RYA SRC Part 3 — The VHF Set: Controls, Antennas, and Power

21 May 2026 PersonalSRCRYAvhf-equipment

Syllabus coverage: CEPT/RYA sections B1 (VHF radio installation, basic controls, handheld VHF) and B3 (antennas, interfacing, power sources).

Part 2 covered what the radio transmits on. This post is about the radio itself — what every knob does, what’s different between fixed and handheld sets, and how the antenna and power supply behind the radio shape whether your transmissions actually go anywhere.

Fixed versus handheld

Both share the same band, channel plan, and DSC core. The differences are mechanical and electrical, not regulatory.

Fixed VHF DSC sets are mounted at the chart table or helm, powered from the vessel’s 12 V DC system, fed by an external antenna (typically masthead on a sailboat), and rated for 25 W output. They support full DSC functionality and usually integrate with the vessel’s GNSS for automatic position embedding in distress alerts.

Handheld VHF DSC sets are battery-powered, internal antenna (a stubby rubber duck), and rated for 5–6 W max. Newer ones include their own GNSS receiver. They’re rated to IP67 or better — designed to survive immersion. They’re the radio of choice for kayaks, paddleboards, dinghies, and as a backup on yachts.

Both can hold MMSIs. A handheld typically requires a Ship Portable Radio Licence (covered in Part 9) with a portable MMSI prefixed 8 in the UK (the “8MID” format — 235 8XXXXX for UK portables). A handheld permanently installed on a vessel can sit under the vessel’s standard Ship Radio Licence.

The controls — what every knob does

A modern Class D DSC VHF has the following controls. Every exam asks about several.

Power on/off. Self-explanatory. Some sets hold the volume knob and power button together; others split them.

Volume. Adjusts received audio level only. Does not affect transmit power.

Squelch. This is the one the syllabus drills hardest. The squelch circuit mutes the receiver until incoming signal exceeds a threshold; without squelch, you hear the hiss of background RF noise constantly. Setting procedure for the exam: turn squelch fully down (or anti-clockwise) until you hear hiss, then turn it up slowly until the hiss just disappears. That’s the correct setting — sensitive enough to catch weak signals, deaf enough to reject pure noise. Too tight a squelch and you’ll miss distant traffic.

PTT (Press-To-Transmit). Pressed = transmitting, released = receiving. You cannot transmit and receive simultaneously on a simplex channel. Common operator error: leaving the PTT held down with no message, blocking the channel.

High/low power switch. Fixed sets toggle between 25 W (high) and 1 W (low). Handhelds typically toggle between 5–6 W and 1 W. Use low power whenever you can — on intership/port channels at short range, low power reduces interference to other users and extends handheld battery life. Some channels are restricted to low power only: CH15, CH17 (guard bands either side of CH16) and CH75, CH76 (guard bands either side of CH70) are 1 W maximum. Class D sets enforce this automatically.

Channel selector and CH16 priority key. A dedicated key jumps straight to CH16 from any other channel. Critical in distress situations — don’t fumble.

Dual-watch and tri-watch. Dual-watch monitors CH16 plus one other channel; the set briefly hops between them. Tri-watch adds a third channel (usually a marina/port channel). Useful underway when you want to keep the calling watch on 16 while waiting for a marina to call you back.

Scan. Cycles through all channels (or a programmed subset) looking for active traffic. Stops on a busy channel. Useful for monitoring port operations on transit; not for normal operation.

Dimmer. Adjusts display backlight. Night sailing.

DSC distress button. Usually under a hinged red flap to prevent accidental presses. Press and hold (typically 3–5 seconds depending on manufacturer) to send a distress alert. Covered in detail in Parts 4 and 5.

Channel and mode display. Shows the selected channel, dual/tri-watch state, power level, squelch level, battery indicator (handhelds), and DSC menu state.

DSC menu navigation buttons. A combination of soft keys and a directional pad. Used for sending individual or all-ships announcements, entering manual position, browsing the directory, reviewing received messages, and self-testing.

Handheld specifics

The CEPT syllabus has a separate section for handheld features (B1.3). Things the exam expects you to know:

  • Power output is typically 5–6 W on high, 1 W on low. A handheld will never reach as far as a 25 W fixed set, especially with its tiny antenna at deck level.
  • IPX7 / IPX8 water rating is standard now — immersible for short periods. Salt spray after a long sail still wants rinsing off.
  • Floating handhelds exist — handy for MOB scenarios.
  • Always carry a spare battery or have a charging routine that keeps your handheld at full charge when you leave the dock. A dead handheld at the wrong moment is worse than not having one.
  • Handhelds rarely interface to external GNSS, so position usually has to be entered manually (or comes from the handheld’s own built-in GNSS on newer models).
  • The DSC distress function exists on Class D handhelds, with the same flap-and-hold pattern.

Antennas — line of sight wins

VHF is line-of-sight (Part 2). Antenna height matters more than antenna gain in almost all practical small-craft cases. A masthead antenna at 15 m beats a deck-mounted antenna at 2 m every time, regardless of gain.

Antenna gain — what it means

Gain in VHF antennas is measured in dBd (relative to a dipole) or dBi (relative to an isotropic radiator; dBi = dBd + 2.15). It’s not “more power” — it’s a focusing of the radiated power into a narrower vertical pattern.

  • 3 dBd antenna — short, wide radiation pattern. Donut-shaped emission with significant vertical spread.
  • 6 dBd antenna — taller, narrower pattern. More effective horizontal reach but tighter vertical.
  • 9 dBd antenna — even narrower. Mostly used by stable powerboats with low antenna heights.

Why sailboats use low-gain mast-top antennas

A sailboat heeled at 25° has its masthead antenna tilted at 25°. A high-gain antenna with a narrow vertical pattern will radiate most of its power above or below the horizon when the boat heels — so under sail you lose more than you gain. Sailboats typically use a 3 dBd antenna at the masthead.

Powerboats sit more level and use 6 or 9 dBd antennas mounted lower on a radar arch or coachroof.

Construction

Maritime VHF antennas are typically fibreglass-encapsulated whip antennas with a stainless steel mounting and a coaxial feed. Cable loss matters on long runs — every metre of RG-8X or similar coax loses a few percent of signal at 156 MHz. A masthead antenna with 20 m of cheap cable can have less radiated power than a deck antenna with 2 m of good cable. For sailboats, low-loss coax (RG-213, LMR-400) is worth the extra cost.

Mounting and positioning

  • Antenna up high.
  • Antenna vertical.
  • Connectors waterproofed (self-amalgamating tape over the PL-259 / N connector).
  • Clear of other metal structures that distort the radiation pattern.
  • For sailboats with windvanes/wind instruments at the masthead, the VHF antenna usually sits on a small bracket on the masthead crane.

The exam may ask you to compare two configurations (handheld at sea level vs. fixed set with masthead antenna) and identify which has the longer range. The answer is always: line of sight, so the higher antenna wins.

Power sources

Fixed sets

Fixed VHF DSC runs from the vessel’s 12 V DC. Typical current draw: a few hundred milliamps on receive, around 5 A on transmit at 25 W. A small fuse on the supply line (typically 7.5 A) protects the wiring.

The set will tolerate a voltage range — typically 10.8 V to 15.6 V — but if the battery sags below the lower limit during transmit (because the alternator isn’t running and the battery’s tired) the radio may brown out mid-MAYDAY. Worth knowing for the exam: monitor your battery state, especially after a night on anchor.

Handheld batteries

Modern handhelds run on lithium-ion battery packs, typically 7.4 V nominal, 1500–2500 mAh. Older sets use NiMH. A few accept alkaline AA backup in an emergency tray.

  • Lithium-ion: best energy density, no memory effect, but degrades with deep discharge and high temperature. Don’t store at full charge in a hot cabin; don’t store at 0% charge for months either. Around 50% charge is best for long storage.
  • NiMH: tolerant of partial cycling but does suffer mild memory effect. Discharge fully every few months.
  • Charging routine: keep one battery on charge always; rotate batteries every few weeks if you have multiple.

The syllabus expects you to be aware that:

  • Different battery chemistries have different requirements.
  • A spare battery is part of standard equipment for a handheld.
  • Batteries have a useful life of a few years and need replacing when capacity falls.

EPIRB and SART batteries

EPIRBs and SARTs use specialised long-life lithium batteries with a printed expiry date — typically 5 to 10 years. Replace at expiry by the manufacturer or an authorised service agent, not at home. Activation in a real emergency must work; you cannot test the genuine transmit chain without an actual satellite alert. Some EPIRBs allow a self-test that confirms the battery and beacon electronics without transmitting to satellites.

Interfacing — getting position into DSC

DSC distress alerts include the vessel’s position, time, and (if known) nature of distress. The set needs to know its position. Two ways:

  1. External GNSS via NMEA — the chartplotter or dedicated GPS sends a position string (NMEA 0183 at 4800 baud, or NMEA 2000) to the VHF set. The set parses the position out of $GPRMC or $GPGGA sentences and uses it automatically. Fastest, most reliable.
  2. Built-in GNSS — modern VHF DSC sets often include their own GNSS receiver. The set is self-sufficient; no chartplotter needed.
  3. Manual entry — if neither is available, you can enter position via the menu. The exam expects you to know: manual position must be updated at least every 4 hours, otherwise the DSC alert carries stale data. The set may prompt you periodically.

A DSC distress alert with no position is still useful — RCCs can direction-find on the alert and ask follow-up questions — but a precise position cuts SAR response time dramatically.

Maintenance

A VHF set lives in a salty, vibrating, occasionally wet environment. Routine attention:

  • Rinse handhelds in fresh water after use in spray.
  • Check antenna connectors for corrosion every season.
  • Listen on CH16 occasionally just to confirm reception works.
  • Replace handheld batteries at the manufacturer’s interval (usually 3–5 years for genuine performance).
  • Test DSC functionality (using the set’s built-in test function, not a real distress alert) periodically.
  • Replace EPIRB and SART batteries at their printed expiry date, with the manufacturer.

What to take into the next post

You should leave Part 3 able to:

  • Describe the function of every front-panel control on a Class D DSC VHF set.
  • Explain how to set squelch correctly.
  • State when to use low power and where it’s mandatory (CH15, 17, 75, 76).
  • Explain why antenna height matters more than antenna gain.
  • Choose between 3, 6, and 9 dBd antennas for sail versus power.
  • Describe the three ways position gets into a DSC alert and how often manual position must be updated (4 hours).

Part 4 takes the deepest dive in the series — Digital Selective Calling itself, the MMSI structure that addresses every DSC station in the world, and the menu paths you’ll actually press during the practical exam.