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NAVTEX and NDBs

     NAVTEX is a system of transmitting text over the radio, similar to mobile 'phone texting. These text messages are sent by coastal radio stations and include such things as navigational warnings and weather forecasts, intended for reception by shipping. Indeed, all ships above a certain size are required to carry NAVTEX receivers. Three LF frequencies are used, 518kHz is the main worldwide frequency, 424kHz, and 490kHz for 'local' language broadcasts. Reception is simple and requires a communications receiver with the audio output connected to a computer sound card. A readily available computer program, such as Yand, will decode the audio signal into a text message. At G4AYT the RX is tuned to the stated frequency in CW mode and a narrow filter selected, Yand is then set to the CW offset frequency in the RX (in this case, 600Hz). To receive these signals a small aerial is required as stations within normal range will be quite strong. A better aerial may be necessary for DXing (long distance reception). Navtex stations have a range of a few hundred kilometres in daylight, but after dark, especially during the winter months, signals may travel several thousands of kilometres. G4AYT has logged 60 different NAVTEX stations *VIEW LIST* with the best DX being New Orleans at 7538km. NAVTEX LF frequencies are very close to the LF end of the medium wave broadcast band, so DXing these stations is very similar to medium wave DX, except (subject to enough data being received) the computer program will identify the station for you - meaning you don't have to listen for hours to pick out an ID from noise and other interference!

     England has two NAVTEX stations, Niton on the Isle of Wight and Cullercoats in the north east, although signals here in Whitstable are often stronger from Belgium (Ostend) and Holland (Den Helder).

     NDBs are non-directional beacons which send a callsign in morse code every few seconds. They are generally (but not always) sited at airports or coastal locations for navigational use by aircraft or ships. These beacons are usually much weaker than NAVTEX signals, with a daylight range of little more than 100km. Winter nights are best for long range reception. They usually occupy the band of frequencies between the medium wave and long wave broadcast bands, although a few are actually in the broadcast bands, e.g. Lichfield on 545kHz and Cranfield on 850kHz in England are in the medium wave band. G4AYT has logged 325 NDBs in 46 ITU countries *VIEW LIST*  with a best DX of  Wilmington, Carolina Beach, North Carolina, USA at a distance of 6395km.

    DXing NDBs

    There is quite some interest among radio enthusiasts for DXing NDBs, although it takes a lot of patience, a DX signal can be very strong one night and no trace the next. Checking up to date lists (most aren't) can be helpful too, avoiding wasting time listening for a beacon which no longer exists! Modulation of NDBs varies, in the UK a 400Hz tone is used to modulate the callsign only every few seconds, whereas in Canada there is also six seconds of continuos 400Hz tone between callsigns. In the USA a modulating tone of 1010 or 1020Hz is used. Tha Canadian NDBs tend to TX the upper sideband only, so if the receiver is in CW mode and using a narrow filter, it is necessary tune to the beacon carrier frequency plus 400Hz. The Greenland NDB at Prins Christian Sund is a good indicator of cross Atlantic DX conditions. It has a carrier frequency of 372kHz with 400Hz modulation on both sidebands and is often well audible before midnight in Whitstable. If you like a challenge, try for the Canadian beacon AY at St. Anthony, Newfoundland. This beacon runs only 25W and is on the same frequency as the Wolverhampton, England, NDB at 356kHz. In a more southerly direction from Whitstable, the powerful (3kW) NDB SAL at Cape Verde just off the central west African coast on 274kHz is a good indicator of conditions towards the Canary Islands, Morocco etc. This beacon does not use a modulating tone but keys the carrier directly. Some DX NDBs operate in the European Long Wave broadcast band making reception difficult, however, several of the European broadcasters in this band close down for a few hours at night.

    Probably the easiest Canadian NDBs to get you started are DF on 350kHz and JC on 396kHz. Remember to add the 400Hz if using a narrow mode and a helpful indicator is the six second tone between callsigns. These beacons become audible from about 2230 - 2300 local time most evenings in Whitstable in the winter.

    A photograph of the nearest NDB to Whitstable, located at Manston Airport, can be found on the index page.

Examples of NDBs Received in Whitstable 

        

         ND - North Denes, Great Yarmouth, England.                       SAL - Sal Island, Cape Verde.                                     VAR - Stavanger, Norway.

       

               JC - Rigolet, Newfoundland, Canada.                         QY - Sydney, Nova Scotia, Canada.                    DF - Deer Lake, Newfoundland, Canada.

        

            HO - Hopedale, Newfoundland, Canada.                            PST - Porto Santo, Madeira.                                  RWY - Ronaldsway, Isle of Man.

       

           AY - St. Anthony, Newfoundland, Canada.                   BX - Blanc Sablon, Quebec, Canada.                       OZN - Prins Christian Sund, Greenland.

Examples of NAVTEX Messages Received in Whitstable on 518kHz 

  (1) From San Juan, Puerto Rico in the Caribbean, received on 12th January 2011:-

  20110112 0204 518 $04R NMR San Juan,PTR    6911
  02:03:15> ZCZC RA22
  02:03:20> BCST ON VHF-FM AND 2670KHZ
  02:03:27> CG SECTOR SAN JUAN PR BNM 291-10
  02:03:35> W INDIES-VI-ST THOMAS-FLAMINGO BAY
  02:03:45> A PARTIALLY SUBMERGED G OBJECT HAS BEEN LOCATED IN THE E
  02:03:56> GREGERIE CHAN. MARINERS ARE REQUESTED TO TRANSIT THE AREA WITH A
  02:03:59> CAUTION.
  02:04:06> CX AT TIME//142359Z JAN 11// 
  02:04:09> NNNN

  (2) From Malta, received on 1st January 2011:-

  20110101 1823 518 $03O 9HD Malta,MLT       2055
  18:23:01> ZCZC OA03
  18:23:14> TUNISIA EAST COAST, TRAWLER SUNK IN VICINITY OF THE FOLLOWING POSN 34-29.9N 011-
  18:23:15> 24.2E
  18:23:17> NNNN

  (3) From Archangel on the White Sea, Northern Russia, received on 14th December 2010:-  

  20101214 0051 518 $17F UGE Arkhangelsk,RUS 2677
  00:50:40> ZCZC FA77
  00:50:43> 101330 UTC DEC 10
  00:50:49> COASTAL WARNING ARKHANGELSK 85
  00:50:51> SOUTHERN PART WHITE SEA
  00:50:59> 1. MISSILES LAUNCHES 17 DEC 0100 TO 0800
  00:51:05> 18 THRU 20 DEC 0100 TO 1800 21 DEC
  00:51:12> 0100 TO 1600 NAVIGATION PROHIBITED IN AREA
  00:51:18> 65-12.5N 036-37.0E 65-37.2N 036-26.0E
  00:51:26> 66-12.3N 037-19.0E 66-04.0N 037-47.0E
  00:51:33> 66-03.0N 038-38.0E 66-06.5N 038-55.0E
  00:51:39> 65-10.5N 037-30.0E 65-12.1N 036-49.5E 
  00:51:46> THEN COASTAL LINE 65-12.2N 036-47.6E
  00:51:51> 2. CANCEL THIS MESSAGE 211700 DEC=
  00:51:52> NNNN

      LF Antenna at North Foreland Lighthouse

      There has been a light of some sort at North Foreland, Broadstairs, on the north eastern tip of Kent, since 1499. The first lighthouse was built in 1637 but was subsequently destroyed, the current building was put up in 1691.

      The LF antenna at the site consists of three parallel wires supported at one end by the lighthouse itself and the other by a mast which also has numerous other antennas on it. The 'T' arrangement is centre top connected by three wires which taper down to a common feedpoint near the ground. This was probably the out of service 'NF' beacon (NDB) on 311kHz and is now part of the DGPS system, transmitting on 299.5kHz.

      Marine radio station North Foreland Radio was probably better known to radio amateurs and SWLs. This station was located at a different site not too far away and was taken out of service in 1991, the building which housed the equipment no longer exists.