It is my understanding that test equipment is exempt from all
RoHS requirements.

-Chuck Harris

Magnus Danielson wrote:

that's for sure.. I think all the Hg ion traps are still laboratory
curiosities.. but, 10 years from now?

A problem with Hg ion traps

And Cs or Rb don't have the same sorts of issues?

I was thinking about changing the problem somewhat.  You'd have your
stations separated by km, but each station has several receivers and can
compare the phase of the signals.  You can solve for range rate
(Doppler) and angle (delta phase), and that can go into your position
solution.  (this is how we navigate spacecraft, after all, and it's also
used for a variety of target tracking systems)

Changing it from a rho-rho nav problem into a theta-theta problem
(triangulation vs trilateration).  The goal is to get target position
to 10 meters, at a distance of, say, 20km, so you need angular
measurements on the order of 0.5 milliradian (0.03 degree).  Offhand,
that might be easier than time to 30 ns.  There are some significant
issues here.. is the pulse long enough and enough power to make the
required differential phase measurement, are there propagation issues
(refraction, diffraction, multipath) that make milliradian precision
impossible.

The added hardware cost at each receiver site isn't much (compared to
site costs, etc.) especially since you probably already need at least
dual redundancy, so you can do N+1 redundancy, using 3 antenna/receivers
at each site, using 2 of them at any given time.

The wavelength at the transponder frequency is about 30cm, so with a
moderate spacing of the receive antennas (say a meter), you'll get
grating lobes and an angle ambiguity, but I think that could be resolved
with the other information available (e.g. a coarse fix)

On 09/11/2010 05:29 PM, jimlux wrote:

Sure, but that assumes his target deployment is 10 years ahead.

No.

http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive

Yes, but now you shifted from "time-support system of transciever boxes"
to modifications of the boxes themselves or at least use multiple boxes
for angle determination only (wasting much of the rest of the receiver
structure).

Yes, yes... I understood perfectly what you where describing and no
doubt such a hint would be most useful, but it may not be applicable to
his problem. The question is really if he has complete boxes to build
with or can alter their design. Additional delta-channels is best
handled in a combined receiver, as being done in many other similar
heading receivers... such as GPS receivers with angular orientation such
as used in airplanes and on ships.

Cheers,
Magnus

On Sep 11, 2010, at 12:13 PM, Magnus Danielson wrote:

Much closer than 10 years. The idea is to use existing or soon to be deployed infrastructure from the US ADS-B installation to also perform multilateration.

Multilateration can be performed with existing radios being deployed, deriving time synchronization from GPS. Future revision of radio specifications are possible, but are more likely to be incremental changes of existing design rather than more significant architectural changes.

Ralph

May it be assumed that the sites are on the regular electric grid?

If so, being within 300 miles of each other suggests that they are
most likely all on the SAME section of the grid, in which case the
phase time of arrival of the electric power waveform should be
constant between them (the zero crossing may not be perfectly
aligned, but it should always be the same differential).

Whether you can measure it to within 30 ns I'm not sure...

Simpler thought - is the telco fiber?  Could they drop a second
dedicated one to link the sites?

The notion that GPS will suddenly 'go away', without any other issues
being present, is rather silly.  That same solar flare that takes out
GPS for all your sites is going to most likely render your other gear
inoperative as well...

Tom Frank, KA2CDK

In message 8459B572-1428-4F6A-8375-AFB4F7225945@cox.net, "Thomas A. Frank" wr
ites:

Won't work.  Utility transformers have load-dependent parasitics
which mess this up.  It is one of the biggest challenges in
doing "autonomous cell based grid control" and similar schemes.

--
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.

On 09/11/2010 08:24 PM, Ralph Smith wrote:

I assumed within 1 or 2 years. This rules out waiting for
commercialisation of new standards or new approaches on ADS-B receivers
unless you control that process yourself.

As expected. The concept for ADS-B multilateration is already set down,
so the available parameters is really providing a timing system,
algorithms of multilaterations and possibly aiding to sort things out.

Cheers,
Magnus

Hi

You also have load dependent harmonic energy on there that messes up the zero crossings at the micro second level.

Bob

On Sep 11, 2010, at 3:45 PM, "Poul-Henning Kamp" phk@phk.freebsd.dk wrote:

On 09/11/2010 11:08 PM, Bob Camp wrote:

Not to speak about the highly shifting reactive load, which can shift
both negative and positive... and mess about the transitions.

Cheers,
Magnus

If the odd harmonics were filtered out, would the zero crossing of the
60 (50) Hz fundamental
be stable enough ?

Thanks  Stan,    W1LE      Cape Cod      FN41sr

On 9/11/2010 5:08 PM, Bob Camp wrote: