Empathy List Archives

DI

David I. Emery

Sun, Oct 4, 2009 6:08 PM

On Sun, Oct 04, 2009 at 09:14:29AM +0000, Robert Atkinson wrote:

Hi,

This is correct. There was also an issue with harmonics from the local
oscillator in the aircraft's own VHF nav/comm receivers blocking the
GPS. The answer is a 1575MHz notch filter, e.g.
http://www.edmo.com/index.php?module=products&func=display&prod_id=18006

I have not (not being involved in avionics professionally) heard

of any problems with GPS receivers causing interference to other GPS
receivers or other avionics ... I would be interested in your comments
on whether you know of any such issues and what the mechanisms are.

Obviously I - and I think most anyone on this list - would never

consider doing anything or using any equipment that might endanger an
aircraft (especially one I am flying on, needless to say) - so I have
tried to keep aware of any issues that might remotely exist with
handheld GPSes on planes.

Another problem was bias oscillators in tape players, these could
interfere with Omega/VLF receivers. Not a problem now of course. While
on the subject of Omega/VLF If you come across a Global GNS-500A OEU
box, it has a Efratom FRK Rb in it. There is one on ebay at the moment,
item 150257671674, but the price is way to high.

I had heard of that, I know many cheap tape recorders radiate

enough to be detected at some distance - this has been used in the past
by TSCM specialists to find covert planted recorders.

It's very had to predict interference on aircraft. While the
probability is low the consequences during take-off and landing are
severe. Hence the total ban on electronics during these flight phases.
The "illegality" is endangering an aircraft, however you do it. Avionics
design is my day job.

I have read that there have been studies with a spectrum

analyzer system on planes that have shown that compliance with the no
radiating device rules and electronics off during takeoff and landing is
far less than 100% though I certainly would not personally deliberately
violate the law whether or not the probability of it causing a problem
is significant. Apparently one or two cellphones can be seen registering
with cell systems during takeoff and landing on many flights - probably
most of them unintentionally left on.

Publicly discussed and documented cases of interference causing

serious problems are fairly rare... it is unclear how many actual cases
there have ever been.

--
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."

On Sun, Oct 04, 2009 at 09:14:29AM +0000, Robert Atkinson wrote: > Hi, > This is correct. There was also an issue with harmonics from the local > oscillator in the aircraft's own VHF nav/comm receivers blocking the > GPS. The answer is a 1575MHz notch filter, e.g. > http://www.edmo.com/index.php?module=products&func=display&prod_id=18006 I have not (not being involved in avionics professionally) heard of any problems with GPS receivers causing interference to other GPS receivers or other avionics ... I would be interested in your comments on whether you know of any such issues and what the mechanisms are. Obviously I - and I think most anyone on this list - would never consider doing anything or using any equipment that might endanger an aircraft (especially one I am flying on, needless to say) - so I have tried to keep aware of any issues that might remotely exist with handheld GPSes on planes. > Another problem was bias oscillators in tape players, these could > interfere with Omega/VLF receivers. Not a problem now of course. While > on the subject of Omega/VLF If you come across a Global GNS-500A OEU > box, it has a Efratom FRK Rb in it. There is one on ebay at the moment, > item 150257671674, but the price is way to high. I had heard of that, I know many cheap tape recorders radiate enough to be detected at some distance - this has been used in the past by TSCM specialists to find covert planted recorders. > It's very had to predict interference on aircraft. While the > probability is low the consequences during take-off and landing are > severe. Hence the total ban on electronics during these flight phases. > The "illegality" is endangering an aircraft, however you do it. Avionics > design is my day job. I have read that there have been studies with a spectrum analyzer system on planes that have shown that compliance with the no radiating device rules and electronics off during takeoff and landing is far less than 100% though I certainly would not personally deliberately violate the law whether or not the probability of it causing a problem is significant. Apparently one or two cellphones can be seen registering with cell systems during takeoff and landing on many flights - probably most of them unintentionally left on. Publicly discussed and documented cases of interference causing serious problems are fairly rare... it is unclear how many actual cases there have ever been. -- 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."

LJ

Lux, Jim (337C)

Sun, Oct 4, 2009 6:56 PM

On 10/4/09 11:08 AM, "David I. Emery" die@dieconsulting.com wrote:

On Sun, Oct 04, 2009 at 09:14:29AM +0000, Robert Atkinson wrote:

Hi,

This is correct. There was also an issue with harmonics from the local
oscillator in the aircraft's own VHF nav/comm receivers blocking the
GPS. The answer is a 1575MHz notch filter, e.g.
http://www.edmo.com/index.php?module=products&func=display&prod_id=18006

     I have not (not being involved in avionics professionally) heard

of any problems with GPS receivers causing interference to other GPS
receivers or other avionics ... I would be interested in your comments
on whether you know of any such issues and what the mechanisms are.

Most of the receiver designs I'm familiar with use some sort of single bit
sampler running at some tens of MHz. If the sample clock happens to be say,
1/3 of a "bad" frequency (e.g. Around 40 MHz, so the third harmonic is 120
MHz, in the middle of the aviation VHF band), you might have an issue with
the clock coupling back out the antenna port. Fortunately, most receivers
ALSO have some sort of filtering (because the receiver would be sensing the
self same 120 MHz aviation signals, etc.) which should suppress the
harmonics. The L band bandpass filter would let a very high harmonic out,
but I'll bet it wouldn't interfere with other GPS receivers.

Then, there's all the usual "radiation through the case" problems, but I
suspect that GPS receivers are no where near as bad an offender as a laptop
or PDA or iPod or or or or..

     I have read that there have been studies with a spectrum

analyzer system on planes that have shown that compliance with the no
radiating device rules and electronics off during takeoff and landing is
far less than 100% though I certainly would not personally deliberately
violate the law whether or not the probability of it causing a problem
is significant. Apparently one or two cellphones can be seen registering
with cell systems during takeoff and landing on many flights - probably
most of them unintentionally left on.

There was an article in IEEE Spectrum about this. A Agilent portable
spectrum analyzer with battery power and a data logger in the overhead bin,
as I recall.

     Publicly discussed and documented cases of interference causing

serious problems are fairly rare... it is unclear how many actual cases
there have ever been.

There's a web page at the FAA website that discusses it, and the events
where interference is suspected. It's not common, but it's also not unheard
of, although usually, it's just inferred that this is what happened.

On 10/4/09 11:08 AM, "David I. Emery" <die@dieconsulting.com> wrote: > On Sun, Oct 04, 2009 at 09:14:29AM +0000, Robert Atkinson wrote: >> Hi, > >> This is correct. There was also an issue with harmonics from the local >> oscillator in the aircraft's own VHF nav/comm receivers blocking the >> GPS. The answer is a 1575MHz notch filter, e.g. >> http://www.edmo.com/index.php?module=products&func=display&prod_id=18006 > > I have not (not being involved in avionics professionally) heard > of any problems with GPS receivers causing interference to other GPS > receivers or other avionics ... I would be interested in your comments > on whether you know of any such issues and what the mechanisms are. Most of the receiver designs I'm familiar with use some sort of single bit sampler running at some tens of MHz. If the sample clock happens to be say, 1/3 of a "bad" frequency (e.g. Around 40 MHz, so the third harmonic is 120 MHz, in the middle of the aviation VHF band), you might have an issue with the clock coupling back out the antenna port. Fortunately, most receivers ALSO have some sort of filtering (because the receiver would be sensing the self same 120 MHz aviation signals, etc.) which should suppress the harmonics. The L band bandpass filter would let a very high harmonic out, but I'll bet it wouldn't interfere with other GPS receivers. Then, there's all the usual "radiation through the case" problems, but I suspect that GPS receivers are no where near as bad an offender as a laptop or PDA or iPod or or or or.. > > I have read that there have been studies with a spectrum > analyzer system on planes that have shown that compliance with the no > radiating device rules and electronics off during takeoff and landing is > far less than 100% though I certainly would not personally deliberately > violate the law whether or not the probability of it causing a problem > is significant. Apparently one or two cellphones can be seen registering > with cell systems during takeoff and landing on many flights - probably > most of them unintentionally left on. There was an article in IEEE Spectrum about this. A Agilent portable spectrum analyzer with battery power and a data logger in the overhead bin, as I recall. > > Publicly discussed and documented cases of interference causing > serious problems are fairly rare... it is unclear how many actual cases > there have ever been. There's a web page at the FAA website that discusses it, and the events where interference is suspected. It's not common, but it's also not unheard of, although usually, it's just inferred that this is what happened.

BH

Bill Hawkins

Sun, Oct 4, 2009 8:06 PM

Group,

This has been a most enlightening discussion. Thank you all for
participating.

Finally found the right words to use with Google (ban gps flight) to get a
list.
See Joe Mehaffey's list of airlines at
http://gpsinformation.net/airgps/airgps.htm
The list of airlines that allow GPS have the caveat that the Captain has the
final decision.

What I've learned from Joe and others is that there are not enough
technically
savvy people to make such technical decisions. You will not always get a
competent decision. But once it is a decision, you must live with it or live
with various law enforcement people. If a flight attendant says No, try
asking
to speak to the Captain, but not when the flight deck is busy.

As to interference with other GPS receivers, my son runs a deep-sea fishing
party
boat out of Ocean City, MD. He is famous for knowing where the fish will be.
There
may be 5 to 20 people on a 50' fiberglass boat using GPS units to log his
fishing
spots. He'd be delighted if those receivers interfered with each other. He
sees no
interference with his GPS navigation system.

Regards,
Bill Hawkins

Group, This has been a most enlightening discussion. Thank you all for participating. Finally found the right words to use with Google (ban gps flight) to get a list. See Joe Mehaffey's list of airlines at http://gpsinformation.net/airgps/airgps.htm The list of airlines that allow GPS have the caveat that the Captain has the final decision. What I've learned from Joe and others is that there are not enough technically savvy people to make such technical decisions. You will not always get a competent decision. But once it is a decision, you must live with it or live with various law enforcement people. If a flight attendant says No, try asking to speak to the Captain, but not when the flight deck is busy. As to interference with other GPS receivers, my son runs a deep-sea fishing party boat out of Ocean City, MD. He is famous for knowing where the fish will be. There may be 5 to 20 people on a 50' fiberglass boat using GPS units to log his fishing spots. He'd be delighted if those receivers interfered with each other. He sees no interference with his GPS navigation system. Regards, Bill Hawkins

TA

Thomas A. Frank

Sun, Oct 4, 2009 8:28 PM

I have read that there have been studies with a spectrum

analyzer system on planes that have shown that compliance with the no
radiating device rules and electronics off during takeoff and
landing is
far less than 100% though I certainly would not personally
deliberately
violate the law whether or not the probability of it causing a problem
is significant. Apparently one or two cellphones can be seen
registering
with cell systems during takeoff and landing on many flights -
probably
most of them unintentionally left on.

Which is why the onus should be on the aircraft manufacturers to make
certain that there is no potential for life threatening danger from
electronic devices.

A blanket ban is the usual response from a bureaucracy to something
that they cannot actually control, and which they do not wish to put
the effort into correcting.

But that doesn't change the fact that if a drunk businessman or a
bored 6 year old with a new toy can stealthily endanger all the
passengers on a plane, the responsibility - and liability - should be
with the aircraft designer.

Bringing it back to the normal topic at hand, I wonder - if you had a
radio receiver tuned to WWV, and a GPS with a 1pps, if you could see
the relativistic effect of flying at 500 knots at 30K feet and log it
on your computer?

Tom Frank, KA2CDK

> I have read that there have been studies with a spectrum > analyzer system on planes that have shown that compliance with the no > radiating device rules and electronics off during takeoff and > landing is > far less than 100% though I certainly would not personally > deliberately > violate the law whether or not the probability of it causing a problem > is significant. Apparently one or two cellphones can be seen > registering > with cell systems during takeoff and landing on many flights - > probably > most of them unintentionally left on. Which is why the onus should be on the aircraft manufacturers to make certain that there is no potential for life threatening danger from electronic devices. A blanket ban is the usual response from a bureaucracy to something that they cannot actually control, and which they do not wish to put the effort into correcting. But that doesn't change the fact that if a drunk businessman or a bored 6 year old with a new toy can stealthily endanger all the passengers on a plane, the responsibility - and liability - should be with the aircraft designer. Bringing it back to the normal topic at hand, I wonder - if you had a radio receiver tuned to WWV, and a GPS with a 1pps, if you could see the relativistic effect of flying at 500 knots at 30K feet and log it on your computer? Tom Frank, KA2CDK

LJ

Lux, Jim (337C)

Sun, Oct 4, 2009 9:16 PM

On 10/4/09 1:06 PM, "Bill Hawkins" bill@iaxs.net wrote:

Group,

As to interference with other GPS receivers, my son runs a deep-sea fishing
party
boat out of Ocean City, MD. He is famous for knowing where the fish will be.
There
may be 5 to 20 people on a 50' fiberglass boat using GPS units to log his
fishing
spots. He'd be delighted if those receivers interfered with each other. He
sees no
interference with his GPS navigation system.

Interesting.. He's got an incentive to figure a way to prevent all those
folks from knowing precisely where he is, while he still needs GPS to
navigate there, so a simple short range jammer (leaving aside the legal
issues about jamming in general) wouldn't serve.

A GPS signal simulator with a bogus (but close) location would be useful,
and might actually fly under the Part 15 rules. The radiated power would be
very low (a few mW) so it probably would fit in the "not interfere" rules,
in general (e.g. You can radiate on your own property, e.g. In an anechoic
chamber for testing, it's only if you interfere with someone outside your
"boundary" that it gets sticky).

On 10/4/09 1:06 PM, "Bill Hawkins" <bill@iaxs.net> wrote: > Group, > > As to interference with other GPS receivers, my son runs a deep-sea fishing > party > boat out of Ocean City, MD. He is famous for knowing where the fish will be. > There > may be 5 to 20 people on a 50' fiberglass boat using GPS units to log his > fishing > spots. He'd be delighted if those receivers interfered with each other. He > sees no > interference with his GPS navigation system. Interesting.. He's got an incentive to figure a way to prevent all those folks from knowing precisely where he is, while he still needs GPS to navigate there, so a simple short range jammer (leaving aside the legal issues about jamming in general) wouldn't serve. A GPS signal simulator with a bogus (but close) location would be useful, and might actually fly under the Part 15 rules. The radiated power would be very low (a few mW) so it probably would fit in the "not interfere" rules, in general (e.g. You can radiate on your own property, e.g. In an anechoic chamber for testing, it's only if you interfere with someone outside your "boundary" that it gets sticky).

LJ

Lux, Jim (337C)

Sun, Oct 4, 2009 9:21 PM

But that doesn't change the fact that if a drunk businessman or a
bored 6 year old with a new toy can stealthily endanger all the
passengers on a plane, the responsibility - and liability - should be
with the aircraft designer.

Bringing it back to the normal topic at hand, I wonder - if you had a
radio receiver tuned to WWV, and a GPS with a 1pps, if you could see
the relativistic effect of flying at 500 knots at 30K feet and log it
on your computer?

500 kts = about 250 m/s.
C^2 = 9E16 m^2/s^2
V^2/C^2 = 6.2E4/9E16 = .6E-12

A pretty small thing to look for

Uncertainty in frequency from WWV due to ionospheric issues is on the order
of 0.1 to 1 Hz. Call it about 0.1 ppm for the 10 MHz signal.

Doppler effect on frequency from WWV is 2.5E2/3E8 = 1E-5 (10 ppm), which is
orders of magnitude larger than anything else you're going to see.

> > But that doesn't change the fact that if a drunk businessman or a > bored 6 year old with a new toy can stealthily endanger all the > passengers on a plane, the responsibility - and liability - should be > with the aircraft designer. > > Bringing it back to the normal topic at hand, I wonder - if you had a > radio receiver tuned to WWV, and a GPS with a 1pps, if you could see > the relativistic effect of flying at 500 knots at 30K feet and log it > on your computer? 500 kts = about 250 m/s. C^2 = 9E16 m^2/s^2 V^2/C^2 = 6.2E4/9E16 = .6E-12 A pretty small thing to look for Uncertainty in frequency from WWV due to ionospheric issues is on the order of 0.1 to 1 Hz. Call it about 0.1 ppm for the 10 MHz signal. Doppler effect on frequency from WWV is 2.5E2/3E8 = 1E-5 (10 ppm), which is orders of magnitude larger than anything else you're going to see.

DI

David I. Emery

Sun, Oct 4, 2009 11:14 PM

On Sun, Oct 04, 2009 at 03:06:12PM -0500, Bill Hawkins wrote:

See Joe Mehaffey's list of airlines at
http://gpsinformation.net/airgps/airgps.htm
The list of airlines that allow GPS have the caveat that the Captain has the
final decision.

It is interesting that American is listed as banning them as of

October 2009 (apparently they have switched back and forth on this
policy)...

The list of banned devices did not include them when I checked

it in August before using my GPS... would at least help if they had their
rules (they tell you to check) up to date.

--
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."

On Sun, Oct 04, 2009 at 03:06:12PM -0500, Bill Hawkins wrote: > See Joe Mehaffey's list of airlines at > http://gpsinformation.net/airgps/airgps.htm > The list of airlines that allow GPS have the caveat that the Captain has the > final decision. It is interesting that American is listed as banning them as of October 2009 (apparently they have switched back and forth on this policy)... The list of banned devices did not include them when I checked it in August before using my GPS... would at least help if they had their rules (they tell you to check) up to date. -- 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."

KE

Keith E. Brandt, WD9GET

Mon, Oct 5, 2009 12:02 AM

See Joe Mehaffey's list of airlines at
[1]http://gpsinformation.net/airgps/airgps.htm
The list of airlines that allow GPS have the caveat that the Captain has the
final decision.

    It is interesting that American is listed as banning them as of

October 2009 (apparently they have switched back and forth on this
policy)...

Earlier this week the Mehaffy list had American as approving GPS, but I
checked the AA website earlier this week and it listed them as being
banned. I contacted Mehaffey and maybe he updated the list after
contacting AA. I'm flying AA this coming Friday, so I'll see how it
goes. I flew up on Delta and used my Garmin Legend HCx in a window seat
and it worked beautifully. My next leg was on a United Shuttle, and
despite their website saying GPS was approved, the flight attendant
specifically announced that they were not approved. I didn't push it
since it was a 0.5 hr commuter flight.

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Col Keith E. Brandt, MD, MPH
Chief, Aerospace Medicine Consultation Division
Brooks City Base, San Antonio, Texas
[2]keith.brandt@gmail.com
Goodbye cruel world that was my home-
there's cleaner space out here to roam
Put my feet up on the moons of Mars-
sit back, relax, and count the stars
*This message transmitted with 100% recycled electrons

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Col Keith E. Brandt, MD, MPH
Chief, Aerospace Medicine Consultation Division
Brooks City Base, San Antonio, Texas
[3]wd9get@amsat.org
Goodbye cruel world that was my home-
there's cleaner space out here to roam
Put my feet up on the moons of Mars-
sit back, relax, and count the stars
*This message transmitted with 100% recycled electrons

References

http://gpsinformation.net/airgps/airgps.htm
mailto:keith.brandt@gmail.com
mailto:wd9get@amsat.org

See Joe Mehaffey's list of airlines at [1]http://gpsinformation.net/airgps/airgps.htm The list of airlines that allow GPS have the caveat that the Captain has the final decision. It is interesting that American is listed as banning them as of October 2009 (apparently they have switched back and forth on this policy)... Earlier this week the Mehaffy list had American as approving GPS, but I checked the AA website earlier this week and it listed them as being banned. I contacted Mehaffey and maybe he updated the list after contacting AA. I'm flying AA this coming Friday, so I'll see how it goes. I flew up on Delta and used my Garmin Legend HCx in a window seat and it worked beautifully. My next leg was on a United Shuttle, and despite their website saying GPS was approved, the flight attendant specifically announced that they were not approved. I didn't push it since it was a 0.5 hr commuter flight. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Col Keith E. Brandt, MD, MPH Chief, Aerospace Medicine Consultation Division Brooks City Base, San Antonio, Texas [2]keith.brandt@gmail.com Goodbye cruel world that was my home- there's cleaner space out here to roam Put my feet up on the moons of Mars- sit back, relax, and count the stars *This message transmitted with 100% recycled electrons -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Col Keith E. Brandt, MD, MPH Chief, Aerospace Medicine Consultation Division Brooks City Base, San Antonio, Texas [3]wd9get@amsat.org Goodbye cruel world that was my home- there's cleaner space out here to roam Put my feet up on the moons of Mars- sit back, relax, and count the stars *This message transmitted with 100% recycled electrons References 1. http://gpsinformation.net/airgps/airgps.htm 2. mailto:keith.brandt@gmail.com 3. mailto:wd9get@amsat.org

MS

Mark Spencer

Mon, Oct 5, 2009 2:37 AM

I'd also think twice before using a shortwave receiver on a comercial air craft (: I'd be worried about the emissions from the various local oscilators interferring with the HF and VHF radios on board the air craft.

Many years ago I used to use a portable sony shortwave receiver as a simple signal generator for making go / no go checks on UHF receivers. It's local oscilators put out easily detecable harmonics thru 470 Mhz.

Regards
Mark VE7AFZ

----- Original Message ----
From: "Lux, Jim (337C)" james.p.lux@jpl.nasa.gov
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Sun, October 4, 2009 2:21:22 PM
Subject: Re: [time-nuts] GPS from a window seat

But that doesn't change the fact that if a drunk businessman or a
bored 6 year old with a new toy can stealthily endanger all the
passengers on a plane, the responsibility - and liability - should be
with the aircraft designer.

Bringing it back to the normal topic at hand, I wonder - if you had a
radio receiver tuned to WWV, and a GPS with a 1pps, if you could see
the relativistic effect of flying at 500 knots at 30K feet and log it
on your computer?

500 kts = about 250 m/s.
C^2 = 9E16 m^2/s^2
V^2/C^2 = 6.2E4/9E16 = .6E-12

A pretty small thing to look for

Uncertainty in frequency from WWV due to ionospheric issues is on the order
of 0.1 to 1 Hz. Call it about 0.1 ppm for the 10 MHz signal.

Doppler effect on frequency from WWV is 2.5E2/3E8 = 1E-5 (10 ppm), which is
orders of magnitude larger than anything else you're going to see.

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

  __________________________________________________________________

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I'd also think twice before using a shortwave receiver on a comercial air craft (: I'd be worried about the emissions from the various local oscilators interferring with the HF and VHF radios on board the air craft. Many years ago I used to use a portable sony shortwave receiver as a simple signal generator for making go / no go checks on UHF receivers. It's local oscilators put out easily detecable harmonics thru 470 Mhz. Regards Mark VE7AFZ ----- Original Message ---- From: "Lux, Jim (337C)" <james.p.lux@jpl.nasa.gov> To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Sun, October 4, 2009 2:21:22 PM Subject: Re: [time-nuts] GPS from a window seat > > But that doesn't change the fact that if a drunk businessman or a > bored 6 year old with a new toy can stealthily endanger all the > passengers on a plane, the responsibility - and liability - should be > with the aircraft designer. > > Bringing it back to the normal topic at hand, I wonder - if you had a > radio receiver tuned to WWV, and a GPS with a 1pps, if you could see > the relativistic effect of flying at 500 knots at 30K feet and log it > on your computer? 500 kts = about 250 m/s. C^2 = 9E16 m^2/s^2 V^2/C^2 = 6.2E4/9E16 = .6E-12 A pretty small thing to look for Uncertainty in frequency from WWV due to ionospheric issues is on the order of 0.1 to 1 Hz. Call it about 0.1 ppm for the 10 MHz signal. Doppler effect on frequency from WWV is 2.5E2/3E8 = 1E-5 (10 ppm), which is orders of magnitude larger than anything else you're going to see. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now http://ca.toolbar.yahoo.com.

RA

Robert Atkinson

Mon, Oct 5, 2009 7:05 AM

Hi David,
I know of no specific problems with a correctly functioning GPS compared to any other PED (Portable (or Personal) Electronic Device) as the aviation industry likes to call them. Thes is as others pointed out problems with clock leakage. There is also the issue that a lot of PED's can't be fully turned off, just put to sleep. The only "special" risk with GPS's would be a fault condition with an active antenna or LNA oscillating and radiating on L1. There have been problems with active TV antennas doing this and they don't have a nice resonant antenna or filter to keep them on frequency.

Robert G8RPi.

--- On Sun, 4/10/09, David I. Emery die@dieconsulting.com wrote:

From: David I. Emery die@dieconsulting.com
Subject: Re: [time-nuts] GPS from a window seat
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Date: Sunday, 4 October, 2009, 7:08 PM

On Sun, Oct 04, 2009 at 09:14:29AM +0000, Robert Atkinson wrote:

Hi,

This is correct. There was also an issue with harmonics from the local
oscillator in the aircraft's own VHF nav/comm receivers blocking the
GPS. The answer is a 1575MHz notch filter, e.g.
http://www.edmo.com/index.php?module=products&func=display&prod_id=18006

I have not (not being involved in avionics professionally) heard
of any problems with GPS receivers causing interference to other GPS
receivers or other avionics ... I would be interested in your comments
on whether you know of any such issues and what the mechanisms are.

Obviously I - and I think most anyone on this list - would never
consider doing anything or using any equipment that might endanger an
aircraft (especially one I am flying on, needless to say) - so I have
tried to keep aware of any issues that might remotely exist with
handheld GPSes on planes.

Another problem was bias oscillators in tape players, these could
interfere with Omega/VLF receivers. Not a problem now of course. While
on the subject of Omega/VLF If you come across a Global GNS-500A OEU
box, it has a Efratom FRK Rb in it. There is one on ebay at the moment,
item 150257671674, but the price is way to high.

I had heard of that, I know many cheap tape recorders radiate
enough to be detected at some distance - this has been used in the past
by TSCM specialists to find covert planted recorders.

It's very had to predict interference on aircraft. While the
probability is low the consequences during take-off and landing are
severe. Hence the total ban on electronics during these flight phases.
The "illegality" is endangering an aircraft, however you do it. Avionics
design is my day job.

I have read that there have been studies with a spectrum
analyzer system on planes that have shown that compliance with the no
radiating device rules and electronics off during takeoff and landing is
far less than 100% though I certainly would not personally deliberately
violate the law whether or not the probability of it causing a problem
is significant. Apparently one or two cellphones can be seen registering
with cell systems during takeoff and landing on many flights - probably
most of them unintentionally left on.

Publicly discussed and documented cases of interference causing
serious problems are fairly rare... it is unclear how many actual cases
there have ever been.

--
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."

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Hi David, I know of no specific problems with a correctly functioning GPS compared to any other PED (Portable (or Personal) Electronic Device) as the aviation industry likes to call them. Thes is as others pointed out problems with clock leakage. There is also the issue that a lot of PED's can't be fully turned off, just put to sleep. The only "special" risk with GPS's would be a fault condition with an active antenna or LNA oscillating and radiating on L1. There have been problems with active TV antennas doing this and they don't have a nice resonant antenna or filter to keep them on frequency. Robert G8RPi. --- On Sun, 4/10/09, David I. Emery <die@dieconsulting.com> wrote: From: David I. Emery <die@dieconsulting.com> Subject: Re: [time-nuts] GPS from a window seat To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Date: Sunday, 4 October, 2009, 7:08 PM On Sun, Oct 04, 2009 at 09:14:29AM +0000, Robert Atkinson wrote: > Hi, > This is correct. There was also an issue with harmonics from the local > oscillator in the aircraft's own VHF nav/comm receivers blocking the > GPS. The answer is a 1575MHz notch filter, e.g. > http://www.edmo.com/index.php?module=products&func=display&prod_id=18006 I have not (not being involved in avionics professionally) heard of any problems with GPS receivers causing interference to other GPS receivers or other avionics ... I would be interested in your comments on whether you know of any such issues and what the mechanisms are. Obviously I - and I think most anyone on this list - would never consider doing anything or using any equipment that might endanger an aircraft (especially one I am flying on, needless to say) - so I have tried to keep aware of any issues that might remotely exist with handheld GPSes on planes. > Another problem was bias oscillators in tape players, these could > interfere with Omega/VLF receivers. Not a problem now of course. While > on the subject of Omega/VLF If you come across a Global GNS-500A OEU > box, it has a Efratom FRK Rb in it. There is one on ebay at the moment, > item 150257671674, but the price is way to high. I had heard of that, I know many cheap tape recorders radiate enough to be detected at some distance - this has been used in the past by TSCM specialists to find covert planted recorders. > It's very had to predict interference on aircraft. While the > probability is low the consequences during take-off and landing are > severe. Hence the total ban on electronics during these flight phases. > The "illegality" is endangering an aircraft, however you do it. Avionics > design is my day job. I have read that there have been studies with a spectrum analyzer system on planes that have shown that compliance with the no radiating device rules and electronics off during takeoff and landing is far less than 100% though I certainly would not personally deliberately violate the law whether or not the probability of it causing a problem is significant. Apparently one or two cellphones can be seen registering with cell systems during takeoff and landing on many flights - probably most of them unintentionally left on. Publicly discussed and documented cases of interference causing serious problems are fairly rare... it is unclear how many actual cases there have ever been. -- 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." _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

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