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> Radio signals for Beginner, Explanation of how radios work
Eagle
post Sep 30 2005, 02:01 PM
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Ok, there seems to be some confusion of how radio waves work, so I'll try to pass on my professional knowledge

A basic radio system needs two basic components: a transmitter and a receiver.

The transmitter determines the range of the radio signal by the amount of power it is pushing out, the more power, the greater the range (for those of you who are interested it work on a distance squared basis, so you need 4 times the power to transmit twice the distance, though again this is simplified)

The receiver takes this signal and converts it in a useable format. The receiver does not change the distance of the signal, this is why receivers can always be small.

In a two way system, on which the RFID system seems to work, require that each RFID to have a transmitter and a receiver. The transmitter has a short range, a few meters depending on model, while the receiver as long as it is within the foot print of transmitter can receive a signal at any distance. This means a RFID tag could receive a signal from a powerful transmitter, but be unable to respond.

This means that the RFID rating purely corresponds to its transmitter.

There are however a subtle means of using this to track an RFID which is out of range its transmitter range. Activate the RFID with powerful transmitter, the RFID logs onto local network and sends a text message, using a pre arranged email/text account (similar to current mobile phones), a hacker then backtracks the signal to nearest fixed node and RFID is located to within a few meters.

The advanced course:

Radio antenna are based on a 1/4 of the wavelength of radio wave, as this is the most efficient transmission mode.

There are two types of antenna omni direction (equally strong transmission in all directions) and directional (stronger signal in certain directions)

Currently the two most common antenna are the pole plus ground plane (which is usually non existent) and the loop, which circular with one or more loops. The pole is more or less omni directional, but is larger, while the loop is 3d figure of 8 (pinch a balloon in the middle, where the more in certain direction, the stronger the signal).

Size matters:
At above 300 Gigahertz, the atmosphere becomes opaque to radiowaves, so is unusable.
At 30 GHz+ rain can cause serious problems with the radio signal.
A 30GHz signal has a wavelength of 10mm, so 1/4 is 2.5mm which means it is probably about the right size to fit into an RFID.
A 3GHz signal has a wavelength of 100mm, so 1/4 is 25mm a bit large for an antenna, but ok for a loop with radius of 8mm.

So at a guess the wifi system has to be using a signal in the range of 3-30GHz. This also allows plenty of bandwidth, because of the signal encoding you generally can't transmit more data than you have bandwith, so 30GHz of bandwidth means that you can transmit about 30Gb of data per second. You just have to careful to limit the radio strength to the minimum possible or else you can reduce your neighbours bandwidth, sort of like radio pollution from shouting.

Funny things about radiowaves is that they bounce off things especial metal, these reflected signals can play merry hell with signal strength, cancelling it out in some locations while boosting it in others, so metal heavy environments may severely reduce signal ratings. The other thing is that they are absorbed by materials, when you buy a cordless phone or doorbell, have you noticed that they have an open air rating (usually ~200m) but if you try this in the home, their range is much less typically ~30m. And that's for a relatively low frequency (400Mhz), it gets much much worse at a higher frequency.

So bear in mind when working at the extreme range of the signal, you may be fine and in fact may get some extra range or you may not have any reception to speak of.
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Lord Ben
post Sep 30 2005, 02:07 PM
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QUOTE (Eagle)
In a two way system, on which the RFID system seems to work, require that each RFID to have a transmitter and a receiver. The transmitter has a short range, a few meters depending on model, while the receiver as long as it is within the foot print of transmitter can receive a signal at any distance. This means a RFID tag could receive a signal from a powerful transmitter, but be unable to respond.

Are you sure this is the way the system works in the book?
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Eagle
post Sep 30 2005, 02:09 PM
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Unless it ignores normal laws of physics, yes.
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blakkie
post Sep 30 2005, 02:15 PM
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QUOTE (Eagle)
Unless it ignores normal laws of physics, yes.

Unfortunately you didn't include the possibility that a higher Signal rating could also include as part of that abstraction a higher gain antenna and/or better receiver electronics that are able to pull out the data from a weaker signal.
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Lord Ben
post Sep 30 2005, 02:20 PM
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Or with transmitters on cheeseburgers that a higher rating means it can seperate the all the background noise from the right signal.
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Eagle
post Sep 30 2005, 02:24 PM
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I'm assuming that it's already included and that the signal limits are that the radiowave has pretty much reached the ambient noise level. At the RFID tag level you pretty much limited by power and antenna size.
Plus the high gain antenna are very directional which is somewhat incompatible with the purpose of the RFID tag, which can be in any orientation.

I'll admit there are a few tricks that can boost the signal but they are pretty useless if the signal is too weak. They mainly involve limit the amount of radio noise coming in so the signal is clearer, but again I'm assuming that would be pretty standard
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blakkie
post Sep 30 2005, 02:32 PM
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I see a lot of "assuming" going on there. ;)

P.S. Yes, the Laws of Physics are occationally repealed in SR for simplicity and "story".
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Eagle
post Sep 30 2005, 02:42 PM
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Ok there might a way to increase the receiver strength (but not at the tag level) and I'm not sure how much of signal boost it would give.

You can create a very directional antenna based on a certain wavelength and bandwidth (which looks like a tv antenna, same principal) now if you include this with morphing technology and some sophisticated algorythms (it's a real pain to calculate distance and spike lengths) you could tune in, in real time, to the signal. This would limit the noise level due to receive it in one direction only.

And in second thought a radio dish would achieve similar result (d'oh).

The signal boost would be in proportion to receiver size, with a maximum limit.

This has got me thinking as to whether a miniature antenna with morphing properties and advanced electronics could steer it's signal in a specific direction significantly increasing its range.

The RFID tag receives signal and calculates direction (requires 3 antenna on tag), then morphes transmit antenna into correct direction and beams it's signal out. If that signal, instead of being omni directional, goes down a 3 degree cone then power goes up by approx 10,000 increasing range 100 fold. A 30 degree cone is 100 times more powerful or 10 times the distance. And this could be dynamically tuned using the receiving antenna. Whether it's fast enough to cope wth movement would depend on the technology.

This would take some very sophisticated electronics and software but it is within the realms of possibility.
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Azralon
post Sep 30 2005, 04:00 PM
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Well, "smart materials" are within the scope of SR's 2070 technology. Heck, 2060, even. Thanks, Deus!

A morphable antenna might be standard equipment for all we know. On the other hand, they didn't go into detail enough to say that when A is in a two-way with B, then C has a hard time talking to either.
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kigmatzomat
post Oct 1 2005, 01:51 AM
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I thought the RFID systems were passive, unpowered radio "echo chambers" that reflect RF signals of a specific frequencies and introduce a standardized distortion. Kind of like sympathetic resonance.

So in sound terms, it's like holding a tuning fork playing A up to a chamber that reflects B-flat. You check your handy-dandy decoder wheel and find out that A->B- means "3". Then you play B, C, D, E, etc and wind up with a string of letters/numbers that is the RFID tag (e.g "3T soycaf SKU#116451")

Secure RFID would have a destructive interference system that traps any signal except for the specific one it was designed for.
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hahnsoo
post Oct 1 2005, 03:41 AM
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RFIDs can be passive (requires no power source, using the energy of received radio to transmit) or active (requires a power source). I'm assuming that SR4 has both types running around.
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Eagle
post Oct 1 2005, 09:48 AM
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Passive RFID use the power of radio signal to power themselves and their logic cicuits, so can choose to reradiate what they want.

However with the amount of radio waves flying around in 2070 I'd use them to slowly charge an onboard battery, effectively making every device powered.
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