NASA Navtex - testing

[Relax]

Just spent a frustrating afternoon trying to get my Nasa PC navtex to work.

I did get it to work on the hard - in fact several miles from the sea -when I first fitted it.

Its getting power and the serial/USB cable is OK (it connects the GPS to the chart plotter program OK) and the program is telling me the connection is 'OK' but 'no messages'.

So whats the problem and how can I test it? How can I test the reception and the antenna performance?

I have looked at the Nasa website - not very helpfull but hav'nt contacted them as yet.

(BTW - I am a techinoprol)

Looking for some insight here from some of the great minds out there /forums/images/graemlins/grin.gif

 

[dalex]

Sorry but I have no knowledge of the kit you are setting up. I do have some ideas though which have scrambled or stopped messages altogether on my set up you may find useful:
1) Navtex operates on a very noisy part of the radio spectrum. It needs a good aerial signal. Your distance from the sea is pretty much irrelevant as these signals can cross hundreds of miles overland.
2) Navtex is a 2 tone system with one note determining a logic 1, and another tone for logic 0. If these are reversed, your navtex might not make any sense of the signal at all, requiring a predictable start sequence to know when to interpret the message. Not sure what this is, but they all end in ZCZC.
3) I find at home, near a PC, my own navtex is swamped by stray data from many sources. I keep my reciever as far from the pc as possible - it works best with a laptop rather than a desktop.

Hope this helps.

 

[Gwylan]

Make sure it has power for at least 24 hours - that charges the little battery inside it somewhere!
Check which frequency the unit is listening on
Then look in the almanac or similar for the broadcast times from your nearest station.
Make sure the unit is programmed to receive that station, or all stations and wait
..... and wait! Does need a little patience, up to 24 hours.

 

[Relax]

Thanks for that but nothing to make me think that what I have should'nt work.

I have the aerial mounted on the outside of the pushpit near (but not at) the top.

I'm using a laptop connected to the storage/base unit in the saloon. It's a bit difficult to increase the distance one to t'other - its a tichy boat (Sadler 25).

Maybe I should at least try to contact Nasa? Anyone any experience of the usefulness (or otherwise) of this?

 

[Relax]

Well there you go - thats something I hav'nt yet tried - patience /forums/images/graemlins/tongue.gif

I usually switch all power off when leaving the boat. I assumed that Navtex transmissions were continuous - albeit not necessarily all stations at all times?

I will give it a go tonight /forums/images/graemlins/smirk.gif

 

[Gwylan]

Must leave it powered on, all the stations have broadcast time windows.
Also, since your aerial is v near the water - try connecting the aerial to the mast, via the rigging [that's the wire at the centre of the coax - you can just use any old bit of cable to see if the reception improves] and earthing the screen of the cable [that's the thin wires that surround the core - or any bit of wire to test the idea] to the engine or other large bit of metal connected to the water.
You will be surprised that generally in this case the unit does not always need the NASA aerial

 

[Relax]

I'll try leaving it on for 24 hours first then if that does'nt work I'll start fiddling with the aerial - one thing at a time!!

The next phase is to move on to RTTY from a short wave Rx ......... wish me luck /forums/images/graemlins/tongue.gif

 

[simonfraser]

-------------------------------------
I usually switch all power off when leaving the boat. I assumed that Navtex transmissions were continuous - albeit not necessarily all stations at all times?
-------------------------------------

/forums/images/graemlins/laugh.gif have you got any eletrical item on the boat that works when you switch ALL the power off ???

leave it ON and patience please ;-)

 

[Oldhand]

[ QUOTE ]

2) Navtex is a 2 tone system with one note determining a logic 1, and another tone for logic 0. If these are reversed, your navtex might not make any sense of the signal at all, requiring a predictable start sequence to know when to interpret the message. Not sure what this is, but they all end in ZCZC.


[/ QUOTE ]

No, they all start with ZCZC and end with NNNN

 

[eastcoastbernie]

In my non-techno experience, you turn the thing on when you arrive on the boat in the evening and hope it has received something by the time you wake up in the morning.

You programme in all sorts of codes which you get from the appropriate sections in the almanac.

In spite of copying religiously all the same codes as used by your neighbour in the berth next to you, you get different information from him, but hey, that's life.

Sometimes you get stuff in French or Spanish or some other foreign tongue even though you have not asked for it.

Sometimes it works like a dream, other times you get lots of asterisks or nothing at all.

My aerial is on the top of the pulpit. When it stopped working altogether, re-making all the connections sorted it out.

Although mine is - theoretically - programmed to received navigation warnings I don't seem to get any.

NASA are normally really helpful people but I didn't get much help from them when I asked. They told me all the transmissions come from Germany. So there you are. /forums/images/graemlins/confused.gif

 

[Bilgediver]

No, they all start with ZCZC and end with NNNN

These are old fashioned logic commands and in real hi tech applications like manual teleprinters switched the printer on and off......were often used to show start and end as even a human could understand these complex commands ..

/forums/images/graemlins/laugh.gif

 

[Relax]

I have it switched on now - will wait until tomorrow and see what happens.

As I said at the top it did get it to work when I fitted it - and this was with the aerial inside the saloon. I had a problem prior to that with the serial/USB connector but this is working now.

Fingers crossed.