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
