Antenna Education Needed

[ChristineBCW]

Yes, the success of a broadcast isn't in a one-piece vacuum - there has to be a relationship (with causes and effects) with Receiver units.

This will bring up Topic #2 - how does a Receiver damage or affect an Antenna or its output signals.

A microwave oven creates a collision-zone at the Mass of objects, and those collisions heat up (excite) the molecular structure of the matter. (Of course, radio electromagnetic waves aren't molecular, although they are affected by matter-molecules. The joys of lead-lining, metals and stone pillars.)

Since Receivers are sending back ACK-NoACKs, I'd suspect moving the receiver very close to the antenna would create that "microwave oven" effect on all signals, making data-reading fail.

But that's a different subject!

 

[thiggins]

No, the effect is more like the distortion produced when you overdrive an amplifier.

 

[azazel1024]

When I look at oscilloscope drawings of waves, I see the fluid-style troughs and peaks, spacing in between those points and the height of the wave.

But this is a single wave.

When I see animations of omni-directional antennas, those waves are illustrated as almost donut-shaped waves, rippling outward. And gaining space between each emanation as distance from the antenna is gained.

Plus, the length of the antenna is generating these in not just longitudinals (spanning parallel to the floor, for example) but also latitudes (upwards and downwards at some ?? angle ??). It's truly 3D, not like the 2D oscilloscope.

These are infinite waves, but digital transmissions - 1, then 2, then 3, so on. It's that spacing between those that I'm thinking is lessened at the antenna, and grows as the 'wave' ripples outward.

Or not?

You are looking at it completely wrong. Frequency doesn't shift (there is no change in wave length). What you are seeing is density reduction (IE field strength goes down). The radio waves spread-out, but the distance between peak and trough does not. Inverse square law, field strength reduces with inverse square of the distance.

Picture it as trillions of individual photons being emminated from the antenna, each moving wave like. The distance between photons spreads out, but the movement of the photons doesn't change at all.

 

[azazel1024]

As said above, radio waves' frequency, the "space" (time) between wave peaks, doesn't change in the air. The transmitter can alter the phase for complex reasons, but for this topic, that's not relevant.

Someone here said that the radio wave's amplitude doesn't change in transmission. Well, of course we all know that it gets weaker with distance. The "attenuation" or loss of signal power isn't a linear math function. Per laws of physics, the signal "weakens" in an inverse square law characteristic. Essentially, double the distance, halve the signal strength.

So the bluetooth earphone's RF transmitter starts out inside the plastic, then weakens about like 1cm, 2cm, 4cm, 8cm, ... 1m, 2m, 4m, 8m and so on.
Good thing because for BIG distances like from the Voyager spacecraft, outside our solar system, doubling the distance takes a long travel time!

Same holds true for WiFi - double the distance, etc. But to that loss you have to add losses due to path blockages like walls, floors, foliage, terrain. Drywall (two layers) is not a high attenuator. Masonry is, and so on.

Lower the frequency, the lower the losses in free space, and generally, lower in penetrating blockages. Much lower.

Actually technically the amplitude of the radio waves doesn't change, the field strength does. The amplitude stays the same, roughly 10uev (microelectron volts) for 2.4GHz and 20uev for 5GHz. However, you have fewer photons in a given area, so lower field strength. If the amplitude actually changed, you'd have a shift in frequency.

When the radio waves hit an obstacle, some of them either get absorbed or reflected, but some will continue through the obstacle, and for the most part they are unchanged (though some/most/all CAN have a frequency shift depending on the material, but this isn't something we want to get in to right now). Polarization can also change.

PS There can be perfectly polarized radio waves if you pass them through a polarizer or use a maser to generate them.

 

[ChristineBCW]

The distance between photons spreads out, but the movement of the photons doesn't change at all.

YOU'VE FINALLY GOT IT! I've been talking ALL about that "spread out" issue. You've finally understood. I don't know how else to explain it - "splatch" didn't work, and everyone kept seeing "distance between peaks" instead of this "spread out spacing".

 

[azazel1024]

As said above, radio waves' frequency, the "space" (time) between wave peaks, doesn't change in the air. The transmitter can alter the phase for complex reasons, but for this topic, that's not relevant.

Someone here said that the radio wave's amplitude doesn't change in transmission. Well, of course we all know that it gets weaker with distance. The "attenuation" or loss of signal power isn't a linear math function. Per laws of physics, the signal "weakens" in an inverse square law characteristic. Essentially, double the distance, halve the signal strength.

So the bluetooth earphone's RF transmitter starts out inside the plastic, then weakens about like 1cm, 2cm, 4cm, 8cm, ... 1m, 2m, 4m, 8m and so on.
Good thing because for BIG distances like from the Voyager spacecraft, outside our solar system, doubling the distance takes a long travel time!

Same holds true for WiFi - double the distance, etc. But to that loss you have to add losses due to path blockages like walls, floors, foliage, terrain. Drywall (two layers) is not a high attenuator. Masonry is, and so on.

Lower the frequency, the lower the losses in free space, and generally, lower in penetrating blockages. Much lower.

Also unless I've badly missed something, in free space the losses between 1khw and 1thz is roughly the same. What can come in to play is any physical obstruction. Whether it is a wall, or just air. Air will cause greater losses to higher frequency transmissions, though in the radio and microwave ranges, the differences are negligible until you start getting in to the mid/high microwave ranges where, especially, atmospheric moisture (IE humidity) can take a bigger toll than long frequency radio waves. There are also other things like ionosphere interference that have to be taken in to account at very long distances.

 

[ChristineBCW]

...the field strength...

Can I consider a "field strength" to be comparable to "photons within a cube"? In a cube near the antenna, X-number of photons would be high. Ten feet away, the same cube's capacity would have fewer photons.

Is that a correct analogy for 'field strength'?

(I'm just not sure antennas generate "photons", though. I'm not sure how electromag waves are "particle-ized" but obviously since wavelengths don't change, as distance changes there must be more 'space' between waves or their particles.)

 

[azazel1024]

YOU'VE FINALLY GOT IT! I've been talking ALL about that "spread out" issue. You've finally understood. I don't know how else to explain it - "splatch" didn't work, and everyone kept seeing "distance between peaks" instead of this "spread out spacing".

Just to be clear though, in the photon wave pattern, the photon's frequency and amplitude do not change, but the distance between each photon does. So the wave doesn't spread out, but the individual photons do.

Talking about the wave spreading out would mean a change in amplitude or frequency (or wave length if you would).

 

[ChristineBCW]

Oh my. My TOT (Tendency Of Typo) showed up.

AZA quoted me and I read my original typing: "These are infinite waves, but digital transmissions..."

My fingers typed that. I DID NOT. I meant to type "These are NOT infinite waves..."

Oh my. My TOT is often dropping a Negative out, especially when edit/proofing.

I don't consider ElectroMag Waves to be "infinite", unless infinity has changed to include measurable limits.

But electromag-radio waves might TRAVEL infinite distances in space, I suppose. I just don't think THEY are infinite. Or are they?

 

[azazel1024]

Can I consider a "field strength" to be comparable to "photons within a cube"? In a cube near the antenna, X-number of photons would be high. Ten feet away, the same cube's capacity would have fewer photons.

Is that a correct analogy for 'field strength'?

Correct-ish. Generally it is a 2D area, not a 3D area that is looked at (so /m^2, not /m^3) There are a number of ways to express it. A common one if mW/cm^2 (miliwatts of radio power per square centimeter), in radio broadcast dBmV/m is typically used, (decibles milivolt per meter, so it is a logorithmic expression).

In wifi we use dBm, which is decible-miliwatt (measurement standardized on one miliwatt of received or broadcast radio power, it is not a field measurement, you need the antenna taken in to account, so it is just what an antenna receives or broadcasts), but it isn't a field strength measurement.

 

[azazel1024]

Oh my. My TOT (Tendency Of Typo) showed up.

AZA quoted me and I read my original typing: "These are infinite waves, but digital transmissions..."

My fingers typed that. I DID NOT. I meant to type "These are NOT infinite waves..."

Oh my. My TOT is often dropping a Negative out, especially when edit/proofing.

I don't consider ElectroMag Waves to be "infinite", unless infinity has changed to include measurable limits.

But electromag-radio waves might TRAVEL infinite distances in space, I suppose. I just don't think THEY are infinite. Or are they?

There is no clear evidence that a photon will ever decay (there are a few alternate theories outside classical physics that propose that a photon might decay eventually, but the time scales are many times that of the universe (>trillions of years). So, so long as the photon doesn't run in to a physical obstacle, it is infinite if you look at it in terms of it never decaying in to something else and it'll continue moving forever until it hits something.

 

[ChristineBCW]

...the photon's frequency and amplitude do not change, but the distance between each photon does. So the wave doesn't spread out, but the individual photons do.

Yes, this is exactly what I've always meant. No one's read my statements like that, and I found myself trying to find different phrases to have this understanding. I wasn't certain I wanted to 'particle-ize' waves into sub-objects like "photons" and cheetos, chiclets or whatever humans have recently 'discovered'.

In my first allusions, I mentioned a "flight path" or some 'form up' process - that refers to the photons, therefore - individual objects within a 'flight' or wave.

So near the antenna, we can have photons with little or no 'space' between them.

 

[azazel1024]

Yes, this is exactly what I've always meant. No one's read my statements like that, and I found myself trying to find different phrases to have this understanding. I wasn't certain I wanted to 'particle-ize' waves into sub-objects like "photons" and cheetos, chiclets or whatever humans have recently 'discovered'.

In my first allusions, I mentioned a "flight path" or some 'form up' process - that refers to the photons, therefore - individual objects within a 'flight' or wave.

So near the antenna, we can have photons with little or no 'space' between them.

Correct, but that has no impact in what the receiving radio receives, other than that more photons are hitting the antenna and knocking electrons loose and the frequency of the electrons in the circuit is still the same. So there isn't any change in form up, or flight path or anything. Just more photons, not a change in "flight path".

 

[ChristineBCW]

Correct-ish. Generally it is a 2D area, not a 3D area that is looked at (so /m^2, not /m^3) There are a number of ways to express it. A common one if mW/cm^2 (miliwatts of radio power per square centimeter), in radio broadcast dBmV/m is typically used, (decibles milivolt per meter, so it is a logorithmic expression).

OK, maybe a bit further afield here - can a Radio Wave - or any energy or mass - be '2D'? (I want to avoid the 3D vs 4D-etc issue for the moment.) But this 2D formula is probably what throws me - isn't the 3D actually what happens?

Can a radio wave actually be created in a 2D scale, or is that a simplified calculation for a conceptual reference? (And an easier answer when I take my socks and shoes off... 18... 19... etc. ha ha)

 

[azazel1024]

Yes it can be 2D. It is induced voltage (or power) on a two dimensional area. An antenna, no matter its physical shape, mathematically is equivelent to a 2D plane when determining how the field effects the antenna (and vice versa).

You can look at 3D to determine how many photons are present in a 3 dimensional area and with 2D it is how many photons are passing through a plane at one time (or in this case, it is the voltage/power induced by those photons passing through/absorbed in to a 2D plane).

The wave pattern of a photon is described in 2D, as it oscillates up and down, there is no side to side movement (unless induced by an electric/magnetic field). If you take in to account the electromagnetic properties of a photon wave function, it is 3D-ish, as the EM wave is perpendicular to the actual photon movement.

Anyway, to get back to everything, what matters is, to dumb it down, how many photons and with what energy (their frequency) are they passing through a plane perpendicular to their travel at a distance that is important to you at a fixed time (IE dimensionless in time (no 4D)). This determines the voltage/power induced in an antenna. So field strength is this quatitization (W/cm^2) generally.

 

[ChristineBCW]

Ah yes. Receipt and Measurement vs. Transmitter's Volume.

The Transmitter's volume may be calculable, but if a Receiver (that 2D Perpendicular Plane) can't access it, transmission - like writing descriptions vs. reading and understanding) - is rather mute for our purposes.

Thanks.

Tim discussed a Receiver/Adapter's nearness to an Antenna offering some splash-black/reflective issues and thus reducing performance due to nearness alone. This is the Moe Effect. Spread out.

 

[TonyH]

Hi,
So you are familiar with quantum theory? We engineers just deal with our training and experience when designing, installing antennas of various kinds.

 

[azazel1024]

Ah yes. Receipt and Measurement vs. Transmitter's Volume.

The Transmitter's volume may be calculable, but if a Receiver (that 2D Perpendicular Plane) can't access it, transmission - like writing descriptions vs. reading and understanding) - is rather mute for our purposes.

Thanks.

Tim discussed a Receiver/Adapter's nearness to an Antenna offering some splash-black/reflective issues and thus reducing performance due to nearness alone. This is the Moe Effect. Spread out.

If the signal strength to too high (generally caused by receivers proximity to the transmiter) it causes the signal to become distorted, and the receiver losses sensitivity. Too powerful and the signal goes from distorted to "blown out" and too, too high and it can damage the radio itself (well, one or more various subcomponents, like the analogue to digital converter, amp, etc.). The last generally takes quite a lot of power to accomplish and isn't something you are likely to cause by just sticking your cell phone on top of your router.

The relection issues can also be caused as not 100% of photons are absorbed by a real antenna, which results in reflection from it. However, you have similar issues of any transmitter near any physical object. Things like drywall are poor absorbers of 2.4 and 5GHz radiation, but will absorb some, and they are terrible reflectors, but there WILL be some microwaves reflected. Other substances are better absorbers or reflectors. Powerful enough reflections with the right path and it can overwhelm the original signal at the receiver and the reflections are generally out of phase with the originals contributing noise instead of enhancing the existing signal even if they don't overwhelm it.

That said, sometimes reflections can actually be stronger than the original signal after it passes through obstructions, in a beneficial way.

Empirical testing is really the only way to figure out any of this. I did see a lovely animated matrix algebra calculation someone did for various field strengths for a sample apartment someone put together (with more smarts and time than I have). However, it is demonstrative only, as it cannot and didn't take in to account every single difference in wall composition, furniture, true material reflective and refractive properties, outside noise sources, etc.

 

[ChristineBCW]

I like to pretend that these photons obey behaviors (motion) similar to molecules in a fluid (or gas), simply because I can see molecular fluid motions. Fluid molecules do move in those environments. We all see that.

When I compare a electromag wave's transit thru a gaseous atmosphere, it's easy to pretend the same likely motion-behaviors can occur.

But the core of the antenna isn't fluid. And it's not a gas. Or, when i imagine a copper wire, and understanding how these photons "move" within those 'solid state' environments, it's harder for me to associate "photon motion behaviors" being the same whether they 'transit' in a gas or in a solid copper wire.

The signals do get thru, though. All I have to do is get Hubby to stick his tongue in a wall-socket, and Motion does occur! (OK OK, I know - a good science project should be repeatable and, well, frankly, I'll have a hard time getting him to do that a second time! Heck... I had to use a lotta duct tape on him for that first time!)

(Another tangent... from Calgary, take 1 west to 93-north and Jasper. Stop and say howdy. Then cut back to 16 west and after the second BOWRON LAKE sign, start looking for our turnoff. It's an old logging road. Two miles - er, 3.3km - in, our cabins start to show up. Great trout, lousy salmon - leave those to the bears.)

 

[TonyH]

At close distances, you are likely seeing the effects of receiver overload than anything to do with squished radio waves.

Hi,
In extreme case the front end will be desentisized and even burn up.