[TenTec] Airpax circuit breaker

[Robert & Linda McGraw K4TAX]

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.
>>