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Comparing phase of physically distant signals

Then you may be home already, almost for free.

A way to do something like this is signature analysis. You watch each unit while it sends out a certain pattern that's always the same. The pattern has to come in response to some other pattern that gets sent to it, and the response time (turn-around time) must be very determined and validated. Now you can correlate the heck out of it and get almost any precision you want.

Yeah, but you don't want to have to temporarily re-shuffle a customers wiring installation. It'll be labor-intense and also interrupt their normal business.

Tricky but not impossible. That's why the test should run for a longer time, to see if anything changes. You also have another tool, RSSI. If the RSSI is markedly different from when the system was installed then something in the path has changed.

[...]

If this doesn't add value to the customer, why do it in the first place? If calibration is required then that is of value to the customer.

Yup. Didn't know that it was leagally or technically possible in your case.

[...]

The method above (sine wave trains) is usually better. Lower bandwidth, more SNR, better accuracy, much cheaper hardware.

That's where engineering begin to be fun :-)

The best comment I ever got after finishing a prototype that then did exactly what the client wanted, after one of their engineers looked into the rather sparse collectioon of parts: "You mean, THAT's IT?"

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg
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Yep.

Frequency selective fading. That can happen, but only requires moving

1/4 wavelength in any direction to make it go away. With a sufficiently strong signal, moving a few inches in any direction should eliminate the null. If nulls are deemed a problem, then a system that uses OFDM (such as cellular), which is much less susceptible to frequency selective fading, can be used. The time data is still there in todays digital TV in the PSIP data:

The 19 khz pilot tone might work. It's about 20 dB down from peak modulation or about +/- 7.5 kHz deviation: It's the spike at 19000 to the right. Looks like we have about 20dB SNR to play with. Yeah, that should work with a PLL or narrow filter.

As you note, cycle counting is a problem. I can't offer a solution.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

It is actually easier than I thought this morning:

You can perform round-trip calibration and timing in rapid succession, for both units. Unless the elevator has a rocket motor and goes at Mach-2 it should be accurate enough.

Ok, if an F-16 roars through the path at full throttle you'd have a problem :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

That's an old wives tale. It was only true if the transmitter was fed directly from the network feed. Otherwise, it went through a 'Frame Synchronizer' with it's own timebase. Typically, a 14.318180 MHz crystal, and not ovenized. They were used to hide any glitches in switching between signal sources. Rarely was the TV studio feed & the network in perfect sync & phase.

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

We (I'm probably dating myself now...) used to switch everything on Line-10, in the blanking interval. Perfect hiding space for slop.

To your point, even more rarely, were the test patterns 6 MHz wide at your bench, having gone through a dozen D/A's and 500 feet of coax. For that matter, I'm not even sure it was 6 MHz at the generator's output.

Reply to
mpm

It never was 6 MHz wide, even at the camera. There were guard bands, and the aural channels(s) 4.2 Mhz was normal for the video, dependent on how much slop the FCC let a station get away with, on the unused sideboard in the filtering & diplexer. A good video D/A was good to 10 Mhz, to minimize phase distortion in the video. SDI video, (Standard resolution, digital video) is flat to 270 MHz. HD digital runs into the GHz range. They are literally tons of surplused Analog video D/As that make great amps to distribute the 10 MHz frequency standard around your shop or factory. Loopthrough input, and eight outputs per board and ten boards to a frame for under $50 is hard too beat. Even though they are designed for 75 Ohm, they work fine. You can change the series output termination to get 50 Ohms if you want to. The Grass Valley are my favorites. They were a division of Tektronix at one time. The common as dirt 8901 D/A is rated at -1 dB at 16 MHz. The 8900 frame will hold ten boards, two power supplies and an ethernet interface to monitor & control the frame.

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

You might find this of interest and useful if you had a couple of fibres in your installed bundle. I was chatting to one of the guys visiting JET from CERN today and he stated that the timing accuracy is 1ps on phase and 1ns on time synchronicity.

--
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Reply to
Paul E Bennett

I was at Intergroup, and all our D/A's and input matrix designs (switching) looked the same as GV or Utah. I think we all used the same design engineers at one point or another.

But back to my earlier 6 MHz comment - I left out the fact that the sales and marketing folks claimed linearity out to 20 MHz (which of course, we could never verify on the bench - even though it probably met that spec.)

Reply to
mpm

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