[time-nuts] Stephen Hawking, an honorary time-nut

[Tom Van Baak]

"Stephen Hawking dies aged 76"
http://www.bbc.com/news/uk-43396008

"Obituary: Stephen Hawking"
http://www.bbc.com/news/science-environment-1565

"Stephen Hawking, modern cosmology's brightest star, dies aged 76"
https://www.theguardian.com/science/2018/mar/14/stephen-hawking-professor-dies-aged-76

"Stephen Hawking obituary"
https://www.theguardian.com/science/2018/mar/14/stephen-hawking-obituary

/tvb
http://www.leapsecond.com/great2016a/
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Re: [time-nuts] Terrestrial GPS

[Bill Byrom]

Have you noticed that your mobile devices (smartphone, iPad, tablet PC,
laptop PC) can often know your location when you inside a  building
shielding you from GPS satellites (or producing multipath confusing the
GPS receiver)? Here is a quick test you can do if you have a PC with no
GPS receiver but with WiFi capability:
Start up a browser and go to http://maps.google.com (which redirects to
https://www.google.com/maps/...) with a WiFi connection. Near the lower
right of the screen you should see the + - zoom buttons, and above these
a target icon. Click that target icon. If asked, enable location
finding. You may also need to enable your browser to release location
information.  In my case, I am now sitting near the middle of my house
and the laptop Windows 10 PC Google Maps locator places my location on
the street adjacent to my house, about 25 meters or so from my actual
location. My iPhone iOS map shows my location more closely (inside my
house) and it very accurately shows the location of the minivan I parked
in the driveway several hours ago (as "parked car").  My iPad also shows
my location within my house.
How do these devices know your location without GPS? Several methods are
used to produce a hybrid positioning system[1]:(1) Your IP address from your 
ISP. This gets me within a few km of my
location. See: https://www.iplocation.net/(2) WiFi positioning system[2] - 
This makes use of databases which
contain the geographic location of WiFi access points. The data is
collected by methods such as comparing the GPS receiver location
reports of mobile devices with the signal strength of access points.(3) 
Cellular radio location - Various techniques allow accurate
mobile phone tracking[3]. The signal strength and propagation
delay from cellular base stations allow moderately good
determination of location.
If you are in an area without GPS receiver coverage, your mobile device
or PC can determine the time using various techniques:(1) Crystal oscillator 
for short-term time stability.
(2) NTP: https://en.wikipedia.org/wiki/Network_Time_Protocol
(3) Cellular timing - cellular phone networks require very accurate
timing of the RF signals.
It would be hard to place terrestrial transmitters on the GPS satellite
frequencies without dynamic range and other problems, and of course
someone could use this technique to jam GPS reception in an area. But
several terrestrial geolocation and timing dissemination systems have
been proposed, and some limited deployment has been 
achieved.https://en.wikipedia.org/wiki/NextNav
http://www.nextnav.com/technology
http://esatjournals.net/ijret/2013v02/i04/IJRET20130204031.pdf
https://spectrum.ieee.org/tech-talk/telecom/wireless/us-master-clock-keepers-test-ground-alternative-to-gps--
Bill Byrom N5BB



On Tue, Mar 13, 2018, at 5:17 PM, Stewart Cobb wrote:
> Peter Reilley suggests a backup to GPS using terrestrial
> transmitters. This> idea has been around since the early days of GPS. The 
> terrestrial
> transmitters were called "pseudo-satellites", or "pseudolites"
> for short.> The big problem with this idea is that the GPS signal format has
> a narrow> dynamic range. The signal strength from a terrestrial
> transmitter varies> widely (inverse square law) from positions near the 
> transmitter to
> positions far away. The variation in any practical system is
> larger than> the GPS signal format can handle. This is called the "near-far
> problem".> For an extensive discussion of the pseudolite concept, including 
> the
> near-far problem, see my dissertation. You can find it with a
> web search> for my full name and the word "pseudolites".
> 
> Cheers!
> --Stu
> _
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> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> and follow the 
> instructions there.


Links:

  1. https://en.wikipedia.org/wiki/Hybrid_positioning_system
  2. https://en.wikipedia.org/wiki/Wi-Fi_positioning_system
  3. https://en.wikipedia.org/wiki/Mobile_phone_tracking
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Re: [time-nuts] Suggest time-and-tech related locations in Switzerland

[Scott McGrath]

swisswatchtours.com

https://m.myswitzerland.com/en-us/factory-and-technical-visits/clock-and-watch-museum-beyer.html

Content by Scott
Typos by Siri

On Mar 13, 2018, at 5:58 PM, David Witten  wrote:

My wife and I are traveling to Switzerland for the last week in May.  I
have never been there before.

I would appreciate suggestions for time / tech sites of interest to visit.

We plan to fly to Zurich, but travel immediately to Geneva and then work
our way back to Zurich by train, stopping (at least) in Bern.

I would like to see what I can at CERN, I plan to attend the Ham meeting in
in Friedrichshafen June 1 - 3.

Dave
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[time-nuts] Terrestrial GPS

[Stewart Cobb]

Peter Reilley suggests a backup to GPS using terrestrial transmitters. This
idea has been around since the early days of GPS. The terrestrial
transmitters were called "pseudo-satellites", or "pseudolites" for short.
The big problem with this idea is that the GPS signal format has a narrow
dynamic range. The signal strength from a terrestrial transmitter varies
widely (inverse square law) from positions near the transmitter to
positions far away. The variation in any practical system is larger than
the GPS signal format can handle. This is called the "near-far problem".
For an extensive discussion of the pseudolite concept, including the
near-far problem, see my dissertation. You can find it with a web search
for my full name and the word "pseudolites".

Cheers!
--Stu
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[time-nuts] Suggest time-and-tech related locations in Switzerland

[David Witten]

My wife and I are traveling to Switzerland for the last week in May.  I
have never been there before.

I would appreciate suggestions for time / tech sites of interest to visit.

We plan to fly to Zurich, but travel immediately to Geneva and then work
our way back to Zurich by train, stopping (at least) in Bern.

I would like to see what I can at CERN, I plan to attend the Ham meeting in
in Friedrichshafen June 1 - 3.

Dave
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Re: [time-nuts] Recommendations for Mains Power Monitor / Logger

[David G. McGaw]

I expect 1/R^2 would prevent such a scheme from working as the 
terrestrial transmitters would vary widely in signal strength in a way 
that GPS satellites do not and could overload the receiver.


David N1HAC


On 3/12/18 9:54 AM, Peter Reilley wrote:

Reading this paper makes one wonder if there are other improvements that
can be made to increase the robustness against jamming, software bugs, 
solar events

or hostile attacks to the GPS system

A suggestion:

Create a parallel terrestrial GPS system.   This would be a system of 
GPS transmitters
mounted on cell phone towers.   They would masquerade as GPS 
satellites (but unusually low
and stationary).   It would be ideal if they could have unique 
identifiers and be integrated
into the GPS receivers timing and location calculations as any other 
satellite.   If there
is no room in the existing ID space then the terrestrial node would 
take over the ID of
a satellite that is below the horizon.   When the satellite reappeared 
the terrestrial node

would simply take over a different below the horizon satellite's ID.

Such a system could be built out as needed.   It may not require any 
alterations to existing
GPS receivers.   It would not disrupt the operation of the existing 
satellite constellation.
It would protect against attacks on the satellite system by either a 
human enemy or a natural

one, the sun.

Each node need not contain an accurate time source like a cesium 
standard.   They could
derive timing from a neighbor.   Cesium reference nodes would be 
periodically placed around the
system.   Timing derivations would be more accurate since the 
distances would be much closer and

thereby encounter less environmental disturbance.

GPSDO units would prefer such close and stationary references vs 
distant moving ones.


Pete.

On 3/11/2018 5:26 PM, Magnus Danielson wrote:

Hi Andy,

On 03/11/2018 08:40 PM, Andy Backus wrote:

Thank you for your posting, Magnus.

Your information is very interesting.

Do you mind saying a little more about the "incident" on 
26-JAN-2016?  I don't find reference to it in the link.  And my own 
TE plot for then shows no obvious disturbance.


Thanks.

Please read this:
https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Frubidium.dyndns.org%2F~magnus%2Fpapers%2FGPSincidentA6.pdf&data=02%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7Ca4a010b972b74eba0aa208d5890f2665%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636565620521190534&sdata=DvYknd%2F9wuMeyr0DaSNwdZPuPunA8I8XBmSp1nXnm38%3D&reserved=0 



In short, the GPS to UTC time correction polynomial got screwed up.

I got email from NASA, ended up having to call NASA HQ and got invited
to Washington DC to present before the US PNT advisory board.

Among the stranger things I've done in my life, but it was fun.

Cheers,
Magnus
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Re: [time-nuts] Recommendations for Mains Power Monitor / Logger --> GPS Issues

[Bob kb8tq]

Hi

> On Mar 12, 2018, at 9:54 AM, Peter Reilley  wrote:
> 
> Reading this paper makes one wonder if there are other improvements that
> can be made to increase the robustness against jamming, software bugs, solar 
> events
> or hostile attacks to the GPS system
> 
> A suggestion:
> 
> Create a parallel terrestrial GPS system.   This would be a system of GPS 
> transmitters
> mounted on cell phone towers.   They would masquerade as GPS satellites (but 
> unusually low
> and stationary).   It would be ideal if they could have unique identifiers 
> and be integrated
> into the GPS receivers timing and location calculations as any other 
> satellite.   If there
> is no room in the existing ID space then the terrestrial node would take over 
> the ID of
> a satellite that is below the horizon.   When the satellite reappeared the 
> terrestrial node
> would simply take over a different below the horizon satellite's ID.

If it takes over the ID of an existing satellite, it also takes over the 
ephemeris and almanac 
information for that satellite. There is only a *very* finite amount of “data 
space” in the transmissions
for that stuff. 

Simple answer - it would have to be an independent system. You need a unique 
almanac for it
and unique ID numbers for the stations. 


> 
> Such a system could be built out as needed.   It may not require any 
> alterations to existing
> GPS receivers.   It would not disrupt the operation of the existing satellite 
> constellation.
> It would protect against attacks on the satellite system by either a human 
> enemy or a natural
> one, the sun.
> 
> Each node need not contain an accurate time source like a cesium standard.   
> They could
> derive timing from a neighbor.  

If you do that, you make your backup system *very* open to attack. Spoof one 
and all the 
rest tracking it follow ….


> Cesium reference nodes would be periodically placed around the
> system.   Timing derivations would be more accurate since the distances would 
> be much closer and
> thereby encounter less environmental disturbance.

Only if you distributed a *lot* of very good clocks *and* monitored them the 
same way as you 
monitor a GPS sat. Since they are all low to the ground, that would take a 
*very* different 
setup for monitoring. 

> 
> GPSDO units would prefer such close and stationary references vs distant 
> moving ones.

Ummm …… er ….. not so much. A GPSDO simply locks up to “all in view”. 
Unless you 
tell it to reject a sat, it uses it. To the degree that there is a rejection 
process (TRAIM), it 
looks at the group solution. If the “majority time” looks ok … off we go. 

==

The idea of using cell tower signals for timing was at the heart of a couple of 
systems. The gotcha 
turned out to be that not all tower operators are created equal. Unless you 
have direct control
over the gear ( = you own and operate it) there is no way to keep it “correct”.

If you are going out to buy up a bunch of cell tower space, that is quite 
expensive. There are
other *much* less expensive ways to create an independent system. In fact, we 
already have
several alternate systems (Glonass and Galileo and BeiDou). They are already 
available (or will
soon be available) in the data stream of a lot of GPS modules. Working out what 
to do with
them is less complex than adding a “something else” system.

Bob


> 
> Pete.
> 
> On 3/11/2018 5:26 PM, Magnus Danielson wrote:
>> Hi Andy,
>> 
>> On 03/11/2018 08:40 PM, Andy Backus wrote:
>>> Thank you for your posting, Magnus.
>>> 
>>> Your information is very interesting.
>>> 
>>> Do you mind saying a little more about the "incident" on 26-JAN-2016?  I 
>>> don't find reference to it in the link.  And my own TE plot for then shows 
>>> no obvious disturbance.
>>> 
>>> Thanks.
>> Please read this:
>> https://rubidium.dyndns.org/~magnus/papers/GPSincidentA6.pdf
>> 
>> In short, the GPS to UTC time correction polynomial got screwed up.
>> 
>> I got email from NASA, ended up having to call NASA HQ and got invited
>> to Washington DC to present before the US PNT advisory board.
>> 
>> Among the stranger things I've done in my life, but it was fun.
>> 
>> Cheers,
>> Magnus
>> ___
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>> and follow the instructions there.
>> 
> 
> ___
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[time-nuts] Power line frequency monitoring using a PICPET

[Mark Sims]

I kludged up a very simple power line interface (3VAC transformer -> 10K 
resistor -> diode -> PICPET) and fed the (unfiltered) output into a PICPET.   
The PICPET was clocked using a 10 MHz TTL oscillator.  I used Lady Heather to 
capture and analyze the data.  It was measuring the time interval between 60 
cycles on the input waveform and calculating the frequency error, phase, and 
xDEVs.

It worked surprisingly well.   Overnight the freq varied over a 0.0475 Hz 
range.   Average freq was off by -0.005 Hz___
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[time-nuts] Recommendations for Mains Power Monitor/Logger

[Thomas D. Erb]

Who made that one?

I have  three power station master clocks.

http://electricclock.omeka.net/items/browse?tags=Power+Station+Master+Clock




[electrictime]

Thomas D. Erb

o:

508-359-9684

p:

508-359-4396 x 1700

f:

508-359-4482

a:

97 West Street, Medfield, MA 02052 USA

e:

t...@electrictime.com

w:

www.electrictime.com

[https://s3.amazonaws.com/htmlsig-assets/square/facebook.png]
  [https://s3.amazonaws.com/htmlsig-assets/square/twitter.png] 
   
[https://s3.amazonaws.com/htmlsig-assets/square/pinterest.png] 





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[time-nuts] Why European Clocks are Running Slow, and British Clocks Aren't

[Thomas D. Erb]

You tube video about line frequency time keeping issues in the EU.

https://www.youtube.com/watch?v=bij-JjzCa7o


[electrictime]

Thomas D. Erb

o:

508-359-9684

p:

508-359-4396 x 1700

f:

508-359-4482

a:

97 West Street, Medfield, MA 02052 USA

e:

t...@electrictime.com

w:

www.electrictime.com

[https://s3.amazonaws.com/htmlsig-assets/square/facebook.png]
  [https://s3.amazonaws.com/htmlsig-assets/square/twitter.png] 
   
[https://s3.amazonaws.com/htmlsig-assets/square/pinterest.png] 





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Re: [time-nuts] Recommendations for Mains Power Monitor / Logger

[Peter Reilley]

Reading this paper makes one wonder if there are other improvements that
can be made to increase the robustness against jamming, software bugs, 
solar events

or hostile attacks to the GPS system

A suggestion:

Create a parallel terrestrial GPS system.   This would be a system of 
GPS transmitters
mounted on cell phone towers.   They would masquerade as GPS satellites 
(but unusually low
and stationary).   It would be ideal if they could have unique 
identifiers and be integrated
into the GPS receivers timing and location calculations as any other 
satellite.   If there
is no room in the existing ID space then the terrestrial node would take 
over the ID of
a satellite that is below the horizon.   When the satellite reappeared 
the terrestrial node

would simply take over a different below the horizon satellite's ID.

Such a system could be built out as needed.   It may not require any 
alterations to existing
GPS receivers.   It would not disrupt the operation of the existing 
satellite constellation.
It would protect against attacks on the satellite system by either a 
human enemy or a natural

one, the sun.

Each node need not contain an accurate time source like a cesium 
standard.   They could
derive timing from a neighbor.   Cesium reference nodes would be 
periodically placed around the
system.   Timing derivations would be more accurate since the distances 
would be much closer and

thereby encounter less environmental disturbance.

GPSDO units would prefer such close and stationary references vs distant 
moving ones.


Pete.

On 3/11/2018 5:26 PM, Magnus Danielson wrote:

Hi Andy,

On 03/11/2018 08:40 PM, Andy Backus wrote:

Thank you for your posting, Magnus.

Your information is very interesting.

Do you mind saying a little more about the "incident" on 26-JAN-2016?  I don't 
find reference to it in the link.  And my own TE plot for then shows no obvious 
disturbance.

Thanks.

Please read this:
https://rubidium.dyndns.org/~magnus/papers/GPSincidentA6.pdf

In short, the GPS to UTC time correction polynomial got screwed up.

I got email from NASA, ended up having to call NASA HQ and got invited
to Washington DC to present before the US PNT advisory board.

Among the stranger things I've done in my life, but it was fun.

Cheers,
Magnus
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[time-nuts] Recommendations for Mains Power Monitor / Logger

[Mark Sims]

Lady Heather v6 now supports the PICPET.   I don't think it would like a 60 Hz 
input, though.   When testing receivers with a high navigation rate (like over 
20 Hz) it gets overwhelmed processing the data stream and updating the screen.  
It might work with the PICPET since the sole message that it sends is rather 
short.  I have been meaning to try it.   Or, perhaps I can add some code to 
skip some messages and get to a friendlier effective data rate.
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