WiFi aerials and range - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: July 16, 2012, 03:13:03 pm
content: Now that I have my flashy new phone that can go online with wifi I'd like it to pick up all over the house and garden. As a consequence of getting a NAS box i will be getting a new better router and moving it upstairs to a cupboard in my room. So will this improve the range of the wifi or not ?If I want to get a higher gain aerial what can I expect in coverage reduction versus gain increase ? Where should i stop expecting more gain in favour of actually covering my target aria ? as i understand it the standard aerials supplied pretty much cover a sphere around them, and as the gain goes up this gradually reduces to a thinner disk. My thoughts are that as most routers have two aerials I can keep one standard aerials and change the other for a high gain one. does that make sense ? why so routers come with two identical aerials right next to each other ?

author: G7PSK
author_rank: Super Contributor
timestamp: July 16, 2012, 03:26:20 pm
content: You could try something like this booster. Otherwise you may need to get a more commercial unit.http://www.edimax.com/en/produce_detail.php?pd_id=33&pl1_id=1&pl2_id=8http://www.ecrater.co.uk/p/13810435/outdoor-wifi-booster-14dbi-wireless?gps=1http://www.caworldwifi.com/5-Watt-WiFi-Access-Points-Bridge-802.11b/

author: Simon
author_rank: Unknown
timestamp: July 16, 2012, 03:32:45 pm
content: that last one is a bit over the topReally i want to make best use of my aerials first, then think of boosters. I could for example use my old router as a boost station.

author: T4P
author_rank: Super Contributor
timestamp: July 16, 2012, 03:37:39 pm
content: You can have a old router as a boost station if they support DD-WRT...Or you can may as well use a long antenna.I decided to use my TP-Link tl-wr1043nd that remained unused for a year now to be a wireless repeater and it's working brilliantly*I used DD-WRT

author: madires
author_rank: Super Contributor
timestamp: July 16, 2012, 06:42:01 pm
content: Hi!Yep, it's coverage vs. gain for antennas. Check the radiation diagram and you'll see if that antenna helps or not. High gain verticals got a doughnut shaped pattern. If you need a better coverate just at one side of your house go for a plat panel antenna. Keep one of the original 2dBi antennas attached and replace the second one.The two antennas for WLAN routers and access points are mostly used for diversity reasons. Newer protocols using MIMO require multiple antennas (3 for 802.11n) for proper operation. There's a major drawback with all antennas attached on one small box. If the distance between antennas is less than lambda/2 the antennas are interacting with each other. Unfortunately that's the case with all the boxes. By moving one of the antennas a little bit aside (use one of those small magnetic mountings with 0.5m coax) you may improve the signal (and/or signal noise ratio) considerable.Cheersmadires

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 16, 2012, 08:37:14 pm
content: Quote from: madires on July 16, 2012, 06:42:01 pm2.4Ghz = 12.5 cm wavelength, so the antenna's need to be apart more than 6.25 cm, which is mostly the case...

author: Simon
author_rank: Unknown
timestamp: July 16, 2012, 08:43:37 pm
content: so where do I find the graphs for shape versus gain ? should it be on the areal spec or is it generic ? what about placing the router on the first floor rather than the ground floor ?

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 16, 2012, 08:56:43 pm
content: Quote from: Simon on July 16, 2012, 08:43:37 pmIt's simple, if you radiate the power over 180 degrees and not over 360 degrees you will double the power in that direction. The more interesting question is what that does for the distance... It's hard to say what moving the router to the first floor does for you, it depends on a lot of things like the construction of the house, where the windows are, where you want to pick up the signal... What you are asking at the moment is a bit open ended, are you having problems at certain locations at the moment?

author: IanB
author_rank: Super Contributor
timestamp: July 16, 2012, 08:59:45 pm
content: I have used the venerable WRT54G in various situations and found the coverage is quite good without any special modifications. It has twin hinged aerials that you can bend and rotate for the best coverage. It also helps a lot to try different channels and find the one with clearest reception and least interference. If all your neighbours are broadcasting on the same default channel there will be a poor signal to noise ratio and range will suffer.In UK houses with solid interior walls (brick or breeze block) the walls can block the signal quite strongly. So it helps to find a position for the router that has fewest walls in the way.

author: Simon
author_rank: Unknown
timestamp: July 16, 2012, 09:03:01 pm
content: hm yes the walls are a problem, I want to get it into the garden. I have an ex council house so plenty of brick

author: RCMR
author_rank: Frequent Contributor
timestamp: July 16, 2012, 10:13:44 pm
content: 2.4GHz doesn't much like passing through things like brick and concrete so you may have a bit of a task ahead of you.You can get some fairly high-gain antennas that will deliver as much as 9dBi in a flattened toroidal pattern which, for all intents and purposes (since you won't be flying overhead) remains omnidirectional.Boosters are an option -- but be aware that we're talking about bidirectional communications here and a booster only increases the output power of the router. Some do claim to have pre-amps to boost the received signal but with only a few exceptions, these don't actually do very much so, unless you're using a booster at each end of the link, you'll still get bad performance because the router won't hear your laptop trying to talk to it.The benefit of high-gain antennas is that they produce a gain on transmit and receive.

author: codeboy2k
author_rank: Super Contributor
timestamp: July 17, 2012, 12:03:34 am
content: it's very directional, but you can build a yagi relatively quickly, and experiment, if your willing.you can get 15-20db gain and it's bidirectional, in the sense that the extra gain of the antenna will pickup the lower power of the laptop out in the garden.You probably don't need this much gain to get to the garden, you can probably go a kilometer or so in open air, but the extra gain does help get through those pesky brick walls.http://www.ab9il.net/wlan-projects/wifi6.html

author: RCMR
author_rank: Frequent Contributor
timestamp: July 17, 2012, 03:51:53 am
content: It's even easier to build a helical antenna. Yes, you'll lose 3dB or so because you're working with a linearly polarized antenna at the other end but a helical can be made using some cardboard tubing, a sheet of aluminium (or PCB) and some hot-glue. Pretty simple.We use 5-turn helical antennas with our FPV gear and get over 5Kms of range with 200mW of transmit power at 5.8GHz.And if you want a hi-gain 2.4GHz antenna there are plenty of them available from the likes of DX -- for a song.

author: G7PSK
author_rank: Super Contributor
timestamp: July 17, 2012, 11:06:18 am
content: You could try a parabolic reflector on the aerial that you have first easy to make out of card and kitchen foil.http://www.freeantennas.com/projects/template/http://www.wotnext.com/Info.aspx?Parabolic-Reflector-for-Wifi-Antennahttp://metasofa.org/vansprouts/parabolic.htmlI have a spare aerial that you can have Simon at no charge, its one of those things that I just could not bring myself to bin so if you want it it's yours.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 05:32:19 pm
content: Quote from: PA0PBZ on July 16, 2012, 08:37:14 pmThe interaction doesn't stop immediately at lambda/2, it just decreases as the distance grows. RF isn't as simple as Ohms law :-)

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 05:37:14 pm
content: Quote from: Simon on July 16, 2012, 08:43:37 pmThe antennas datasheet should include a diagram with its radiation pattern. If it's missing you may have a look at the diagram of a similar antenna (same type and gain).

author: Simon
author_rank: Unknown
timestamp: July 17, 2012, 05:40:42 pm
content: I'll try other channels. My NAS box is maxing on 5 MB/s on a wireless N connection

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 05:44:16 pm
content: Quote from: IanB on July 16, 2012, 08:59:45 pmGood point! Most attenuation is caused by metal in the near of the WLAN router and metal in the walls and ceilings. And window glasses with sun protection are nice too :-)

author: IanB
author_rank: Super Contributor
timestamp: July 17, 2012, 05:44:54 pm
content: Quote from: Simon on July 17, 2012, 05:40:42 pmFor most people 5 MB/s over wireless would be considered bloody good...

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 05:48:47 pm
content: Quote from: Simon on July 16, 2012, 09:03:01 pmAn outdoor flat panel antenna may help.

author: Simon
author_rank: Unknown
timestamp: July 17, 2012, 05:50:16 pm
content: Quote from: IanB on July 17, 2012, 05:44:54 pmon 150 Mbps equipment

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 05:52:36 pm
content: Quote from: Simon on July 17, 2012, 05:40:42 pmIs the WLAN or the NAS the bottleneck?

author: Simon
author_rank: Unknown
timestamp: July 17, 2012, 06:04:06 pm
content: well the NAS is supposed to be 70+ MB/s but now you mention it is on 100 Mb lan so I guess 10 MB lan connection, I can get more by trying more than one transfer at once. Need to get the Gb router I guess

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 06:21:08 pm
content: Quote from: Simon on July 17, 2012, 06:04:06 pmYep. For a FastEthernet you won't get more than about 9 MBytes/s. BTW, a lot of 802.11n routers and access points supporting 300 or even 450 Mbit/s (effective bandwidth: 150 or 220 Mbit/s) only got FastEthernet ports ;-( Silly design!And regading crowded channels there's an import thing to know. The channels are just 5MHz apart but the bandwidth of a single channel is 20 MHz. For 802.11n it may be set to 40 MHz. it's broken by design :-( And if you go for the 5GHz band you got more channels but also more problems with attenuation (walls ...). I don't know Ofcoms specifics for the 5GHz band, but it might be allowed to transmit 200mW RF for the upper half of the channels. 2.4 GHz is limitted to 100mW (20dBm, this includes any gain of the antenna).

author: Unknown
author_rank: Unknown
timestamp: July 17, 2012, 06:30:34 pm
content: 802.11b has a slight advantage in weak signal range compared to 802.11g and maybe even 802.11n networks.Made a few yagi and other antennas with mixed results. Simply no way to fine-tune them with the equipment at hand. If somebody has experience with impedance matching 2.4 GHz antennas I am all ears.

author: IanB
author_rank: Super Contributor
timestamp: July 17, 2012, 06:41:31 pm
content: Quote from: Simon on July 17, 2012, 05:50:16 pmThere is often a gap between advertised "nameplate ratings" and what you can get in practice. In general I don't think you will easily get a wireless speed equivalent to a wired network. But if technology has moved on enough to change this I'm happy to be corrected...

author: Simon
author_rank: Unknown
timestamp: July 17, 2012, 06:46:07 pm
content: Well I'm no expert

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 06:51:44 pm
content: Quote from: HAL-42b on July 17, 2012, 06:30:34 pm802.11n is better than 802.11g regarding speed and coverage. If all your devices and gadgets support 802.11n set the WLAN to 802.11n only.QuoteImpedance matching isn't as important as you might think. In practice the loss of RG174 is higher than the loss caused by an acceptable impedance mismatch (50 <-> 75 ohms). HAMs will disagree, but we're talking about 100mW and not 100W.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2012, 06:58:00 pm
content: Quote from: IanB on July 17, 2012, 06:41:31 pmThe effective bandwidth of WLANs is about half of the speed advertised or claimed. And that speed is achieved only if you're in line of sight with the access point and not away too far.