WLAN QUESTIONS & ANSWERS LAST UPDATED: Friday 13th April 2002
#5 .........bloody meetings etc. etc. I don't have to do that to plug another machine into my regular LAN - so why do I need to if I'm trying to install a couple of microwave dishes pointing across the valley? Can't I just buy the kit and hook it up?--
#12 But what's the real position with this particular technology - is it not the case that the antennae are very 'focused' and 'laser like" in their point to point precision? Could I not safely install a couple of half-mile dishes and establish a link without causing anyone any problems?
#17 What kind of costs would be involved (license, dish/antenna)? As far as I know 802.11b wavelan cards are available for around £140, and it is probably possible to obtain otherwise defunct computers to use as routers from companies wishing to get rid of them.
#18 On the subject of dishes/antennas I found this page http://home.iprimus.com.au/jhecker/ on the web involving another group staring a community LAN in Australia. It seems this design has been put into use by a few other projects around the globe. Is it any use here, or does it make more sense economically and practically to buy a dish?
#19 As for the height of the dish, I think the highest I could probably get it is the roof of my house. I don't think there is anywhere else nearby I could use. Is it feasible to put up a cheap antenna to work as a repeater from a local vantage point?
#20 I've been contemplating getting one of the Hypergain 24dbi reflector grid antennas:- http://www.hyperlinktech.com/html/products/hg2424g.html though the cost I've been quoted does not seem too bad the shipping is going to be nearly as much.- I wondered if you knew of a source of similar antennas in the UK?
#22 We are interested in starting a free public WLAN in [our named UK.city] . Can you point us in the direction of the best supplier of base station equipment. We are looking to accommodate as many simultaneous users as possible, and cover the widest possible area with one unit.
Yes. The idea behind the wireless network is network connections without wires. Any service available over wired networks is deliverable over "wireless" limited only by the wireless bandwidth or bit rate, on any single point to point link (currently limited at 11Mbits/sec) or ability to pay.
To connect to the internet using wireless requires a pathway or route to an Internet Access Provider (IAP)..... One of the first duties of a pioneering local WLAN Club might be to provide a low cost shared Wireless Internet Access (WIA). The 2Mbit/sec Astra satellite (downlink) http://www.ses-astra.com/multimedia/ for example can be received almost anywhere in Europe and costs only £150 Sterling per year (which distributed amongst say 100 club members can be delivered for just a few pennies per week). A large regional or national body might in future negotiate free (or very low cost) connections.
For the time being, any system which provides Internet Access to a small
home or office network (e.g. at a Telecentre) can with the addition of
a WAP pack provide a Wireless Internet Access (WIA).
The wireless initially provides a means for extending your telecottage's "network" into the immediate neighbourhood. Assuming all your PCs at the telecottage are linked by a wired LAN the strategically placed (rooftop) WAP which costs about £250 Sterling, connects to that network via a RJ45 "ethernet" connector and requires a 9 Volt, 8 Watt DC supply (costing about £6 Sterling per year in electricity).
The ordinary user's "WLAN station" can be put together today for under UK pounds £170.......about the same price as a CB home station. These are the cost of WLAN adapter (wireless modem) at under £130 Sterling PLUS any extra antenna, dish or mast. If they can provide DIY antennas or make do with the supplied antenna, the users' only real cost is that of the WLAN adapter at under £130 Sterling.
In the simplest mode, machines can connect peer to peer on an ad hoc and adaptive network basis. The next step would be where a central PC is configured as a "Webserver" with a WLAN card and act as a community resource, providing a faster local interconnection. A "village" could then share any broadband service starting perhaps with a £150 Sterling per year asymmetrical Astra satellite internet link (2 Mb/sec downlink 54 Kb uplink).
When enough people follow this example free or very low cost internet
access can be organised at a national or regional level and delivered into
your village by similar broadband wireless technologies.
The WLAN (Wireless Local Area Network) card is the basic "wireless adapter" which connects PC users to others (on one of 13 possible U.K. wireless network channels) via an aerial at up to 11,000 Kbits/sec. For just a few PCs this kind of casual "adhoc network" is ideal but raises "continuous running" and "insoluble antenna positioning" problems when more than just a few locations are to be covered.
A Wireless Access Point (WAP) connects a large number of WLAN equipped PCs (up to 256) with much more efficient management of the radio environment. When activity expands in a neighbourhood, a group of private users can benefit from a Wireless Access Point (WAP) set up as a club or community project. Alternatively a local business such as a computer shop or The Village Post Office might provide a WAP as a community business service. With 13 separate channels at present there is room for choice.
One major technical advantage by moving to a formal "star and hub" layout for wireless is that all users antennas need only be positioned for best results with this one community mast/antenna. All network facilities can be made always available to every user on a 24 hour basis through a single wired of wireless downlink from the community mast/antenna.
WAPs can be hardwired to provide a bridge to an existing standard Wired LAN (such as a public library, college or telecentre) thereby connecting the radio users to other machines and any service available on that Wired LAN (e.g. An Internet connection).
As a low power, low voltage (8 Watts max.) unit, the WAP is also very
important for "stand-alone" and "unattended" relay purposes.
The £170 Sterling mentioned is the cost of a PC card (£127 Sterling - best so far) plus any special antenna requirements. . The ordinary user's "WLAN station" can be put together today for under £170 Sterling.......about the same as a CB base station. This is the cost of the WLAN adapter (wireless modem) at about £130 Sterling, plus any extra antenna, dish or mast. If they can provide DIY antennas or make do with the supplied antenna, the user's only real cost is that of the WLAN adapter.
Pacific Wireless offer a 24 dBi ( x 16 range) parabolic antenna PMANT25 for about £80 Sterling or these can be homemade using standard amateur radio constructional techniques for the 2.4GHz band. Standard satellite T.V. dishes can be used with a custom feed at point of prime focus made for 2.4 GHz.
A neighbourhood mast will ideally be situated at a local community resource
such as a college, village hall or telecentre with a dedicated WAP (preferably
but not necessarily) attached to a network The WAP or its antenna need
be located (on a pole/mast) as high and visible as possible.
What puts me off is that you seem to be suggesting that in order to use this technology one needs to set up a complex organisation of some sort and have bloody meetings etc. etc. I don't have to do that to plug another machine into my regular LAN - so why do I need to if I'm trying to install a couple of microwave dishes pointing across the valley?
Can't I just buy the kit and hook it up?--
Yes sure.....but.... The amateur radio thing is about legally increasing range to more than 500 metres. The club a way of equitably sharing costs and quality of service. There is also the forward looking need to be organised to campaign for this type of thing to be protected. Having a "non-profit" and local "club status" also helps you to get strategic installations into (local tall) community and public buildings at the lowest non-commercial cost.
What you might need here is a "INFRASTRUCTURE WIRELESS NETWORK" to share your small office/home office LAN and new ASDL with other users. The kit required your end is a WAP box currently at approx. £250 Sterling. (Alternatively a £130 Sterling WLAN Card and an old LINUX PC operating as "client server").
The ready made WAP connects to the LAN via a standard RJ45 network connector. The WAP is initially set up with its IP address, SSID, "name", "workgroup" and unique 64 bit encryption key - (WEP key) using a RS232 Serial connection. Thereafter the WAP can be accessed as a networked device. Its antenna should be visible to all intending users.
Wireless Clients at extreme range will need to put up a rooftop pole with a dish pointing at the server. Heavy duty Amateur Radio "antenna rotators" may be useful here at about £65 Sterling. It is more likely that any given domestic user will have less flexibility regarding antenna azimuth bearings (e.g. only a narrow outlook to say the South) - or even suffer from prohibitions on installing larger antenna.
These practical difficulties require use of an intermediary or more local "wireless relay" point which may belong to someone else. It is these very scenarios which inexorably lead one back to the conclusion that to be sure of connecting all members of any given "workgroup" in any given area, the only productive effort which enables this in all cases is the creation of "a community wide solution".
The analogy of "throwing an ethernet cable over the garden wall" holds good for this if each neighbour then seeks to connect to his/her immediate neighbour in terms of being part of a "autonomous municipal area net" where imbued by revolutionary fraternal spirit they in their turn connect on to their neighbours an so on.
This is the principle of a "community network" - in which you build
your local links as an individuals, but interconnect to a larger collective
web. In order to connect to any particular one, we need the
potential to connect to every one.
No.. It is quite feasible for a community to operate a viable Community WLAN entirely with 100% licence exempt equipment. It requires a lot of community solidarity and a fraternal spirit of generous co-operation amongst members such as for some members of a community (initially at least) to install antenna and operate equipment not specifically for their own use but for the greater benefit of the immediate WLAN community as a whole.
The need for "Amateur Radio" is for the pioneering technology in the construction and use of high gain antennas or use of enhanced transmitting power, cross-band working and other essentially long-range interconnections which are outside the remit of ordinary "licence-exempt use".
The "Amateur Radio Repeater Group" provide us with a working model and Radio Society of Great Britain's model constitution for "wireless clubs" also seems and excellent foundation on which to build a new amateur wireless service.
A single radio amateur licensee might operate a "Club Station" say at a "Telecottage" with a transmitter power amplifier enhancement. The increased transmitting power permitted to Radio Amateurs is little benefit unless possible at each end of a link (say for long range amateur licenced interconnections).
Antenna improvements at any end of a link, on the other hand enhance
the range in both directions.
Yes.. But since criminalisation issues arising from The 1988 Telecommunications
Act, A licenced amateur operating layer allows being able to legally
organize, advertise, promote, discuss, make, import or distribute equipment
choices! Additionally, if the sell-off of franchises for "Commercial
Fixed Broadband" are complete - it will be necessary for us as non-profit
operators to show we are clearly not operating within any profit-centred
commercial context and avoid acting in breach of the (nationally purchased)
commercial franchise. This enforced division of cultures is sort
of advantageous in that it clearly separates the two....
Initially an isolated node has a maximum service radius of no more than say 500 metres or a third of a mile. Any public spirited enthusiast(s) can however provide a dedicated public node or even a chain of unattended nodes which relay "through traffic" for other distant users, thereby extending his/her range to that of all other connected nodes.... With numerous Internet Gateways, widespead public co-operation and participation there need be NO THEORETICAL LIMIT to distances covered. (The American equivalent of the RSGB is appropriately called the Amateur Radio Relay League)
There are several innovations and technical advances which allow ordinary licence exempt users to magnify their operating range much further than the few hundred metres maximum originally envisaged by the IEEE 802.11 Standards Committee:-
1) While in the U.K. it is now a criminal offence to exceed the permitted EIRP... Asymmetrical working, that is using only the range advantage of a high gain antenna in the receiving circuit only is a way of getting round that..... The disadvantage being that such a configuration must be implemented at each end.
1) Just placing both antennas of a link centered and in front of 120mm flat metal panels at about 15mm will enhance range of each by 6dB (or x 2 range magnification). Dense polymer "dielectric lenses" can do a similar job. Large horns (like old fashioned tin megaphones) can do an even better job.... Better than a dish of the same cross-sectional aperture.
2) The "Community Mast" licenced under Amateur Radio regulations can have a high gain omnidirectional antenna (at 20dBi) giving licence exempt users access up to a x 10 range magnification.
3) Directional narrow beam parabolic antennas (at 2.5 metres diameter!)
used by licenced amateurs may have up to x 30 range magnification when
to licence exempt users.
In the U.K. there are 13 channels to use. The 802.11 standard has a number of built-in mechanisms to ensure "graceful degradation" of services in the event of (co-channel) congestion on the same channel. At the physical layer the wireless signals themselves are "spectrum spread" using a simply generated digital pseudo random code sequence. This and the "capture effect" eliminantes the total wipe out effect of interference to and from other services even if (co-sited) in the same room/box.
The practical result is that:- as USERS increase, CELLS
shrink, but the network still functions UPSCALED with more, but smaller
Methods of security developed for the Internet are applicable for the use of WLANs since the threat of interception of microwave carriers used for the telephone traffic is much the same.
Whilst general access to a network can be open to the public as "Guest Users" permission to fully use the WLAN and "User Permission" must be obtained as with any other multi-user system.
Regarding "eavesdropping" or "misuse"; that small number of possible
unwanted users and destructive "hackers" can be dealt with under the same
recent legislation which protects all unauthorized access of networks.
A Public WLAN can be made a secure as required.
The 802.11 "appliances" have a built in very secure 64 bit Wired Equivalence Privacy (WEP) facility which enables all local club WLAN equipment to have entered a common key code without which they cannot interconnect (and which may of course be changed from time to time).
The WLAN/WAP network protocol allows a unique SSID code to be entered. All intercommunicating WLAN cards and WAPs must have the same (or ANY) SSID without which they will not interconnect.
Access to a PRIVATE WLAN requires users being set up at a high level to use a named WORKGROUP without which they will not interconnect.
Once connected to a server, users must use a recognised name or password (or guest login) without which they will not enter the system.
The latest Netscape Navigator offers users a "military grade" 128K encryption
useable on any mail or file system.
Infra Red (& laser) Wireless Links offer this narrow beam capability but not 2.4GHz radio waves.
The 60 cm satellite dish systems I am advocating (being widespead and cheap) are approx. 15 deg.. beamwidth (defined as the half-power beam width) ... i.e. rather broad beam ...about as wide as a car headlamp......
The 2.4GHz wavelength is about 12 cm. You get lots of signal even "off the back" of a 60 cms dish. (its only 5 wavelengths after all)
A 2.5M (8ft) dish will magnify range by x 32 and have a beamwidth of about 5 degrees (a thumb at arms length).
The "spread spectrum mode" is ideal for clandestine operation and was originally invented for military use (by glamorous HollyWood Actress Hedi Lamar). It was not however employed here to support clandestine radio but rather because of its graceful degradation in "pile-ups" (lots of stations in range transmitting at the same time).
Channels 7 & 8 (2442 & 2447MHz) are the ones most affected
(and "camouflaged screened") by domestic and commercial microwave
cookers at 2445 MHz.
These are radio propagation programs. The G4JNT programs ( reviewed first page of the links page: http://www.wlan.org.uk/page7.html) enables one to draw polar horizon plots, plots of intervening terrain between two radio antennas and false colour topographical maps of U.K. localities... It is great for predicting microwave (line of sight) propagation.....
If you can't see your nearest WAP, there may well be spots which could
link you (and your immediate neighbourhood) to an early 10 Mb/sec Wireless
I'm very glad you managed to do that. There's an good little manual
see #8 above. Assuming "barefoot" ranges of 300 metres
@ 11Mb/sec and 600 metres @ 1Mb/sec. About 300 - 600 metres
to a similarly licence-exempt AP. 3000 - 6000 metres
to a 20dBi omnidirectional antenna.
Yes this is absolutely true. The amateur radio community certainly
has the POTENTIAL to lead the way in this. The extensive coverage
of the ATV Repeater Network at 23cms in the U.K. is similar to what might
be achieved with just a few dozen "Ham-LAN" sites.,
The cheapest cards are about £110. WAPs at £250.
You can make 24 dBi antenna based of an old satellite dish (60cms dia.or
more) Linux runs quite well on older equipment like P75s.
This is a very nicely put together article which I will link to our
wlan.org.site site. Helical antenna are circular polarised so you
loose 3dBi working plane polarised systems. The resultant 15dBi
is approximately what you can get with the required "feed" for the geometry
of a standard satellite dish. So is not too hot in terms of performance.
Certainly. We are checking out the possibility of using WAP-WAP
links at the moment. If WAPs can be resolved which can
be operated in "Stand Alone Mode" they offer the best option for say wind
and solar power remote hill-top relays. There is some data
on diffraction loss.... i.e working over a distant obstructing ridge
etc. but I think that the little reserves available to us are only going
to make this useful for people a few Km. range.
Hello...... Great to get a call from your.... The latest (Intel
2011) APs offer "AP to AP bridging" so you could as a last resort set up
a relay around or over the dreaded trees. Hypergain seems good and
are linked on our "Antennas Page". For DIY I advocate using
ex-satellite dishes starting with 60cms (2ft) Round. In these parts
these are often thrown away (I have collected 4 from off dumper bins/skips
in the last 2 years!) CPC Ltd. Preston sell these NEW for £15.90.....
(US$25) You can find out all you need about dish feeds in the RSGB "Jessop"
VHF/UHF Manual.....ISBN 0 900612 63 0 These are made to match
the f/D ratio of the dish.... One feed will work for larger and smaller
dishes providing the f/D is correct...... You can expect 26 or 27dBi
from a 2ft dish. Bigger dishes are available. A 2.4metre dish (8ft)
will offer you a mega 35dBi ....My calcs are that a British satellite dish
has an f/D ratio of 0.72 so requires a feed system which generates
a beam of 43 degrees at -3dB half-power points (80 deg at -10dB).... The
double quad illustrated on the "Antenna Page" is sufficiently close to
this (see also my attached dwg).
A new long range solution requiring no soldering connectors or RF cables,
is to weather-proof (foam) and fix a USB wireless adapter so that the antenna
element is at the point of focus of a satellite TV dish..... A plane "reflector"
of 125mm dia. behind (spaced at 14mm) and a "director" disk of 45mm (spaced
10mm) will give a fair to good feed to a 0.7 fD Ratio Dish... With a single
4 ft dia. dish, this can increase range by x30 or more - yet the electrical
integrity of the sealed and type approved unit is not compromised! With
this latter 4ft dia. dish system, one of our local users has made a 30km
a) An Intel 2011B Access Point... USD $750These are not the cheapest, but offer extra features which the majority of alternatives don't have such as:-
(i) "software power regulation" (for using big antenna
but remaining compliant with licence free use regulations)
b) A High gain Omni (greater than 15dBi) http://www.wlan.org.uk/antenna-page.html
(As a Free/Community Service, you can have one of my "Hot Spot 16s" development samples at half price).
c) A computer (Gateway/Proxy Server) connecting to the
internet running say Winroute (unlimited user edition about $750)with WLAN
card fitted and in range of the Community Antenna.
Using a 2ft (Astra) dish to a >15dBi "Hot Spot 16" antenna, "clients" here have connected at 14km range....
1. "WLAN Clients" use a D-Link DWL-120 adapter (£85 exc. VAT) Astra Dish (£18).
2. The easiest set up is to put up a cheap AP such as the SMC (£250) at a prime location with a top spec omni-directional service antenna (£400) The best you can afford. This constitutes something like a VHF/UHF Packet Repeater.... i.e. Anyone in range can use it as an "ethernet" hub and do whatever you do on a wired ethernet, but remotely...
3. Anyone with internet access of any sort, WLAN equipped and in range can ADD Proxy Server software (Winroute Lite works well with Win 2000). This enables anyone else on the wireless hub to share the internet connection (£350).
4. Paying £450 for one of the top spec APs (such as Intel 2011B) enables THESE access point to "daisy-chain" 2nd, 3rd or 4th hand...
5. DIY Low cost solutions are possible with just a cheap wireless network adapter and a Linux machine.....
6. Use of G4JNT-ATV program recommended for checking out people's QTH's.
73 Henry G8OTA
The wlan.org.uk site lacks humour and it was great to add the WLF bit.......If YOU want to smile when you look at your (G8OTA Dish Feed Antenna) use a so called "100% FREE INTERNET" CD - as a reflector disk!
Please e-mail YOUR suggestions / "public"
questions to firstname.lastname@example.org.