TPAS and Transponder - Blind Spot

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

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.

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 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...

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

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

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

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/...id,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

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...

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/...id,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