There are on-line petition sites where people can sign on to support a
particular cause. Has anyone started such a petition to save LORAN?

I've not seen one.

Best,
-John

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

Time and frequency measurement people were specifically
exclude from the polls I have seen to determine whether
or not Loran should continue.  They only wanted navigation
users input... and I guess there weren't any.

-Chuck

J. Forster wrote:

My impression is that significant stake-holders (e.g. Telecom service
providers, ILECs, AOPA, National Laboratories, FAA, NIST, DHS, CG, and
others) were unwilling  - at an institutional level - to embrace or own any
aspect of LORAN preservation and unable - at an individual level - to
influence "policy" decisions with any consideration for technical
viability or necessity.
Stated  differently  - this nations  NTP policy is totally driven  by
political considerations without regard to demonstrable critical
infrastructure technical evaluation.
Standard disclaimer: My opinions only
khartman

On Sat, Nov 28, 2009 at 2:36 PM, Chuck Harris cfharris@erols.com wrote:

Hi

Some of us have been trying to get the telcom OEM's to embrace a backup for GPS. There are a number of possible things they could do at various points in their networks. Different companies have pushed different approaches for many years. In all cases the response has been "the carriers don't want it". If you go to the carriers it's "the regulations don't require it".  I suspect if you go to the regulators they have their answer as well.

The net result is that something like 99+% of the GPS based stuff out there has no real backup (other than holdover) built into it. Without a backup already built into the gear, keeping Loran up or not has very little impact. Without a regulatory change none of the alternatives are going to get built in. They don't all depend on Loran's unclear future. None of them will go in unless there's a requirement to do so ...

That's true worldwide. It's not an issue with one country or another. It's not an issue with one system or the other. It's not an issue of a level of system or quality of carrier. It's not even an issue of military versus commercial. They just plain don't do it. Backup for timing simply isn't on anybody's list.

Sad but very true.

Bob

On Nov 28, 2009, at 4:04 PM, ken hartman wrote:

Well that surely is pretty clear.
Now will DHS sign off I suspect yes

On Sat, Nov 28, 2009 at 2:09 PM, ken hartman kdhartman@gmail.com wrote:

If any one is intersted this doccument provides some insight into the isssues involved in using Loran for "industrial timing"

http://tf.nist.gov/general/pdf/2193.pdf

As a side note in the past I have encountered "Legacy Loran" as a timing source in telecom carrier networks.   The last time I saw this was 7 or 8 years ago IIRC.  

As a side note does any one know how prevalent Cesium Stratum one clocks are in the telcom world these days ?

 
----- Original Message ----
From: Bob Camp lists@cq.nu
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Sat, November 28, 2009 2:47:55 PM
Subject: Re: [time-nuts] LORAN-C demise

Hi

Some of us have been trying to get the telcom OEM's to embrace a backup for GPS. There are a number of possible things they could do at various points in their networks. Different companies have pushed different approaches for many years. In all cases the response has been "the carriers don't want it". If you go to the carriers it's "the regulations don't require it".  I suspect if you go to the regulators they have their answer as well.

The net result is that something like 99+% of the GPS based stuff out there has no real backup (other than holdover) built into it. Without a backup already built into the gear, keeping Loran up or not has very little impact. Without a regulatory change none of the alternatives are going to get built in. They don't all depend on Loran's unclear future. None of them will go in unless there's a requirement to do so ...

That's true worldwide. It's not an issue with one country or another. It's not an issue with one system or the other. It's not an issue of a level of system or quality of carrier. It's not even an issue of military versus commercial. They just plain don't do it. Backup for timing simply isn't on anybody's list. 

Sad but very true.

Bob

On Nov 28, 2009, at 4:04 PM, ken hartman wrote:

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and follow the instructions there.

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Any thoughts on how complex a receiver would need to be to produce a 1 pps signal that was locked to the carrier frequency it was receiving ? Lot's of comercial transmitting equipment is designed to use an external frequency standard and if a transmitter at a high altitude site was locked to a cesium source it could serve a typical metroplitan area.  Locking an existing transmiiter to a cesium standard would not require any special signals or wave forms to be transmitted.  To be usefull the receiver would need to produce a standard 1 pps output.

Stanley Reynolds wrote:

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Hi guys,

Are there any manufacturers that currently produce LORAN receivers?  I
talked to a pilot friend who is very active in my area and he said he is
only aware of one person he knows that has a LORAN receiver in his aircraft
and the guy doesn't use it.  None of my other pilot buddies seem to know of
anybody even having a LORAN receiver in GA.  None of the planes I flew ever
had a LORAN receiver in them.  Between VOR beacons, GPS, street maps and a
compass, I don't see any need for a backup specifically in the scope of
general aviation.  If your visibility degrades to a point where you can't
see the ground, while simultaneously your standard cockpit instruments go
out, you have bigger problems than somebody jamming GPS.

My other buddy who runs a commercial fishing operation does rely on GPS to
an extent.  He basically said it would be an annoyance if it went out but
wouldn't be a show stopper.  He did say it would be pretty hard to find his
fishing spots without it though but navigating in coastal waters that he
knows would not be an issue.

is why it's going away.  From talking to my Navy buddy who was one of their
keepers of the time, they don't use LORAN for timing applications as he was
one of the guys that went around synchronizing the Cesium beams.  Is it
really that big of a deal if this system goes away?  I just don't see any
significant reason to keep it around as a backup for a very small minority
of people out there that would wish to continue to use it, especially for
our hobby.

That being said, is there such a thing as an NTP Disciplined Oscillator?
Although, GPS is probably more reliable than my Internet connection!

Thanks,
Bob

On Sun, Nov 29, 2009 at 12:40 PM, Mark Spencer mspencer12345@yahoo.cawrote:

On 11/29/09 11:40 AM, "Mark Spencer" mspencer12345@yahoo.ca wrote:

And how is this is different from time stations like WWV or WWVB?  They're
driven by cesium clocks (or an ensemble of clocks).  The atmospheric
propagation uncertainty means that the received instantaneous frequency
might be off by 1E-7 or so (for HF WWV, at least), but I would imagine that
averaged over a long time, it's quite a bit better (one NIST doc says 1E-9),
but apparently it's tough to do straight averaging. The station clocks at
WWV is is good to something like 1E-13  (adev of 1E-13 at tau of 10,000
seconds, down to about 2E-13 at tau of 1E6 seconds)

WWVB at 60kHz is different.. It's from the same master clock, but the NIST
doc says that received phase is stable to 1E-8 at tau of 2 seconds, down to
1E-9 at a tau of 1000 seconds, with a WWVB disciplined oscillator getting
down to around 1E-12 for averaging over a day (which NIST says is about 1
order of mag worse than a GPS disciplined oscillator)

Of course http://tf.nist.gov/general/pdf/1969.pdf says they use common view
GPS to sync the WWV transmitter to the clocks in Boulder. It doesn't use GPS
for time, just as a source visible to both at the same time)  The same
document claims that 0.1 millisecond absolute time uncertainty should be
achievable with the received signals of WWV/WWVH and perhaps <1 microsecond
for WWVB.

One can propose, say, VHF or UHF signals radiated from a high location which
would potentially have better instantaneous frequency stability (because the
propagation is more stable), but at some point, you're still going to have
to deal with things like SNR and propagation.  Granted a lot of those issues
are "solved" in some sense (e.g. You could set up a GPS pseudolite, like
they do for approach/landing navigation experiments)

The main difference is that receiving lf signals is challenging in many areas built up areas and the doppler shift of hf via sky wave reduces the accuracy considerably, while there are already a large number of exisiting high power transmitters that can be locked to an external time base and have line of site paths to many locations in a typical metropolitan area.  If a sutiable receiver existed this might be a feasible means of distributing accurate frequency info and then with a suitable reciever you could generate a 1 pps signal.  That being said a dedicated uhf or shf transmiter that could send accurate 1 pps signals (as well as providing a very accurate carrier frequency) might be an easier solution.  In any event if there was a market for such a system I believe it would have emerged by now.
I imagine you could even design a gps timing receiver that could also receive terristerial signals as a backup, but again it does not seem there is a market for this (:

Lux, Jim (337C) wrote:

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On Sun, Nov 29, 2009 at 12:25:06PM -0800, Mark Spencer wrote:

As I suggested earlier, I believe that relatively simple tweaks

to a broadcast ATSC transmitter/modulator/mux chain to lock both carrier
frequency, symbol clock, and say PCR clock to a local cesium standard
with time of day based (initially)  on GPS would probably be quite
practical and perhaps even little more than using the 10 Mhz (or 27 MHz
derived from it) from the cesium as clock input for existing plant and
setting some firmware settings correctly.

OBVIOUSLY as others have pointed out someone has to pay for this

even though the actual costs might be very small compared to the other
operating and engineering costs associated with the broadcast
transmitter plant.  It is hard to think of a more powerful signal for
time sync in a metro area...

As for receivers, existing ATSC tuner/demod chip sets and a FPGA could

no doubt supply all the usual timing signals (10 MHz, 1 PPS, time of day
in some  standard format).  One imagines sub microsecond PPS accuracy
(once propagation skew is measured) is quite possible.

One would clearly need to use a GPS based measurement to establish

the propagation based skews...

Network effects apply here - if there is no signal to lock to,

then there is no market for a receiver - if there is no receiver even rather
low cost changes to TV plant aren't gonna happen or be justified...

And I suppose the bottom line is that we'd better hope that no

natural (or perish the thought deliberate man made) event takes out
enough of GPS to cause GPS based timing to fail.  And system designers
had better start thinking about very local jamming of GPS timing
receivers at targeted sites that might cause a vital system (say public
safety radio) to degrade or fail.

--
Dave Emery N1PRE/AE, die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

Hi,

Well, most of this discussion is about GPS backup. The GLONASS system has
received global coverage (again) for navigation. Timing is less demanding
if we consider the static and known position case. In some years we will
have Galileo (Euro) and Compass (China). Perhaps also regional Japanese
and Indian (global?) systems. These are systemwise independant of GPS.
Looking at spectral redundancy - we have L2C available on some GPS SVs, L5
will come. The other coming systems are also multi carrier frequency. One
could argue that a jammer on the whole of the 1GHz to 2GHz will take all
services. But such a wide band jammer is very much less efficient than a
narrowband L1 carrier version.

How about using SBAS (WAAS, EGNOS, MSAS) for single satellite timing use?
That should be possible? The SBAS do provide a ranging signal if running
in the right mode, and that should be usable for a timing receiver. Having
a GEO signal, there should be no problem in using a high gain (parabol)
pointing directly to the GEO. This will steal many dB from the jammer
power budget.

Perhaps the way to redundancy is getting GNSS receivers using multiple
carrier frequencies and multiple constellations. Even though it is sad
Loran-C seems to go away soon.

--

Björn

David I. Emery wrote:

There's a standard for ATSC SFN configuration.

Unless SFN operation is applied, it is fairly unreasnoble to expect that
it would happend.

The propagation delay from the transmitter tower and any delay-offsets
of the tower would add up.

Certainly.

Only within SFN regions the receivers would be usefull.

There are several man-made things which may cause loss of signal,
including firmware errors, bad antenna connections, water in antenna
(actually happend to me) etc. etc. There are many reasons for the full
function to fluke out.

Cheers,
Magnus

bg@lysator.liu.se wrote:

L1, L2, L3, L4 and L5 jammers is off the shelf. Not particular
efficient, not to speak of L3 and L4 being of no significant use.

Spectral diversity of the signal, system diversity and coding diversity
helps for some of the failure modes, but you have common aspects such as
receivers, antennas and distance to the sats.

The GEO orbit is given and the time of the systems is fairly well kept,
at least so that it would suit many, but not all, needs. Parabol or
hexical antennas could be used. Linear array is another possibility,
althought a simplified approach could be used since it could be oriented
towards the target just as a parabol. For fixed locations elaborate
antennas is possible regardless.

I still wait for L2C receivers to become commonplace enought.

Cheers,
Magnus

In message 4B130050.1050002@rubidium.dyndns.org, Magnus Danielson writes:

Not to mention the fact that there is a good probability that
GPS and Galileo will jam each other, degrading both signals more
than the benefit of having twice as many birds will be able to
compensate for...

--
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.

Poul-Henning Kamp wrote:

That particular aspect have been in deep investigation, and so has the
M-codes. Their similarity in strength and code separation make the
effect less than the gain you get. The BOC code aids to insert signal in
the null of the L1 code which causes additional spectral/code division.

Cheers,
Magnus

There has been rather elaborate studies conducted on Galileo signals
disturbing GPS and vice versa. The chosen/negotiated signals give minimal
interference to others.

There has been bilateral agreements reached between all (?) future global
GNSS-systems. I think unintentional jamming between the systems are
unlikely.

An unintentional mishap like the recent GPS-L5 debacle is ofcause a
possibility.

--

Björn

bg@lysator.liu.se wrote:

The BOC signal approach has been agreed upon.

Besides, considering similar signal strength, the VCA would not be
significantly affected if at all while the coding gain would reduce the
other signals. Also consider that dopplers isn't make perfect matches
and that BOC signals and C/A does not correlate while BOC signals can
have better coding gain.

I think they learned the hard way from that bird. Then again, it does
one of its intended missions, preserve the L5 allocation with ITU, so
that part of the mission is good. Javad says they can overcome the bias
error.

Cheers,
Magnus