In article ,
Richard Casady wrote:

On Mon, 19 Jul 2010 01:42:33 GMT, (patric albutat)
wrote:

So how exactly are we going to create superior charts in regions with
no GPS coverage? Or what use would these charts be to a sailor trying
to navigate a tricky coast without sat nav to give him his position?

Just where are these areas without coverage? Hint: the G in GPS stands
for Global. It's like taxes: everywhere.

Casady

Just about ANY Military Nuclear Site in the USA. Most of the FEMA
Bunkers. Most of the SAC Bases have that capability, but only test it
unless at DefCon 2 or higher. White House & Capitol Building, depending
on the immediate Threat Level. Places like that here in this country.
Overseas, Many of the National Parliament buildings, and Presidential
Palaces, and major Military installations, and places like that. Global
means Global Coverage from the Sky, not global coverage on the Ground
when local Jammers are active. This isn't Rocket Science, and many
Militaries around the world can, and do Jam the Civilian Datastreams,
within their boarders. The P-Code & Military Datastreams, are a lot more
resistant to such Jamming.

--
Bruce in alaska
add path after fast to reply

On Mon, 19 Jul 2010 11:48:28 -0800, Bruce in alaska
wrote:

Just about ANY Military Nuclear Site in the USA. Most of the FEMA
Bunkers. Most of the SAC Bases have that capability, but only test it
unless at DefCon 2 or higher. White House & Capitol Building, depending
on the immediate Threat Level. Places like that here in this country.
Overseas, Many of the National Parliament buildings, and Presidential
Palaces, and major Military installations, and places like that. Global
means Global Coverage from the Sky, not global coverage on the Ground
when local Jammers are active. This isn't Rocket Science, and many
Militaries around the world can, and do Jam the Civilian Datastreams,
within their boarders. The P-Code & Military Datastreams, are a lot more
resistant to such Jamming.

Good information. Do you have an estimate of how far offshore a local
jamming effort might extend?

NOTAM:

Oakland Center (Fremont CA) [ZOA]: April NOTAM #31 issued by Gps Notam OA [GPS]
Navigation GPS is unreliable and May BE unavailable WITHIN A 375 nautical miles
RADIUS of 393101N/1175659W LOVELOCK / LLC / VORTAC 141.25 DEGREE radial at 46.65
nautical miles, at FL400; decreasing in area with DECREASE in altitude to 290
nautical miles RADIUS at FL250; 220 nautical miles RADIUS at 10000 ft. mean sea
level, and 220 nautical miles RADIUS at 4000 ft. above ground level. effective
from April 09th, 2010 at 06:00 AM PST (1004091400) - April 09th, 2010 at 11:30
AM PST (1004091930)

On Mon, 19 Jul 2010 23:18:19 -0500, cavelamb
wrote:

NOTAM:

Oakland Center (Fremont CA) [ZOA]: April NOTAM #31 issued by Gps Notam OA [GPS]
Navigation GPS is unreliable and May BE unavailable WITHIN A 375 nautical miles
RADIUS of 393101N/1175659W LOVELOCK / LLC / VORTAC 141.25 DEGREE radial at 46.65
nautical miles, at FL400; decreasing in area with DECREASE in altitude to 290
nautical miles RADIUS at FL250; 220 nautical miles RADIUS at 10000 ft. mean sea
level, and 220 nautical miles RADIUS at 4000 ft. above ground level. effective
from April 09th, 2010 at 06:00 AM PST (1004091400) - April 09th, 2010 at 11:30
AM PST (1004091930)

Those ranges quoted are for aircraft thousands of feet above sea
level. The jamming range would be much shorter for boats, probably
10 miles or less.

Wayne.B wrote:
On Mon, 19 Jul 2010 23:18:19 -0500, cavelamb
wrote:

NOTAM:

Oakland Center (Fremont CA) [ZOA]: April NOTAM #31 issued by Gps Notam OA [GPS]
Navigation GPS is unreliable and May BE unavailable WITHIN A 375 nautical miles
RADIUS of 393101N/1175659W LOVELOCK / LLC / VORTAC 141.25 DEGREE radial at 46.65
nautical miles, at FL400; decreasing in area with DECREASE in altitude to 290
nautical miles RADIUS at FL250; 220 nautical miles RADIUS at 10000 ft. mean sea
level, and 220 nautical miles RADIUS at 4000 ft. above ground level. effective
from April 09th, 2010 at 06:00 AM PST (1004091400) - April 09th, 2010 at 11:30
AM PST (1004091930)

Those ranges quoted are for aircraft thousands of feet above sea
level. The jamming range would be much shorter for boats, probably
10 miles or less.


aSSuming it's a linear relationship, I get 202 mile radius...




--

Richard Lamb

On 7/20/2010 1:41 AM, cavelamb wrote:
Wayne.B wrote:
On Mon, 19 Jul 2010 23:18:19 -0500, cavelamb
wrote:

NOTAM:

Oakland Center (Fremont CA) [ZOA]: April NOTAM #31 issued by Gps
Notam OA [GPS]
Navigation GPS is unreliable and May BE unavailable WITHIN A 375
nautical miles RADIUS of 393101N/1175659W LOVELOCK / LLC / VORTAC
141.25 DEGREE radial at 46.65 nautical miles, at FL400; decreasing in
area with DECREASE in altitude to 290 nautical miles RADIUS at FL250;
220 nautical miles RADIUS at 10000 ft. mean sea level, and 220
nautical miles RADIUS at 4000 ft. above ground level. effective from
April 09th, 2010 at 06:00 AM PST (1004091400) - April 09th, 2010 at
11:30 AM PST (1004091930)

Those ranges quoted are for aircraft thousands of feet above sea
level. The jamming range would be much shorter for boats, probably
10 miles or less.


aSSuming it's a linear relationship, I get 202 mile radius...




Not linear: for a ground level jammer,
The line of sight estimator for distance versus height above sea level
goes something like this:
distance n.m. = 1.2 sqrt (Height ft MSL)

Those ranges quoted are for aircraft thousands of feet above sea
level. The jamming range would be much shorter for boats, probably
10 miles or less.


aSSuming it's a linear relationship, I get 202 mile radius...




Not linear: for a ground level jammer,
The line of sight estimator for distance versus height above sea level
goes something like this:
distance n.m. = 1.2 sqrt (Height ft MSL)

...and of course that assumes that the emitter is at sea level, so if it
is at any appreciable height (or in another aircraft) then you have to
add the result of the same equation again!!

Jeff

brian whatcott wrote:
Not linear: for a ground level jammer,
The line of sight estimator for distance versus height above sea level
goes something like this:
distance n.m. = 1.2 sqrt (Height ft MSL)

That calculation follows directly from the Taylor series for Cosine:

1 - x^2/2! + x^4/4! - ...

It means that for very small angles, the height above the sea is

1 - (1 - x^2/2!) = x^2/2! = x^2/2 (when R == 1)

Insert the radius of the Earth (in nautical miles, 3500 or so) and
multiply the result by the number of feet in a nautical mile (about
6000+) and the 1.2 factor should pop out.

Terje
--
- Terje.Mathisen at tmsw.no
"almost all programming can be viewed as an exercise in caching"

On 25/07/10 10:54, Jeff wrote:

Those ranges quoted are for aircraft thousands of feet above sea
level. The jamming range would be much shorter for boats, probably
10 miles or less.


aSSuming it's a linear relationship, I get 202 mile radius...




Not linear: for a ground level jammer,
The line of sight estimator for distance versus height above sea level
goes something like this:
distance n.m. = 1.2 sqrt (Height ft MSL)

..and of course that assumes that the emitter is at sea level, so if it
is at any appreciable height (or in another aircraft) then you have to
add the result of the same equation again!!

and ignores the surface effect that allows UK TV & VHF signals to be
picked up as far away as in the Netherlands.

The line of sight estimator for distance versus height above sea level
goes something like this:
distance n.m. = 1.2 sqrt (Height ft MSL)

That calculation follows directly from the Taylor series for Cosine:

1 - x^2/2! + x^4/4! - ...

It means that for very small angles, the height above the sea is

1 - (1 - x^2/2!) = x^2/2! = x^2/2 (when R == 1)

Insert the radius of the Earth (in nautical miles, 3500 or so) and
multiply the result by the number of feet in a nautical mile (about
6000+) and the 1.2 factor should pop out.

Terje

For a more exact result you only need to use Pythagoras.

Jeff