VHF Survival Craft Transceiver (SCT)
GMDSS Survival Craft Transceivers (SCTs) are portable, two-way VHF transceivers capable of radiotelephone communications. These small lightweight radios are used for on-scene communications between rescue units and the survival craft. These SCT's can be used as on-board communications when the batteries are of the re-chargeable type and they are capable of operating on the appropriate frequencies.
The Survival Craft Transceivers are manufactured under IMO standards and are required to
Be operated by unskilled personnel.
Have channel 16 and one other channel
Withstand a drop of 1 meter on a hard surface
Watertight to a depth of 1 meter for 5 minutes
Power minimum of 0.25 watts (1/4 watt)
Where power exceeds 1 watt a power reduction switch to less than 1 watt must be available.
Antenna to be vertically polarized and omni-directional
Battery power capacity for 8 hours on a 1:9 duty cycle
These SCTs use phase modulation (G3E) in lieu of true Frequency Modulation (FM). The battery packs are using NiCad batteries for day-today operations some use the non-rechargeable lithium battery pack for a strictly SCT radio (These batteries are integrated into the transceiver).
The battery pack in all cases must have sufficient capacity to ensure a minimum of 8 hours of operation at the highest SCT RF power output. The batteries are based on a duty cycle of 1:9 for the non chargeable type as well as the rechargeable type. Batteries are marked with month and year of manufacture. These batteries must be replaced on or before the expiration date, there is no grace period.
The IMO has set up some specifications that we should be aware and give minimum requirements for these units. The SCT must be capable of radiating a minimum Radio Frequency (RF) power of 250 mw (milliwatts) or 1/4 watt.
Again if the transmitter of the SCT has a power excess of 1 watt then a switch must be provided to reduce the power to less than 1 was. Thus providing reduced drain on the battery. The receiver used in the SCT must have a sensitivity of less than 2 microvolts to produce a noise/signal to noise distortion (SINAD) of 12 db (decibels). What this all means is that the signal into the antenna of the receiver plus any distortion on the signal must provide noise reduction of 12 decibels within the receiver and have a reading of 2 microvolts at the antenna .
Contrast this sensitivity for the VHF Radio on the bridge having the same (SINAD) requirements but having a 0.5 microvolt signal at the antenna. This makes the SCT operating under these specifications a less sensitive receiver than the bridge radio. In effect the receiving range will be much shorter. But will be sensitive enough to provide a usable radio for the SCT and will of course cost less.
Among other requirements the IMO has stated that the Antenna on the SCT be vertically polarized. This is a requirement to keep all the antennas within the same plane to obtain maximum transfer of energy from radio to radio.
IMO has certain carriage requirements for various type of ships. At least 3 two-way VHF Survival Craft Transceivers must be provided on every Passenger ship and cargo ships of 500 tons and upwards. At least 2 two-way VHF Survival Craft Transceivers must be provided on ever cargo ships between 300 and 500 gross tonnage.
There are certain stowage requirements for the SCT and GMDSS SCTs must be stowed in such locations that they can be rapidly placed in any survival craft (other than life rafts required by the SOLAS convention. This is not to say that we cannot provide a SCT that can be fitted as a fixed two-way VHF radiotelephone installation in survival craft. These fixed installations must adhere to the same performance standards of portable SCTs as above .
There are of course some testing requirements for Survival Craft Transceivers and they must be tested at intervals not to exceed 12 months. If the SCT has rechargeable batteries be sure to let them run down then recharge the batteries prior to testing the radio. This will prevent a "memory" to be set up in the Ni-Cad battery and preventing it from fully charging.
