How Does a VHF Radio Work?

Good to know: Since the reform of the 240 division in May 2015, the fixed VHF radio is mandatory as of 1 January 2019 more than 6 miles (10km) from a shelter (Ocean navigation). 

First and foremost safety equipment, like sounders or marine GPS, VHF marine radio plays several roles at sea: ensuring contact with both the surrounding boats and the coast (port services, marinas, etc.), get weather info, and finally send distress and safety messages. These marine electronics devices operate at high frequencies between 156 and 162.025 MHz. That being said, it remains to be seen on which VHF marine radio to orientate, as the choice offered by the specialized brands in this sector (Navicom, Cobra, Garmin, etc.) has become important. 

How does it work? 

The radio is based on a communication system that works on the diffusion in the electron wave space. The radio link is possible thanks to a transmitter and a receiver which are both connected to an antenna.
The microphone that receives the voice transforms and encodes it into an electrical signal. The transmitter processes this signal step by step which will then go to the antenna-transmitter through a cable. This antenna transforms it in turn to make an electromagnetic wave. These waves will travel subsequently from the antenna-transmitter to the antenna-receiver. 
On the side of the receiver, its antenna transforms the electromagnetic wave that has reached it again into an electrical signal. Transmitted by cable to the receiver, this signal will be processed by the elements of the receiver which will turn it into a sound signal, the one that can be heard coming out of the speakers. 
The VHF band is shared between many users, aeronautical, maritime, private, military and FM radios. 

Fixed or Portable VHF Radio?

As seen previously, the marine portable VHF has a so-called “optimal” range, varying according to the height and the length of the antenna as well as the power of the transmitter. Parameters that penalize the portable VHFwhose power extends between 1 and 6 watts and has a compact antenna. Thus its range will not exceed 5 miles.

For its part, the fixed VHF multiplies the advantages: its emission power first of 25 watts maximum which allows a boat-boat communication of 30 to 40 miles to a coast station and a fixed antenna positioned most of the time at the highest on the boat. Its autonomy is 5 to 8 hours under normal use. Also, it benefits from DSC (Digital Selective Call) technology or French ASN (Digital Selective Calling), a security system initially implemented on commercial and fishing vessels, but which has become increasingly popular. For pleasure.

The DCS is also part of the characteristics of some portable models: the VHF RT 420 DCS from Navicom is one of them. 

Regulation

Marine VHF, whether fixed or portable, are subject to common regulations. They must first be declared to the National Agency of Frequencies (ANFR) which issues a free license and a personal call sign (MMSI). This document must be on board.

Also, until March 2011, a Restricted Radiotelephone Operator Certificate (CRR) was mandatory for portable VHFs with a power of fewer than 6 Watts. As regulations have evolved, the CRR is no longer mandatory in French territorial and internal waters. Finally, the use of VHF on land is prohibited, walkie-talkies will be used.

This regulation is valid for both fixed and portable VHF.

Protection index (IP)

Present on all marine VHF, the protection index meets an international standard of the International Electrotechnical Commission. Its index varies from 0 to 8, the IPX 8 corresponding to the highest level of sealing (1.5 meters for 30 minutes).

Index	Sealing
IPX 0	Without protection
IPX 1	Protection against vertical drops
IPX 2	Protection against oblique drops (maximum inclination 15 °)
IPX 3	Protection against water ” in the rain”
IPX 4	Splash protection
IPX 5	Protection against water jets
IPX 6	Protection against water packets
IPX 7	Immersion protection (up to 1 meter for 30 minutes)
IPX 8	Protection against permanent immersion (up to 2 meters for 30 minutes)

What are the differences between the models?

Since VHFs are identical regarding mandatory functions and transmission powers, another series of criteria will make the difference in the purchase of your communication tool.

As for the fixed VHF marine, the difference between the models will be played on the tightness of the device or the addition of additional functions such as the possibility to configure them in-network in order to communicate with the other VHF of the edge (intercom), to be equipped with DSC outputs, “Digital Selective Call”: this service makes it possible to send a distress call. The peculiarity is that the transmitted message is digital, uniquely identifying the transmitter by containing its position and the nature of the disaster (to be selected beforehand by the issuer or after 30 seconds of non-selection, transmits a generic signal). Or  AIS ( Automatic Identification System ) for interfacing with a compatible card reader, etc.

Portable VHF, meanwhile, are distinguished by their autonomy, size, tightness, and buoyancy.

Below is the table of VHF mono and bi-frequency channel assignments in the mobile maritime service:

Channel	Frequency (kHz)	Frequency (kHz)	affectation
	Program	Reception
3	156 150	160,750	CROSS
4	156,200	156,200	CROSS
5	156,250	156,250	Port Authorities
6	156,300	156,300	Ship Ship
7	156,350	156,350	Navy
8	156,400	156,400	Ship Ship
9	156,450	156,450	PLAISANCE PORTS – Capitainerie Plaisance
10	156,500	156,500	National Marine (semaphore)
11	156,550	156,550	Navy
12	156,600	156,600	Port Authorities
13	156 650	156 650	CROSS and Port Authorities
14	156,700	156,700	Port Authorities
15	156,750	156,750	BEACH SURVEILLANCE
16	156,800	156,800	CALL – DISTRESS – SECURITY
17	156,850	156,850	National Marine and Port Authorities
18	156,900	161,500	Locks – CP – France Telecom
19	156,950	161,550	Port Authorities
20	157,000	161,600	Port Authorities
21	157,050	161,650	Port Authorities
22	157,100	161,700	Port Authorities
23	157 150	161,750	PNM
28	157,400	162,000	PNM
63	156,175	160,775	CROSS and Port Authorities
64	156,225	160,825	CROSS and Port Authorities
67	156,375	160,975	CROSS
68	156,425	161,025	CROSS
69	156,475	161,075	Navy
70	156,525	156,525	DIGITAL – DISTRESS SECURITY
71	156,575	161,175	Navy
72	156,625	161,225	Ship – Ship
73	156,675	161,275	National Marine and Port Authorities
74	156,725	161,325	Navy
75	156,775	161,375	Canal 16 guard band
76	156,825	161,425	Canal 16 guard band
77	156,875	161,475	Ship – Ship
79	156,975	161,575	CROSS and Port Authorities
80	157,025	161,625	CROSS and Port Authorities
82	157,125	161,725	National Marine and Port Authorities
83	157,175	161,775	Port Authorities
85	157,275	161,875	Navy
86	157,325	161,925	Navy

Channel 16 is an international maritime distress frequency. It must be continuously watched by all the ships because at sea we are all solitary (it is especially a non-assistance of a person in danger). For an antenna at 1.80 meters, the operating range is 13km which gives a meager window of distress. Vessels are required to watch over this frequency to rescue or relay the distress of another vessel. 

As stated at the beginning of the article, the obligation to have a fixed VHF radio is imposed by the 240 Division. This also requires to have an offshore license, but in international waters, it is necessary to have the Restricted Radiotelephone Certificate (CRR).

Similar to the driver’s license code, the exam consists of an MCQ on the marine preparation manual program. The CRR in your pocket will then have a radio-maritime identifier for the use of VHF, beacon.

Glossary

• RADIO: Receiver of Emissions broadcast by 
• VHF Radio waves: Very High Frequency