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Re: Comparing phase of physically distant signals

Cross-posted to 3 groups.

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Don Y wrote:
> Hi Joerg,
> 
> Tooth settled down, yet?
> 
>>>>> You still don't know what the difference in the propagation
>>>>> (through air) from each transceiver.
>>>>
>>>> With calibrated radios that's a piece of cake to find out. Pulse-echo.
>>>> Or let the whole link oscillate.
>>>
>>> With calibrate network interconnects, the problem wouldn't exist!  :>
>>> I'm trying to reduce the complexity of the measurement (verification?)
>>> system to *a* device -- preferably something non-esoteric (so folks
>>> don't have to buy a special piece of gear to verify proper operation
>>> and diagnose problems).
>>
>> The interconnects would calibrate themselves during the test. It doesn't
>> matter whether it's a radio link or a wired link.
> 
> You'd have to locate a piece of kit at each end of each link.
> I.e., three devices (assuming a common reference point) to
> test two links.  (Or, hope nothing changes in the minutes
> or fractional hours that it takes you to redeploy for the
> "other" link)
> 
> [E.g., the timing protocol updates itself at ~1Hz just to deal
> with things like drift in the local oscillator]
> 

Yes, either that or you have to make it part of the standard on-board
equipment (which I understand you don't want). There is no other way.
The locations have to broadcast their timer ticks and that requires
hardware.


>>>>> I.e., if the distance to device 1 is A and the distance to device 2
>>>>> is B, then there will be a difference between the signals arriving
>>>>> that corresponds to the difference between A and B.  Even after you
>>>>> compensate for any differences in the radios themselves.
>>>>>
>>>>> [The same is true with a single radio at device 1 "received" at
>>>>> device 2 -- how much time did the RF signal take to get to device
>>>>> 2 cuz it's arrival will occur after device 2's notion of the
>>>>> device 1 event with which it is intended to correlate.]
>>>>>
>>>>> That's the appeal between "two equal lengths of wire" -- the
>>>>> delay through each can be made "identical".
>>>>
>>>> But radio can measure them. How much precision do you need?
>>>
>>> As I said (elsewhere), I can currently verify performance at the
>>> ~100-200ns level "with a scope".  [I am trying to improve that
>>> by an order of magnitude.]  But, that's with stuff sitting on
>>> a bench, within arm's reach (physically if not electrically).
>>>
>>> So, I need a (external) measurement system that gives me at least
>>> that level of performance.  Without necessitating developing
>>> yet another gizmo.
>>
>> I am afraid you will have to develop a gizmo. Because there ain't enough
>> of a market for what you are trying to do and I doubt there is
>> off-the-shelf stuff.
> 
> That's what I've feared.  Once you start having to support "test kit"
> your TCO goes up, fast!  ("authorized service personnel", etc.)
> 
> Part of the appeal of legacy devices (60's) was that a "tech"
> could troubleshoot problems with common bits of test equipment.
> E.g., the original ECU's could be troubleshot (?) with a VOM...
> (no longer true though that market is large enough that OBD
> tools are relatively inexpensive)
> 

I find it's even better today. Back in the 60's, just the thought of
schlepping a Tektronix "portable" (as in "has a handle but take a Motrin
before lifting") could make you cringe. Then you had to find a wall
outlet, plug in, push the power button ... TUNGGGG ... thwock ... "Ahm,
Sir, sorry to bug you but where is the breaker panel?"

Nowadays they already have laptops for reporting purposes and all you
need to do is provide a little USB box and software. TI has a whole
series of ready-to-go radio modules, maybe one of those can be pressed
into service here. The good old days are ... today. Doing this
wirelessly was totally out of the question in the 60's. The wrath of FCC
alone was reason enough not to.


>> Except for very expensive test equipment that can
>> probably be programmed to do this job (the stuff that costs as much as a
>> decent car).
>>
>>> [E.g., the 'scope approach is great:  set timebase accordingly;
>>> trigger off pulse from device 1; monitor pulse from device 2; count
>>> graduations on the reticule!  This is something that any tech
>>> should be able to relate to...]
>>
>> But you need a link to each unit.
> 
> Yes.  And, relies on a *wired* link (or equivalent hooks in a wireless
> implementation)
> 

Wired works, as long as the infrastructure in the wiring won't get in
the way too much (Hubs? Switches? Routers?).


>> And this is also easy if a scope
>> approach is acceptable:
>>
>> a. Provide a full-duplex radio link to each unit, meaning two different
>> frequencies each. Can purchased. Send tone burst out, measure phase
>> difference when it comes back.
>>
>> b. Do the same with unit B.
> 
> This has to happen "nearly coincident" with "a)." to be able to
> ignore short term variations in the signals.  E.g., if you
> were troubleshooting an analog PLL, you wouldn't measure the
> phase of the input signal against some "reference"; then, some
> seconds later, measure the phase of the synthesized signal against
> that same reference.  Rather, you would measure the synthesized
> signal against the input signal "directly" so the measurements
> appear to be concurrent.
> 

Not really. How should an RF path change much in just a few minutes?
Unless someone moves a massive metal file cabinet near the antennas, but
you'd see that.


>> c. Listen for timer tick and measure delta.
> 
> Also coincident with a & b.  I.e., you want to deploy to pairs
> of radios and this "tick measurement" device to take/watch
> an instantaneous measurement free of jitter, and short term
> uncertainty, etc.
> 

Since it seems you are not after picoseconds I don't see where the
problem is. You can do that simultaneously, it's not problem, but it
isn't necessary.


> I'm not claiming it can't be done.  Rather, I'm trying to show
> the height at which it sets the bar for a "generic technician".
> 
> It may turn out that this becomes a specialized diagnostic
> procedure.  I would just like to avoid that, where possible,
> as it makes such a system "less ubiquitous" in practical
> terms.
> 

Take a look at SCADA softare. Something like this could be pieced
together and then all the tech would need to be told is "Hook all this
stuff to the units, plug this gray box into a USB port your laptop,
click that icon over here, wait until a big green DONE logo appears,
then retrieve all the stuff".


> (Alternatively, *guarantee* that the system always knows when
> things are not in sync and have *it* report this problem)
> 

That would be by far the best solution and if I were to make the
decision that's how it would be done.


>> d. Subtract difference found in steps a and b.
>> You might want to take a look at Daqarta. I found it to be very precise
>> in measurement precision when it comes to phase delays:
>>
>> http://daqarta.com/dw_0o0p.htm
>>
>> Not sure how far down in precision this app would go but it'll even give
>> you a histogram of timing errors:
>>
>> http://daqarta.com/dw_psth.htm
>>
>> The author is very responsive and knowledgeable when it comes to
>> specialty applications you want to pursue. Speaking from experience here.
> 
> At 256KHz sample rates, I think it is probably too slow to get the
> sort of resolution I would need (I'll examine the site more carefully
> to see if there is some "extended precision" scheme that could be
> employed)
> 

Mostly this only samples at 44.1kHz, 48kHz or 96kHz, depending on the
sound hardware you use. Unless I misunderstand your problem at hand,
that isn't an issue. AFAIU all you are after is a time difference
between two (or maybe some day more) events, not the exact occurrence of
an event in absolute time. So if each event triggers a sine wave at a
precise time you can measure the phase difference between two such sine
waves transmitted by two different units. Combining it with a complex
FFT of sufficient granularity you can calculate the phase difference
down to milli-degrees. 1/10th of a degree at 10kHz is less than 30nsec
and to measure that is a piece of cake.

You can get much more accurate than that. In fact, one of the big
projects I am involved in right now (totally different from yours) fully
banks on that and we have our first demo behind us. Since the system
aced it so well I tried to push it, measuring the phase shift in a
filter when a capacitor goes from 100000pF to 100001pF. It worked.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 00:45 -0700
  Re: Comparing phase of physically distant signals Jan Panteltje <pNaonStpealmtje@yahoo.com> - 2013-08-03 07:51 +0000
  Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 09:58 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 13:21 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 12:16 +0100
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 11:56 -0700
        Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:17 +0100
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 13:41 -0700
            Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 22:46 +0100
              Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 14:57 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 23:09 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 13:58 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 12:30 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 16:08 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 14:22 +0100
        Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 16:38 +0300
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 10:46 -0700
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 10:40 -0700
        Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:04 +0100
        Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 15:55 +0200
          Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-04 19:42 +0300
            Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 21:08 +0200
              Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-05 15:28 +0300
                Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-05 22:17 +0200
                Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-05 23:20 -0400
    Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 14:26 +0100
    Re: Comparing phase of physically distant signals George Neuner <gneuner2@comcast.net> - 2013-08-03 14:47 -0400
  Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 08:17 -0700
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:08 -0700
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:37 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:57 -0700
          Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 15:58 +0200
      Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 12:44 -0700
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 18:36 -0700
          Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-04 09:56 -0700
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 14:53 -0700
              Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-05 15:38 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 01:25 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-07 08:06 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-07 09:21 -0700
  Re: Comparing phase of physically distant signals josephkk <joseph_barrett@sbcglobal.net> - 2013-08-03 15:40 +0000
    Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 10:05 -0700
      Re: Comparing phase of physically distant signals John S <Sophi.2@invalid.org> - 2013-08-03 12:13 -0500
        Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 10:26 -0700
          Re: Comparing phase of physically distant signals John S <Sophi.2@invalid.org> - 2013-08-03 12:51 -0500
            Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 11:54 -0700
              Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:27 +0100
                Re: Comparing phase of physically distant signals George Neuner <gneuner2@comcast.net> - 2013-08-05 03:26 -0400
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-05 10:34 +0100
                Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-05 23:29 -0400
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 08:53 +0100
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:49 -0700
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:34 -0700
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:18 -0700
        Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 12:52 -0700
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 13:21 -0700
            Re: Comparing phase of physically distant signals Jeff Liebermann <jeffl@cruzio.com> - 2013-08-03 13:31 -0700
              Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 14:46 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 15:03 -0700
                Re: Comparing phase of physically distant signals Jeff Liebermann <jeffl@cruzio.com> - 2013-08-03 17:25 -0700
            Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 14:50 -0700
    Re: Comparing phase of physically distant signals "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-08-04 11:06 +0100
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-04 12:19 -0700
  Re: Comparing phase of physically distant signals John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> - 2013-08-03 11:47 -0700
  Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-03 18:23 -0400
  Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-05 16:53 +0100
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 13:19 -0700
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 00:27 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 20:09 -0700
          Re: Comparing phase of physically distant signals Paul Rubin <no.email@nospam.invalid> - 2013-08-05 22:12 -0700
            Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 09:12 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 01:47 -0700
              Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 10:08 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:25 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:48 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 10:49 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 03:06 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 11:57 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 10:28 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 21:52 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 01:34 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 09:46 +0100
              Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-06 07:22 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 10:42 -0700
                Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-06 23:04 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 23:50 -0700
                Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-07 13:05 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 18:22 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-08 09:35 +0100
              Re: Comparing phase of physically distant signals Paul Rubin <no.email@nospam.invalid> - 2013-08-06 22:18 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 03:09 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 12:39 +0100
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 13:18 +0100
          Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 09:23 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:02 -0700
          Re: Comparing phase of physically distant signals "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-08-06 09:49 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:17 -0700
  Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-16 21:07 +0100
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-16 14:50 -0700
      Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-18 19:55 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-19 11:43 -0700
          Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-20 21:43 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-20 14:49 -0700

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