24 August 2014

CARB messages

CARB is the acronym for Channel Availability and Receipt Broadcast, these transmissions radiate information on the frequencies available for ship-shore traffic and to pass control and receipt messages; sometimes also indicated as FAB or Frequency Availability Broadcast. Some naval stations use both RTTY and STANG-4285 for CARBs, sometimes interspersed with pseudo-random encrypted data (see CTA CARBs).

CARB procedures are used to automatically perform a channel-link before a message could be sent.
A number of receivers ashore are combined to omni-directional aerials, the frequencies being those advertised on the CARB. A ship wishing to send a message raises a transmitter on the optimum frequency available and send a test message. This message includes an indication of the ship's position with reference to the directional aerials available to the receivers ashore. The shore station selects the best directional aerial to receiver and acknowledges the receipt of the test message by a condition code on the CARB transmission. A second test message from the ship measures the quality of reception and requests transmission of traffic. The ship then passes its traffic, receiving recepits on the CARB until its traffic is cleared. The shore station then returns his receiver to an omni-directional aerial and resets the CARB.

Some CARBs examples (the ending "I" usually stands for I(N) IDLE)

CTA NATO Lisbon, POR (STANAG-4285)

PBB Dutch Navy Den Helden, HOL (RTTY 75/850)
02A 04B 06A 08B 12A 16X PBB
04O 06A 08B 12A 16X 22X PBB 

IDN Nato Allied Joint Force Command Naples, I (STANAG-4285)

IDR/IGJ Italian Navy Rome, I (STANAG-4285)
IDR2 /IGJ42 /IGJ43 /IDR8 /IDR3 /IGJ41 /
IDR2 /IGJ42 /IGJ43 /IDR8 /IDR3 /IGJ41 /
IDR2 /IGJ42 /IGJ43 /IDR8 /IDR3 /IGJ41 /
IDR2 /IGJ42 /IGJ43 /IDR8 /IDR3 /IGJ41 /

In this real-world CTA message (courtesy by Wolfgang from UDXF) they QSL #3849
and the QSX seems to be on 6 MHz (CTA06)
Some CARBs transmissions heard at my side
PBB CARB transmission

IDN CARB transmission

CTA CARB transmission

IDR Rome CARB transmission
TBB Turkish Navy Ankara, CARB Transmission

CTA/CTP CARB transmission

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