Radiotelephones came into use in the 1920's and 1930's.  Radiotelephones are a means of voice communications with a shore or ship telephone via marine operator, directly with a dispatcher, agent or owner, or directly with other vessels.

The first radiotelephones were amplitude modulated (AM).  These were subject to interference by atmospheric noise and man-made noise.  The operating frequencies range between 2 and 23 Megahertz; the operating range under favorable conditions is several thousand miles.

In the 1950's a very high frequency (VHF) band of frequencies was set aside for marine use.  At first there were 26 channels.  Communication is essentially line-of-sight, making the useful range about 20 miles offshore from a shore station.  In the late 1960's the number of channels was doubled by making each channel half of the bandwidth (50 kilohertz per channel was changed to 25 kilohertz).

The VHF marine channels are frequency modulated (FM), providing some immunity to noise.

In the 1960's, Single Sideband (SSB) began to come into use.  SSB has an advantage of needing less then one-half the bandwidth that AM requires.  With the reduced bandwidth, interference by noise is somewhat reduced, and the number of available channels was more then doubled.  The use of SSB was encouraged.  In 1977 AM usage by law ceased; all high seas communications were mandated to be SSB.


VHF-Radio Telephone

Modar Electronics – D33ADA1020A

Manufactured by: Modar Electronics, Subsidiary of Motorola

Model: D33ADA1020A

Capacity: 55 Channels Synthesized, 25W/1W

Frequency Range: 156-157.45 MHz TX

                            156-163 MHz RX

Power Requirement: 12VDC


Standard Comm. Corp. – Horizon MAXI

Manufactured by: Standard Comm. Corp.

Model: Horizon MAXI

Capacity: 55 Channels Synthesized, 25W/1W

Frequency Range: 156-157.45 MHz TX

                            156-163 MHz RX




Intech – V-108

Manufactured by: Intech

Model: V-108

Date of Mfg: 1-78

Capacity: 12 Channels, Crystal, 25W/1W

Power Requirement: 12VDC 5 Amp




Cybernet – CTX7800S

Manufactured by: Cybernet

Model: CTX7800S

Capacity: 55 Channels, Synthesized, 25W/1W







Intech – Mariner 90

Manufactured by: Intech

Model: Mariner 90

Date of Mfg: 4-81

Capacity: 55 Channels, Synthesized, 25W/1W





Konigsberg Electronics – KR-25W

Manufactured by: Konigsberg Electronics (Konel)

Model: KR-25W

Capacity: 12 Channels, Crystalled, 25W/1W






Ray Jefferson – 7878M

Manufactured by: Ray Jefferson, Div of Jetronic Industries Inc.

Model: 7878M

Capacity: 55 Channels, Synthesized, 25W/1W







Single Sideband Receivers

Harris – RF-230M

Manufactured by: Harris

Model: RF-230M

Capacity: 95 Channels Synthesized

Frequency Range: 2-23MHz






Hull – 922

Manufactured by: Hull

Model: 922

Capacity: 22 Channels Synthesized

Frequency Range: 2-10MHz





Northern Radio Company – N550A

Manufactured by: Northern Radio Company

Model: N550A

Capacity: 48 Channels Synthesized

Frequency Range: 2-23MHz





Intech – Mariner 500

Manufactured by: Intech

Model: Mariner 500

Date of Mfg: 9-83

Capacity: 12 Channels

Frequency Range: 2-3.4MHz

Power Requirement: 13.6VDC 20 Amp



Watch Receiver

A watch receiver is a receiver dedicated to guarding a distress frequency. A high seas watch receiver is usually quiet. It will unsquelch when a distress signal of the proper format is received. It will not respond to ordinary calls to establish communication. The frequency is 2.182MHz, the international distress and calling frequency.

A marine V.H.F. watch receiver is dedicated to guarding channel 13 (156.650MHz) for safety (security) broadcasts. It is especially useful for vessels running coastwise or in harbors. Some channel 13 receivers include a transmitter so that a safety situation can be transmitted to other stations in the vicinity.

Intech Mariner 1511

Manufactured by: Intech

Model: Mariner 1511

Date of Mfg: 5-81

Capacity: 12 Channels Crystal

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