date:20140602

[time-nuts] Is it Hz or MHz ?

2014-06-02 Thread Kit Scally

Team Nutters,
 

GPSDO's are often specified for stability as so many parts per x.  Using a
Symmetricom 8040C as an example, this has a quoted accuracy of typically
5E^-11 at shipment.  Ageing (monthly and yearly) and ADEV stability rates
for 1, 10  100 seconds are also given. This particular device as 1, 5 and
10 MHz outputs.

The question - is this accuracy with respect to 1Hz - or 10MHz ?  If the
latter, then the accuracy figures quoted needs to be modified by 10^6 (Hz to
MHz) to get a feel for the actual frequency changes at 10MHz.

Glossies of many GPSDO manufacturers seem deathly silent on this point, so
clearly, something is assumed.  I have seen an oscillator comparison chart
by Meinberg (a German company) that in their comparison chart, the accuracy
references need scaling to relate to 1Hz.
 
Appreciate some advice and/or direction on this before madness overtakes me
!
 
 
Kit 
Canberra
Australia

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Re: [time-nuts] Is it Hz or MHz ?

2014-06-02 Thread Poul-Henning Kamp

In message 595D85DC050442D88D7AC80A4476610B@dd09, Kit Scally writes:

The question - is this accuracy with respect to 1Hz - or 10MHz ?

Both, because it's a relative measure:

Your 1Hz will be between 0.999 and 1.001 Hz

Your 10MHz will be 999. and 1000.0001 Hz.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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.
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Re: [time-nuts] Is it Hz or MHz ?

2014-06-02 Thread wb6bnq


Hi Kit,

The value of 5E^-11 refers to the resolution that the precision can be 
relied upon after taking into account all the factors that influence 
it.  It means that there is an error that can be as much as +/-5 parts 
per e^-11.


At 10 MHz that is +/- 0.0005 Hertz error.  At 5 MHz that is +/-0.00025 
Hertz error.  At 1 MHz it is +/-0.5 Hertz error.  And, finally, at 1 
Hertz it is +/-0.005 Hertz error.


BillWB6BNQ


Kit Scally wrote:


Team Nutters,


GPSDO's are often specified for stability as so many parts per x.  Using a
Symmetricom 8040C as an example, this has a quoted accuracy of typically
5E^-11 at shipment.  Ageing (monthly and yearly) and ADEV stability rates
for 1, 10  100 seconds are also given. This particular device as 1, 5 and
10 MHz outputs.

The question - is this accuracy with respect to 1Hz - or 10MHz ?  If the
latter, then the accuracy figures quoted needs to be modified by 10^6 (Hz to
MHz) to get a feel for the actual frequency changes at 10MHz.

Glossies of many GPSDO manufacturers seem deathly silent on this point, so
clearly, something is assumed.  I have seen an oscillator comparison chart
by Meinberg (a German company) that in their comparison chart, the accuracy
references need scaling to relate to 1Hz.

Appreciate some advice and/or direction on this before madness overtakes me
!


Kit 
Canberra

Australia

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Re: [time-nuts] Is it Hz or MHz ?

2014-06-02 Thread Tom Van Baak

 The value of 5E^-11 refers to the resolution that the precision can be 
 relied upon after taking into account all the factors that influence 
 it.  It means that there is an error that can be as much as +/-5 parts 
 per e^-11.

No, it can be way more. A 5e-11 spec value is likely just RMS, or 1-sigma. 
Actual measurements will show significantly larger 2-sigma, 3-sigma, etc. value.

Your as much as wording sounds more like a 6-sigma, or peak-to-peak spec.

One must be very careful to match the measurement used to make the spec with 
how the device is intended to be used. For example, Magnus will likely tell us 
about MTIE, which is a perfect-storm, worst-case time error spec. It's very 
different from rough 1-sigma specs we usually talk about.

/tvb


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[time-nuts] Boeing 787 GPS reception trouble

2014-06-02 Thread Tom Van Baak

1) When I fly I often use my iPhone while on the ground, before take-off or 
after landing.

2) I sometimes carry a GPS receiver. When permitted (varies by airline), it's 
fun to log NMEA data for a flight and later plot the flight path and duration 
with UTC accuracy.

3) On occasion I also bring a logging Geiger counter. It's amazing how much 
background radiation there is up at flight altitude compared to down at ground 
level. You can go from 10 or 20 CPM (counts per minute) at home to, say, 500! 
CPM at 40k feet. Those of you who live in mile-high Colorado enjoy higher 
background levels. I know, because my Geiger counter was wonderfully close to 
60 CPM (= 1 CPS) in a hotel near NIST. Yes, I have the 1PPS ADEV plot for this 
and, yes, background radiation makes the world's worst atomic clock.
 
Anyway, over the years I've collected some nice GPS latitude/longitude/altitude 
data sets as well as background radiation as a function of altitude. Just to be 
clear, I do turn off these devices according to airline regulations.

Now I have never had a problem with reception in the terminal, walkway, or even 
while seated inside a plane. I figured the aluminum frame of the plane was thin 
enough that photons at cell, GPS, and gamma frequencies easily pass through the 
outer shell or the windows.

But last week I flew the new composite Boeing 787 Dreamliner and noticed 
something quite different. From the second I entered the plane, I lost both 
cell and GPS reception. It didn't matter how close I was to a window or not. I 
know the word composite sounds inert, but carbon fiber must be somewhat 
conductive, yes? And there must be serious lightning suppression layers too, 
maybe? Furthermore, the B787 windows are exotic; like giant oval LCD screens 
which electronically dim from near transparent to very opaque. Does all this 
make the new 787 a record-holding RF-tight flying Faraday cage?

Is this the first airplane in history where a time-nut can't receive GPS? At 
least gamma rays make it though, so I got RAD data. But no GPS data. Not a 
single SV fix the entire time I was inside the plane.

Has anyone else noticed this? Or know about this? Please respond only if you 
have real information. I can speculate as well as anyone; so it's solid 
technical, RF, EMF, or composite carbon fiber engineering info I'm looking for.

Thanks,
/tvb

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Re: [time-nuts] Boeing 787 GPS reception trouble

2014-06-02 Thread John Marvin

Did they make any announcements regarding this? Most people aren't going
to care about GPS, but many people are used to using their cell phones
while waiting for the door to close and/or as soon as the wheels touch
the ground when landing. If this doesn't work in a 787 I would think
that they would make a PA announcement to that effect, rather than
having to continuously answer questions regarding the problem.

Regards,

John

On 6/2/2014 2:55 AM, Tom Van Baak wrote:

But last week I flew the new composite Boeing 787 Dreamliner and noticed something quite
different. From the second I entered the plane, I lost both cell and GPS reception. It
didn't matter how close I was to a window or not. I know the word composite
sounds inert, but carbon fiber must be somewhat conductive, yes? And there must be
serious lightning suppression layers too, maybe? Furthermore, the B787 windows are
exotic; like giant oval LCD screens which electronically dim from near transparent to
very opaque. Does all this make the new 787 a record-holding RF-tight flying Faraday cage?

Is this the first airplane in history where a time-nut can't receive GPS? At
least gamma rays make it though, so I got RAD data. But no GPS data. Not a
single SV fix the entire time I was inside the plane.

Has anyone else noticed this? Or know about this? Please respond only if you
have real information. I can speculate as well as anyone; so it's solid
technical, RF, EMF, or composite carbon fiber engineering info I'm looking for.

Thanks,
/tvb

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Re: [time-nuts] Boeing 787 GPS reception trouble

2014-06-02 Thread Poul-Henning Kamp

In message BB41DBA7E336413BB9D643DF4D4F613D@pc52, Tom Van Baak writes:

I know, because my Geiger counter was wonderfully close to 60 CPM
(= 1 CPS) in a hotel near NIST. Yes, I have the 1PPS ADEV plot for
this and, yes, background radiation makes the world's worst atomic
clock.

Only for short tau.  It should be pretty good at tau  1e3 years or so ?

But last week I flew the new composite Boeing 787 Dreamliner and
noticed something quite different. From the second I entered the
plane, I lost both cell and GPS reception.

This is by design, so the plane can contain its own in-flight
wireless services.

WLAN in planes is no problem, there is a subset of channels which are
almost globally safe to use.

However, the next big cash-cow is supposed to be inflight mobile
phone + data, and bringing a Mobile Femtocell into any country
you might happen to fly over is a regulatory violation and paperwork
nightmare.

Originally the GSM spec had a sort of RFC1918 facility, were one
specific frequency would be local space, for exactly this kind of
application on marine vehicles.  Your phone would never automatically
roam to such a net, you'd have to explicitly select that a 'local space'
base-station, and you'd be stuck to it, until you manually released it.

However, given governments gold-hunt in spectrum allocations, that feature
died in the crib, and has not subsequently been revived.

Therefore airlines and cruise boats have to use regulated frequencies
if they want to offer cell-service.

Cruise-boats use a loophole in the international maritime treaties,
even when in harbour, they're under their national flag, and since
most of them are Bahamas or similar, getting a mobile license and
frequency allocation is cheap.  (Usually they crank up the power
when in harbour and milk any unsuspecting land-locked tourists with
exorbitant roaming-charges.)

Planes are not similarly nationalized and apart from the aeronautical
spectrum, they cannot emit any radiation for which they are not
licensed by the country they overfly.

And so they've started to build the planes as farady-cages.

It would be trivial to add a passive GPS repeater to the plane, but
the airtraffic industry has never been happy about people being
able to receive navigation signals inside planes, worrying that
somebody might try to blow up the plane at some specific place
(or non-place), so that ain't gonna happen.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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.
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Re: [time-nuts] Is it Hz or MHz ?

2014-06-02 Thread Tom Van Baak

Hi Kit,

For convenience, accuracy is often given as a relative, unit-less value. Think 
of values like 1%, or 20 ppm, or 5e-11. These are all are unit-less numbers. To 
translate to absolute units just multiply:

50 Hz times 1% is 0.5 Hz.
1 meter times 20 ppm is 20 microns.
10 MHz times 5e-11 is 500 uHz.
5 MHz times 5e-11 is 250 uHz.
1 MHz times 5e-11 is 50 uHz.
1PPS times 5e-11 is 50 ps.

Two issues arise with GPSDO specs:

1) When you talk about frequency, you have to specify the averaging 
interval(s). Performance can vary considerably depending on interval. It sounds 
your data sheet does this correctly.

2a) When you talk about time, there are often two meanings. One is relative 
time, as in pulse to pulse interval accuracy or stability. This is almost 
always the spec used in the commodity GPS receivers we play with. It's the only 
spec that matters if the receiver is used for a GPSDO.

2b) The other meaning is absolute time, as in conformance with UTC(k), where k 
is your local National Measurement Institute (NMI). This is a much more 
difficult problem, since it requires independent antenna + cable + receiver + 
TIC calibration against some portable gold standard, and likely 
re-calibrations every year.

/tvb

- Original Message - 
From: Kit Scally kitsca...@iprimus.com.au
To: time-nuts@febo.com
Sent: Monday, June 02, 2014 12:28 AM
Subject: [time-nuts] Is it Hz or MHz ?


 Team Nutters,
 
 
 GPSDO's are often specified for stability as so many parts per x.  Using a
 Symmetricom 8040C as an example, this has a quoted accuracy of typically
 5E^-11 at shipment.  Ageing (monthly and yearly) and ADEV stability rates
 for 1, 10  100 seconds are also given. This particular device as 1, 5 and
 10 MHz outputs.
 
 The question - is this accuracy with respect to 1Hz - or 10MHz ?  If the
 latter, then the accuracy figures quoted needs to be modified by 10^6 (Hz to
 MHz) to get a feel for the actual frequency changes at 10MHz.
 
 Glossies of many GPSDO manufacturers seem deathly silent on this point, so
 clearly, something is assumed.  I have seen an oscillator comparison chart
 by Meinberg (a German company) that in their comparison chart, the accuracy
 references need scaling to relate to 1Hz.
 
 Appreciate some advice and/or direction on this before madness overtakes me
 !
 
 
 Kit 
 Canberra
 Australia


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Re: [time-nuts] Boeing 787 GPS reception trouble

2014-06-02 Thread Jim Lux


On 6/2/14, 1:55 AM, Tom Van Baak wrote:


Has anyone else noticed this? Or know about this? Please respond only if you 
have real information. I can speculate as well as anyone; so it's solid 
technical, RF, EMF, or composite carbon fiber engineering info I'm looking for.

I haven't noticed it myself, but when Beechcraft was making their pusher 
twin with carbon fiber, there was a whole raft of stuff they did to make 
sure it could take a lightning strike, including adding a conductive 
layer to the skin.  It doesn't have to be all that thick, since it's not 
structural.  This is a very real concern for carbon fiber components.


And, as you note, since the windows have electric shutters, there's 
probably an Indium Tin Oxide or similar coating on them, which would 
make an effective shield.

(http://gizmodo.com/5829395/how-boeings-magical-787-dreamliner-windows-work)

The basic rule on shielding is that holes where the perimeter is 1/2 
wavelength will pass some amount of RF, and when the perimeter is 1 
wavelength (e.g. a slot half wavelength long) will pass virtually all of 
it.  So your speculation about the windows in the plane being the 
pathway through which cell/gps/etc signals pass is a good one.



See also
http://www.boeing.com/assets/pdf/commercial/airports/acaps/787.pdf

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Re: [time-nuts] Is it Hz or MHz ?

2014-06-02 Thread wb6bnq


Hi Tom,

My experience is the manufacturer's, of hp or fluke quality, reported 
error band (their spec sheet) is the worst case (or at least 3 sigma) 
provided that the device is operated according to the recommended 
environment, etc.


Nonetheless, my statement you quoted is still accurate as to the purpose 
of the specification.  Although I probably should have qualified a bit 
more.  It goes without saying that one should be careful when it comes 
to specmanship no matter who it is.


BillWB6BNQ

Tom Van Baak wrote:

The value of 5E^-11 refers to the resolution that the precision can be 
relied upon after taking into account all the factors that influence 
it.  It means that there is an error that can be as much as +/-5 parts 
per e^-11.
   



No, it can be way more. A 5e-11 spec value is likely just RMS, or 1-sigma. 
Actual measurements will show significantly larger 2-sigma, 3-sigma, etc. value.

Your as much as wording sounds more like a 6-sigma, or peak-to-peak spec.

One must be very careful to match the measurement used to make the spec with 
how the device is intended to be used. For example, Magnus will likely tell us 
about MTIE, which is a perfect-storm, worst-case time error spec. It's very 
different from rough 1-sigma specs we usually talk about.

/tvb


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Re: [time-nuts] Boeing 787 GPS reception trouble

2014-06-02 Thread Jim Lux


On 6/2/14, 2:27 AM, Poul-Henning Kamp wrote:



It would be trivial to add a passive GPS repeater to the plane, but
the airtraffic industry has never been happy about people being
able to receive navigation signals inside planes, worrying that
somebody might try to blow up the plane at some specific place
(or non-place), so that ain't gonna happen.




I don't know that it's that reasoning.  It's more about the innate 
conservatism of people who make things that fly.


The reason for radio receiver ban originally was fear that Local 
Oscillator leakage would adversely affect cockpit instrumentation: 
particularly things like low frequency beacon receivers, which were none 
too selective, and since navigation using the ADF and tuning to a AM 
broadcast station wasn't unusual. I had to learn how to do it when 
taking flying lessons: it was widely acknowledged ( in 1980) to be 
nearly useless, but, hey, if all the other radios fail, any port in a 
storm, etc.  About the only older radio nav technology is A-N ranges (if 
you believe Wikipedia, they were gone by 1980 mostly disappearing by 
the 1970s)


Birdies in a consumer radio in your living room or car aren't a big 
problem. Birdies in a navigation instrument are a potentially big problem.


Even in the 1980s, there were a lot of planes flying with fairly archaic 
radios, although I suspect no commercial jet was using a VFO tuned 
radio:  they'd be using banks of crystals or PLL tuning. In general 
aviation, the first non VFO radios were from King in the 60s, and I 
think synthesizers came in around 1970 (King KX 170 and 175).  I was 
astounded at the number of crystals in one of my Narco radios when I 
took it out of the plane to fix it (a 1973-74 vintage radio).  Half that 
box was basically a big rotary switch and dozens of crystals.


Typical spurious responses in a COM or NAV receiver would be something 
like -60dB down, but a few milliwatts leaking from some guy's FM radio 
on board would easily be bigger than than that, since the receiver 
threshold is about 1 microvolt into 50 ohms (-110 dBm).


Once the rule is in place, it's very, very hard to get it removed, 
because of the if we allow X, and a plane has a problem, everyone is 
going to say it was because of X even if it wasn't, so let's just keep 
things the same.


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Re: [time-nuts] Boeing 787 GPS reception trouble

2014-06-02 Thread Brian Lloyd

On Mon, Jun 2, 2014 at 8:57 AM, Jim Lux jim...@earthlink.net wrote:

 On 6/2/14, 2:27 AM, Poul-Henning Kamp wrote:


 It would be trivial to add a passive GPS repeater to the plane, but
 the airtraffic industry has never been happy about people being
 able to receive navigation signals inside planes, worrying that
 somebody might try to blow up the plane at some specific place
 (or non-place), so that ain't gonna happen.



 I don't know that it's that reasoning.  It's more about the innate
 conservatism of people who make things that fly.

 The reason for radio receiver ban originally was fear that Local
 Oscillator leakage would adversely affect cockpit instrumentation:
 particularly things like low frequency beacon receivers, which were none
 too selective, and since navigation using the ADF and tuning to a AM
 broadcast station wasn't unusual.


Well, it is quite unusual for IFR (instrument flight rules) operation. But
VFR pilots would sometimes use an AM broadcast station for navigation
assistance.


 I had to learn how to do it when taking flying lessons: it was widely
 acknowledged ( in 1980) to be nearly useless,


Not entirely. I still make sure my planes are equipped with ADF (LF/MF
direction finding) due to my experience with GPS outages over the Caribbean
and Atlantic. I have experienced outages of over an hour where both my
panel-mount and hand-held GPS receivers stopped working. ADF was all I had.
I suspect that since I was flying a plane popular with drug-smugglers (a
Piper Aztec), I was being tracked, followed, and GPS jammed. (I lived in
the Virgin Islands, traveling to Florida on a regular basis. I would stop
in the Turks and Caicos or Bahamas to refuel.)


 but, hey, if all the other radios fail, any port in a storm, etc.  About
 the only older radio nav technology is A-N ranges (if you believe
 Wikipedia, they were gone by 1980 mostly disappearing by the 1970s)

 Birdies in a consumer radio in your living room or car aren't a big
 problem. Birdies in a navigation instrument are a potentially big problem.


They could be and they are. Interestingly enough, the only radios that ever
interfered with my VHF nav receivers were my own VHF comm and nav
receivers. LO leakage from one radio would show up on one of the others. I
have never experienced that problem with any consumer device.

Even in the 1980s, there were a lot of planes flying with fairly archaic
 radios, although I suspect no commercial jet was using a VFO tuned radio:
  they'd be using banks of crystals or PLL tuning. In general aviation,
 the first non VFO radios were from King in the 60s, and I think
 synthesizers came in around 1970 (King KX 170 and 175).  I was astounded at
 the number of crystals in one of my Narco radios when I took it out of the
 plane to fix it (a 1973-74 vintage radio).  Half that box was basically a
 big rotary switch and dozens of crystals.


A crystalplexer radio that was dual-conversion with both LOs using
switched crystals. CB radios used the same thing back in the late 1960s and
early 1970s. PLL LOs came later.

Typical spurious responses in a COM or NAV receiver would be something like
 -60dB down, but a few milliwatts leaking from some guy's FM radio on board
 would easily be bigger than than that, since the receiver threshold is
 about 1 microvolt into 50 ohms (-110 dBm).


That may be true but I have never experienced it, even when I tried. The
only time I have ever experienced interference with my comm or nav radios
it was from another comm or nav radio in the plane. Most use a 10.7MHz IF
which means, for the spectrum from 108MHz-138MHz, you are very likely to
have a lot of overlap between LO and desired receive frequency.

Once the rule is in place, it's very, very hard to get it removed, because
 of the if we allow X, and a plane has a problem, everyone is going to say
 it was because of X even if it wasn't, so let's just keep things the
 same.


Amen.

-- 
Brian Lloyd
Lloyd Aviation
706 Flightline Drive
Spring Branch, TX 78070
br...@lloyd.com
+1.916.877.5067
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[time-nuts] VNA design

2014-06-02 Thread Attila Kinali

Hi,

I know this is not exactly a time-nut question, but i guess this is
the best place i know to ask about this stuff.

I recently got introduced into the usefullness of a VNA. But these
things are horribly expensive for home use, even if bought from ebay
(before you say anything, remember i live in europe, where every
boat anchor hast to travel a long way). But given that most of the
designs that are on ebay are from the 80s and early 90s, i thought that
with todays ICs it should be easy to come up with a design that does
the same thing but can be build on a kitchen table.

Well, my problem now is, that i don't know how to build a VNA.
Yes, i understand the basic principle. I can come up with a design
that should work. But i have no clue about any problems or difficulties
in building these devices. Ie it's very likely that i fall into a dozen
traps when i try to build one.

I tried to get information on how to build a VNA, or what kind of trouble
people had operating one, but beside the VNA book[1] Rick mentioned a couple
of months ago and ko4bb's site (thanks man! your manual collection is a gold
mine!), my searches came out blank. As i'm quite sure that there is
information of that kind out there, i would like to ask whether someone
could point me to some documents, webpages, books, papers, etc that would
show me the detailed design of VNA, the problems people had with some
designs or anything else that would be of interest in such an endavor.


Also, any good resource on how to build a directional coupler that
does 10-3000MHz without going to exotic materials would be much
appreciated. All papers i found deal mostly with stuff above 5GHz.
Seems like low frequency couplers are considered a solved problem.


Attila Kinali

[1] Handbook of Microwave Component Measurements: with Advanced VNA Techniques
by Dunsmore, 2012

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
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