6.3 MF-HF Equipment Controls (Key Topic 15)

6.3 MF-HF Equipment Controls (Key Topic 15)

Quick Answer: Copy high-seas traffic lists on SSB and FEC. Distress, Urgency, and Safety on MF-HF stay on the six assigned frequencies in simplex. Voice to a coast station is J3E. TELEX is F1B or J2B depending on the manufacturer. Use the lowest power that still works. RIT (clarifier) fine-tunes receive only.

From VHF line-of-sight to MF-HF skywave

VHF is a harbor and coastal tool. Medium frequency (MF, roughly 1.6–4 MHz in the marine radiotelephone sense) and high frequency (HF, the 4, 6, 8, 12, 16, and 22 MHz maritime bands) carry ship-to-shore voice and radiotelex beyond VHF range. Compulsory small passenger vessels 20–150 nautical miles from land, GMDSS A2–A4 ships, and high-seas commercial operators all sit in front of an MF-HF console. Key Topic 15 tests whether that operator can choose mode, frequency class, power, and fine-tune without wrecking a safety circuit or a traffic list. Independent OpenExamPrep study material covering those Element 1 MF-HF controls stays at operator depth: you select J3E or TELEX, you do not redesign the synthesizer.

The six facts are: traffic lists received on SSB and FEC; Distress, Urgency, and Safety confined to the six assigned frequencies in simplex (both to maximize reception by non-GMDSS ships and as DSC follow-up for GMDSS ships); J3E for a voice call to a coast station; F1B or J2B for TELEX depending on manufacturer; lowest power necessary; and RIT/clarifier as a receive-only fine-tune. Key Topic 16 will add 2182 kHz, paired public-coast frequencies, and ITU channel numbering. This section is the control layer those frequencies assume.

Traffic lists: SSB and FEC

A public coast station that holds radiotelegrams or voice traffic for ships at sea does not call every ship individually on a distress frequency. It transmits, at advertised times, an alphabetical traffic list of call signs (or ship names) for which it has traffic. Key Topic 8 already taught that method. Key Topic 15 asks which receive modes can copy those lists from high-seas shore stations.

The tested pair is SSB and FEC:

• SSB (single-sideband radiotelephony, J3E in modern marine use) lets the operator hear the coast station read the list.
• FEC (forward error correction, SITOR-B / Mode B narrow-band direct printing) lets the operator print the list. FEC is a one-way broadcast. The ship does not acknowledge each block. That is why a coast station can send one list to every ship in the ocean that is listening.

Wrong pairs:

• AM and VHF-FM mix an obsolete marine AM voice mode with a short-range VHF system that is not a high-seas traffic-list path.
• VHF-FM and SSB includes SSB (correct) but VHF-FM is not how you copy a high-seas list from a shore station hundreds or thousands of miles away.
• ARQ and FEC includes FEC (correct) but ARQ (automatic repeat request, SITOR-A / Mode A) is a two-way handshake with one coast station. ARQ is how you pass a TELEX after you have been listed, not how you copy a broadcast list intended for all ships. If you initiate ARQ, you occupy the coast station in a point-to-point circuit; you do not receive the FEC broadcast.

Practical setup: at the published UTC list time, select the coast station's MF or HF voice frequency in J3E or its FEC/NBDP broadcast frequency in FEC, according to the ITU List of Coast Stations or the station's traffic list schedule. Do not retune to Channel 16. Do not start an ARQ call just to hear whether your call sign is on the list.

Six assigned frequencies, simplex, for Distress, Urgency, and Safety

All MF-HF Distress, Urgency, and Safety communications take place solely on the six assigned frequencies and in the simplex operating mode. ITU Radio Regulations Appendix 15 assigns those six radiotelephony distress and safety frequencies as:

They are simplex: every station transmits and receives on the same carrier. Voice emission on these frequencies is J3E. Each has a matching DSC distress frequency (2187.5, 4207.5, 6312, 8414.5, 12577, and 16804.5 kHz) used to alert, after which voice traffic moves to the radiotelephony frequency in the same band.

Element 1 asks why those six simplex frequencies, and treats two reasons as both correct:

1. For non-GMDSS ships, simplex on the assigned frequencies maximizes the chance that other vessels receive the Distress, Urgency, or Safety communications. A ship with only an old 2182 kHz watch receiver still hears both the distressed ship and the coast or RCC replies.
2. For GMDSS or DSC-equipped ships, the same simplex voice frequencies maximize the chance that other vessels receive those communications following the transmission of a DSC call of the correct priority. The DSC alert (distress, urgency, or safety) tells listening ships which band and which priority; the follow-up voice must be on the matching simplex distress/safety frequency, not on a duplex public-correspondence pair and not on a private working channel.

The distractor that an RCC or coast station should hear only the vessel actually in distress is the same bad argument as on VHF: rescue needs a public circuit. Duplex would hide the coast station from nearby ships. A random working frequency would hide the event from ships that keep watch only on the six assigned channels. Stay on the assigned simplex frequency until the RCC moves you, and understand that both the non-GMDSS reception reason and the DSC follow-up reason are part of the tested answer.

Voice to a coast station: select J3E

To set up the MF-HF transceiver for a voice call to a coast station, the operator must select J3E for proper voice operations. J3E is single-sideband telephony with suppressed carrier — USB in standard marine practice. It is the emission Key Topic 16 will also require on 2182 kHz. It is not SITOR, and selecting J3E does not configure TELEX.

Wrong setups:

• Selecting J3E for SITOR confuses voice with radiotelex.
• Selecting F1B or J2B for a voice call puts a digital or subcarrier telegraphy emission on a voice channel. The coast operator hears warbles, not speech.
• Choosing F1B/J2B or J3E depending on whether you prefer FEC or ARQ is a TELEX decision, not a voice-call decision. For voice, the mode is J3E. Period.

Tune the coast station's ship-to-shore working frequency for that voice circuit (Key Topic 9: you call a coast station on that coast station's ship-to-shore working frequency), not 2182 kHz for routine traffic. 2182 kHz remains available for distress, urgency, safety, and calling, still in J3E.

TELEX to a coast station: F1B or J2B depending on manufacturer

To set up the MF-HF transceiver for a TELEX call to a coast station, the operator must select F1B mode or J2B mode, depending on the equipment manufacturer. TELEX here means maritime radiotelex / NBDP / SITOR, the printed service that carries messages, weather, and some MSI on MF-HF.

• F1B is frequency-shift keyed telegraphy (the classic SITOR/NBDP designator).
• J2B is an SSB, suppressed-carrier emission with an audio-frequency telegraphy subcarrier — some manufacturers implement DSC or NBDP this way and label the front-panel mode TELEX, NBDP, or FSK even though the ITU designator is J2B.

You do not have to calculate the designator on watch. You do have to select the radio's TELEX / NBDP / SITOR mode rather than J3E voice, and you must accept that the correct ITU designator is F1B or J2B according to how that model is built. Do not select J3E for SITOR. Do not treat FEC versus ARQ as the thing that chooses between J3E and F1B: FEC versus ARQ is the protocol (broadcast versus handshake) inside the TELEX mode, not a reason to switch into voice.

After the traffic list has named your ship, initiate ARQ to that coast station on the working TELEX channel and wait for answerbacks (Key Topic 17 tests that as the best NBDP test). The control fact for Key Topic 15 is only the emission class: F1B or J2B, manufacturer-dependent.

Lowest power necessary

MF-HF transceiver power levels should be set to the lowest level necessary for effective communications. That is the same conservation idea as VHF 1 watt, applied to a transmitter that may be able to deliver 60, 120, or more watts PEP. Excess power on MF-HF skips off the ionosphere into oceans where you are not trying to talk, overloads nearby receivers, and makes a busy working frequency unusable for the next ship.

Do not set power to maximize the propagation radius as a matter of habit. Do not set the highest level so other stations cannot break in — maritime working frequencies are shared, and distress, urgency, and safety must be able to break in. A choice that combines lowest power with maximum power to lock out others is internally contradictory and wrong. Start low, raise if the coast station reports you weak, and drop again when the circuit is solid. Compulsory MF transmitters still must be capable of at least 60 watts PEP (Key Topic 1); capability is not an order to run 60 watts into a ship 20 miles away on a night when 10 watts PEP is loud.

RIT / clarifier: receive fine-tune only

Receiver Incremental Tuning (RIT), often labeled clarifier on marine SSB, is a fine-tune control on the receive frequency. It does not change the transmitted frequency. It does not fine-tune both sides at once.

SSB voice is unintelligible if the receiver is even a few hundred hertz off the transmitter. Two ships, or a ship and a coast station, may not be on exactly the same millihertz. The clarifier lets you make the incoming voice sound natural without dragging your transmitter off the assigned channel. If you instead retune the main VFO to sweeten the receive audio, you will transmit off-frequency and the other station will have to chase you.

Operating habits:

• Leave RIT at zero when you initiate a call, so you start on the assigned channel.
• If the other station sounds low or high in pitch, adjust RIT only until speech is natural.
• If they still cannot copy you, your transmit frequency or their receiver is the problem — not something RIT will fix.
• Do not use RIT as a substitute for selecting the correct ITU channel, USB, or J3E.

Some amateur transceivers offer a transmit clarifier or XIT. Marine Element 1 does not treat RIT as a transmit control. If the distractors say it fine-tunes transmit, or both transmit and receive, they are wrong.

MF-HF console checklist

Set mode first, frequency second, power third, clarifier last. That order keeps a TELEX modem out of a MAYDAY, keeps a MAYDAY on a simplex assigned frequency, and keeps your carrier on the channel the coast station published.