Carry your compass
 

On Mon, 05 Jan 2009 13:47:13 -0500, wrote:

On Mon, 05 Jan 2009 06:12:16 -0500, Tom Francis - SWSports
wrote:


I've heard that before and I find it an interesting comment. We have
some fairly dense woods around my house - 100 plus acres of woods in
fact mostly swamp oak, pine, hemlock, birch and sugar/swamp/rock
maple. Most trees are in the 40/45 foot category and in the summer
there is a dense canopy.

Back when I was still an active hunter, I used my GPS all the time
over in the Natchaug Forest and up along the Mass border where there
are more pine trees in the swamps than you can shake a stick at.

Never had a problem getting three satellites to obtain a fix.

Maybe it is just the shape/composition of the mountains, the latitude
or something but neither GPS worked worth a damn in Alaska, Idaho or
the Dakotas.
They were OK in Arizona and New Mexico. I have no problems in my boat
either but I am never lost enough to need one poking around in the
mangroves.

I can't say anything other than it's worked for me. Much to my
embarrassement, I was talking to a friend who is a big time deer
hunter and he was telling me, unsolicited I might add, that his GPS
gave him fits this weekend during bow season for deer. He was hunting
my property so it wasn't a location thing.

And, strangely, I've had problems with the RC400 even on open water
with the receiver losing lock although that was fixed with a firmware
update.

I've had this opinion, based on nothing other than observation and a
very megar understanding of GPS satellite communications (which is
nothing like other satellite communications) that folks in the
northern latitudes don't get as strong a signal as folks further
south. Just this past week, I got instant locks on my car's GPS - a
full spectrum of 12 satellites even time I turned it on and that was
in South Carolina. Up here, it takes a good 30 seconds for it to get
a 5 satelite lock to start working and the constellation is generally
clustered around the satellite that traverses the North Pole at the
time which limits the amount of sky available. Compared to the
constellation aquired in SC which was a fairly broad spectrum of sky.

Dunno.

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

Carry your compass
 

On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

As a general rule, yes.

You can receive signals away from windows depending on where the
constellation is at any one given time, but that can be a hit or miss
situation. If it's located near the floor, probably not. If it was
sitting on your lap though, it will work, but not with the same
accuracy - it all depends on the location of the constellation at the
time, where the GPS is located, etc.

There are situations where even situated near glass it will struggle
with finding satellites - something about how the glass is coated or
the composition of the substrate film used to make safety glass. Some
RFI devices (like Easy Pass transponders) don't work on certian cars
for that reason.

I can receive GPS signal in the middle of my house - then again, I'm
located fairly high and it's a one story ranch.

Carry your compass
 

On Mon, 5 Jan 2009 09:00:32 -0800 (PST), wrote:

On Jan 5, 9:40*am, Dave Brown wrote:
wrote:
On Sun, 4 Jan 2009 19:06:23 -0800 (PST), Frogwatch
wrote:

Being somewhat of a "high Tech Luddite", *I also prefer my compass to
GPS and would pack it before the GPS. *I can almost instantly use the
compass to take a bearing on something to be sure I have cleared a
potential obstacle. *Being a trigonometry geek, I just think
navigating with a compass and taking bearings is just elegant.
BTW, also being a caver, GPS doesnt work in caves, compass does.

A GPS really doesn't even work that well in the woods. I have 2 and I
always carry them on vacation (Idaho, Alaska, the Dakotas and Wyoming)
but you have to climb a tree to get enough satellites to establish a
fix. My wife was constantly making fun of me waving these in the air
trying to get 3 satellites.
They do work OK in the desert.

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

--
Regards,
* * * Dave Brown
* * * Brown's Marina Ltd
* * *http://brownsmarina.com/- Hide quoted text -

- Show quoted text -

Dave, they do need to be near glass if they only have an internal
antenna. There are models that have a connector for an external, and
the external itself costs around $25. There are also units made that
have the external already with it. Especially on trips to places I've
never been, I don't know how I ever got along without a GPS. And
before Mapquest, how did I EVER know where I was?

Heh - good one.

Funny story. When we redid the 911 system and turned it into the
E-911 system, I (and a couple of other radio enthusiasts on the
rebuild committee) fought tooth and nail to get GPS incorporated into
the system. We even worked up a deal with Garmin who would provide
the GPS units at cost for all eleven departments to equip every
vehicle with a unit.

Coulnd't get that one past the local chiefs - they just coulnd't wrap
their collective brains around the concept of exact locations. :)

Eventually though, we won.

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

Carry your compass
 

On Mon, 05 Jan 2009 13:49:18 -0500, wrote:

I am sure the antenna itself is the key

It is and it depends on whether it's a passive or active antenna. You
can also modify passive antennas to make then semi-active and actives
to make them semi-passive.

It's a whole science unto itself.

Most internal GPS antennas (and external antennas also) are bifilar
meaning that the antenna acts as a simple 1/2 wave dipole antenna but
it has reduced axial length - constructed as a helix antenna in which
the turn angle can be used to control the ratio of the orthogonal
linear field components and the input impedance. The advantage being
that you can build a flat, round, square, oblong, egg shaped or what
ever type antenna which will receive signals along the edges of the
antenna in addition to signals at acute 90 degree angles.

Aren't you glad you asked? :)

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

Carry your compass
 

On Mon, 05 Jan 2009 18:04:26 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

Metal blocks all radio.

As a strict statement, that is true, however radio signals can bend
around objects (demonstrated by radar's ability to see behind
objects). As such a car presents the opportunity to receive signals
inside by virtue of the physics of radio wave propogation and the
ability to move along the surface of metal.

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

Carry your compass
 

On Mon, 05 Jan 2009 16:39:33 -0500, Tom Francis - SWSports
wrote:

Funny story. When we redid the 911 system and turned it into the
E-911 system, I (and a couple of other radio enthusiasts on the
rebuild committee) fought tooth and nail to get GPS incorporated into
the system. We even worked up a deal with Garmin who would provide
the GPS units at cost for all eleven departments to equip every
vehicle with a unit.

Coulnd't get that one past the local chiefs - they just coulnd't wrap
their collective brains around the concept of exact locations. :)

They put up reflective house numbers out at the street out here in the
sticks for the benefit of the cops and fire departments. You cannot
get a cab. They simply cannot find the place. Nobody has ever found
this place that hasn't been here before. I like it that way. My
address is not on my checks. My phone is under a fake name. As a
friend once said, ' it doesn't pay to advertise.'

Casady

Carry your compass
 

On Mon, 05 Jan 2009 17:19:12 -0500, wrote:

On Mon, 05 Jan 2009 16:50:32 -0500, Tom Francis - SWSports
wrote:

I am sure the antenna itself is the key

It is and it depends on whether it's a passive or active antenna. You
can also modify passive antennas to make then semi-active and actives
to make them semi-passive.

It's a whole science unto itself.

Most internal GPS antennas (and external antennas also) are bifilar
meaning that the antenna acts as a simple 1/2 wave dipole antenna but
it has reduced axial length - constructed as a helix antenna in which
the turn angle can be used to control the ratio of the orthogonal
linear field components and the input impedance. The advantage being
that you can build a flat, round, square, oblong, egg shaped or what
ever type antenna which will receive signals along the edges of the
antenna in addition to signals at acute 90 degree angles.

Aren't you glad you asked? :)

In my modestly equipped mind I just sum it up that the best radio in
the world will suck if you don't have a decent antenna system.
That is from the Breaker Breaker good buddy days of Children's Band
radio.

10-4.

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

Carry your compass
 

On Mon, 05 Jan 2009 22:29:23 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 16:39:33 -0500, Tom Francis - SWSports
wrote:

Funny story. When we redid the 911 system and turned it into the
E-911 system, I (and a couple of other radio enthusiasts on the
rebuild committee) fought tooth and nail to get GPS incorporated into
the system. We even worked up a deal with Garmin who would provide
the GPS units at cost for all eleven departments to equip every
vehicle with a unit.

Coulnd't get that one past the local chiefs - they just coulnd't wrap
their collective brains around the concept of exact locations. :)

They put up reflective house numbers out at the street out here in the
sticks for the benefit of the cops and fire departments. You cannot
get a cab. They simply cannot find the place. Nobody has ever found
this place that hasn't been here before. I like it that way. My
address is not on my checks. My phone is under a fake name. As a
friend once said, ' it doesn't pay to advertise.'

We did that too. As a large geographic area that is almost completely
rural in nature, it was very important as some driveways can be a 1/4
mile long.

We also have an odd situation on my street in that it is actually two
roads that are similar in name - three of the houses on my town's side
have the same number as the houses on the same street in the next town
over.

That is a problem. :)

I'm not too sure about being unfindable. You'd be surprized at what a
competant 911 operator can find out quickly through the phone
companies.

Fake name or no fake name.

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

Carry your compass
 

On Mon, 05 Jan 2009 17:01:19 -0500, Tom Francis - SWSports
wrote:

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

Tin-foil hats don't work?
Oh wait, that's "different" waves.
I thought Maxwell Smart had this stuff figured out with the cone of
silence.

--Vic

Carry your compass
 

On Mon, 05 Jan 2009 17:01:19 -0500, Tom Francis - SWSports
wrote:

On Mon, 05 Jan 2009 18:04:26 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

Metal blocks all radio.

As a strict statement, that is true, however radio signals can bend
around objects (demonstrated by radar's ability to see behind
objects). As such a car presents the opportunity to receive signals
inside by virtue of the physics of radio wave propogation and the
ability to move along the surface of metal.

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

That is true enough, but you generally need to have a view of the sky
unblocked by solid metal. The closer to the glass, the more signal you
get. No problem in an open boat, or inside a fiberglass pilot house.
Now tell how me the cell phone worked inside a steel ship a thousand
miles from land. Magic, obviously. Nothing on the bill from either the
ship or the phoneco, so it must have been magic.

Casady