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AERO DX
AERO DX.
Aeronautical Communications on HF.
Introduction:

Trans Atlantic Aircraft communications can either be very boring or very exciting. Depending on several issues. Most simple explanation could be because these frequencies are not active all the time and are not always on the frequency that you are listening to at the present time. Also the frequencies in use will depend upon, your own location, the time of day or night and conditions which affect radio wave propagation especially on HF frequencies. Most of us are well familiar that at the VHF band (118-136 MHz) for the civil aircrafts and in the UHF band (225-400 MHz) for the Military aircrafts allots of air traffic can be monitored. In consideration with HF Air Communications this is quit another story, it even becomes a challenge some times. The frequency tables below will hopefully helps you succeeding in your first contact with AERO DX'ing. Hearing aero stations from more than 8000 miles distant isn't impossible. it just seems that way!

HF Enroute Aero Frequencies
NAT-A NAT-B NAT-C NAT-D NAT-E NAT-F
3016 2899 2862 2971 2962 3476
5598 5616 5649 4675 6628 6622
8906 8864 8879 8891 8825 8831
13306 13291 13306 11279 11309 13291
17946 17946 17946 13291
17946
13354 11339

The aeronautical HF Network
  In many parts of the world, Oceans, Deserts or Jungles, the use of the VHF band is impractical for passing the ATC or flight information messages used by Air/ground communications. The aeronautical HF Network is a worldwide network of HF stations equipped with KW transceivers for the use of both Civil and Military en route aircrafts. The ICAO has divided the world in to several HF regions. Witch are shown in the table below.
NAT - North Atlantic EUR - Europe
SAT - South Atlantic MID - Middle East
AFI - Africa INO - Indian Ocean
SEA - South East Asia SAM - South America
CAR - Caribbean P - Pacific Ocean
NCA - North Central Asia CWP - Central West Pacific
CEP - Central East Pacific EA - East Asia
NP - North Pacific SP - South Pacific

  Each of these large regions are then sub-divided into several smaller regions, and allocated a number of HF frequencies. It there fore can always be possible to hear several HF stations operating on the same frequency within such a family. This reduces the change of an aircraft loosing contact with a ground station. It should be pointed out that the areas covered by by a HF family are based upon radio coverage and not on airspace boundaries. All HF transmission is J3E emissions, Single Side Band carrier.

Major World Air Route Frequency List
North Atlantic (NAT) 2872 - 2899 - 2962 - 2971 - 3016 - 3476 - 4675 - 5598 - 5616 - 5649 - 6622 - 6628 8825 - 8831 - 8864 - 8879 - 8891 - 8906 - 11279 - 11309 - 11336 - 13291 - 13306 - 17946
Caribbean (CAR) 2887 - 3455 - 5520 - 5550 - 6577 - 6586 - 8846 - 8918 - 11387 - 11396 - 13297 - 17907
South Atlantic (SAT) 2854 - 2935 - 3452 - 5565 - 6535 - 8861 - 11291 - 13315 - 13357 - 17955
South America (SAM) 2944 - 3479 - 4669 - 5526 - 6649 - 8855 - 10024 - 10096 - 11360 - 13297 - 17907
Europe (EUR) 3479 - 5661 - 6598 - 10084 - 13288 - 17961
Middle East (MID) 2944 - 299 - 3467 - 3473 - 4669 - 5658 - 5667 - 6625 - 6631 - 8918 - 8951 - 10018 11375 - 13288 - 13312 - 17961
Africa (AFI) 2851 - 2878 - 3419 - 3425 - 3467 - 4657 - 5493 - 5652 - 5658 - 6559 - 6574 - 6673 8894 - 8903 - 11300 - 11330 - 13273 - 13288 - 13294 - 17961
Indian Ocean (INO) 3476 - 5634 - 8879 - 13306 - 17961
North Central Asia (NCA) 3004 - 3019 - 4678 - 5646 - 5664 - 6592 - 10096 - 13303 - 13315 - 17958
East Asia (EA) 3016 - 3485 - 3491 - 5655 - 5670 - 6571 - 8897 - 10042 - 11396 - 13297 - 13303 - 13309 - 17907
Southeast Asia (SEA) 3470 - 348 - 5649 - 5655 - 6556 - 8942 - 10066 - 11936 - 13309 - 13318 - 17907
Central West Pacific (CWP) 2998 - 3455 - 4666 - 5652 - 5661 - 6532 - 6562 - 8903 - 10081 - 11384 - 13300 - 17904
Central East Pacific (CEP) 2869 - 3413 - 4657 - 5547 - 5574 - 6673 - 8843 - 10057 - 11282 - 13300 - 17904
North Pacific (NP) 2932 - 5628 - 6655 - 6661 - 10048 - 11330 - 13300 - 17904
South Pacific (SP) 3467 - 5559 - 5643 - 8867 - 10084 - 11327 - 13300 - 17904

Selcal
  In order to reduce pilot workload on long flights, the Selcal system has been called to live to enable crews to receive messages from the ground stations without having to maintain a listenings watch. The system has been called Selective Calling , better known as Selcal.
Each Aircraft is allocated a four digit code; this being transmitted by the ground staton as two short pulses. The equipment is connected to the HF radios on aircraft and monitors for a call even when the squelch is turned up, and the pilots can hear nothing. This enables the pilots to have some aural peace when crossing the Atlantic or other oceans as HF radios can be very noisy. Selcals are made up of a four letter code and when heard have a distinctive bing-bong sound. As a flight enters the Oceanic FIR, a Selcal check is made the signal activates the on board Selcal receiver which alerts the pilots with a flashing warning light and an audible alarm. These pulses can mostly heard very clearly. It is therefore quite possible to ascertain a aircrafts registration from it's Selcal.
Also every effort is made to allocate codes in such a way that no aircraft with the same code are likely to be on the same frequencie at the same time.

 

Issued by Pascal.

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