On Thu, Nov 21, 2013 at 12:52 PM, johncroos@aol.com wrote:

True north or magnetic north? In any case, a good lensatic compass and
knowing your magnetic variation should easily get you to within 2 degrees
and is a lot easier than doing a survey with your GPS.

--
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian@lloyd.com
+1.916.877.5067

Lord no, John. No red wagon is needed. Use a pole and the equation of
time, and a good watch or clock. At local noon, a shadow will be a n-s
line. If you don't have a decent clock, like your cellphone, put in a
pole at one end of your line. Near local noon, which depends on where
you are in the timezone, start sticking pegs in the end of the shadow of
the pole; the shortest shadow will be the n-s line. Accuracy much better
than 2 deg. I'm sure other ways will come to you :-)
Don

johncroos@aol.com

--
"The power of accurate observation is commonly called cynicism by those
who have not got it."
-George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com

For something that crude, I'd consider taking a sight on Polaris. If you
note the time and do the math, you can probably do better than your
bounds.

Also, there is almost certainly an app somewhere to do the math for you. I
think tha reeuction info was in Bowditch or the Nautical Almanac.

FWIW,

-John

===================

In message 8D0B5020292D91E-CC0-4B0E1@webmail-vm026.sysops.aol.com, johncroos@
aol.com writes:

First of all, at that level of precision you will have to decide what
you mean by "north south" ?

Magnetic ?  Geodetic ?  (if so: Which Datum ?)  Meridian ?

So your east-west precision needs to be tan(2)*300ft = 10.5 ft.

I don't think you can do that with a single band GPS.

If you can locate suitable landmarks, you may be able to do with
the arial photograph on maps.google.com (or similar servce) but
you need to get coordinates figured out (not trivial!)

I would raise a pole or other marker at one end (N or S), calculate
when a suitable celestial object crosses your designated line and
that to triangulate the opposite end.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

John: for local noon:
http://education.illinois.edu/noon-project/noontime.html

Don
johncroos@aol.com

--
"The power of accurate observation is commonly called cynicism by those
who have not got it."
-George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com

If you want true north, set up a camera that has time or bulb shutter at the south end of your property. Put in a marker stake. take a time exposure at night with the camera facing north. If you expose for about 30 minutes, you will get a landscape with the stars rotating around the north star. You can then mark the north location on your property under the north star.

A compass siting can give the mag north.

From: time-nuts-bounces@febo.com time-nuts-bounces@febo.com on behalf of Brian Lloyd brian@lloyd.com
Sent: Thursday, November 21, 2013 2:04 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Crude Survey Technique

On Thu, Nov 21, 2013 at 12:52 PM, johncroos@aol.com wrote:

True north or magnetic north? In any case, a good lensatic compass and
knowing your magnetic variation should easily get you to within 2 degrees
and is a lot easier than doing a survey with your GPS.

--
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian@lloyd.com
+1.916.877.5067

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

CONFIDENTIALITY NOTICE: The information contained in this electronic message is confidential information intended for the use of the individual or entity named above. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this electronic message to the intended recipient, you are hereby notified that any dissemination or copying of this communication is strictly prohibited. If this message contains non-public personal information about any consumer or customer of the sender or intended recipient, you are further prohibited under penalty of law from using or disclosing the information to any third party by provisions of the federal Gramm-Leach-Bliley Act. If you have received this electronic message in error, please immediately notify us by telephone and return or destroy the original message to assure that it is not read, copied, or distributed by others.

How do the car mounted GPS guidance devices find North?
Is it by deciding which direction you are moving on the map that they have stored?
It is amazing how quickly they show the orientation of the map/your direction of travel.
Do they have a sensor to register when you turn a corner?
What they do does not seem possible from just a series of position fixes.
cheers,
Neville Michie

On 22/11/2013, at 7:45 AM, TMiller@skylinenet.net wrote:

The simplest ones do it by difference in position from one fix to another. no need for a map for True North, just trig. For Magnetic North you need a map with variation data. More advanced units have magnetic sensors and accelerometers. An interesting question that I once spent some hours discussing in a pub (bar) about 20 years ago is how does an inertial navigation unit determine True North without the aircraft moving? No magnetic sensors, just a self contained black box. We know it did it because we had just finished installing one and watched it do it. We worked it out after a few pints ;-) Hint, it takes longer the closer to the pole you are. For Magnetic headings you still need a table of variations. At least one common aircraft inertial nav unit has magvar tables that are several years out of date with the OEM (well current IP owner, they bought out the real OEM) say it's not possible to update them!

Robert G8RPI.

From: Neville Michie namichie@gmail.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, 21 November 2013, 21:46
Subject: Re: [time-nuts] Crude Survey Technique

How do the car mounted GPS guidance devices find North?
Is it by deciding which direction you are moving on the map that they have stored?
It is amazing how quickly they show the orientation of the map/your direction of travel.
Do they have a sensor to register when you turn a corner?
What they do does not seem possible from just a series of position fixes.
cheers,
Neville Michie

On 22/11/2013, at 7:45 AM, TMiller@skylinenet.net wrote:

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi Neville:

Most low cost hand held and car GPS receivers can only display direction based on changes in position.
While on vacation in Japan I was using a hand held Garmin 12-channel GPS, but when standing still the compass did not
work, I needed to run a block to get a bearing.
My Honda van GPS includes a gyroscope so it know you have turned even in an urban canyon where there may not be enough
satellites visible to get a fix.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Neville Michie wrote:

The INS has to be 'aligned' before takeoff.

Remember, the earth is spinning on an axis, and the INS's platform is
stable in Inertial space.  If you know the INS is sitting on the ground
(or even deep in a mine shaft) it's just trig. Nothing external needed,
not even stars.

-John

====================

FWIW, my Garmin Nuvie 40 (el cheapo) only takes moving maybe 10' to get a
rough compass direction. I doubt it has any gyro or accelerometers.

-John

===============

On Thu, Nov 21, 2013 at 11:11 AM, Don Latham djl@montana.com wrote:

How accurate do you need to be?  The above requires a very tall pole
to case a 300 foot long shadow.  Then you have to be quick to measure
because the Earth turns at  .25 degrees per minute.

If you need a very tall pole that is 100% vertical then hang a
weighted rope from a tall support.  Then go to the other end and watch
the seconds tick down.

A GOOD magnetic compass can do this job too.  Easier then finding s
1,000 food tall pole.  The better compasses have some kind of optical
aid for sighting a line.

--

Chris Albertson
Redondo Beach, California

On Thu, Nov 21, 2013 at 12:45 PM,  TMiller@skylinenet.net wrote:

I vote this suggestion as the winner.  The north ster is offset a
little from the pole but if will make an arc like the others and you
can find it's center.  This method could get you to better than a
degree..

Chris Albertson
Redondo Beach, California

As I said before, the RA and Dec of Polaris is well known.

Spherical trig and the Siderial Time will give you the offset from the
true pole in Az and El.

With corrections for refraction, this is good to better than an arc-second.

-John

==============

On Thu, 21 Nov 2013 15:28:32 -0800, Chris Albertson wrote:

Be carefull!...  A plumb bob does not hang vertically (point to center of Earth).
Since the suspension point is undergoing accelerated motion the bob will be
deflected toword the equator.  This problem also applies to bubble levels, etc.
And there are other perturbations due to Sun, Moon, Jupiter, etc. which are not constant.
Which leads to the question:  How to make the pole vertical?

Newtons laws are NOT valid in a noninertial frame.  (That's why the Coriolis force
was invented.)

Thus the term "rocket science".

Bill Beam
NL7F

Coriolis ain't a force :-)
A real tall pole isn't required, just another person

Bill Beam

--
"The power of accurate observation is commonly called cynicism by those
who have not got it."
-George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com

Southward (toward equator) deflection would actually improve
the geometry.  All non-north vectors would
be lengthened in proportion.

On 11/21/2013 6:37 PM, Bill Beam wrote:

That's my point.  'Coriolis force' was invented to make it appear that Newtons laws
were valid in an Earth based frame.

On Thu, 21 Nov 2013 18:06:54 -0700, Don Latham wrote:

Bill Beam
NL7F

On 11/21/13 3:28 PM, Chris Albertson wrote:

The original request was for "accurate to a degree or two", so he has
4-8 minutes to make the measurement.

The sun is 1/2 degree wide, which is actually the practical challenge in
measuring using shadows, because the shadow is not sharp edged.

I don't know why you need a 300 foot long shadow.

Let's assume I have a 1 meter tall rod that is 1cm in diameter.
The sun isn't that high in the sky at noon these days (in the Northern
Hemisphere).. let's say it's about 45 degrees, so the 1 meter long stick
casts a shadow that is 1 meter long.  If the sun were a point source,
the shadow would be 1 cm wide, or 1 part in 1/100 which is about half a
degree.  That's comparable to the width of the sun, so you might want to
choose a "bigger stick".  maybe a 2" piece of pipe?  estimate the center
of the shadow, which could easily be done within 1/2".

You now have your north direction.

Solar noon is trivial to find out.  The USNO Astronomical Applications
page will give you a solar ephemeris for a specified lat/lon.  or
knowing your longitude and applying the equation of time, you can
calculate when solar noon is.

Or, whip out your current copy of the Nautical Almanac

Getting 1 degree accuracy with a magnetic compass is challenging.
Finding out the current magnetic variation is only part of the
challenge, because it varies (about 1 degree in 10 years in Southern
California, last I checked).

I'd also go for a compass if you want magnetic north, but then I have a good one, a "medium landing compass". Mine dates from WWII but they are still made http://www.sirs.co.uk/ground/landing_compasses/patt2/landing_resource
These are used to align the standbay and remote reading compasses on aircraft. Good to half a degree. If you need better ther is the Watts Datum Compass.
 
Robert G8RPI.

From: Chris Albertson albertson.chris@gmail.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, 21 November 2013, 23:28
Subject: Re: [time-nuts] Crude Survey Technique

On Thu, Nov 21, 2013 at 11:11 AM, Don Latham djl@montana.com wrote:

How accurate do you need to be?   The above requires a very tall pole
to case a 300 foot long shadow.  Then you have to be quick to measure
because the Earth turns at  .25 degrees per minute.

If you need a very tall pole that is 100% vertical then hang a
weighted rope from a tall support.  Then go to the other end and watch
the seconds tick down.

A GOOD magnetic compass can do this job too.  Easier then finding s
1,000 food tall pole.   The better compasses have some kind of optical
aid for sighting a line.

--

Chris Albertson
Redondo Beach, California

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

John,

We had a similar problem when we're trying to setup various antennas at
various locations pointing at different true North bearings. It turned out
quite hard to find true North.

We found single carrier GPS surveyed points to be inaccurate to produce
good bearings across such a short base line. Also, you'll end up with two
points with some bearing w.r.t. North. Now the problem is that of finding a
third point to give you your N-S base line.

In the end we used a tripod, calibrated gun sight and a turn table with
degrees markings (those that the photonics people use). If you'd like to
use this method, you survey a single point on your property (preferably on
the base line your interested in). Also survey a land mark, like a radio
mast a few km's away. The further away (the longer the base line) the less
accurate your surveyed points need to be. Now calculate the North
bearing of this base line using these two points. Now back at your property
at the surveyed point, point your cross hair at the radio mast and set the
number of degrees on the turn table to that you have calculated. Fix the
turn table. 0 degrees should now be true North, and you could now use the
cross hair to survey the other point.

The tripod should be levelled very carefully, since errors here will put
you in a different plane and you will end up calculating vector components
in that plane.

On 21 November 2013 20:52, johncroos@aol.com wrote:

On 11/21/13 11:32 PM, Robert Atkinson wrote:

That compass is precise to 1/2 degree, but not accurate to 1/2
degree. It comes with a calibration card, and is presumably used in a
place with a uniform field (e.g. for calibrating an aircraft compass,
which is done in an open area with no known magnetic anomalies).  If
you're in a different environment, the card values may be incorrect.

It is essentially as "comparison standard".  You put it next to the
aircraft and move both in a systematic pattern and you use it to
"calibrate out" the variations in the plane's internal compass.

However you're going to be subject to the local magnetic field anomalies
(and they're surprisingly large).

http://minerals.usgs.gov/news/newsletter/v1n2/3aeromag.html

On the 1km scale maps in the USGS reports, you can see magnetic
anomalies of 500 nT.  Earth's field is about 30-60 microTesla, so these
anomalies are in the "one part in 100" kind of range.  It is true that
the gradient is fairly small: It is unlikely you have an anomaly of 500
nT and your neighbor has -200 nT. But it's obvious that the magnetic
variation (angle between true and indicated magnetic north) isn't the
nice smooth surface implied by the map of variation you get with the
compass.

http://dspace.sunyconnect.suny.edu/bitstream/handle/1951/47859/Winslow_MS.pdf;jsessionid=7D7A116045A54816C9DCF963AF3D2580?sequence=1

is a short paper that talks about gradients in a small scale anomaly of
0.22 nT/meter  (and I get the impression that that is big).

There's also other locally produced magnetic fields you'd have to worry
about.

I gave an E&M class a problem to figure out if you could tell whether
you could use a hand compass to tell if the Pacific Intertie 1MV HVDC
link (3000 A) was operating bipolar or unipolar. (at 50 meters, the
field from one wire is about 6 microTesla, so yes, you can detect it)

http://msi.nga.mil/MSISiteContent/StaticFiles/HoMCA.pdf
is all about calibrating a ship's compass

Hi Jim,
I disagree, the Medium Landing Compass IS accurate to better than 30 minutes (0.5deg). This is also the smallest graduation so it can be read to better than 15 minutes. The calibration chart is given to 10 minutes every 15 degrees. It does of course indicate the orientation of the local magnetic field. To ensure there is no local distortions you need to do a site survey. This can be acheived by comparing bearings to a distant object along a baseline or taking reciprical bearings. CAA CAP562 part 8 leaflet 1 http://www.helitavia.com/docs/CAP562_2007_08.pdf 
has lots of good info.

(full version here http://www.caa.co.uk/docs/33/CAP562RFS.pdf  large file over 10MB)

Robert G8RPI (CEng, licenced aircraft engineer for 30 years, I've done many aircraft swings) 

From: Jim Lux jimlux@earthlink.net
To: time-nuts@febo.com
Sent: Friday, 22 November 2013, 14:25
Subject: Re: [time-nuts] Crude Survey Technique

On 11/21/13 11:32 PM, Robert Atkinson wrote:

That compass is precise to 1/2 degree, but not accurate to 1/2
degree. It comes with a calibration card, and is presumably used in a
place with a uniform field (e.g. for calibrating an aircraft compass,
which is done in an open area with no known magnetic anomalies).  If
you're in a different environment, the card values may be incorrect.

It is essentially as "comparison standard".  You put it next to the
aircraft and move both in a systematic pattern and you use it to
"calibrate out" the variations in the plane's internal compass.

However you're going to be subject to the local magnetic field anomalies
(and they're surprisingly large).

http://minerals.usgs.gov/news/newsletter/v1n2/3aeromag.html

On the 1km scale maps in the USGS reports, you can see magnetic
anomalies of 500 nT.  Earth's field is about 30-60 microTesla, so these
anomalies are in the "one part in 100" kind of range.  It is true that
the gradient is fairly small: It is unlikely you have an anomaly of 500
nT and your neighbor has -200 nT. But it's obvious that the magnetic
variation (angle between true and indicated magnetic north) isn't the
nice smooth surface implied by the map of variation you get with the
compass.

http://dspace.sunyconnect.suny.edu/bitstream/handle/1951/47859/Winslow_MS.pdf;jsessionid=7D7A116045A54816C9DCF963AF3D2580?sequence=1

is a short paper that talks about gradients in a small scale anomaly of
0.22 nT/meter  (and I get the impression that that is big).

There's also other locally produced magnetic fields you'd have to worry
about.

I gave an E&M class a problem to figure out if you could tell whether
you could use a hand compass to tell if the Pacific Intertie 1MV HVDC
link (3000 A) was operating bipolar or unipolar. (at 50 meters, the
field from one wire is about 6 microTesla, so yes, you can detect it)

http://msi.nga.mil/MSISiteContent/StaticFiles/HoMCA.pdf
is all about calibrating a ship's compass

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

John

In answer to your original questions,

No problem if you have a good setup including a good sky view, antenna, and
TBolt setup.
It is important to do each run at the different locations at the same time
of the day and average the results for as long as you can.
Best is to do a 24 Hr survey at each location.
see the attached LH plot for the effect of time on location reading error.

Multiple Tbolts on the same antenna don't help, unless they are on different
antennas.

ws

----- Original Message -----
From: johncroos@aol.com
To: time-nuts@febo.com
Sent: Thursday, November 21, 2013 10:52 AM
Subject: [time-nuts] Crude Survey Technique

The Thunderbolt uses single precision floating point and digital filtering for temperature so yes, you are going to see values like this. This is not unusual (precision clearly out of step with accuracy), like the HP network analyzers returning gain in dB with 4 decimals at microwave frequencies.
Not sure what your point is?
Should Lady Heather pretend to know better and muck with what's sent by the receiver?
I prefer not but it's a matter of opinion.

Didier KO4BB

David J Taylor david-taylor@blueyonder.co.uk wrote:

--
Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things.