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Curiosity Insight

Curiosity Insight

Learning never exhausts the mind

How Does a VHF Radio Work?

August 8, 2020 By Miranda Jackson Leave a Comment

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 

Filed Under: Science & Technology, Topics

About Miranda Jackson

I am a chemistry researcher and research various household products to make life easier and enjoyable for people around the world.

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