245. Give the full names of the following abbreviations or acronyms:

a. R/T =                   Radio Telephone or Radio Telephony 

b. MF =                    Medium Frequency

c. RSGB =                Radio Society of Great Britain

d. SES =                   Ship Earth Station

e. USB =                   Upper Side Band

f. OWF =                  Optimum Working Frequency

g. INMARSAT =     International Maritime Satellite Organisation

h. RF  =                   Radio Frequency

i. ITU =                    International Telecommunication Union

j. ATU =                  Aerial Tuning Unit

246. What is: – 

a. a Hertz? =              1 cycle per second (1 c/s)

b. KiloHertz? =         1000 Hertz

c. MegaHertz? =      1000 kiloHertz (one million Hertz)

d. 1 GigaHertz? =     1000 megaHertz (one thousand million Hertz)

e. Wavelength? =    length of an electromagnetic radiowave from peak to peak, and is

                                                       inversely proportional to frequency, so that…

                               Wavelength (metres) =        300 x 106       .

                                            Frequency (kHz)

247. Describe two ways in which intelligence can be impressed upon a radio wave.

Intelligence can be impressed on a radio emission by modulation.

c. Amplitude Modulation (AM) where the amplitude of the carrier is varied by the audio

    waveform from the sound source (speech, music., etc)

d. Frequency Modulation (FM) where the frequency is fluctuated by the audio waveform with

the amplitude staying constant (used in high quality broadcasting and for VHF R/T)

248. List six radio communication systems of interest to small craft mariners and indicate which of these are of particular interest for long-distance communication.

Radio communication systems available to small craft include:

a. VHF radiotelephony – short distance (line of sight) communication in coastal waters

b. MF radiotelephony – range approximately 200 – 300 miles

c. *HF SSB Marine Radio – possible world-wide radiotelephone communication.

d. *INMARSAT-C and *INMARSAT-M satellite communication systems.

e. CD Radio – limited to coastal waters for social and club purposes only.

f. *Amateur SSB Radio – possible world-wide communication for those suitably qualified.

Systems marked * are suitable for long-distance communication.

249. List the units comprising a complete marine SSB station.

e. A Marine SSB Station  comprises a transceiver, aerial, aerial tuner unit and a

    ground-plane (earth)

f. An Aerial Tuner Unit (ATU) is necessary to tune (automatically) the aerial to the

     Frequency being used by the transceiver and is mounted

     between the two units.

g. A Ground-plane system  for a sailboat usually has 60-100 sq ft (6-9 sq metres) of 

     metal surface below the hull earthing the ATU and the

     transceiver. A lead keel may be used for the ground-plane.

 

250. What is the ATU and what is its purpose?

Power Input for most small craft SSB sets is 12 volts but radio transmitters are particularly sensitive for variations in input and will normally only give their optimum output for a specific (usually 13.6v) input voltage. Consequently the battery charger (engine or generator) should be kept running while the transmitter is in operation.

251. Describe a ground-plane system suitable for a sailing yacht.

h. Ionospheric layers are reduced to two by night because they are formed by intense ultra violet radiation from the Sun, and      this disappears at night.

i. Because of the weakly ionised F layer, the maximum HF frequency which can be refracted is reduced by a factor of about 2.

252. What power input is required for a marine SSB set and why is this critical?

253. Why are there only two ionospheric ‘layers’ at night as opposed to four by day?

254. How does this affect the propagation of HF (short wave) radio during the day?

255. What is a CRS and on what frequencies do they usually operate?

j. Coast radio Stations (CRS)  usually operate on VHF and MF, occasionally HF.

k. Portishead Radio   is used for world-wide R/T communication with the UK on HF.

l. Distress frequencies are:

                                                                        VHF : Channel 16 (156.8 Mhz)

                                                                        MF : 2182 kHz

                                                                        HF : 4125 kHz or 6215 kHz

256. What is the difference between Marine HF SSB Radio and Amateur HF SSB Radio?

257. Briefly describe the Maritime Mobile Networks.

m. Amateur (‘Ham’) SSB Radio differs from Marine SSB Radio in that it is basically a person-to-person fun activity where licensed amateurs communicate with other licensed amateurs. The equipment is inhibited to transmit only on allotted amateur bands and does not have the accuracy or stability required for Marine SSB Radio. Messages for third parties (links to shore telephones) are strictly prohibited.

n. Maritime Mobile Networks are groups of frequencies and set times at which ocean cruising mariners can communicate with each other and with amateurs ashore, e.g., the Atlantic Net, the Caribbean Net, etc.

258. Why is INMARSAT-C more suitable for small craft than Inmarsat-A or Inmarsat-B?

259. What is the difference between a Class 1 SES and a Class 2 SES?

260. Why is INMARSAT-M the ideal satellite communication system for leisure craft?

a. The INMARSAT-C system of satellite communication is preferred for small craft because it uses a fixed omni-directional antenna instead of the large steerable dish necessary for Inmarsat-A and Inmarsat-B.

b. A Class 1 SES can be used only for ship/shore messages and distrsess alerting.

c. A Class 2 SES is as Class 1 plus the capability of receiving Enhanced Group Calls (EGC) – maritime safety information from authorised providers.

d. INMARSAT-M is ideal for leisure craft because:

      i. terminals can be fitted to craft as small as 10 metres in length

     ii. Initial outlay and call charging is relatively small

    iii. Offers voice, facsimile and data communications.