Barrett 900 Series, Technical Manual

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BARRETT 900 SERIES TRANSCEIVERS
Tuning Algorithm
Specifications
Current Draw
Input Power
A tune is initiated by pulling the tune line low whilst simultaneously sending RF. By default the tuner
assumes that the whip looks capacitive. Firstly it will find a starting inductor, determined by whichever
inductor makes the whip look slightly inductive, and then initiate a binary search algorithm. Once this is
completed the impedance transformer will attempt to match the whip to the transmitter by switching its three
impedance ratios and optimising the RF feed current. If this current is not high enough the binary search
algorithm is reinitiated with series capacitor C1 switched in. This takes care of the whip above resonance
where the inductance is small. The impedance transformer will try to match the whip to the transmitter to
give highest feed current.
If the feed current is not high enough the tuner assumes that a long wire antenna is connected. Generally
use of the long wire will involve tuning out much larger inductances so shunt capacitors C2 and C3 are
employed to make the wire appear slightly capacitive. Since the required reactance to tune out this residual
capacitance will be small, a sequential tuning algorithm is employed using only the smaller tuning inductors.
The combination which produces the highest feed current is assumed to be the optimum. Finally the
impedance transformer will attempt to match the resistive component of the long wire to the transmitter.
Tuning time will vary from half a second to four seconds depending on whether a whip or long wire is used.
Static: < 20mA
Tune: 500mA (Max).
Supply Voltage: 10V - 15V.
Maximum input Power: 25W
Operating Frequency: 2.5MHz - 30MHz (8ft whip)
2MHz - 30MHz (Long wire)
Tuning Time: 1s-4s.
Maximum output Voltage: <2kV.
The Barrett 980 GMDSS transceiver is technically identical to the Barrett 950L but has a high stability
oscillator and a 500Hz filter for F1B (AFSK) operation fitted as standard. It can also be supplied with a 300 W
switch mode power supply fitted in a standard 900 series enclosure. This switch mode power supply has an
input voltage of 24 VDC and provides galvanic isolation of the transceiver from the power as required by
GMDSS regulations.
9.5 Barrett 980 GMDSS transceiver - P/N BC98000
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