Some questions regarding frequency stemmed from coax cables

[Longbow]

Re: Some questions regarding frequency stemmed from coax cables

My confusion stems from when I picture electronics I refer to two points (+/-)

+ and - markings are almost always used in d.c. circuits because those connections don't change over time. Diagrams that you might be looking at (where are they?) could have these markings to indicate instantaneous values of current and voltage in an AC circuit - which will reverse themselves during the next half cycle of the applied signal.

So I reference that in terms of radio waves and how an antenna can only have one connection starts to confuse me

That question is quite different than the subject of coaxial cable. I suggest a beginning book on antenna theory if you want to go in that direction. A long wire or a telescopic antenna does in fact have a "return" path through ground or an artifical ground (counterpoise) even though the path might not be obvious at first.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

So is it safe to assume (for mental simplicity) that an antenna is connected like a coil (with two ends) so that the radio waves can enter it the same way a coil can be energized, like the secondary windings of a transformer?

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

A radio receiver doesn't need to have a return path to the point of origin at the transmitter, it only needs to detect a minute voltage difference at the transmitted frequency between the transmitted wave energy and any other point of voltage reference, the earth, ground, a vehicle body, a ground plane, anything conductive that is at a sufficient different voltage potential (in microvolts) at that frequency.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

A radio receiver doesn't need to have a return path to the point of origin at the transmitter, it only needs to detect a minute voltage difference at the transmitted frequency between the transmitted wave energy and any other point of voltage reference, the earth, ground, a vehicle body, a ground plane, anything conductive that is at a sufficient different voltage potential (in microvolts) at that frequency.

Thank you! That helped clear it up for me. I'm still bit confused at how an antenna is connected to a receiver circuit. In the example of a telescopic antenna it just looks like a hollow aluminum metal with one screw connected to the circuit. So I don't see how there's another connection point on it for a ground? Unless a ground point just has to be near it and not physically attached?

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

Just read up on it yourself. That's all you're getting from me.

[goontron]

Re: Some questions regarding frequency stemmed from coax cables

Thank you! That helped clear it up for me. I'm still bit confused at how an antenna is connected to a receiver circuit. In the example of a telescopic antenna it just looks like a hollow aluminum metal with one screw connected to the circuit. So I don't see how there's another connection point on it for a ground? Unless a ground point just has to be near it and not physically attached?

you need a difference in potential. that's it.

[rhomanski]

Re: Some questions regarding frequency stemmed from coax cables

The transmitter is connected to earth ground, the electromagnetic wave goes forth to it's destiny, the receiver is connected to the same earth ground. Your circuit is complete electrically.

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

The transmitter is connected to earth ground, the electromagnetic wave goes forth to it's destiny, the receiver is connected to the same earth ground. Your circuit is complete electrically.

That doesn't account for extra-terrestrial radio communications when there is no connection to earth at the receiver nor between spacecraft.

[stj]

Re: Some questions regarding frequency stemmed from coax cables

groundplane is more important for the transmitter.

for the reciever the antenna length is the main thing - it should relate to the frequency.
(it should be a multiple of the wavelength)

[Longbow]

Re: Some questions regarding frequency stemmed from coax cables

Well, for the sake of clarity it is necessary to separate the subjects of electrical circuits and that of the propagation of EM energy through space. Do not confuse yourself before you have a chance to begin. It is still not obvious from the OP's questions what exactly he is asking about.

Are we talking coax, antennas, or radio waves? A receiving antenna does not rely on any kind of electrical connection to a transmitting antenna. Otherwise you would not need the antennas at all. Time to break out the reading materials.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

I'm not wondering how a receiver is connected or not connected to a transmitter.

My confusion stems from how an antenna or coax cable is physically connected to a receiver circuit board. For example the antenna in a portable radio, or antenna in a mobile phone.

I'm used to an electronic component having two points of connection like a capacitor, coil, etc. when I see an antenna it looks like there couldn't be two points of connections to it but only one. If that helps clarify what I'm asking

[rhomanski]

Re: Some questions regarding frequency stemmed from coax cables

Is that you Sheldon? I thought you figured out sarcasm a couple seasons ago.

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

One end is connected to space where it picks up the electrical changes caused in space by the transmitter, the other end is connected to the receiver which detects and processes the changes into useful information. It's magic.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

One end is connected to space where it picks up the electrical changes caused in space by the transmitter, the other end is connected to the receiver which detects and processes the changes into useful information. It's magic.

Perfect thanks

[keeney123]

Re: Some questions regarding frequency stemmed from coax cables

One has carrier frequencies and intelligence in radio wave. The carrier frequencies are what go through a medium, earth, atmosphere,etc., to get to your antenna. The antenna is tuned to receive certain frequencies while rejecting other frequencies. The transmission line from the antenna is somewhat tuned to the receiving circuit on what ever device you are using. This is just a very basic definition of what can very quickly become very complex. The government has electrical engineers that do nothing but specialize in radio waves.
Of course the intelligence of the wave is of less frequencies than of the high frequency radio waves. An the carrier waves do just that they carry the intelligence to your set. Not the actual intelligence but facsimile of the actual intelligence. Usually frequencies are made up of many frequencies that either combine of subtract to give one frequency. That one frequency is not usually pure, meaning it has other frequency that make it up.

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

Considering that the current state of science is unable to define exactly what an electromagnetic wave is, I am certain that none of us will be able to define it either. We can say what it does, what conditions cause it and how it behaves in different situations and how we use it, but at a certain point one has to take a sort of leap of faith and concede that it is something not fully understood.

[momaka]

Re: Some questions regarding frequency stemmed from coax cables

Well, for the sake of clarity it is necessary to separate the subjects of electrical circuits and that of the propagation of EM energy through space. Do not confuse yourself before you have a chance to begin.

Exactly!

My guess is, the OP was confused how the signal is carried through the air vs. in a coaxial cable.

In a coaxial cable (or any cable for that matter), the "signal" is carried by electric current flow - i.e. electricity, or charges moving from + to - (or - to +, depending on where you learned the stuff).

On the other hand, radio waves (or any type of electromagnetic radiation for that matter) is NOT an electric current, so you can't really think of "what's the ground or reference point" for the wave. EM radiation is basically photons (a tiny particle with supposedly no mass and charge) just moving about. But rather than get caught up in the physics, it helps to think with practical examples in mind. The light we see, for example, is a form of EM radiation. Let's say I grab a flash light and stand at one end of the room. If I point the flash light at you and turn it ON, you will see the light - a perfect example of an electrical circuit sending a "wireless" signal.

So how does the magic work? Basically, as current flows through the flashlight's bulb (and let's assume a classic incandescent bulb for simplicity here), the Tungsten wire in the bulb becomes extremely hot - to the point of glowing. That glow is actually photons being emitted by the Tungsten wire. The emitted photons then travel through the air and reach your eyes. Your eyes have sensitive receptors that react when they are struck by the moving photons. They then send and electric impulse to your brain and that's how you see. Of course, we only see EM radiation in the "visible light spectrum" - that is, photons that are oscillating at certain frequencies. That glowing light bulb in the flashlight is also likely emitting infra-red light, but we don't see it, because our eyes, much like radios, work only with certain frequencies.

As such radio transmitters/receivers work very similarly and how the "magic" happens there is not really any different. In the transmitter, you have electric current flowing through the circuit. Certain parts of the circuit oscillate at the frequencies they were designed for. The antenna is attached to those "parts". Thus, as the circuit oscillates at its set frequency, the potential (voltage) of the antenna relative to the circuit ground plane varies with the same frequency. This produces EM radiation, just like the Tungsten element in the flashlight bulb example. The EM radiation (which is the signal) then travels through the air. The receiver basically does the reverse of the transmitter. It has an antenna that is designed to pick up certain frequencies. When the EM radiation from the transmitter "passes over" the receiver circuit, the potential of the antenna in the receiver differs by small amounts from that in the ground plane of the receiver circuit. An amplifier in the receiver then amplifies the small differences in potential between antenna and ground, so that the amplified potential can be used to "do something else" in the circuit.

[keeney123]

Re: Some questions regarding frequency stemmed from coax cables

A physics professor I worked for once told me that when he was a student his professor ask the students, do you really know what an electron is. He told me he is still thinking about that question from time to time.