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Amateur Wireless Fidelity

I think most readers already know the existence of a new standard for wireless computer networks. It is the 802.11b standard, using a no-license ISM band that, in Europe, goes from 2400 to 2483 MHz. The band is divided into 13 overlapping channels, each 22 MHz wide. Modulation used is DSSS - Direct Sequence Spread Spectrum, with a maximum EIRP power of 20 dBm, that is 100 mW, and with a speed of 11 Mbps (megabits per second). These modem are now quite cheap and can be used by everyone to make a private network inside his/her house or company building.
Recently in Italy companies can also install public hot spot sites, to make people connect to Internet from their laptop or handhelds.

There are also related standard that are very interesting. Here is a highly uncomplete table:
Up to 100 mW on 2.4 GHz at 11 Mbps, with fallback to 5.5, 2 and 1 Mbps
802.11b (modified)
Up to 100 mW on 2.4 GHz at 22 Mbps, with fallback to 11, 5.5, 2 and 1 Mbps (compatible with 802.11b)
Up to 100 mW on 2.4 GHz at 54 Mbps, with fallback to 48, 36, 24, 18, 12, 9 and 6 Mbps (also compatible with 802.11b ant its data rates)
Up to 25 mW on 5.7 GHz at 73 Mbps, with many fallback data rates (NOT compatible with 802.11b and g)

The interesting thing here is that in many countries part of the ISM 2.4 GHz band is also assigned to the radio amateur service. For example in Italy we have assigned the spectrum from 2300 MHz to 2450 MHz, so we can use commercial WiFi modems as ham radios, provided we don't go over the limit of 2450 Mhz. For 802.11b and g I think this means we can use only channels from 1 to 6 (and only 2 non-overlapping: the 1 and the 6).
Even more interesting is the fact that, as licensed radio amateurs, we can use more power than commercial users. In Italy we could go theoretically up to 57 dBm (!), but I doubt someone will do this, unless you want to put online a microwave oven... In fact, it becomes possibile to transmit up to 30 or 40 dBm, covering wide metropolitan areas.
And probably you don't even need all this power: much better to stay at the beginning with 20 or 23 dBm and use high gain antennas. A vertical antenna at the access point can easily provide +8 to +18 dBi gain and a small parabolic dish up to +24 dBi gain at client stations. Apparently this is enough to cover 20 or more miles (32 km), line of sight.

Why the name AWF?

This is my first contribution to the amateur WiFi experimentation: I propose to use the name Amateur Wireless Fidelity (AWF) for this new mode of operation. I like this name because it has a double meaning:
  1. A technical one, referring to the WiFi standard used as radio amateurs
  2. A sentimental one, because I hope that digital transmission modes will help most people not to abandon amateur radio
I suggest also to use of the word AWF as ESSID of the amateur wifi networks to be built (if different subnets share the same ESSID it becomes possibile to connects among them and to roam from one subnet to another one).

Here are some features we can use as AWF users:

The setup of my AWF node

Here is the setup of the AWF node I am thinking of:

Radio amateurs participating to the AWF tests would only need a Linux or Windows computer (any kind is ok) with a wifi lan card. These cards exist in many flavours: external USB devices, internal PCI cards, etc. Depending on distance, they should also install an external, possibly directional, antenna aimed at the access point (my node). There are many antenna types usable: Yagi, can antenna, patch, parabolic dish, etc. The higher the distance, the higher the antenna gain required, of course. Each doublig of distance should require about 6 dB more gain, if I remember well.
I recommend (to myself and others) to consult the data sheet of the cards before buying them, because they have not the same transmitting power or (more important!) the same sensitivity at the receiver. You should compare the sensitivity at the same data rate because if you go slower, the sensitivity would be better.

Why 802.11b and not 802.11g?

This is interesting question, beacause 802.11g can reach 54 Mbps and is compatible also with 802.11b cards. But if you look at the specifications, you will see that to obtain these data rates you need much more dB of S/N ratio. Translated to English, this means LESS distance. Since AWF is not for a local, fast, computer LAN, but should connect radio amateurs at the maximum possible distance, I think it's better to stay with slower but more sensitive 802.11b (and perhaps not even at the full 11 Mbps). As a collateral effect, 802.11b equipment costs much less than 802.11g stuff. However, if someone wish to test distances with 802.11g, results are highly welcome.

Let's begin!

I hope to start as soon as possible my node. I already have two USB wifi modems and I am trying them. I have also the Linux box, with web and ftp server already working. I need more work to set up the POP3 server and possibily also the News server.

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