Active and Passive
Posted on August 22, 2012
The recent very fascinating discussion in which certification of the ATU (Antenna Tuning Unit), as found with certain iAM or T.H. transmitters, was predicated upon the ATU being “the final RF stage” as specified in 15.219, brought about use of the words “active and passive”.
At least two members hold fast to a belief that 15.219 refers to an active circuit component when it says “The total input power of the final radio frequency stage (exclusive of heater or filament power) shall not exceed 100 milliwatts”.
I am not re-staging the argument over what the rule really means, but rather, I am putting to the test the terms “active and passive” as they pertain to radio technology. I thought I knew, but as I reconsider it turns out there is room for uncertainty.
Conventionally a tube or transistor is regarded “active” because unless operating voltage is applied, it will not perform a function. The difference seems to be the power supply.
A passive component requires no external power supply, a loading coil is our example, which lays dormant until RF is passed through it and then it performs its function of resonating the antenna.
But I have two reasons for regarding a loading coil an active component:
1.) It is activated by its input;
2.) It HAS HAD an external power input in the form of design and physical construction, giving it the qualities required to perform.
Therefore the power supply is no longer the difference, because manual human input is also a form of power supply.
The difference between a transistor and a loading coil is a matter of timing: WHEN was the external power introduced.
What have I done with my argument? I have erased the difference between active and passive electronic components.
But that isn’t the real point of this inquiry…….
I would like to understand why it is that anyone would presume that the wording of 15.219 absolutely applies only to the active component, the final RF amplifier?
Is a loading coil not an RF stage?
Is it not the final RF stage in a part 15 transmitter circuit?
Why should being passive matter at all?
I may have re-staged the 15.219 argument after all