Modern VHF Marine Band Radios: Transmitters and Receivers

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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Modern VHF Marine Band Radios: Transmitters and Receivers

Postby jimh » Sun Oct 15, 2017 9:09 am

VHF Marine Band radios now contain many receivers connected to the same antenna. In addition to the primary tunable voice receiver, all VHF Marine Band radios with digital selective calling (DSC) contain a second receiver that is also connected to the antenna so it can receive DSC transmissions at 156.525-MHz. In a similar manner, a VHF Marine Band radio with an AIS receiver will also have two more receivers connected to the antenna, one listening at 161.975-MHz and a second listening at 162.025-MHz.

The receiver sensitivity of a VHF Marine Band radio with DSC or with DSC and AIS is rated the same as similar radios without the additional one to three receivers connected to the antenna. I do not see much cause for concern that the receiver performance will suffer if a VHF Marine Band radio has a DSC receiver or integral AIS receivers.

Note that whenever a VHF Marine Band radio is transmitting, the receivers are not connected to the antenna. They cannot affect the transmitter performance.

To summarize, the SIX receivers and transmitters contained in a modern VHF Marine Band DSC radio with AIS receive are:

RECEIVERS
--tunable receiver for marine band voice signals, 156 to 162-MHz; 161 to 163-MHz for weather band voice signals
--fixed tuned receiver for DSC digital signals at 156.525-MHz
--fixed tuned receiver for AIS digital signals at 161.975-MHz
--fixed tuned receiver for AIS digital signals at 162.025-MHz

TRANSMITTERS
--tunable transmitter for voice signals, 156 to 162-MHz
--fixed tuned transmitter for digital DSC at 156.525-MHz

Some VHF Marine Band radios may include an AIS transmitter, adding a SEVENTH device:

--tunable transmitter for digital AIS signals, either 161.975 or 162.025-MHz

In a radio with an integrated AIS transmitter, it would be typical that the AIS receives and transmitter would utilize a separate antenna dedicated only to that purpose.