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Old 20-06-2012, 00:23   #1
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Do you recomend NAVTEX on shortwave

I am training in Germany sailors for the LRC examination. The classroom is a 3 mast vessel Alexander von Humboldt II passing from Spain to Canarias.
There are some questions in the LRC examination regarding NAVTEX on shortwave on 4209,5 kHz.
Reading the GMDSS Master Plan, I found NAVTEX weather services on shortwave only in Turkey, US, Mexico and Vietnam. So in my opinion there are only for some areas NAVTEX messages available and the question is if it is recomendable to buy a NAVTEX receiver capable for SW.

Is there thunderstorm made athmospheric noise disturbing the reception on 518 kHz?
And is the reception on SW significant better than on the standard 518kHz band?
Can you recomend to use NAVETEX on shortwave?
In the caribe or ocean crossing?
Thanks, Willy
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Old 22-06-2012, 10:04   #2
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Re: Do you recomend NAVTEX on shortwave

I was glad to have 500 kHz Navtex on my Atlantic crossing. Conventional weather fax was my primary source of weather but the Navtex forecasts were a helpful supplement. You don't need an independent Navtex receiver. An SSB receiver or transceiver and a laptop (which also support nets and wefax) is fine.
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Old 22-06-2012, 11:27   #3
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Re: Do you recomend NAVTEX on shortwave

I have only seen dedicated NAVTEX receivers capable of receiving on 518 and 490kHz only.
Looking at the 2011 edition of the GMDSS Manual, Annex 5.7 gives details of NAVTEX services available on the 4 Mhz band.
The list of countries given for this service are:
Cote D'Ivoire
Turkey
Mexico
USA
Vietnam
Egypt

Only Turkey, Egypt and Vietnam are listed as being operational, the others are "planned"
Looking at the details, the average range stated for the 4MHz service is between 250 and 400 Nautical Miles.

Most if not all GMDSS compliant vessels use Sat C to receive long range weather and nav messages (Enhanced Group Call messages - EGC), Sat C can also be set up to receive NAVTEX Messages

I have not noted any degradation of signal due to weather on the 518 Navtex receiver, and I cannot give a comparison between 518 and 4MHz, as I have never used it, and until I saw you post, was completely unaware of such a service (maybe I fell asleep at the back of the class on the GMDSS course).

If I had the money, and space on my own boat, a SAT C receiver would be a nice to have item, as it covers all the bases
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Old 22-06-2012, 12:13   #4
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Re: Do you recomend NAVTEX on shortwave

Yes, Inmarsat C terminal is the ultimate NavTex device. You can receive for any area so also the one you are heading to but can't receive well on 518kc yet.

cheers,
Nick.
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Old 22-06-2012, 14:10   #5
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Re: Do you recomend NAVTEX on shortwave

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Originally Posted by s/v Jedi View Post
Yes, Inmarsat C terminal is the ultimate NavTex device. You can receive for any area so also the one you are heading to but can't receive well on 518kc yet.

cheers,
Nick.

Sorry, should have made it a bit more clear. SAT C is a satellite receiving system, does not work on the NAVTEX frequencies, but reproductions of NAVTEX messages are transmitted on the SAT C system
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Old 22-06-2012, 14:53   #6
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Re: Do you recomend NAVTEX on shortwave

The whole point about NAVTEX is its short range....
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Old 22-06-2012, 16:06   #7
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What is not clear about my post? Inmarsat C is the ultimate way to receive FULL navtex data. This is part of MARCOM and not just some shady copy... it's original data just like what you get from a 518kc receiver. On your receiver, you can select the region(s) that you want to receive data for. You do the exact same thing on Inmarsat C. The difference is that Inmarsat C can receive data for any region regardless of your position, while for 518kc you need to be close enough.

At least, this is what they told me 10 years ago when I got my MARCOM-A license.

cheers,
Nick.
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Old 22-06-2012, 20:46   #8
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We have inmarsat-c on our boat and yes it receives the navtex messages you specify.
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Old 23-06-2012, 03:01   #9
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Re: Do you recomend NAVTEX on shortwave

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What is not clear about my post?
It was this bit Nick

Quote:
but can't receive well on 518kc yet.
I thought you were taking the p#ss and saying that Sat C does not receive well on 518kHz.

Having re-read your post, I see that your are saying that Sat C has the advantage of receiving Navtex messages in area's where a Navtex Receiver could not.
Which is the great thing about Sat C, you can set it up to receive Navtex messages for any area covered by the LES that the Sat C is using.
Apologise for confusion and mis-understanding
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Old 23-06-2012, 04:33   #10
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Quote:
Originally Posted by nigel1

It was this bit Nick

I thought you were taking the p#ss and saying that Sat C does not receive well on 518kHz.

Having re-read your post, I see that your are saying that Sat C has the advantage of receiving Navtex messages in area's where a Navtex Receiver could not.
Which is the great thing about Sat C, you can set it up to receive Navtex messages for any area covered by the LES that the Sat C is using.
Apologise for confusion and mis-understanding
No need for apologies as it's me who should have been more elaborate in explaining

cheers,
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Old 25-06-2012, 08:53   #11
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Re: Do you recomend NAVTEX on shortwave

Willy,
The short answer is:

This was discussed here over three years ago....
NAVTEX for Pacific



The long answer:

a) while the GMDSS committee added the 4mhz Navtex frequency to the system design to reduce the "atmospheric interference" that 518/490 khz signal can suffer from, the range of 4209.5khz Navtex is designed to be the same / similar to 518/490khz Navtex....

b) the real-world, practical application of 518/490 khz Navtex has shown no real significant issues with "atmospheric interference"....(it just hasn't an issue....perhpas due to the narrow rec. bandwidths and digital signal processing, etc....perhaps just the GMDSS Committee being cautious???)

c) there are only a few 4209.5 NAVTEX stations out there.....
According to my data (from 2009) there is one in Turkey, one in Vietnam, and two in Egypt and Taiwan.......
However, ALL of these nations also have 518khz NAVTEX signals as well, and their specs of their 4209.5khz stations show the effective/useful ranges as the same......
And, unless you read Turkish, Egyptian, Vietnamese, and/or Chinese, you'd not get any real benefit from these 4209.5 khz Navtex sugnals.....




I do hope this helps...

John
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