gliders+radar

Would the MTI also filter you out if you had a Mode C transponder?

Mike Schumann

"Bob Salvo" wrote in message
. ..
Reflectivity is not the problem. We conducted experiments with Boston
control many years ago. They got good radar returns from our glass ships.
The problem is the slow speed we generally fly. Usually the center's
radar
uses MTI (moving target indicator), which gets rid of ground clutter
returns
and returns from flying birds. When Boston control deactivated the MTI
function, they could easily see us. Adding a lens to increase our
reflectivity would not help. But if we had doppler generator built into
the
lens (maybe a spinning wheel propelled by air; we have lots of that
available), the lens would be removed from the clutter notch. Maybe


"Mike C 17" wrote in message
oups.com...
http://www.sailorssolutions.com/inde...ails&Item=RR01


Big John wrote:
Johan

Look up Luneberg Lens via Google.

We hung them on T-33 target aircraft in exercies to give a radar
return the size of a B-47.

You could make one out of foam and Rennels (sp) Wrap and put inside
your plastic bird and get a much larger radar return for just a few
ounces for the lens.

These are passive devices and no power is required.

Big John
`````````````````````````````````````````````````` ````````````````

On 19 Jul 2006 18:25:38 -0700, wrote:

Modern gliders are small and made of materials that show up poorly on
radar.

Are we basically flying stealth aircraft?

Johan Larson

Mike Schumann wrote:
Would the MTI also filter you out if you had a Mode C transponder?

Mike, AIUI there are two quite different radar types. The originals,
now know as Primary Radar, send out a signal and deduce your range and
direction (azimuth) from a reflection. That sort does not know whether
you have a transponder or not, reflections could be improved by large
enough Luneberg lenses (of dubious benefit for the size we could get
into a glider fuselage), and is subject to MTI if they switch it on.
Also, on a visit to Stansted UK (London's "third" airport) some years
ago, their ATC explained to me that not only did it fail to see slow
moving targets when MTI was on - which it almost always was, to reduce
screen clutter; it was also blind to anything with a radial speed
towards or away from the radar head at certain harmonics of the wave
length - in practice at 37.5 knots, 75 knots, and multiples. So even
with MTI off, thermalling gliders that were good reflectors would be
invisible half the time, and cruising towards or away from them would
also reduce or eradicate their trace of us.

Transponders use SSR (Secondary Surveillance Radar) which sends out an
APB to all transponders within range - "Oi, anyone out there?" to which
they all respond. No transponder, no response, SSR cannot see you.
With Mode S (for Selective), the Controller can then tweak it to say
next time around "Oi, only those transponders I have Selected - where
are you now?". Gliders etc. not so selected will then not be seen by
ATC. This has three effects (at least):

They have less cluttered screens, seeing only those that they want to
for control purposes;

Each Mode S transponder has a unique code identifying it to the
aircraft it is in, so they never run out of codes (unlike Modes A and
C, where Europe already has problems, because the existing 7xxx - type
codes are too few for ATC's purposes);

And transponders NOT selected by ATC would not be made to transmit a
signal zillions of times per second like a Mode A or C is, only say
once per second, so they still show up to TCAS units in the area but
save a lot of power compared with Mode A or C. This seems to be why,
in Europe at least, the authorities are looking at Mode S, rather than
A or C, as a mandatory standard. They know gliders would never have
enough power for Mode A or C with the expected growth in utilisation of
airspace and hence growing number of interrogations making transponders
squawk.

TCAS etc. in airliners etc., however, will still see all transponders
within their range, so will still give collision avoidance in respect
of gliders.

Hope that helps. Any experts care to correct this if necessary?

Chris N.

no... because you are sending a coded reply to a specific interrogation.
BT

"Mike Schumann" wrote in message
ink.net...
Would the MTI also filter you out if you had a Mode C transponder?

Mike Schumann

"Bob Salvo" wrote in message
. ..
Reflectivity is not the problem. We conducted experiments with Boston
control many years ago. They got good radar returns from our glass
ships.
The problem is the slow speed we generally fly. Usually the center's
radar
uses MTI (moving target indicator), which gets rid of ground clutter
returns
and returns from flying birds. When Boston control deactivated the MTI
function, they could easily see us. Adding a lens to increase our
reflectivity would not help. But if we had doppler generator built into
the
lens (maybe a spinning wheel propelled by air; we have lots of that
available), the lens would be removed from the clutter notch. Maybe


"Mike C 17" wrote in message
oups.com...
http://www.sailorssolutions.com/inde...ails&Item=RR01


Big John wrote:
Johan

Look up Luneberg Lens via Google.

We hung them on T-33 target aircraft in exercies to give a radar
return the size of a B-47.

You could make one out of foam and Rennels (sp) Wrap and put inside
your plastic bird and get a much larger radar return for just a few
ounces for the lens.

These are passive devices and no power is required.

Big John
`````````````````````````````````````````````````` ````````````````

On 19 Jul 2006 18:25:38 -0700, wrote:

Modern gliders are small and made of materials that show up poorly
on
radar.

Are we basically flying stealth aircraft?

Johan Larson

Bob

I played with rotating Lens some years ago in a project to develope a
high speed radar return that could be detected by Police Radar
Detectors without the results I wanted. I wanted to 'pin the needle'
on detector at max so true speed wouldn't show. (I'm a dirty old man
)

Your idea for gliders might work? Not expensive to try/test.

Big John
``````````````````````````````````````
On Thu, 20 Jul 2006 20:43:39 -0400, "Bob Salvo"
wrote:

Reflectivity is not the problem. We conducted experiments with Boston
control many years ago. They got good radar returns from our glass ships.
The problem is the slow speed we generally fly. Usually the center's radar
uses MTI (moving target indicator), which gets rid of ground clutter returns
and returns from flying birds. When Boston control deactivated the MTI
function, they could easily see us. Adding a lens to increase our
reflectivity would not help. But if we had doppler generator built into the
lens (maybe a spinning wheel propelled by air; we have lots of that
available), the lens would be removed from the clutter notch. Maybe


"Mike C 17" wrote in message
roups.com...
http://www.sailorssolutions.com/inde...ails&Item=RR01


Big John wrote:
Johan

Look up Luneberg Lens via Google.

We hung them on T-33 target aircraft in exercies to give a radar
return the size of a B-47.

You could make one out of foam and Rennels (sp) Wrap and put inside
your plastic bird and get a much larger radar return for just a few
ounces for the lens.

These are passive devices and no power is required.

Big John
`````````````````````````````````````````````````` ````````````````

On 19 Jul 2006 18:25:38 -0700, wrote:

Modern gliders are small and made of materials that show up poorly on
radar.

Are we basically flying stealth aircraft?

Johan Larson

Mike

Make one for pennies and few Oz vs 2.2# and $139.95.

Big John
`````````````````````````````````````````````````` ``````````

On 20 Jul 2006 14:36:09 -0700, "Mike C 17"
wrote:

http://www.sailorssolutions.com/inde...ails&Item=RR01


Big John wrote:
Johan

Look up Luneberg Lens via Google.

We hung them on T-33 target aircraft in exercies to give a radar
return the size of a B-47.

You could make one out of foam and Rennels (sp) Wrap and put inside
your plastic bird and get a much larger radar return for just a few
ounces for the lens.

These are passive devices and no power is required.

Big John
`````````````````````````````````````````````````` ````````````````

On 19 Jul 2006 18:25:38 -0700, wrote:

Modern gliders are small and made of materials that show up poorly on
radar.

Are we basically flying stealth aircraft?

Johan Larson

Big John wrote:
Mike

Make one for pennies and few Oz vs 2.2# and $139.95.

I did a search for info about Luneberg Lenses - found plenty of
definitions/explanations/units for sale but nothing on DIY Luneberg,
how to make a ball with a radially varying refractive index or sources
of materials with suitable refractive index gradations.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

"Martin Gregorie" wrote in message
...
Big John wrote:
Mike

Make one for pennies and few Oz vs 2.2# and $139.95.

I did a search for info about Luneberg Lenses - found plenty of
definitions/explanations/units for sale but nothing on DIY Luneberg, how
to make a ball with a radially varying refractive index or sources of
materials with suitable refractive index gradations.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

A corner reflector is easy and effective...

http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/142806/0/0/radar%20reflector/All_2/mode+matchallpartial/0/0

If you make one out of foam core board and aluminium foil, be sure to keep
all the angles at 90 degrees. The overall shape can be whatever you want.


--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

What kinda Rennels numbers would I get? Is this a new
kinda airfoil?

At 16:48 20 July 2006, Big John wrote:
Johan

Look up Luneberg Lens via Google.

We hung them on T-33 target aircraft in exercies to
give a radar
return the size of a B-47.

You could make one out of foam and Rennels (sp) Wrap
and put inside
your plastic bird and get a much larger radar return
for just a few
ounces for the lens.

These are passive devices and no power is required.

Big John
````````````````````````````````````````````````` `````````````````


On 19 Jul 2006 18:25:38 -0700,
wrote:

Modern gliders are small and made of materials that
show up poorly on
radar.

Are we basically flying stealth aircraft?

Johan Larson