In looking at the control method, Tentec uses a current sensing circuit
associated with the DC Input Board, being R5 in the Omni VI+, with sensing
voltage being fed to the 9 MHz Filter Board, U2, which will then control
drive based on current draw by the PA and Driver stages. In theory the
system could deliver rated power into a dead short up, negating PA source Z,
to the point that the current reaches the set point determined by the gain
of U2 and associated circuit. At that point, 20 amps at 13.8 volts is still
276 watts {DC input power}. An open circuit or no load on the PA should not
cause any concerns either as PA current is somewhat inversely proportional
to the load Z.
Now, enter complex values of Xl and Xc + R for the PA load and things
actually change a bit. But still, the radio is protected by it's internal
circuits where PA excitation comes from within the driver/exciter stages.
At the same time, it does require some value of current limiting from the
power supply as broadband circuits {1.5 MHz to 30.0 MHz} are known to become
unstable, outside of the control loop, with odd values of Z. Thus the
reason for using current limited power supplies or other means to limit
total current. Hence the reason for concern when using power sources of
higher rated current capacities such as battery power or high current rated
supplies.
73
Bob, K4TAX
Vic Klein wrote:
Ten Tec design philosophy for radio finals is to run them full power
into
any load, rather than folding back the power as SWR increases.
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