRX
> > and tranponder antennas. So I might have to take back my previous
> > concern about transponder antennas being really close to the MRX
> > antenna.
>
> > See
> >http://www.zaonflight.com/component/option,com_docman/task,cat_view/g...
>
> > Cheers
>
> > Darryl
>
> > On Mar 10, 5:37 pm, "jcarlyle" > wrote:
> >> Darryl, I admit I oversimplified things. One of the reasons was that I
> >> deal with analog ultrasonic signals produced by nature, not digital
> >> pulse trains from transponders, so it made a first cut analysis easier
> >> for me.
>
> >> Hopefully Zaon will be willing to tell Eric what they're really doing
> >> inside the box. Since I own a MRX and am planning on installing a
> >> transponder, I'd be more than happy if my analysis at the start of
> >> this thread is wrong!
>
> >> Meanwhile, it sounds like you understand transponders, RF and digital
> >> processing. Can you refer me to something on the web that would
> >> explain the basics of how partially overlapped pulse trains are
> >> differentiated? Using a stand-alone detector on analog signals of
> >> similar frequency and fairly similar shape, I know I can't detect a
> >> second signal 20-30 dB below an overlapping signal - so the
> >> possibility you hint of for digital signals is outside of my
> >> knowledge. Thanks!
>
> >> -John
>
> >> On Mar 10, 1:34 pm, " >
> >> wrote:
>
> >> > Also it is worth remembering the Zaon PCAs devices are not just
> >> > "blanking" the receiver during the local transponder reply. The Zaons
> >> > are reading and doing an altitude decode of the local transponder
> >> > signal and using that if possible for the altitude reference rather
> >> > than the built in altimeter. How good their RF front end and post RF
> >> > digital processing is will determine how well they can differentiate
> >> > partially overlapping pulse trains from the local and other
> >> > transponders. And you better believe they have to do this since the
> >> > most nieve approach of "blanking" during the entire ~20us transponder
> >> > pulse train (ignoring the ident pulse) would give a dead zone of
> >> > ~6km. I'd love to see a schematic.. :-)
>
> >> > Like other posters I suspect this not much of an issue in practice
> >> > because of multipe illuminations from SSR, TCAS etc. However one thing
> >> > with some of the funkier glider tranponder antenna installs is that
> >> > the PCAS may be seeing much more RF power from the local transponder
> >> > than the designer expected, especially for situations like with RF
> >> > transparent fiberglass fueslages and maybe a less than great ground
> >> > plane betwen the PCAS and antenna, tranponder antennas mounted in the
> >> > cockpit etc. In which case maybe the dead zone is larger because of
> >> > the Zaon's reduced ability to detect overlapping pulse trains.
>
> >> > Darryl

[Eric Greenwell]

jcarlyle wrote:
> A few days ago, Bumper mentioned his TPAS "went deaf" in his
> transponder equipped glider while flying near other transponders. Jim
> S asked about the blanking distance, and Eric Greenwell found in the
> manual for the Zaon MRX that this was about 0.4 miles.

Not quite: 0.4 mi
> Now consider the other transponder being farther away from ATC than
> you, on the line that connects you and ATC. Your transponder fires
> first and blanks the ZAON. The ATC pulse has to propagate to him for
> his transponder to fire, then his transponder pulse has to propagate
> back to you to be detected by the ZAON. The net result is that he can
> be as close as 0.2 nm for you to detect him.
>
> Now suppose the other transponder is between you and ATC, on the line
> that connects you and ATC. Guess what? You'll never detect him! The
> ATC pulse reaches him first, firing his transponder, and both pulses
> reach your ship at essentially the same time. Your transponder then
> fires, blanking the ZAON. By the time it unblanks, his pulse and your
> pulse have propagated far beyond the ZAON antenna - they aren't around
> for detection.

John's analysis seemed plausible, so I contacted Zaon about it.
Summarizing a fairly technical reply:

"The situation described can produce a dead zone. Generally it is not a
problem in practice, because there are many other interrogation sources
(mainly other ATC radars and TCAS systems) that interrogate transponders
besides the ATC radar in line with your glider and the other aircraft.
These replies will not be masked, so range and altitude can be
determined by the MRX."

I'd add that it's unlikely an aircraft could stay directly between you
and the ATC radar for very long. If it was climbing, you'd have to climb
even faster, and vice versa. If it was coming straight out from the
radar, you'd have to be flying directly towards or away on the sloped
line going to or from the radar, and so on.

So, it's an event with a low probability in the first place, and a high
probability of mitigation by interrogations from other sources. Further,
if it's an airliner, it has TCAS (he'll see you, you'll see him); if
it's a GA aircraft, it might be in contact with ATC and warned of your
presence, or it might have a PCAS unit and detect your transponder; and
finally, you might visually detect each other! My opinion: the dead zone
risk is insignificant.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[bumper]

"Eric Greenwell" > wrote in message
news:nt1Kh.5445$0W5.1788@trndny05...

My opinion: the dead zone
> risk is insignificant.
>
> --
> Eric Greenwell - Washington State, USA
> * Change "netto" to "net" to email me directly
> * "Transponders in Sailplanes" http://tinyurl.com/y739x4
> * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org


Having flown with a TPAS for about 5 years now, my experience backs up what
Eric is saying. While I've noticed the "blind spot" often, mostly while
flying with other gliders, I've always had visual contact on the other
aircraft. I think this is because the blind spot doesn't extend all that far
from my aircraft.

bumper

[jcarlyle]

Eric,

Thanks so much for following up with Zaon. Kudos to Zaon for being
forthcoming with you, too. I love my MRX, and the attitude Zaon
expressed in answering you makes me like the company that much more.

By the way, I think there's a typo in your reply regarding minimum
detectable distance - I think you meant to say 0.1 mi, not 0.4 mi.

-John

On Mar 14, 8:39 pm, Eric Greenwell > wrote:
>
> Eric Greenwell found in the
> manual for the Zaon MRX that this was about 0.4 miles.
>
> Not quite: 0.4 mi
>
> John's analysis seemed plausible, so I contacted Zaon about it.
> Summarizing a fairly technical reply:
>
> "The situation described can produce a dead zone. Generally it is not a
> problem in practice, because there are many other interrogation sources
> (mainly other ATC radars and TCAS systems) that interrogate transponders
> besides the ATC radar in line with your glider and the other aircraft.
> These replies will not be masked, so range and altitude can be
> determined by the MRX."