Flight Lessons

(Harry Andreas) wrote:

Most airborne GPS systems have multiple antennas and can be
made directional.
Not sure how much I can say in this forum until I check security.

AvWeb published a fairly recent article GPS jamming:

http://www.avweb.com/news/avionics/182754-1.html

-Mike Marron

Harry Andreas wrote:

In article , Michael Williamson
wrote:

Cub Driver wrote:

as long as the GPS is working. But it's a low-powered signal from orbit
and it's easily jammed.


How true is this, really? In an aircraft, you are between the ground
and the satellite. How does someone on the ground interfere with the
signal?


I don't believe that the antenna for the GPS is directional enough
that someone off axis couldn't put a signal into your system- after
all, a single antenna is used to pick up every satellite above the
horizon.

Wrong on both counts.
Most airborne GPS systems have multiple antennas and can be
made directional.
Not sure how much I can say in this forum until I check security.

--
Harry Andreas
Engineering raconteur


Must be quite complex to track multiple moving satellites scattered
around the sky from a moving platform with limited antenna real-estate.

From what I understand, from publicly available literature, multiple
balloon mounted jammers could pose a real, and relatively economical,
problem.

Dave

In message , Michael Williamson
writes
Cub Driver wrote:
How true is this, really? In an aircraft, you are between the
ground
and the satellite. How does someone on the ground interfere with the
signal?

I don't believe that the antenna for the GPS is directional enough
that someone off axis couldn't put a signal into your system- after
all, a single antenna is used to pick up every satellite above the
horizon.

It can be made directional, for a cost. It can even be persuaded to null
out jammers... for a cost.

Trouble is, jammers are cheap.

--
When you have to kill a man, it costs nothing to be polite.
W S Churchill

Paul J. Adam MainBoxatjrwlynch[dot]demon{dot}co(.)uk

In message ,
Harry Andreas writes
In article , "Paul J. Adam"
wrote:
It's not the end of the world if the enemy whips out a few jammers, and
it's harder to do well than some would have you believe, but it's still
a genuine concern with fewer easy answers you suggest.

If there's a cheap, quick, easy and reliable magic bullet to make GPS
unjammable, then hasten down to your patent office at once.

I might mention that as of the first of '03 I'm pretty much off of
AESA radars and have been working on airborne GPS receivers.
It's my first experience with them and it's illuminating,
but I've learned enough to:
a] be dangerous, and
b] know enough of the performance limits to not be pessimistic.

Fair enough - in the same timescale I've been doing work for NAVWAR and
the RN on the effects of GPS denial, how it might happen, how to work
around it, and how to prevent it

--
When you have to kill a man, it costs nothing to be polite.
W S Churchill

Paul J. Adam MainBoxatjrwlynch[dot]demon{dot}co(.)uk

Most airborne GPS systems have multiple antennas and can be
made directional.
Not sure how much I can say in this forum until I check security.

The one on Zero Six Hotel is velcro'd to a plastic picture frame,
mounted upside-down over the front seat. (I generally don't carry a
passenger.) It has that little swivel "ear" antenna that points up.

I suppose it would work equally well pointing down, but I've never
tried it.

The problem I have in visualizing a jam on an aircraft is this: the
jammer is at sea level, the plane at 20,000 feet and looking to dive
to 4,000, and the satellite is at whatever, feet or miles.

So I'm on the ground on horseback with my handy Green Beret Jamming
Unit, aiming a signal at this plane that wants to attack me. Are you
saying that I can send up this umbrella beam that will wrap around the
GPS in the F-15 and thereby get between it and the satellite?

(You have probably guessed already that I majored in government.)


all the best -- Dan Ford
email: www.danford.net/letters.htm#9

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

In article , Dave Holford
wrote:

Harry Andreas wrote:

In article , Michael Williamson
wrote:

Cub Driver wrote:

as long as the GPS is working. But it's a low-powered signal from orbit
and it's easily jammed.


How true is this, really? In an aircraft, you are between the ground
and the satellite. How does someone on the ground interfere with the
signal?


I don't believe that the antenna for the GPS is directional enough
that someone off axis couldn't put a signal into your system- after
all, a single antenna is used to pick up every satellite above the
horizon.

Wrong on both counts.
Most airborne GPS systems have multiple antennas and can be
made directional.
Not sure how much I can say in this forum until I check security.

--
Harry Andreas
Engineering raconteur


Must be quite complex to track multiple moving satellites scattered
around the sky from a moving platform with limited antenna real-estate.

That's why we have the contract instead of some commercial firm.


From what I understand, from publicly available literature, multiple
balloon mounted jammers could pose a real, and relatively economical,
problem.

Not unsolvable. Just a bit more hardware and some money.

--
Harry Andreas
Engineering raconteur

(ArtKramr) wrote:

[...]
There has been number of comments on how much more complicated things are now
as compared to WW II. But I dont k now about that. When I talk to guys at
[...]


Plus ça change.

WWII navigation might well have looked complicated by the standards of
the twenties:


From:

http://www.imperial-airways.com/History_page_1.html

#In January 1927 a service was opened between Cairo and Basra,
#in the Persian Gulf. To solve the difficulty of navigating
#across the trackless desert between Palestine and Baghdad,
#a furrow, several hundred miles long, was ploughed in the
#sand. It was probably the longest furrow ever ploughed.
#

Anyone know if this is still there ?

Presumably it was filled-in as advances in furrow-less navigation took
place, due to the number of explorers spraining their ankles by
stepping into it while staring intently at the burning horizon, etc.

Subject: Flight Lessons
From: funkraum SPAM
Date: 10/6/03 3:15 PM Pacific Daylight Time
Message-id: etp3ovsqa5thsov4uinu5t0

WWII navigation might well have looked complicated by the standards of
the twenties:

Don't know. I never flew in rhe 20's. But I'll take your word for it.

Arthur Kramer
344th BG 494th BS
England, France, Belgium, Holland, Germany
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer

funkraum wrote:


#In January 1927 a service was opened between Cairo and Basra,
#in the Persian Gulf. To solve the difficulty of navigating
#across the trackless desert between Palestine and Baghdad,
#a furrow, several hundred miles long, was ploughed in the
#sand. It was probably the longest furrow ever ploughed.
#

Anyone know if this is still there ?

Presumably it was filled-in as advances in furrow-less navigation took
place, due to the number of explorers spraining their ankles by
stepping into it while staring intently at the burning horizon, etc.

Lesson 1 in geology - the landscape changes all the time!

The problem would be in maintaining the furrow, wind and water would fill it
in in a short period of time and it would not be detectable with the MK1
eyeball from the air within a period of months? years?.

It may be detectable now by eye from the ground close up if you knew exactly
where to look and looked at the right angle. From the air hi res multi
spectral imagery would probably show it for many years to come. This of
course is for areas of soil with some (not much but some) vegation which is
true for most desert areas.

In the rare areas of a sand sea (rather than discrete moving dunes on soil)
it would completely disappear with the first high wind.

regards

jc

The problem would be in maintaining the furrow, wind and water would fill it
in in a short period of time and it would not be detectable with the MK1
eyeball from the air within a period of months? years?.

I live on salt water, with extensive mud flats. I walk out at low tide
to set a mooring etc. My footprints are visible for at least a week,
maybe two. That would be the low end of "Look on my works, Ye Mighty,
and despair!"

On the other hand, I've been told that the scorched earth where
gliders burned at Arnhem? in 1944 are still visible from the air. And
I have walked with great comfort along the former logging railroads in
the White Mountains, the railroads having disappeared 80 years
earlier.

all the best -- Dan Ford
email: www.danford.net/letters.htm#9

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com