Any GPS experts here?

[MW0SEC]

In several projects I have successfully used a NEO-6M GPS receiver. Never had any problems until recently with a new project. The raw data stream shows all the $GPGGA and other streams headers, the time is updated consistently yet the lat/long stuff either registers as 9's or empty comma separators. 
Knowing that it can take a while under bad conditions for proper operation to occur, I was patient, but still no change after an hour's logging.

Suggestions warmly welcomed...

[MW0SEC]

Belay my last request. It was weather related. This morning with clear skies everything works as normal. I'd still love to know though, how the time signal could be reliably received when it is claimed that no satellites are available?

[boater sam]

I would suspect that it could download the time signal from one or more satellites rather than having to triangulate with several.

[BusyBee]

How are time signals from satellites coded such that they relate to a standard?

Tracy

[MW0SEC]

How are time signals from satellites coded such that they relate to a standard?

Tracy

$GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0 0031*4F - the first parameter after the header is the time in UTC.

[Mike Watterson]

Location needs maybe 4 but raw time works with one. Till there is a strong solar flare.
Always have a backup solution. Especially for either actual time or accurate references. It's mad the number of commercial systems that to save < €200 rely entirely on timing derived from satellite. The Internet isn't a backup solution.

I've both a serial port and BT interfaced pair of dedicated GPS receivers. Not used them in years. They only work with USA system. Maybe my TCL phone has all the systems, but location services are disabled.
Also two radios with UK 60 KHz receiver and a clock using the Internet. But I have some ovened crystal osc if I needed a reference or a better local clock than the cheap 32.768 kHz ones.

[BusyBee]

How are time signals from satellites coded such that they relate to a standard?

Tracy

$GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0 0031*4F - the first parameter after the header is the time in UTC.

Thank you.

Tracy

[Craig]

I've experience with GPS navigators - that I use as a walking tour leader, clipped onto my pack. But they get fooled under some circumstances.

1. Adverse weather conditions
2. In a wood or forest
3. In mountain valleys, where satellite visibility is restricted

That is why I always pack a map and compass. However even that has got gotchas

1. Proximity of magnetic parts of your kit, (mitts, water bladder attachments etc). Been there, done that. Takes a while to work out how you have magically lost the ability to navigate accurately.
2. Proximity to a mobile phone - these can and do reverse the magnetization of the needle, or demagnetize it entirely. Seen that three times (wife and son are two). In poor visibility that can easily put you over a cliff.

Craig

[ppppenguin]

Add "urban canyons" to the list of areas where GPS is iffy. Same reason as mountain valleys.

[Mike Watterson]

Add "urban canyons" to the list of areas where GPS is iffy. Same reason as mountain valleys.

Though usually there are plaques with the street name and signs at major junctions that aid navigation. I've never felt the need for GPS for driving. I make a list of towns/cities with road IDs if going somewhere new and if it's in the wilds a local map of some kind* of the destination area.

[* Printout, sketch, Ordinance survey]

Sat nav does revolutionise air and sea travel, as long as there is no local war with spoofing. I've not tried it for hiking as I've not done that for decades. I was taught map reading and compass use by professions and always collected OS maps, or borrowed my dad's maps. He left a diary of one hike he was on years before I was born. During the map reading training the issues of compasses were explained and also how to use stick and sun and accurate time on a watch. Also a brief lesson on stars.