A discussion in another thread was about if the type of antennas used with our transmitters are active or passive. The definition of an active device is whether it amplifies needing power to work. A transistor is an active device, a coil,resistor, capacitor is not. An antenna if just a metal rod which includes a dipole that is just a length of conductor is passive as it does not need power to work and doesn't amplify a signal. It is reactive in the fact that it responds to what is fed to it. A speaker would be a similar example as it too is a passive device that doesn't amplify on it's own or need a power supply and just reacts to what it is fed from another amplifier.
Let me explain in another way....I am transmitting on FM here in Canada. Now if I put the transmitter on a metal surface, or line the shelf with aluminum foil, the foil which is passive as no voltage is needed to operate it and it is not an amplifier itself will affect the transmit power(increase it) because it forms a ground plane and radiates but that does not make it an active device. You don't have to supply the foil with power.
The metal antenna is just reacting to what an amplifier is feeding it, but is not an amplifier itself and therefore a passive device.
The antenna is not an amplifier. correct, it is a radiator. It serveds it's own purpose like an amplifier serves it own purpose.
I still don't comprehend how anyone can legitimately state that an antenna is not an active component of a transmitter.
And it's going to get pretty confusing keeping track of whats going on with this topic now that you've inexplicably broke it in to two portions just as it was getting started. But If it keeps the peace, so be it.
How can the final stage be the amp when the current doesn't stop there?
An antenna if just a metal rod which includes a dipole that is just a length of conductor is passive as it does not need power to work
False my friend, at least when it comes to a transmitter. An antenna absolutely needs a current to work, it wont anything without power applied to it. It needs power to work.
@RichPowers - in the field of electronics, the widely accepted definition of an active device is a device that uses external power to modify/process/manipulate a signal, as opposed to a passive device, which does not. By external power, I am not referring to the power inherent in the signal, but power that is not in the main signal path; that is what is meant by the term "external power". Anyone who has studied electronics, whether self-taught, or in school, college or University, will tell you this. Any engineer with experience in electronics will tell you that a transistor, or an integrated circuit, is classified as an active device, whereas capacitors, resistors, diodes, inductors, and antennas such as the ones we have on our Part 15 transmitters, are not.
This catgeorization of active vs passive devices is used throughout the field. When FCC 15.219 was written, the reference to "the final radio frequency stage" was most definitely intended to mean the final amplifier stage that feeds the antenna. I've been reading books and magazine articles on transmitters for around 45 years, and I can assure you that this is what that terminology refers to.
In any scientific field, it is important that terms are clearly defined, so that everyone understands what they are talking about. You can question and disagree with these definitions all you want, but it doesn't change what the intent of the wording in the ruling was. No credible RF engineer would claim that an antenna is what is meant by the term "final radio frequency stage".
@RichPowers - in the field of electronics, the widely accepted definition of an active device is a device that uses external power to modify/process/manipulate a signal, as opposed to a passive device, which does not.
The antenna does "process/manipulate" the signal, no? by radiatiating it? launching it airborne?
By external power, I am not referring to the power inherent in the signal, but power that is not in the main signal path; that is what is meant by the term "external power".
But the power that is inherent in the signal originates from this "external power". It just an extension of the same power source. -- I just don't get what your saying.
Anyone who has studied electronics, whether self-taught, or in school, college or University, will tell you this. Any engineer with experience in electronics will tell you that a transistor, or an integrated circuit, is classified as an active device, whereas capacitors, resistors, diodes, inductors, and antennas such as the ones we have on our Part 15 transmitters, are not.
This catgeorization of active vs passive devices is used throughout the field. When FCC 15.219 was written, the reference to "the final radio frequency stage" was most definitely intended to mean the final amplifier stage that feeds the antenna. I've been reading books and magazine articles on transmitters for around 45 years, and I can assure you that this is what that terminology refers to.
In any scientific field, it is important that terms are clearly defined, so that everyone understands what they are talking about. You can question and disagree with these definitions all you want, but it doesn't change what the intent of the wording in the ruling was. No credible RF engineer would claim that an antenna is what is meant by the term "final radio frequency stage".
Yeah, well, I know I don't know what I'm talking about in this matter, and I'm quite sure you all are correct, but I have an easier time making sense of Carl's suggestion the final RF stage being the antenna then what any of you are trying to drill into my head the reason it's not.
The antenna being the final just makes more sense to me. But I acknowledge now that technically it is not.
But the power that is inherent in the signal originates from this "external power". It just an extension of the same power source. -- I just don't get what your saying.
It hinges on the distinction between the main signal path, and the external power, that is a different and separate thing from the power in the signal path. No external power acts upon the antenna. Yes, the power in the antenna does originate from the external power, but that external power acted upon earlier stages; it is not acting on the antenna.
I am not trying to win an argument here, or discussion for a better word. This not from me it is from electronic theory that I didn't write. This can be looked up. The antenna receives the output from an amplifier as the voltage/current has to have an outlet, somewhere to go to be dissipated. Because the antenna receives the energy from the amplifier it didn't generate the energy and is still a passive component. A speaker is the same thing. It's also the same if it is a receiving antenna. A small signal from a transmitter induces a voltage in the antenna via electromagnetic radiation which is just a piece of wire, and that then gets amplified by an active device at the receiving end but the antenna is passive. A piece of wire is not an active device.
If I have a generator, you know the manual ones that used to be in antique phones back in the 1920s/30s? You can still get them on Ebay. They were called magnetos.
You work them by hand turning the crank and can generate a lot of power, to even light an 120 volt incandescent bulb.
Now, the generator is the active device as my energy creates the power. I am the voltage and the generator is the amplifier. The generator delivers the power to the filament and the bulb reacts by giving off light. The active device is the generator powered by me and the light bulb receives the power and reacts creating light as the energy is received by the bulb. The bulb is still a passive device as it didn't create the energy but reacted to the energy received. Now compare that to the antenna on a Rangemaster transmitter. Instead of the antenna giving off light way up in the visible part of the spectrum it is giving off energy at 1630 kLz with it being modulated by audio as that's what is being delivered by the transmitter's final amp.
The bulb is still a passive device as it didn't create the energy but reacted to the energy received.
Ok, So the antenna does not create any energy, it only reacts to the energy it receives.
What components in a transmitter do create energy?
It hinges on the distinction between the main signal path, and the external power,
ok..
that is a different and separate thing from the power in the signal path.
It's different, ok..
No external power acts upon the antenna. Yes, the power in the antenna does originate from the external power, but that external power acted upon earlier stages; it is not acting on the antenna.
I've re-read it a half a dozen times (estimate), same as I have several of the others and I think it's become clear that I have a mental block in play.
@richpowers The final amp. Anything that needs a voltage from a power supply to work, or be powered, to perform a function is an active device. A transistor, tube, ICs(integrated circuits) Things in a transmitter like the ICs that control the frequency selection and other functions like the chips that work an LCD screen if a transmitter has frequency display....anything that needs power to operate. Any amplifier is creating energy.
In addition to the final amp, the frequency generating stage, whether it's a crystal-controlled or LC oscillator, or some kind of PLL device or DDS circuit, is also an active stage. Any subsequent stages that receive external power, such as buffers, drivers, or modulators, are also active stages.
The final RF stage.. the last component of the circuitry that's used in creating the actual desired radio frequency.. .
The antenna has nothing to do with creating the radio frequency, that is already accomplished before it reaches the antenna.
So that's why it's not the final rf stage - not because it does radiate rf, it does, but because it was not an active component in creating that rf.
it just radiates it to the air
I think I'm beginning to see the distinction.
None of the components of a transmitter create energy, they create or rather formulate a modulation of radio frequency, the antenna simply emits whatever you throw at it.
Yet still, though it plays no part in the creation (as it were) of the radio frequency (not energy), a transmitter can not serve its function without the antenna.. which thus makes it an integral part of the circuitry- and it's the very last stage of it.
So.. I get where y'all are coming from now, I do, but I still tilt my head at it.
No, really I get the distinction, I'm just saying
Carl had a sense of humour and he liked to create skepticism about something to get a discussion going like this one, just by bringing up this idea of what the final stage is even though we all know what is implied by the final RF stage. The wording should have been final RF amplifier stage I agree. If you are around Carl, see what you have caused!
But I will give Rich Powers this. A stage can be any part of electronic circuitry that performs a function whether with passive or active components. So if the term amplifier is left out and is just RF stage it then could be assumed that the antenna is the final stage even though a passive device as it has a separate function.