Re: [time-nuts] GPS altitude somewhat wrong?

[Michael Perrett]

I just checked Google Earth and the elevation of your office is 5260', only
about 24' off of your GPS estimate if that is your location.
Michael

On Wed, Jun 8, 2016 at 1:33 PM, Van Horn, David <
david.vanh...@backcountryaccess.com> wrote:

>
> I have just installed a Thunderbolt here to get our time and frequency
> equipment all on the same page.
> As I was looking at the display on Lady Heather, I was noticing that the
> GPS altitude seems rather wrong.
> We are in Boulder CO, which is nominally 5430' and the antenna is about
> 20' off the ground.
> The display (near overdetermined position) reads 1589.72991 meters or 5216
> and change in feet.
> Altitude is a big deal around here. :)
>
> I suppose 214' isn't that outrageous, but it does bring me to a question:
>
> How accurate is the altitude number really?
>
> Thanks.
>
>
> --
> David VanHorn
> Lead Hardware Engineer
>
> Backcountry Access, Inc.
> 2820 Wilderness Pl, Unit H
> Boulder, CO  80301 USA
> phone: 303-417-1345 x110
> email: david.vanh...@backcountryaccess.com david.vanh...@backcountryaccess.com>
>
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Re: [time-nuts] GPS altitude somewhat wrong?

[Michael Perrett]

A couple of things come to mind:
1) Is this a single measurement or an average over at least 24 hours?
2) Did you get your elevation via the receiver survey mode (recommended)?
3) How close is your "nominal" elevation measurement and what makes you
think it is truth?
4) The vertical component of the GPS position solution is typically 50%
worse accuracy and a lot noisier than the horizontal measurement. If you
have a good horizontal measurement it is unlikely you have a "wrong answer"
on elevation since your receiver is using the same data, just solving the
equation for a different variable.
5) What is your satellite mask angle? The geometry (hence accuracy)
degrades as an increasing function with mask angle. Suggest for the survey
mode you use as low a mask angle as possible (typically 5 to 10 degrees).

Finally, your 214' error is outrageous. For a surveyed position the answer
should be with +/- 10'.

Michael Perrett

On Wed, Jun 8, 2016 at 1:33 PM, Van Horn, David <
david.vanh...@backcountryaccess.com> wrote:

>
> I have just installed a Thunderbolt here to get our time and frequency
> equipment all on the same page.
> As I was looking at the display on Lady Heather, I was noticing that the
> GPS altitude seems rather wrong.
> We are in Boulder CO, which is nominally 5430' and the antenna is about
> 20' off the ground.
> The display (near overdetermined position) reads 1589.72991 meters or 5216
> and change in feet.
> Altitude is a big deal around here. :)
>
> I suppose 214' isn't that outrageous, but it does bring me to a question:
>
> How accurate is the altitude number really?
>
> Thanks.
>
>
> --
> David VanHorn
> Lead Hardware Engineer
>
> Backcountry Access, Inc.
> 2820 Wilderness Pl, Unit H
> Boulder, CO  80301 USA
> phone: 303-417-1345 x110
> email: david.vanh...@backcountryaccess.com david.vanh...@backcountryaccess.com>
>
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Re: [time-nuts] GPS position

[Michael Perrett]

Since, I assume, you are most interested in time/frequency I recommend you
use the position that each device self determined. To verify the 10 Mhz
output it is easy to compare one against the other. If you don't have a
frequency meter with enough digits, just use a 'scope syncing on one and
see if the other trace is stable over time.

The other thing that comes to mind: were all GPSDOs taking the measurements
at the same time? If not, you should EXPECT different positions to be
reported (within the specifications of the receiver)

Michael/K7HIL
On May 2, 2016 4:03 AM, "Joseph Gray"  wrote:

> Now that I have three (maybe four) working GPSDO's, I'd like to set
> the GPS coordinates the same on all of them. The survey that each one
> does produces very similar coordinates, but not exactly the same.
>
> The Z3801A's have VP's, the Lucent has a UT+. I don't know what is in
> the 58540A, as the manual doesn't say and the :DIAG:IDEN:GPS? command
> isn't supported.
>
> Would using a modern GPS, like a uBlox, and averaging for quite a
> while produce acceptable coordinates to manually enter into all of the
> GPSDO's? Of course the uBlox would be on the same splitter and antenna
> as the other units during the averaging.
>
>
> Joe Gray
> W5JG
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[time-nuts] GPS Outage

[Michael Perrett]

I think the following might be relief to all the traffic regards "bad GPS"
ref  January 26th.
http://gpsworld.com/world-dodges-gps-bullet/

Michael / K7HIL
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Re: [time-nuts] Greetings from Australia

[Michael Perrett]

Alex, Brek - the Doppler effect is primarily an effect of the ionosphere
moving. A 24 hour measurement of WWV on 20 Mhz shows as much as +/- 800 mHz
movement, all due to Doppler. Note that if you run the measurement over
several days at the same time of year the measured frequency will strongly
correlate with time of day. This varies both with time of day and season
as the height of the ionosphere varies. To a much lesser effect most of us
nuts see a variation due to room temperature as this effects the frequency
reference of the measurement oscillator. This effect in my shack
(uncompensated) varies about +/- 1 mHz over a 20 degree (F) temperature
change.

73, Michael / K7HIL

On Mon, Jun 29, 2015 at 12:23 PM, Alex Pummer a...@pcscons.com wrote:

 Not exactly Brek, as long as the position of the two stations, which are
 in contact with each other, does not vary in the time, you don't have to
 worry about Doppler effect, also if you are trying to get in touch in SSB
 mode in the 13cm  band, you rather have a precise frequency reference and
 actually the other site should have too to find each other,
 and where the Doppler  would effect your communication a special
 combination of hardware-software could provide a compensation.
 73
 KJ6UHN
 Alex


 On 6/29/2015 9:33 AM, Brek Martin wrote:

 Hi Guys :)
 I thought I’d say thanks for the add to the group and introduce myself.

 I’m only starting to get compulsive about time and frequency.
 My findings so far are that only the timing of the next second matters
 because it’s too late
 to worry about the current second by the time you have the information
 about it.
 It’s +10 hours here so I have to add 10 to everything, and that could
 increment the date,
 so then a whole calendar program is required to know what the next date
 will be,
 just because you need to know what date it will be on the next seconds
 tick that occurs.

 I have a question…
 Is the reason most amateur radio people care about accurate frequency
 mostly about
 operating at higher radio frequencies?
 I imagine if a bunch of radio enthusiasts aligned their HF radios with
 atomic standards for use
 on those bands that doppler shift would ruin everything the additional
 hardware put into it.
 Cheers, Brek.




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Re: [time-nuts] No GPS satellites

[Michael Perrett]

Since your antennas have a lot of gain I assume they are active and require
a DC voltage to the LNA. Does the XL-DC provide that voltage (sometime you
have to select active or passive antenna)?
Michael / K7HIL

On Wed, Feb 25, 2015 at 12:35 PM, Doug Ronald d...@dougronald.com wrote:

 I'm hoping someone can shed some light on my problem receiving any GPS
 satellites.

 I have two TrueTime GPS Time  Frequency Receivers, Model XL-DC. One has a
 regular crystal oscillator, and the other one has a rubidium oscillator. I
 have two outdoor GPS antennas with internal LNAs, one a 28 dB gain unit,
 and the other a 40 dB unit. When either antenna is connected to my Lucent
 KS-24361, it locks right up and tracks up to 8 satellites. When either of
 the antennas is connected to the XL-DCs, they just sit there and status :
 Looking for GPS satellites.

 In the Alarm menu of either XL-DC there is an alarm for Antenna. Both
 units say OK and if I disconnect the antenna they both logically say
 Open. So, what is the problem? I can't believe I don't have enough
 signal, after the Lucent locks-up right away. Is it possible the TrueTime
 sanctioned antenna has a down converter in it, perhaps placing the GPS
 signal from L-band to some lower frequency? I would appreciate any info the
 group might have...

 -Doug Ronald
 W6DSR

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Re: [time-nuts] GPS-III

[Michael Perrett]

Chris,
I disagree only with your statement as a  GPS user you'd never know.

As stated in one of John's references:

The government is in the process of fielding three new signals designed for
civilian use: L2C, L5, and L1C. The legacy civil signal, called L1 C/A or
C/A at L1, will continue broadcasting in the future, for a total of four
civil GPS signals. Users must upgrade their equipment to benefit from the
new signals.


These new signals (will) provide many advantages as seen by the civilian
user, one of the most obvious is the ability to make real time IONO
corrections on civilian receivers (currently restricted to P Code
receivers). Also the new signal structures are more tolerant of both
intended and unintended interference.

Michael
Raytheon Senior Fellow (retired)
Navigation Systems





On Thu, Jul 24, 2014 at 9:32 AM, Chris Albertson albertson.ch...@gmail.com
wrote:

 GPS-III is the wrong term.   You mean block three spacecraft.
 The Air Force is buying 8 new satellites they are calling block III
 and they don't launch until at least 2016.  If the current satellites
 are in good health they could delay the launch.   If the past is a
 guide to the future the AirForce will eventually buy more advanced
 block III called IIIa or something.As a GPS users you'd never
 really know.  Those numbers are contracting terms, not signal terms.
 The signals in question are already being transmitted by a few of the
 latter block II satellites.

 I think you can buy multi-frequency receivers.  Remember GPS is not
 longer the only system.  There are stelites from the US, Europe,
 Russia, China and Japan.Adding more more frequencies allows the
 receiver to detect multi path and makes it harder to jam but the
 timing is not greatly improved over say the M12.

 On Thu, Jul 24, 2014 at 12:14 AM, John C. Westmoreland, P.E.
 j...@westmorelandengineering.com wrote:
  Hello All,
 
  Does anyone know yet of any companies that are making GPS-III receiver
  chip-sets/modules yet?
 
  Some web-sites on GPS-III:
 
  http://www.gps.gov/systems/gps/modernization/
  http://www.gps.gov/systems/gps/modernization/civilsignals/
  http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=18830
 
  Regards,
  John W.
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 --

 Chris Albertson
 Redondo Beach, California
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Re: [time-nuts] GPS antenna length correction

[Michael Perrett]

The ability to correct the position depends on the receiver. Some receivers
have a correction known as the lever arm correction. This is the vector
difference between the antenna centroid and there is also a variable to
enter the cable length. Between these two corrections the receiver time and
position is the same as that at the antenna centroid.

These corrections are normally found on kinematic and military receivers
but may be on any - check the specs / owners manuals.

Michael / K7HIL


On Mon, Apr 28, 2014 at 8:20 AM, Hal Murray hmur...@megapathdsl.net wrote:


 br...@lloyd.com said:
  As I think about the geometry of satellite position and path length, it
  seems to me that, since the geometry is determined by the antenna
 position
  and not the receiver position, additional antenna cable introduces a
 fixed
  delay value and hence a fixed constant that gets added to each path
  regardless of direction. It seems to me that this would produce a much
  fuzzier solution to position and/or variation in timing. Knowing cable
  length and propagation velocity, would allow the software to subtract
 that
  constant from all ranges and thus provide a more correct position and
 time
  solution. Is this not the case? Does it do something simpler but good
  enough?

 If you just do the normal calculations, you get the location of the antenna
 as though you were there a while ago.  If you know the delay in the cable,
 you can correct the time.  There is no way to correct the position.


 --
 These are my opinions.  I hate spam.



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Re: [time-nuts] GPS antenna length correction

[Michael Perrett]

As one responsible for the architecture and design of many military vehicle
GPS based navigation systems I will un-simplify my previous email. The
GPS solution (position or Doppler) is always made at the center of the GPS
antenna; that's where the lines of intersection (3D) from the individual
satellites occur (tri-lateration). You can account for the position
difference between the antenna and the receiver, vehicle center of mass or
another sensor (such as an inertial measurement system, velocimeter,
gravitometer etc.) by application of the lever arm vector. This co-locates
the GPS position with that device. This has the *function* of making the
sensor position and the GPS position both act as if they were at the IMU
location.

An example of this is if you have the GPS antenna located on a ships mast,
and the IMU (whose position defines ships position) located on the bridge,
in order for the navigation Kalman Filter to properly compute the ships
location the lever arm correction must be applied. In this case the antenna
can be several tens, or even hundreds, of meters from the IMU. This needs
to be a vector as can been seen when the ship roles to one side or another.

A second, uncorrelated, correction is for the time (delay) that the RF
signal travels along the transmission line (C x Vf  x L). If that's needed
you can compute the delay, hence phase shifts.

Hopefully this helps,

Michael / K7HIL



On Mon, Apr 28, 2014 at 5:00 PM, Chris Albertson
albertson.ch...@gmail.comwrote:

 On Mon, Apr 28, 2014 at 3:53 PM, Bill Beam wb...@gci.net wrote:
 
  As mentioned earlier the position of the receiver is indeterminate unless
  the vector displacement from the antenna to the receiver is accounted
 for.
  Accounting for the cable delay will only correct the absolute time.
  Imagine a 100m antenna feed line; the receiver could be anywhere within
  100m of the antenna (even above it or at it).  The algorithm that
 computes
  position
  needs to know this.
 

 Yes, of course.  The GPS receiver reports the location of the antenna.  If
 you need to know some other location you have to apply some (x,y,z) offset
 from the antenna.   Actually I doubt anyone would care about the location
 of the receiver.   They might want to know the location of the vehicle's
 center of mass or the location of some display screen.The cable delay
 accounts only for the offset in time.

 Time and location really are different things, especially because a cable
 can take a non-straightline path or even be coiled up.


 --

 Chris Albertson
 Redondo Beach, California
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Re: [time-nuts] new GPSDO kit

[Michael Perrett]

If you are going to plug the unit re time nuts, how about a price break for
said group?
Michael


On Fri, Apr 4, 2014 at 3:39 PM, saidj...@aol.com wrote:

 Hello everyone,

 sorry for the plug, but we just announced a new $568 complete GPSDO
 reference kit.

 This unit is a tiny desktop unit with 10m antenna, power supply, cables,
 CD, and other accessories. It is a low cost addition to our Fury GPSDO
  line,
 and contains a really good TCXO, a uBlox GPS receiver, and various power
 options. I believe this is the lowest-cost real GPSDO in mass production
 available on the market right now, and being a true GPSDO it has  some
 fairly
 good phase noise and stability specs.

 http://www.jackson-labs.com/assets/uploads/main/LC-XO-Plus_PressRelease.pdf

 bye,
 Said
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Re: [time-nuts] NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock

[Michael Perrett]

Wow, if 1 second in 300 million years is correct, that's around 1 E-16th.
M


On Thu, Apr 3, 2014 at 2:51 PM, Edesio Costa e Silva 
time-n...@tardis.net.br wrote:

 Full story at
 http://www.nist.gov/pml/div688/nist-f2-atomic-clock-040314.cfm

 Edésio
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Re: [time-nuts] Looking for WWVB digital wall clock with digital 24 hour UTC display

[Michael Perrett]

I recently bought a La Crosse, See at ebay item 360752857574, that quickly
synced up to WWVB and, at least to my ability to mark a time tick, been
within the second of WWV. Total cost was $43.
Michael / K7HIL


On Wed, Feb 19, 2014 at 4:52 PM, Richard (Rick) Karlquist 
rich...@karlquist.com wrote:

 Can anyone recommend a atomic wall clock
 that displays in digital 24 hour UTC?  Looking for largest
 possible digits and LED preferred over LCD, under $100.
 Any brands to avoid?

 Rick
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Re: [time-nuts] New Acquisition: HP-53132A

[Michael Perrett]

According to the manual (in several places):

*It is normal operation for the fan in the Counter to continue to run after
the Counter is*
*placed in Standby mode. Power to the timebase is continuous to maintain
long term*
*measurement reliability, and the fan helps maintain timebase temperature
stability.*

 perhaps a in-line AC switch?

Michael


On Sat, Feb 1, 2014 at 8:50 PM, stan, W1LE stanw...@verizon.net wrote:

 Hello The Net,

 I just got in the counter and the fan is always ON, even with the front
 panel switch OFF.

 I looked in the manual but could not find anyway to change this.
 The counter has the standard internal 10 MHz reference, but I will be
 using a Trimble T'bolt GPS/DO for the external reference.

 The fan is part of the power supply module. I can see a possible need for
 it if a premium ovenized reference is always ON.
 But I do not have the premium internal reference.

 Is there a way to only allow the fan to be ON, if the front panel switch
 is ON ?  Possibly a jumper setting ?

 Are there any key strokes to determine the software version, other than a
 check sum ?
 I do not have the standard HP serial number, with the vintage
 (manufacturing date code) code first.
 The unit was manufactured in Korea.

 Stan, W1LE on Cape Cod




 z
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Re: [time-nuts] L1/L2 GPS Receiver

[Michael Perrett]

Magnus, I believe that he is referencing the the new L2 C/A code, which is
not protected. Reference
http://www.gps.gov/systems/gps/modernization/civilsignals/

Michael / K7HIL


On Thu, Jan 16, 2014 at 2:04 PM, Magnus Danielson 
mag...@rubidium.dyndns.org wrote:

 On 16/01/14 20:29, Hal Murray wrote:


 anders.e.e.wal...@gmail.com said:

 The real benefit of dual-frequency is you can do post-processing with
 PPP.
 Javad has some modules but they start at 3 kUSD - if anyone knows of
 hobby
 level priced L1/L2 receivers that can produce rinex-files for PPP
 processing
 that would be interesting!


 Has anybody considered doing it in software?

 If I wanted to play with that sort of stuff, is there any particular SDR
 hardware package/project that would good to start with?


 You want P(Y) capable receivers, which means 20,46 MHz bandwidth on both
 L1 and L2 bands. You want say 12 channels. Lots of raw sample data to
 crunch on in real time. I'd say that you would really like to mimic the
 traditional style of doing the mechanical stuff in HW/FPGA and then do the
 remainder in some suitable processor.

 Going from C/A to P(Y) is a bit challangeing on it's own, as you where not
 supposed to be able to do that, only to get the P code.

 Cheers,
 Magnus

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Re: [time-nuts] L1/L2 GPS Receiver

[Michael Perrett]

According to *GPS World*;
The U.S. Air Force is directing transmission of continuous CNAV
message-populated L2C and L5 signals starting in April 2014. . This is
almost always optimistic, I would guess availability within 2014 a very
high probability.

Michael / K7HIL
Ref: http://gpsworld.com/tag/l2c/




On Fri, Jan 17, 2014 at 10:11 AM, Jim Lux jim...@earthlink.net wrote:

 On 1/17/14 8:43 AM, Michael Perrett wrote:

 Magnus, I believe that he is referencing the the new L2 C/A code, which is
 not protected. Reference
 http://www.gps.gov/systems/gps/modernization/civilsignals/


 Is the L2c officially on yet?  and how many S/V are radiating it? I know
 there was some testing last summer for L2c but I don't recall the details.


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Re: [time-nuts] WAAS.....

[Michael Perrett]

It is the receiver, not the satellites, that are WASS enabled.
The WASS differentials are used to correct the ionosphere path lengths.
Michael K7HIL- Sent from my Samsung S4
On Jan 7, 2014 6:07 PM, Bob Camp li...@rtty.us wrote:

 Hi

 The WAAS sat’s are (in general) going to be long path sat’s. That will
 give you more trouble with the ionosphere.

 Are the locations of the receivers well surveyed already?

 Bob

 On Jan 7, 2014, at 8:25 PM, Brian, WA1ZMS wa1...@att.net wrote:

  Hypothetical question
  For a given set of GPS timing grade receivers at multiple locations, is
 there any advantage by limiting allowable SVN numbers to only be the WAAS
 satellites?
 
  -Brian, WA1ZMS/4
  iPhone
 
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Re: [time-nuts] GPS Spoofing

[Michael Perrett]

I have seen a lot of differing opinions on GPS Spoofing and using back up
systems on this thread. Most pretty good, but a couple off the mark a bit.

Here are a couple of comments on GPS Spoofing.

   - There are anti-spoofing GPS receivers available - to authorized
   users. Typically DOD. Most, if not all, military receivers utilize the
   encrypted P-Code, while civilians must use the more vulnerable clear text
   C/A code. The P-Code signals are very difficult to spoof unless you have
   a-pirori knowledge. The newer satellites (GPS III) will have an even more
   robust AS methodology.
  - Note: beware of P-Code, or Military, receivers available on eBay.
  They are useless without the encryption keys distributed by the US
  Government.
  - In the (near?) future there will be four civilian GPS Signals: The
   government is in the process of fielding three new signals designed for
   civilian use: L2C, L5, and L1C. The legacy civil signal, called L1 C/A or
   C/A at L1, will continue broadcasting in the future, for a total of four
   civil GPS signals. Users must upgrade their equipment to benefit from the
   new signals. ref
   http://www.gps.gov/systems/gps/modernization/civilsignals/
   - Receivers utilizing the new civilian GPS frequencies can solve the GPS
   equations from more than one frequency and see if any one signal is being
   spoofed. The new civilian frequencies will be more spoof resistant.

Comments on using inertial measurement units (IMUs) to back up GPS.

   - Current IMUs with even a good drift rate of say, 1 degree per hour,
   available for around a few thousand dollars, will be off 60 nautical miles
   after an hour of uncorrected operation. That can be reduced by other sensor
   inputs (GPS, LORAN, pit-log or what ever you have), but the navigation
   solution will eventually degrade to the accuracy of the external sensor. If
   my memory serves me for a really deep pocket navigator (having tens to
   hundreds of thousands of dollars, and a large amount of available mounting
   space) IMUs with drift rates of up to a thousand times less can be
   purchased (that's ,001 miles per hour, or around a couple of meters per
   hour), think submarines, etc.

Using a dual sensor navigation system (or timing system! ), such as
GPS/eLORAN, would obviously make the system so much more robust.

Michael / K7HIL

On Sat, Jul 27, 2013 at 6:43 AM, Scott McGrath scmcgr...@gmail.com wrote:

 Key here is how does the captain know that GPS is no longer providing an
 accurate fix?   You need 2 or more independent systems to cross check each
 other.

 Sent from my iPhone

 On Jul 27, 2013, at 12:21 AM, Jim Lux jim...@earthlink.net wrote:

  On 7/26/13 8:45 PM, J. Forster wrote:
  I gather from the article, the GPS position was spoofed and the
 autopilot,
  in bringing it back to where it was supposed to be, actually took it off
  course.
 
  There are places where a few hundred feet makes a big difference, viz.
 the
  Costa Concordia.
 
  IMO, this is a very convincing reason for something like LORAN.
 
  I think it's a convincing argument for a captain who pays attention to
 the other navigation instruments and doesn't blindly follow the GPS.
 
  It's also a convincing argument that shipboard
 automation/autopilot/autocontrol vendors need to make more sophisticated
 software (which I suspect they do, particularly on 200+ foot ships.. I
 would imagine that there are some aspects of this demo that are contrived.)
  The ship making and driving business is pretty unregulated. It's all about
 what the owner of the ship is willing to pay (or what he needs to get
 liability insurance, if he wants).  There's nothing even remotely like
 DO-178 for shipboard stuff.
 
  The folks doing stabilized oil rigs probably have sophisticated systems,
 but they're also using IMUs and other stuff. Ditto for high value things
 (oil tankers, warships).  Molasses tankers? They're probably lucky to have
 a functioning compass and some old charts.
 
 
  I'm not sure, though, that looking at the big picture, whether your tax
 dollars are better spent on LORAN, or on some other precision navigation
 method or on making jam resistant GPS receivers (which do, in fact exist,
 and make use of things like direction of arrival of the signal..)
 
  Note that a GPS system with 3 antennas (as is common in systems that use
 GPS to derive attitude/orientation) would be extremely difficult to spoof,
 and would be VERY inexpensive to implement.  Either the carrier phases and
 code phases are consistent for all the received signals or they're not.  A
 jamming signal coming from the wrong direction will not have the right
 direction of arrival relative to the platform orientation.  One wrong
 signal might be tolerable (multipath, etc.) but with a multi satellite fix,
 I suspect it would be hard to do it.
 
  Sure, one could throw up N pseudolites on a bunch of UAVs, etc., but
 that's getting to be a bit noticeable.
 
 
  For 

Re: [time-nuts] Relationship between fixes and time duration?

[Michael Perrett]

There are multiple variables that effect the minimum number of fixes that
will yield a particular position accuracy (and hence a time accuracy when
using that position as truth).

(1) The ability of the antenna to see the entire sky. If a mountain, tall
building or tree is between you and a satellite that signal may be lost. In
this case your position fix will be degraded due to poor trilateralization
geometry.

(2) If you are in a place where you get a bounced GPS satellite signal
then multipath occurs and will degrade that satellites signal and because
it is a bounce the signal path will be longer, resulting in an increase in
time for the signal to reach the receiver. This results in a time error and
is usually the predominate error when it occurs.

Although repetitive, the resultant geometry changes with time of day. There
are 'good' times and 'bad' times. So if you take a one hour fix (3600
points) then it is the luck of the draw whether you get a good position
fix. There are programs on the net which provide plots of HDOP versus time
(or GDOP, TDOP, PDOP etc). One such product is available from ARINC, Inc.
at http://www.arinc.com/gps/gpsapps/sem.html.

My recommendation is to do the longest survey you can, with a 48 hour goal,
in the end there is no downside

Michael / K7HIL


On Sun, May 5, 2013 at 11:18 AM, Magnus Danielson 
mag...@rubidium.dyndns.org wrote:

 On 05/05/2013 04:15 PM, James Robbins wrote:

 What is the relationship between the T'Bolt survey fixes number (e.g.
 2000) and number of hours duration of the survey?  Is it one fix per
 second or something?  What number of fixes should be input to accomplish a
 24 hour or a 48 hour survey?


 If there is too few sats to get a fix, then it waits until it has
 sufficients sats for the next fix. So, rather than a fixed time, you get a
 fixed number of fixes, and the reception situation will decide how long
 time it takes to get the same minimum quality fix.

 Cheers,
 Magnus
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Re: [time-nuts] Introducing myself

[Michael Perrett]

Welcome aboard.

Michel / K7HIL

On Sun, Dec 2, 2012 at 1:06 PM, Erich Heine sophac...@gmail.com wrote:

 Hi everyone.

 I just wanted to introduce myself to the list. My name is Erich Heine, I'm
 a researcher at the University of Illinois. I am a programmer attached to a
 couple of projects, but the one relevant here is called TCIP (Trustworthy
 Cyber-Infrastructure for the Power Grid - url: tcipg.org).

 Our group does computer security research relevant the the US power grid
 infrastructure (and when relevant to all power delivery :) ). Recently
 we've had researchers looking at GPS spoofing, and are beginning to examine
 secure time synchronization more broadly. It's fascinating to discover just
 how much havoc can be caused by assuming the time signal is good enough
 when it may not be. (This seems to be the way of computer security - assume
 something is good or good enough, then someone comes along an breaks
 everything because the assumption was bad. Then everyone scrambles to get
 better solutions, and other areas become assumed good enough. Repeat
 ad-nauseam).

 I was pointed here by Magnus a month or two ago, after a fascinating
 discussion of just how deep this time and timing rabbit-hole goes. I'm
 quite impressed with this community - both in terms of deep knowledge and
 overall friendliness. It's been a pleasure just lurking and soaking up some
 knowledge since then.

 Anyway, I just wanted to say Hi all before I start posting questions,
 comments, etc. :)

 Regards,
 Erich
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Re: [time-nuts] How to start a new topic

[Michael Perrett]

*UNLESS *the subject changes. I get so sick of the title having nothing to
do with the message. Sometimes a thread will completely change and have 20
or more answers. Personally I would prefer a new thread if the subject
changes.

IMHO,
Michael / K7HIL

On Fri, Nov 2, 2012 at 7:20 AM, David C. Partridge 
david.partri...@perdrix.co.uk wrote:

 Yes, you send a mail with a new subject. Please don't CHANGE the subject
 of a thread or topic, as that doesn't actually start a new topic.

 I also suggest that you send email to the reflector as Plain Text.

 HtH,
 David Partridge
 -Original Message-
 From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
 Behalf Of Volker Esper
 Sent: 02 November 2012 13:46
 To: Discussion of precise time and frequency measurement
 Subject: [time-nuts] How to start a new topic

 Fellow time-nuts,

 I am new in this mailing list and a little bit unfamiliar with it, so I
 hope I'm not doing something stupid.

 How do I start a new topic? Simply send a mail with a new subject?

 Thanks a lot

 Volker



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Re: [time-nuts] GPS Jammer

[Michael Perrett]

John,
Coherent reproduction of the spread PRN standard positioning signal (SPS)
signal gives ~30dB of A/J protection, the GPS signal level, as received at
the GPS receiver is on the order of -160 dBW (L1-CA). If the jammer outputs
half a Watt, and is anywhere nearby, the receiver will not maintain lock on
the civilian code as the jammer would overwhelm the receiver front end. A
commercial GPS receiver has a maximum of 20 dB power bandwidth. If the
jammer is present prior to initial acquisition then the receiver would
certainly never acquire lock.

My experience is that the civil signal (SPS) is very easy to jam, where the
precise positioning signal (PPS), using the P(Y) code adds significantly
more protection.

All values are round numbers and the individual receivers signal strategy
can make some difference, as well as GPS aiding (especially a good clock,
known position, velocity and so forth).

Michael, K7HIL

On Tue, Oct 2, 2012 at 7:33 PM, johncr...@aol.com wrote:

 In considering the effect of a simple jammer on a GPS receiver, a simple
 link analysis
 is insufficient.

 What must also be considered is the anti-jam capability of the receiver
 which due to spread spectrum processing gain will reject any simple
 jamming signal even though is it 10's of dB stronger than the desired
 signal.

 73 -john k6iql


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Re: [time-nuts] GPSDO Component Selection

[Michael Perrett]

First - I realize 95% of the folks reading this are well aware of what I am
going to say.

No matter how good your equipment (receiver/antenna) is, the short term
accuracy of GPS time is defined in *GLOBAL POSITIONING SYSTEM STANDARD
POSITIONING SERVICE PERFORMANCE STANDARD (2008)*. This document can be
found at http://www.gps.gov/technical/ps/#spsps.

The guaranteed timing accuracy (short term) is found in Table 3.8-3. SPS
Position/Time Accuracy Standards. The time domain transfer accuracy is
defined as ≤ 40 nsec time transfer error 95% of time
(SIS only). In order to achieve this the (SIS only) comment means you
have a perfect receiver that introduces no errors (good luck with that
one). Most commercial users set their probability at around 30 nS, and
experience virtually no estimates out of that boundary.

The 30 nS error can be reduced to a better number if position is accurately
known and the receiver knows that it is stationary - but still 5% of the
time you can get noisy / degraded time and still be in spec.. I am not
sure over what time span the 95% number is used.

Now: The real answer is to take the relatively noisy GPS timing information
and use it to discipline a device that is (extremely) stable over a short
time such as a OCXO or Rubidium standard. The integration period determines
how much of the very accurate long term GPS information with the short
term, highly stable, clock information. Hence a GPSDO.

Michael / K7HIL



On Sun, Sep 9, 2012 at 3:10 PM, Jerry jster...@att.net wrote:

 Sounds like the Heisenberg Uncertainty principle at work :-)

 jerry

 -Original Message-
 From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
 Behalf Of Bob Camp
 Sent: Sunday, September 09, 2012 5:53 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] GPSDO Component Selection

 Hi

 Position accuracy and timing accuracy are two very different things.
 Firmware is optimized to improve either one. Position firmware is often
 pretty poor for timing.

 Bob

 On Sep 9, 2012, at 5:05 PM, Chris Albertson albertson.ch...@gmail.com
 wrote:

  On Sun, Sep 9, 2012 at 1:14 PM,  b...@lysator.liu.se wrote:
 
  True for a cheap oem navigation receiver. Not true for a geodetic
  quality receiver, who usually have some options (external frequency
  input, PPS_in) to make them the best timing receivers available.
  However they are much more expensive than the typical single frequency
 timing reciver.
 
  I looked at every link and can't see where they give a timing accuracy
  spec on the PPS with respect to UTC.   Possition accurracy is very
  good and we might assume the timing is as good.  But they don't say it
  is.  What's interesting is these GPSes will accept an accurate clock
  input in order to give better location data.   That is the opposite of
  a timing GPS where you tell it accurate location data so that it can
  get better timing.   Cutting down the unknown in one lets you do
  better in the other.   I assume these all cost well over $50.  You can
  get a pretty good timing GPS for $30 and it WILL have the PPS error
  specified.
 
  To the OP.  None of this matters a lot because PPS is a standard input
  signal.  It is easy to swap out a GPS receiver later.  Same with the
  OCXO.  From a control point of view they are all pretty much the same.
  You can swap them out later
 
 
  Chris Albertson
  Redondo Beach, California
 
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Re: [time-nuts] Is this a cesium frequency standard?

[Michael Perrett]

I have found Google translate does a pretty good job on translating manuals
- and it is free
Michael

On Thu, Aug 23, 2012 at 6:40 AM, Richard Parrish calc...@swbell.net wrote:

 The seller of the 'Russian' equipment said that the CCHB-74 frequency
 standard is a rubidium unit.  Manual is in Russian but he can translate
 part
 of the manual into English for an additional fee.

 Thanks,
 Richard Parrish
 Cal Center Inc
 1622 Griffith Ave
 Terrell, Texas 75160-4905
 calc...@swbell.net
 214-577-3515

 -Original Message-
 From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
 Behalf Of David Kirkby
 Sent: Thursday, August 23, 2012 3:18 AM
 To: Discussion of precise time and frequency measurement
 Subject: [time-nuts] Is this a cesium frequency standard?

 There's a seller on ebay by the name of
 electro-radio-device-high-precision, which have some odd things.
 Some seem as if they would be 19th century items, but are sold as new.


 http://stores.ebay.co.uk/electro-radio-device-high-precision?_trksid=p4340.l
 2563

 I suspect his stuff was desgned for the Russian military. Everything he
 sells is described as

 analog of Lutron, Advantest, Avtech, HP Agilent, NoiseCom, General Radio,
 Boonton, Anritsu, Fluke and general Electric, but  has the same or better
 characteristics.

 I thought this one was interesting though


 http://www.ebay.co.uk/itm/5MHz-1MHz-100kHz-Frequency-standard-CCHB-74-an-g-A
 gilent-HP-/330758945645?pt=LH_DefaultDomain_0hash=item4d02c4fb6d

 It has lots of knobs to twiddle, so it might be a cesium, though the specs
 don't seem good enough for a cesium, with a relativa e error of
 +/- 2 x 10^-11 at shipping. That seems more like a rubidium spec.

 He has some bizzare stuff, like a power meter which works to 53 GHz, but
 has
 banana plugs on it. I guess the sensor is connected to the banana plugs,
 though he does not mention it needing an external sensor.


 http://www.ebay.co.uk/itm/0-03GHz-53GHz-1mkWatt-10mWatt-Power-meter-M3-22-an

 -g-Agilent-HP-Marconi-GenRad-/230821610924?pt=LH_DefaultDomain_0hash=item35
 be0a45ac

 Some of his stuff seems very over priced, like a 400-1200 MHz sig gen with
 an error of 1% for $1580, but other things seem quite reasonable.
 If you need a sig gen at 70 GHz, he has them.

 Anyway, its worth checking out his auctions, as he has some test equipment
 which is very different from what one normally sees - and it some cases to
 what one would want to see!

 Dave

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Re: [time-nuts] question about Thunderbolt geo acuracy

[Michael Perrett]

Not for survey type accuracy (sub-meter, short measurement time).

The average (over a 48 hour period) was pretty good (about 1.5 meters,
RMS), but the reading over any 1 minute period can be off as much as 3-5
meters, satellite geometry dependent.

I Have two units with good antennas, mounted roughly 40 meters apart, and
after locating one of the antennas I use the second TBolt in a differential
mode and get the 1-2 meter accuracy all the time.

Michael / K7HIL

On Thu, May 10, 2012 at 5:50 AM, swingbyte swingb...@exemail.com.au wrote:

 Hi all,
 Hope this isn't too chat roomy, however, I have need of a survey precise
 geolocation type gps.  I was wondering if the precise timing abilities
 extend to its precision in position output?  I have a thunderbolt and one
 of those conical white aerials from china and would like to know if this
 combination will give me accurate height data.

 Thanks

 Tim

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Re: [time-nuts] Loran transmitters back on the air

[Michael Perrett]

Loran C absolute accuracy is between 0.1 and 0.25 miles (
http://msi.nga.mil/MSISiteContent/StaticFiles/NAV_PUBS/APN/Chapt-12.pdf)
but the repeatability is way better (from 60 to 300 feet, same ref).

When it was safe and fun to fly to Baja, Mexico I would record both ends of
the runway with my Northstar Loran C. The absolute accuracy was miles off
(geometry was horrible, way out of the coverage area), but once marked, I
could return to the same spot every time. I kept a complete table of the
Baja and west coast of the mainland permanently in my flight bag.

Michael / K7HIL

On Fri, Mar 2, 2012 at 10:15 AM, Mike Naruta AA8K a...@comcast.net wrote:


 In 1983 we were testing Loran for a vehicle
 tracking application.  We had a van with a
 Loran aviation antenna mounted on the roof
 and a relatively inexpensive marine Loran
 receiver.

 We started with an informal test.  This was
 miles inland, about an hour's drive North
 of Detroit, Michigan.

 We parked on the shoulder of the road, beside
 a wooden post.  I wrote down the latitude and
 longitude.  My supervisor then drove the van
 a mile away.  Then I looked at the Loran
 readout while he drove the same road.  I only
 looked at the display, while giving him verbal
 instructions to slow down, slow down more, and
 finally I said, Stop!

 Dick said, You're not going to believe this.
 I looked up and right outside my window was
 the same post!


 On 03/01/2012 11:26 PM, Hal Murray wrote:


 What sort of accuracy can I expect from a Loran type system?


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Re: [time-nuts] OT: GPS satellite spectrum displayed...

[Michael Perrett]

At least that is how the graphic is labeled :).

Per Enge (Author/Contributor of many GPS text books) has some good cartoons
on the current and future GPS Spectrum, and one power spectrum display, on:
http://www.navcanada.ca/ContentDefinitionFiles/IFIS/powerpoint/Session_2/GPS_Modernization_Enge.pdf

Michael

On Thu, Dec 22, 2011 at 12:54 PM, Rob Kimberley robkimber...@btinternet.com
 wrote:

 David,

 Surely the signals displayed in the link below are those of the Galileo
 satellites and not GPS.

 Rob Kimberley

 -Original Message-
 From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
 Behalf Of David J Taylor
 Sent: 22 December 2011 18:56
 To: Time-nuts mailing list
 Subject: [time-nuts] OT: GPS satellite spectrum displayed...

 For those who wondered what the spectrum transmitted by a GPS satellite
 looked like, see:

  http://www.esa.int/SPECIALS/Galileo_IOV/SEM60KBX9WG_0.html

 Cheers,
 David
 --
 SatSignal software - quality software written to your requirements
 Web:  http://www.satsignal.eu
 Email:  david-tay...@blueyonder.co.uk


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Re: [time-nuts] Raven Industries GPS in-line L1 Amplifier

[Michael Perrett]

Just be careful on overloading the front end of a GPS receiver. A typical
(what ever that is anymore) GPS receiver has about a maximum of a 15 dB
power bandwidth. If overloading occurs (minor), it might swamp the strong
signals. If you already have an active antenna the extra 12 dB of the
in-line amp may effectively jam all the signals. That said, thanks for
the heads up and I believe I'll get one just to try :).

Michael / K7HIL

On Sun, Nov 6, 2011 at 11:01 PM, k6...@comcast.net wrote:

 eBay auction for Raven Industries in-line GPS L1 amplifier

 Item number 370437343397

 $25 plus shipping

 Raven Industries Inline GPS Amplifier
 Model LA-12-1575-100N


 http://www.navtechgps.com/Downloads/LA-12-L1L2.pdf

 Female N Connectors on each end




 I've ordered one; he's got around ten remaining.




 73,




 Bob K6RTM



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Re: [time-nuts] Averaging Location for Position Hold

[Michael Perrett]

When GPS was first developed (Late 70's) the DATUM used was the World
Geodetic System, 1972 (WGS-72).  The next release was indeed in 1984
(WGS-84). The early GPS receivers had over 200 datums stored in permanent
memory. In its most basic form a datum defines the center of the earth and
the equation of the earths ellipsoid.

From Wikipedia:

A *geodetic datum* (plural *datums*, not *data*) is a reference from which
measurements are made. In surveying http://en.wikipedia.org/wiki/Surveyingand
geodesy http://en.wikipedia.org/wiki/Geodesy, a *datum* is a set of
reference points on the Earth's surface against which position measurements
are made, and (often) an associated model of the shape of the earth (reference
ellipsoid http://en.wikipedia.org/wiki/Reference_ellipsoid) to
define a geographic
coordinate systemhttp://en.wikipedia.org/wiki/Geographic_coordinate_system
.


The user, mostly military or marine, would choose the datum he/she wanted to
use. This would match up the local map with the GPS derived position. The
difference could be quite large (hundreds of feet), especially important in
the Z (vertical) direction!

Michael / K7HIL

On Tue, Sep 13, 2011 at 2:23 PM, jmfranke jmfra...@cox.net wrote:

 I believe that should read WGS 84 not WPS84.

 John  WA4WDL

 --**
 From: Chris Albertson albertson.ch...@gmail.com
 Sent: Tuesday, September 13, 2011 5:03 PM
 To: Discussion of precise time and frequency measurement 
 time-nuts@febo.com
 Subject: Re: [time-nuts] Averaging Location for Position Hold

  2011/9/13 Miguel Gonçalves m...@miguelgoncalves.com:

 Hi all!

 I am installing a timing GPS unit over a new location where I already
 have a
 NMEA GPS with PPS (let's call it unit A). The NMEA GPS is logging every
 16
 seconds its GPGGA string.


 The Oncore UT+ can does it's own site survey automatically.  That's
 the best way.

 You can only compare the GPS location with Google if both are using
 the same system.  The most common one today is WPS84 but you need to
 check.

 The problem is that the Earth is not a Sphere and different systems
 assume non-sphere shapes.  Getting this wrongs gives about the size
 error you observed, more or less.

 Also, can you really trust Google Earth as an authoritative source?
 I'm not sure.An interesting test would be to go find a USGS
 benchmark or a section marker near you then enter it's location into
 Google.  See if Google hits the marker.
 --

 Chris Albertson
 Redondo Beach, California

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Re: [time-nuts] Averaging Location for Position Hold

[Michael Perrett]

I was speaking in terms of the user. The point I was trying to make is that
if the user had a map, chart or simply a set of three dimensional
coordinates created from one datum, then that user had better use the same
datum or position errors will be evident. The Z direction is typically used
by navigators to indicate vertical direction, an example of this is when
using the north, east, down (NED) references in an inertial reference frame.

Michael

On Wed, Sep 14, 2011 at 2:59 PM, Magnus Danielson 
mag...@rubidium.dyndns.org wrote:

 Michael,

 On 14/09/11 17:05, Michael Perrett wrote:

 The user, mostly military or marine, would choose the datum he/she wanted
 to
 use. This would match up the local map with the GPS derived position. The
 difference could be quite large (hundreds of feet), especially important
 in
 the Z (vertical) direction!


 In GPS, the Z axis is not the vertical axis... X, Y and Z is the receivers
 position in meters according to GPS/WGS84 which is then translated into
 long, lat and height.

 Cheers,
 Magnus

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Re: [time-nuts] Lady Heather help, please

[Michael Perrett]

First: Find the directory where LH resides (mine is D:\Program Files
(x86)\Heather).
Click the Windows start icon
In the search windw type command
Click on the command prompt.
Change to the LH directory (I am using mine, you will have to find your own
location).

enter- D: (return)This puts you on the correct drive
enter - cd Program Files (x86)\Heather (return)  This puts you in the
right directory

Run the program, enter: heather /3 (return) this runs LH in port 3

Hope this helps
Michael / K7HIL







On Mon, Sep 12, 2011 at 11:44 PM, Dick Moore rich...@hughes.net wrote:

 Trying to run LH2 with a TBolt under WinXP. I need to change her com port
 to 3, which is where my serial-to-USB adapter is located -- and port 1 is in
 use.

 I see in the tip sheet that I can use the command line. Trouble is, I
 can't find it. Hitting most keys will display a menu of letters to invoke
 various things, but I can't get to anything that looks like a command line
 to use the /3 command. Suggestions?

 TIA,
 Dick Moore
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Re: [time-nuts] Win 7 and Thunderbolt

[Michael Perrett]

I went a different route - I bought a multiport serial card (PCIE RS232C)
and have a dedicated, unique, serial port for the Tbolt. I put it on COM 15,
which did not even exist prior to the addition and have had no conflicts
since. Just added /15 to the .exe command line.

PC: Home made I7-875 CPU OC to 4GHZ, 12GB RAM, dual 250GB SSD in Raid 0,
Fidelity Titanium audio card, HD-5970 graphics card all operating on WIN 7
64B Ultimate edition.

Michael / K7HIL

On Sun, May 15, 2011 at 12:18 PM, Chuck Forsberg WA7KGX N2469R c...@omen.com
 wrote:

 I replaced a 2.22 version Thunderbolt with a 3.0 version
 and Windows 7 Pro 64 bit went nuts.  After some Googling
 it became apparent that some bagbiter MS software was
 interrogating the serial ports looking for a serial ballpoint
 pointer.   Windows started hallucinating as it tried to parse
 GPS data as cursor movements and mouse clicks.

 After reinstalling Windows twice I saw a message suggesting
 disabling the ballpoint driver.  That works so far.  Don't remove
 it, it will just come back.  Disable it.

 The 3.0 version seems to do a much better job keeping things
 steady than 2.22 dis.


 --
 Chuck Forsberg WA7KGX N2469R c...@omen.com   www.omen.com
 Developer of Industrial ZMODEM(Tm) for Embedded Applications
  Omen Technology Inc  The High Reliability Software
 10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430


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Re: [time-nuts] USB and Mouse conflict persists

[Michael Perrett]

Stan;
I had the same problem. The correct fix (i.e. permanent) is to buy a
RS232C plug-in board for your PC. This allows the port choice to remain
fixed. With the USB to serial adapter the port can change every time you
reboot the computer. I purchased a board with 8 db9 connector 'dongles',
this allowed me to have unique port IDs for all the RS232C devices that I
have afixed to the computer.
Michael

On Wed, May 11, 2011 at 5:52 AM, Stan, W1LE stanw...@verizon.net wrote:

 Hello The Net:

 Since my motherboard died, I want to transfer the T'Bolt to another
 computer.
 I am running XP Pro with a USB laser mouse and a USB to serial adapter to
 the T'Bolt.
 The USB to serial adapter drivers are on hand and they loaded nicely,
 with the computer setting the USB port to COM10.
 System worked fine with Lady Heather on the original computer.

 I tried using the mod to theboot.ini file.I added:

 NoSerialMice:COM10   on the very first line.

 To date I still have a conflict with the mouse

 I can move the COM port assignment for the adapter, but I can not find what
 COM port the mouse is using.
 The mouse does use IRQ 12.

 USBView software does show which USB ports are used, but not the mouse COM
 port assignment.

 How do I fix (permanently assign) the Com port used for the mouse, so there
 is no conflict  ?

 Thanks for the help,

 Stan, W1LE Cape CodFN41sr





 Zz


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