Antenna Education Needed

[ChristineBCW]

Does an antenna's nearness to a wall create a 'splash-back' effect for WiFi signals? (Let's assume it's a transmit-thru capable wall, too.)

I think I need to find out if a signal, once it leaves the antenna, is broken into some packet-sequence that requires "flight distance to form up", like a 300-plane bomber raid takes an hour for all to take-off, so they circle and wait for everyone and then 'form up'.

This assumes, then, that a WiFi signal can self-validate in-flight (NO, IT CANNOT) and thus it could send back re-transmit requests to the WiFi origin point. I prefer to believe packet-validation is only performed upon Destination Receipt, or perhaps in Transmit Checks (the router knows "I coughed - I'll just retransmit that signal now, automatically").

The nearness to a wall might create a validation-error at the Antenna itself if the "flight of WiFi bomber signals" required a flight-formation transit.

I just don't think that's true, though.

Therefore - does an antenna's distance from a wall matter? Is six inches better than 1 inch? Is 18 inches better than 6?

 

[L&LD]

I have found that 10 feet or higher above the ground and as much space around the router gives the best performance in a given area. Two meters is not too much room.

 

[azazel1024]

It can sometimes cause multipath issues, but it depends heavily on wall construction, distance, antenna type, placement, etc, etc, etc.

In answer, it depends.

The best way to figure it out?

Empirical.

I deffinitely found an issue where bigger antennas reduced throughput in some locations, as near as I can tell because of wall composition (right next to a fireplace and chimney). I moved the router and the bigger antennas increase throughput in all locations (except the closet test location which stayed just as fast). So my best guess is the higher signal strength in the compressed pattern was enhancing an issue with reflection/multipath from the construction of the wall, hence reduced performance in some locations with bigger antennas, but increased performance at basically all locations with the bigger antennas once I moved the router.

 

[ChristineBCW]

My allusion to some "flight formation" is probably incorrect because it has an underlying assumption of some Order For Travel - bit 1, 2, 3 followed by 4, 5, 6. And that isn't the order for "travel" - it's the order for "arrival" but "travel order" can't be validated or adjusted.

However, both of your responses brings up another factor - the nearer the antenna, the more compressed the signal. This is, in a way, similar to "flight path" although not "formation".

And if there is indeed Collision Damage being done as a signal is spawned from the Antenna, the more compressed zones would likely have the greatest collision opportunity.

By moving an antenna away from any wall (even a surface like a desk or ceiling?), perhaps the initial, most highly-compressed zone can expand to lessen collisions and, by removing any surface within the most compressed zone, this is a second-order of lessened collision opportunity.

An alternative argument might say, "To achieve greater brute force thru walls, ram the most compressed signals with the antennas nearer, not further away from the wall." (Alas, I'm envisioning Moe and Larry using hand-drills on Curly's head.)

 

[L&LD]

With regards to your last statement, again, I have seen better signal and actual throughput speeds when the antenna or router placement is in an open area than when the it is against a surface like a wall or desk/furniture. Even to the area outside that wall it is against.

A radio signal needs space to develop and the ideal placement would be on a thin pole in the middle of a room and as high as possible above ground.

 

[ChristineBCW]

L, yes indeed. This is what my practical world experience is, too. This is mutating into a radio-wave education I need.

 

[chadster766]

Walls will case radio reflection if they have metallic components in them and the antenna is close (within 10ft from my experience) which will lower your SNL (Signal to Noise Ratio).

When transmitting through walls the composition of the wall will only cause attenuation.

Radio waves are not compressed the closer they are to the antenna AFAIK. If radio waves go through interstellar space with will elongate over massive distances

 

[azazel1024]

Walls will case radio reflection if they have metallic components in them and the antenna is close (within 10ft from my experience) which will lower your SNL (Signal to Noise Ratio).

When transmitting through walls the composition of the wall will only cause attenuation.

Radio waves are not compressed the closer they are to the antenna AFAIK. If radio waves go through interstellar space with will elongate over massive distances

Correct, solid materials (well, anything even a gas) will cause refraction of the radio waves, which WILL cause multipath, as the signal through the wall is going to arrive at a different time than a signal bounced through an open doorway due to difference in path length, photon velocity, etc. There is also SOME amount of reflection, but in general it is going to be pretty small even for 5GHz radio waves, other than a metal surface.

Metal is a fairly good reflector or absorber depending on shape, size, composition, etc.

That is why I think I was having issues, the fireplace has a big old metal pellet stove in it around 2ft from where the router antennas were and the big metal chimney liner for the pellet stove was located even closer. Now the antennas are a good 4-5ft from all of that and most locations don't have to have the signal pass through/by/around all of that to reach the location (and also don't have to pass through all of the stone and cinderblock of the chimney itself, but I doubt that was causing reflection/multipath issues). I think those were causing more issues than the stone and cinderblock was.

 

[ChristineBCW]

Continuing thanks...

I wasn't thinking the signal-waves were compressed - but the space between them would be less at point-of-origin (the antenna) than a 10-20-30 feet away.

 

[chadster766]

Continuing thanks...

I wasn't thinking the signal-waves were compressed - but the space between them would be less at point-of-origin (the antenna) than a 10-20-30 feet away.

Isn't the amplitude and timing of the radio wave a constant once created?

 

[ChristineBCW]

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?

 

[L&LD]

Or not?... I would say it's just become a way to illustrate this in a simple manner.

 

[thiggins]

Continuing thanks...

I wasn't thinking the signal-waves were compressed - but the space between them would be less at point-of-origin (the antenna) than a 10-20-30 feet away.

A radio wave's frequency stays the same. Otherwise, radio wouldn't work because you couldn't tune the receiver to capture the signal.

In today's MIMO systems with beamforming, all sorts of manipulation is done to the phase of signals, i.e. timing of the transmissions WRT each other.

From Wikipedia

Radio waves travel at the speed of light in a vacuum.[3][4] When passing through an object, they are slowed according to that object's permeability and permittivity.

So it's not distance that primarily mucks with RF phase, but physical objects.

 

[TonyH]

L, yes indeed. This is what my practical world experience is, too. This is mutating into a radio-wave education I need.

Hi,
Radio signal is combination of E(electronic) - M(magnetic) field. Frequency and wave length both have a relationship to speed of light. This wave has two components, signal/carrier. Try to find an Antenna Handbook by ARRL for quick study if you are interested. Did not take Physics in high school? Radio waves will reflect, refract, scatter or be blocked(shielded) by solid object in the path. Xray is radio wave in a way with very high frequency. If you throw a little pebble in the middle of pond, water wave propagates that is rough visualization of radio wave
not exact but helpful. Also you;ll have to know the basics of method of modulation.

 

[TonyH]

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?

Hi,
If antenna is resonant to the radio wave you'll visualize wave present on the antenna element. Wave travels little slower in the wire than free space(ideally vacuum) This is the reason we cut the antenna element little shorter than calculated by ~5%. Also there is something called polarization; horizontal, vertical, rotational. When E plane is perpendicular to ground(earth) this is vertically polarized. Please ask specific question(s), then it'll be easier to answer. In real world there is no perfectly polairized wave. Even vertically polarized wave has some horizontal component, other wise horizontl antenna like dipole won't receive any thing from vertically polarized wave, vice versa.
If you want to visualize more of radio wave, use vector representation.

 

[TonyH]

Hi,
Think AM, FM, PM....

 

[TonyH]

Continuing thanks...

I wasn't thinking the signal-waves were compressed - but the space between them would be less at point-of-origin (the antenna) than a 10-20-30 feet away.

Hi,
May I ask what you mean when you say space between them?

 

[stevech]

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.

 

[ChristineBCW]

No high school for me, none of the American middle school either, certainly no physics! Those were working years for me and I scraped thru Calc. I can't tell a sine wave from a cosine wave - when I see 'em on the street, we generally go our tangential ways.

As for "space between" signals...

I am having trouble envisioning the behavior of signals at the antenna vs. the signals at some distance away. A receiver unit 1" away (or less) from an Antenna does not receive signals properly.

Five feet away, it receives properly.

What occurs 60-inches away that doesn't occur at 1", or .5" from the antenna? "More space"? Since the wavelength hasn't changed, what has? "More space" is the obvious inference.

(EDIT: "Signal" may be an imprecise term - a Receiver-WiFi Adapter locates the Frequency and then interprets the data on that frequency/wavelength/"signal". "Signal" may be simply too broad of term.)

 

[thiggins]

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