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$10 app puts Navtex on your Android Phone!

Now and again you see a really good bit of programming.

Check out DroidNavtex.

DroidNavtexThis brilliant little app can decode NAVTEX messages from any SSB, amateur radio, or shortwave receiver.

So you need two things – an Android smartphone and an SSB receiver.

Smartphone – At the moment there is only an Android version of the app so good news if you have an Android smartphone like the Samsung Galaxy Note, Samsung Galaxy SII, or an Android tablet like the Asus Transformer TF101

SSB receiver – I have a Tecsun PL660 on board – but judging by user feedback, people have also used the Sony ICF-SW100 and the Sony ICF-SW7600 successfully.

NAVTEX (Navigational Telex) is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships. It was developed to provide a low-cost, simple, and automated means of receiving this information aboard ships at sea within approximately 370 km (200 nautical miles) off shore.

NAVTEX broadcasts are primarily made on the Medium frequencies of 518 kHz and 490 kHz. The international NAVTEX frequency is 518 kHz, and these broadcasts should always be in English. Regional transmission of NAVTEX uses 490 kHz specifically for broadcasts in local languages. In the USA NAVTEX is broadcast by the U.S. Coast Guard District Broadcast Notices to Mariners affecting ships outside the line of demarcation, and inside the line of demarcation in areas where deep draft vessels operate.

DroidNavtex is able to decode NAVTEX messages from your receiver through the phones/tablets microphone or through a connected interface. Special audio filters even decode very weak signals through the microphone and make DroidNavtex a very affordable alternative to high priced decoders.

Even if you already have a dedicated Navtex receiver on board, you can use this app with your smartphone or tablet while in the marina cafe, or at home when you are planning – brilliant.

  • An “Auto mode” finds the frequency and the sideband of the Navtex signal automatically. With “Auto mode” turned off the frequency and sideband can be adjusted manually
  • Special audio filters decode very weak signals
  • A built-in database stores the received messages which can then be filtered, sorted and shared. Messages can be deleted individually, in groups or by age
  • To save battery power 7 timers can be set to start DroidNavtex at a given time to decode messages. All timers can be set in local time or UTC

I hope they bring out an Apple OS version they really deserve to sell a million! Smile


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Weather for FREE

There are a number of subscription services for weather data, but I really think that whether you are experienced or a novice sailor it is a good idea to practice reading barometric and other weather data for yourself to get accustomed to the connection between the data and the summary weather forecasts that are available from the US and UK Met Office. Please note I am not saying that you can substitute for listening to and heeding the Inshore and Shipping forecasts – but these resources and sofware can help your own decision making in terms of passage planning.

Of course what the paid for services add is “interpretation” and “prediction”…and we all know how accurate the weather forecast is on the TV…well in England that would be funny – perhaps the weather is forecast accurately in your part of the World? There are many models for forecasting but the most prevalent is the US National Center for Environmental Prediction (NCEP) – GFS Model.

Below are a large number of free resources and software that would make you fully capable of seeing all sorts of up to date weather data for FREE.

NOAA Marine Weather Service
This fantastic site gives free TIFF and GIF images for:
You don’t even need fancy software to see these pictures – just double click and the browser (IE or Firefox) will just display the picture for you – and you can save them to your laptop/PC for viewing later when you may not be able to get an internet connection.
NOAA Radiofax Schedule (for any fax viewing software – see below)

GRIB file data goes a step further by giving wind direction and speed using an easy to understand “barbed feather”. This saves you having to measure the distance between isobars to calculate wind strength. Some software even draws isotechs which are lines of constant wind speed. and some software draws arrows of different dimension and colours to represent speed and direction.

UGRIB Screen shotBut, I use the simple free service from UGRIB. This service gives you a free worldwide viewer and free GRIB files for any area that you care to select. You can select GRIB file area by just drawing an area on the map of the world and then the software downloads that area’s data alone – thereby saving on bandwidth for the download, which si a real boon if you are connected to the internet using your GPRS enabled phone! – click on the image for a larger screen shot.

Free GRIB viewer and GRIB data file – UGRIB
Free GRIB data viewer from AIRMAIL

If you have an SSB receiver on board such as the NASA SSB, then you can even get all sorts of free data while on the high seas and no where in sight of an internet connection…yes there are places such as these!

WEFAX is a method to transmit weather facsimile images over radio. Most images are transmitted in black and white, although some are grey scale. To receive wefax images, you need a shortwave receiver and a software decoder to convert audio tones into black and white. Tuning the receiver accurately is a tricky and time consuming process, but essential to receive acceptable pictures. You then have to clean up the audio signal by appropriate filtering to isolate the black and white “tones”.
The connection from the NASA SSB is a cable that plugs into the microphone input on my laptop, and when in operation sounds just like a fax machine or old analogue modem.

The program I use is SeaTTY. This can receive weather reports, navigational warnings and weather charts transmitted in RTTY, NAVTEX and HF-FAX (WEFAX) modes on longwave and shortwave bands. It can decode GMDSS DSC (HF and VHF) messages. The software can also automatically save NOAA Weather Radio SAME voice messages (NWR SAME) and the digital headers. No additional hardware is required — you need only a receiver and computer with a sound card.

Software for WEFAX – SeaTTY
Info and further links The DKZone
Free data by ham radio from Winlink2000
Software for weather fax
WEFAX Resources


Live AIS plot off the coast of East Anglia, England

Antenna2Martin Waller lives in Chelmondiston – a small village in Suffolk, England, on the south bank of the River Orwell, and to the east of the Ipswich.

Martin is obviously a sailor and also a software geek and AIS Live has come up with a web site on which he is plotting AIS signals from vessels off the coast of East Anglia – he has even put this aerial on the side of his house to improve reception – its a Super J-Pole designed for 161 Mhz reception and formed from 15mm copper pipe!

He has not only overlaid AIS transmissions on a Google maps background but also the Navtex transmitter stations as far south as Rome and Croatia.

Remember this is all live and in (almost) real time….

Well done Martin – I like your style, perhaps when I have retired …..:-)


Laptop on board

I wanted to use the Raymarine C120 as the primary means of electronic chartplotting while on board – it is interfaced to all the instruments as well as the the DSC radio, radar, and AIS.


But while onshore, at home, at anchor or in a marina it is often more convenient to use a laptop. It is now so easy to download grib files, look up weather forecasts, email, browse the web, and forums and so on.

I thought I would use the laptop for two main additional purposes.

a) Chartplotting using the software I already had before installing the Raymarine kit on board ie. Garmin’s Map source software which uses the Bluechart charts – all proprietory to Garmin.

b) Interface to the Target SSB radio so that I could get Navtex, RTTY and Weatherfax transmissions and store them on the laptop for reference while on passage.

c) Transfer data to / from the laptop / C120 and the RC400 using a 1Gb Sandisk Compact Flash Card


DSC00008I have been able to achieve all of this but I must admit that using the SSB is a lot more tricky than I anticipated. The picture here shows the audio cable from the SSB radio into the MIC input of the laptop….


The laptop is an ACER Aspire 5020WLMi and is – in hindsight – probably way over specified now that I have experience of using it in action..it has a built in card reader (very useful) 1Gb of RAM and a 100Gb HDD – but at least it will cope with advances in nav software which like all PC software is destined to bloat and bloat..


SSB On board

Well it seemed like a good idea to get an SSB instead of the dedicated Navtex displays that are on the market…there isn’t much price difference and with an SSB you can receive Weather fax, RTTY and Navtex transmissions anywhere in the world and all for free – no subscriptions required!

DSC00010sThis is the SSB that I installed it is the NASA Target HF3M SSB with dedicated antenna and the audio PC cable to interface with the laptop’s soundcard.

This does cover the spectrum from 30Khz to 30Mhz – so you can listen to AM radio (yes, you would have to be a long way offshore to want to do that !) and also receive the teletext transmissions called RTTY, and also the free Weatherfax




I have found the whole process very fragile however – maybe I just need some more patience to wait for the timed broadcasts and then for the slow acoustic modem speed transmissions – remember 300bd modems?…well this is slowwww….

It is best to do this at anchor or in a marina, so that the signal has a reasonable chance of getting through in a stable fashion.

I keep a folder of frequencies and times of broadcasts handy so that you can set up at the appropriate moment instead of having the laptop on for hours on end. This may be an argument for having the fixed receivers from people like NASA instead of the SSB radio coupled to a a laptop….?