F16C clock

[sonicdodo]

Looking for an answer on the following question:

Is the clock of the F16C with SAT link, or has to be manually adjusted.

Watched a video where the time on the HUD does not match the scene, and told that the time was set manually incorrect. Don’t believe that in one of the most advanced electronic fighters, the clock will be left to the pilots?!:confused:
May be one that knows the equipment can help.

Thanks
Sonicdodo

[30mRad]

Many people are unaware that GPS time and real time can vary by up to 4 seconds. The GPS time is updated daily (I believe) to keep in sync with the world time.
The GR4 takes its time from GPS - and has led to 3 sec differences intra-formation - but can be manually adjusted by the Nav, sorry WSO. There have been occasions when the auto-time has been out by some margin ie hours so not surprised that an F16 has the same problem.

[LH2]

The above answer by 30mRad is patently incorrect, at least insofar as "GPS time" is concerned. ICD-GPS-200 for references.

[getsometimein]

Even if the time on GPS was wrong, everyone would have the wrong time so it wouldn't make a difference...

As for the original question.... Do you mean the clock shows 1pm and its pitch black or something like that? Because it could be a simple Zulu/Local difference.

[Army Mover]

The above answer by 30mRad is patently incorrect

Or maybe not - How accurate is the TIME DISPLAY on my GPS? (http://gpsinformation.net/main/gpstime.htm)

[sonicdodo]

The video was based on 2 cameras from formation. There is a difference of 1h 10 min between leader and wingman time. The explanation is that wingman put the time manually, and of course wrongly? Is that possible?

[Torque Tonight]

I had a brief on GPS some time ago and was told that GPS time has almost 'atomic clock' accuracy. He proceeded to explain the very clever mathematics behind the GPS system and it all made sense. As the trigonometry is based on distance from the satellites (not bearings), a very small time error, at the speed of light, would give a very large distance error and a massive volume of uncertainty on the fix.

I have a watch which uses the radio time signal which comes from an atomic clock somewhere. The aircraft I now fly has a clock fed by GPS time. The clock and the watch always match each other perfectly. Of course, the aircraft clock can alternatively be set manually to whatever time I like. The link above actually suggests ten nanosecond accuracy - that's close enough for me.

[Dan Winterland]

Raw GPS time is out of sync with UTC. This is because GPS time is set to UTC when the system was started. Since then, UTC has been changed many times to accomodate changes in the earth's rotation speed and (I think) it's about 4 seconds adrift.

The GPS time signal is about 25 seconds long a section of the initial part of the signal gives general information including the time difference between UTC and GPS time so that your nav system can display UTC if it has the ability to resolve the difference. The box in my present type (Airbus FBW) does and it confidently announces that it is displaying UTC time - and it also updates the aircraft clock.

The difference can be signigficant. During Operation Provide Carpets (sorry, Privide Comfort that should be) in the mid 90s from Incirlik, we in our tanker had devised a racetrack RV based on an accurate arrival at the RV. But each day, the fighters got to the RV just before us insterad of a mile behind and they had a bit of a weave and general faff to get us all together. Tempers were running high and there was much 'banter' at the debriefs. We both were convinved we had an accurate time hack. They were getting theirs from the GPS and us from the good old BBC world service on the HF. It wasn't until I did my ATPL subjects and learned of the difference a few years later that I realised why we were not making the RVs work.



If your Nav system shows a time, you need to know if it's GPS raw time or UTC corrected if you need accuracy to within a few seconds.

[Dan Winterland]

From the US Navy Observatory website.


Modified Julian Date (MJD):
MJD = Julian Date - 2,400,000.5 days
UT2-UT1 = 0.022 Sin(2*pi*T) - 0.012 cos(2*pi*T) - 0.006 sin(4*pi*T) + 0.007 cos(4*pi*T)
where pi = 3.14159265... and T is the date in Besselian years.
T, the Besselian date, is given by T = 2000.000 + (MJD - 51544.03) / 365.2422
TT = TAI + 32.184 seconds
since 00h 00m UTC 01 January 2009, the cumulative leap second count is:
TAI-UTC = 34 seconds (exactly)
and GPS Time-UTC = 15 seconds

So the difference is 15 seconds!

Some basic GPS sets don't have the UTC correction. When sailing, I sometimes have 2 GPS sets running. My boats' GPS Plotter shows UTC and the more basic wrist mounted one I have shows GPS time. I knew there was a difference, but didn't realise how much.



Ohther people other than those who need to navigate also use the GPS time signal. Some traffic systems have a GPS time receiver for traffic light co-ordiantion and banks use it for currency exchanges for split secong timing of transactions to take advantage of changing rates!

[kiwi grey]

Lots of medium-to-large enterprises - including those in the energy distribution sector - use GPS signals to drive a "Network Time Protocol" clock server, which gives all the computer-type gubbins in their network a single, very, very accurate [28ns +/-10ns] time.
Quite important if you want to try and work out whether circuit breaker 'A' popped before or after air break switch 'B' or some such sequence-of-events analysis.
Or if your in a secure environment and want to make sure you don't open any firewall ports you don't actually have to.

Or if the PHB is just an anally retentive type who likes all the clocks to be Just So.:E

Google for "GPS ntp clock" if you're interested

[KiloB]

While it is true that there is now a significant variation (of about 15 sec) between baseline GPS time and UTC, this is not reflected in most GPS based readouts.

The broadcast GPRMC 'sentence' (which includes most Nav data) also includes a corrected UTC value. This can be accessed by GPS Units. There are also dedicated 'sentences' such as GPZDA which contain the same UTC data to a high (sub-second) degree of accuracy.

Anorak mode OFF!

[Wensleydale]

I remember the days when we all used to synchronise to the BT speaking clock (SOP to change ops room clock every day) until it was discovered that the time differed by many seconds depending upon which exchange you were on! I seem to recall that this practise was discontinued after a flypast where every formation turned up at rehearsal with a different time.

T'was in the days of the wind-up watch of course (I still have mine on issue!)

[LH2]

Strictly FWIW

My boats' GPS Plotter shows UTC and the more basic wrist mounted one I have shows GPS time

Most likely because it hadn't yet had a chance to read the IONO UTC subframe of the navigation message (the bit that says "this is the offset you need if you want UTC time"). If you see this, leave the wrist gadget somewhere with a clear view of the sky for at least 15 minutes and you should find that it syncs itself to UTC eventually. In any case, that really is one cheap piece of crap if it doesn't show the correct time to start with.

The broadcast GPRMC 'sentence' (which includes most Nav data) also includes a corrected UTC value. This can be accessed by GPS Units.

a) That is not "accessed" by the GPS receiver. It is produced by it.
b) Standalone NMEA is all but useless for accurate timing applications. NMEA + PPS might in some occasions provide accurate timing, this will generally be detailed in the receiver's technical documentation.

[Dan Winterland]

"Most likely because it hadn't yet had a chance to read the IONO UTC subframe of the navigation message (the bit that says "this is the offset you need if you want UTC time"). If you see this, leave the wrist gadget somewhere with a clear view of the sky for at least 15 minutes and you should find that it syncs itself to UTC eventually. In any case, that really is one cheap piece of crap if it doesn't show the correct time to start with."

The wrist gadget is the Garmin 205 which utilizes quite an old and very basic GPS receiver chip whch doesn't have UTC resolution as part of it's display parameters. I bought it for use on my racing catamaran and when I'm on the trapeze doing 20 knots clinging on for dear life in survival sailing, accurate UTC doesn't seem too important!

The GPS plotter is on the yacht, and at 12 knots flat out, 15 seconds equates to .......not very far. (Can't be bothered to work it out).

[Roadster280]

The more important aspect here is not the actual time, it is the drift. Since the difference between UTC and GPS time is a known, the actual time is a trivial detail.

As has been pointed out, synchronisation of networks (eg every single phone in the Western hemisphere) is achieved using GPS. Mobile handsets can change frequency at the pedestrian rate of 217 times per second, which of course requires some accuracy in the base station, from which the handset derives its timing. If set to "network time", your mobile WILL be accurate.