RECEIVING NAVTEX – A SIMPLE INTRODUCTION: By Brian Keyte, G3SIA NAVTEX provides a fascinating variation on our hobby, needing all the usual skills with receivers and aerials and knowledge of different propagation conditions, but adding some good DX reception, interesting navigational messages and the ability to leave your receiver and PC 'listening all night' while you are fast asleep! These short notes are just intended to get you started, taking some of the initial mystery out of Navtex and Decoding, explaining as simply as possible how to receive your first stations, how to identify them and how to report your loggings. You will find all the extra details and advice to help you in Alan's excellent new Navtex page on his Beaconworld site at: http://www.beaconworld.org.uk/navtex.htm TUNING TO A NAVTEX SIGNAL Set your receiver to 516.30 kHz on the dial for 518 kHz (or 488.3 for 490 kHz) with USB (or CW) setting and use a wide filter such as 2 kHz. You should then occasionally hear the background noise replaced by the warbling sounds of a Navtex signal. GETTING SIGNALS TO YOUR PC Make an audio connection from the receiver to the PC sound card input. It's best to follow the more professional advice about how to do that, but I just take a length of co-ax from the two terminals of one side of some primitive headphones direct to the PC's line input socket. You should be able to hear the signal in the speakers by adjusting the PC volume control settings (playback and/or recording). If necessary you could use the microphone input socket, but avoid overload. INSTALLING A DECODER PROGRAM A decoder program (see Alan's Navtex page, http://www.beaconworld.org.uk/navtex.htm ) is easily installed in your PC - just follow the advice. The new Navtex decoder 2.0 is free of charge and as simple as can be, ideal for a 'starter' - you just save the 'navtex.exe' file (only about 200KB), double click on it, click 'Exit' on the 'About' window and there it is displaying the incoming signals (or, between transmissions, just a dancing frequency spectrum of randomlooking noise). The display should show about 1700Hz (altered by dragging the red line). Click the 'Raw Data' tab, then, when you hear a NAVTEX warble starting, you should see the frequency trace change and a message will start to appear. This decoder displays the raw messages in the left hand part of the screen. It also gives a very nice table of accumulating messages to the right - just click on a message number and there it is. The messages are kept permanently in timed and dated files (unless you delete them) so they are all still there when you start up again. After several hours the raw data display might not have enough space for more to be added to it. Alternatively, SeaTTY is a very good decoder, quite easy to install and use and containing extra features. It can be used for a trial period of 30 days without charge. RECOGNISING THE STATIONS You will find that Navtex messages start with 'ZCZC' and end with NNNN. The ZCZC is followed by two letters and two numbers - e.g. OA12. The first letter gives you a good idea which Station you have received and it tells you the times of day, 4 hours apart, when that station is likely to transmit. Most of the 'O' stations transmit starting at 02:20, then 06:20, 10:20, etc. The World is split into Navtex areas and there is usually only one Navtex station using each letter in each area. In North West Europe (Area 01) an 'O' station heard on 518 kHz is likely to be Portpatrick in Scotland, but it might be from Malta (Area 03) or even St Johns in Newfoundland (Area 04). You need to look at the actual messages to be sure which of the possible stations it is - the messages may include the Station Name (e.g. 'MALTA RADIO'), or the Navtex Area Number or geographical references, latitude/longitude, etc. The second letter (A) tells you what kind of message it is and the rest provides a message number. STATION IDENTS We use our own way of identifying each station in our logs and station lists. This always starts with a $ (which means 'this is a Navtex beacon' and it allows us to include these stations in lists with the other kinds of beacons in Rxx, etc.). Immediately after the $ comes the two-digit Area Number (most of the eastern part of N.America is area 04). Finally is the Station Letter - an important part which provided the main 'key' to the station sending the message. So the 'O' station above would be $01O if Portpatrick, $03O if Malta and $04O if St Johns. You can find lists of the Navtex stations and the times they transmit from Alan's Navtex page at: http://www.beaconworld.org.uk/navtex.htm and in Rxx, etc. OVER TO YOU! You can sit and watch the messages arriving or just leave your receiver and decoder program running overnight, then click through the messages afterwards to see what you have caught. (During the two nights after I installed Navtex V2.0 I left it unattended on 518 kHz, then 490 kHz, and found that it had given positive idents of 31 different Navtex stations from 18 countries). Good Navtexing, Brian.
