Сравнение на WiFI USB адаптери

[dtmf]

2 ватова ALFA AWUS 036 NHR и 0.5 вата TP Link 7200 ND.

Интересното е че TP Link-а хваща по-малко мрежи , но ги показва по силни. Примерно рутера ми го вижда с мощност 20-30 dB, докато Алфа картата никога не показва сигнал по силен от 40-45 dB. В същото време АЛФА картата хваща повече от слабите мрежи. Програмата която ползвам е inSSider

Други наблюдения и сравнения?

[gbdesign]

Я кажи, коя USB пишка може да се пусне в Mode Master под Linux, че ми трябва за една простотия?

[Велин]

това с мощностите явно е много относително, докато няма фиксирани едни и същи антени най малкото заради поляризацията.

[orpheus]

В master mode до колкото си спомням вървяха TP-Link TL-WN321G (с драйвър Ralink rt73 ) и AirLive WL-1600USB (не съм сигурен дали с Realtek rtl8187 или Realtek rtl8180)

[NetworkPro]

...о ги показва по силни. Примерно рутера ми го вижда с мощност 20-30 dB, докато Алфа картата никога не показва сигнал по силен от 40-45 dB...Програмата която ползвам е inSSider

Ужасно зависими са от драйверите всички тези неща. Поради кофти драйвери всичките нестават. Ползвайте Linux.

Master mode: Ubnt WiFi Station; TP-Link TL-WN722NC; Всичко с RTL8187 (g)

Редактирано 14 Февруари, 2012 от NetworkPro

[danielskiii]

master mode мисля че може и TL-WN722N чипа е като на убнт wifi station

[pavlan]

едно добро ревю : http://www.amazon.com/Alfa-802-11b-Wireless-Original-9dBi/product-reviews/B001O9X9EU/ref=cm_cr_pr_redirect?ie=UTF8&showViewpoints=0#RC5VNTAI7GJV0

и сега едно такова питане : тая 2W usb пи*ка как се храни с 500mA от USB порта ?

[master]

е като го сметнеш идва почти .. зависи и колко са загубите. Освен това повечето усб та носят пиково и повече. Проблема е обаче за какво ти трябва такова нещо ?

[NetworkPro]

Alfa 1000mW 1W 802.11b/g USB Wireless WiFi Network Adapter

This review is more for the technically oriented group who want to look more deeply into the technology but written in easy to understand terms.

From what I've seen there is nothing better you can buy anywhere right now. However, let me point out that the 1000mw/1 watt output rating might not always be true but before I start on that let me outline what I like about the unit:

1. The Wi-Fi transceiver produces far more power than what any laptop computer or external Wi-Fi transceiver I know of will output.

2. Has a "RP" or what is called reverse polarity coaxial antenna connector which allows me to use a higher gain antenna. See my notes on this type of connector further in this review.

3. Is external and powered by a USB cord allowing me to place the unit with its whip antenna at a better spot than where my computer is at, up to about 15 feet away if using a USB extension cable.

OK, to get to my question of whether the Alfa produces the amount of RF power they say it can:

I was curious if this unit could really produce 1 watt of output power, it seemed far too light weight to do that so I took my AWUS036H unit and fed its RF output into a lab quality spectrum analyzer on maximum hold to record its highest RF carrier level power output as it pulsed to interrogate a remote Wi-Fi system, which of course it couldn't while hooked up to the spectrum analyzer instead of an antenna. I was right about the lower output power, I measured the output to be about 250 mw or +24 dBm, that's 6 dB lower than its advertised power capability of +30 dBm which is four times lower output than the specified 1000mw/1 watt (The difference between +24 and +30 dBm is a factor of -6 dB which as a logarithmic power factor is four times less power). Just to be clear to the folk who don't work with decibels or dB; +30 dBm (referenced to 1 mw/milliwatt) is 1000 mw or 1 watt or +30 dBm = 1 watt.

IMPORTANT: If you have the one watt output version of this Alfa and have the dual USB cable they are now providing with the units which plugs into two USB receptacles at the same time do so! The second USB connector is needed due to the high current demand of the higher power unit, one is for data the other for more current supply to the Alfa. I did not know this and only used the one USB connector which passed both data and power and now that USB port on my computer does not work. Apparently, too much current had been drawn and damaged it. I expect there is an automatic current limitation built into most computers but in my case it did not prevent the USB port from becoming damaged. Mine ran fine for a week with just one of the USB connectors plugged in to my computer but it eventually caused that port to fail. I would have used both ports but I needed the other USB port for something else, unknowing the resulting damage that action would produce leaving me with just one good USB port on that laptop now.

Finding that my Alfa only produced one forth the advertised RF power output I figured either Alfa was misrepresenting its true output or I had a defective unit. I then went to the Alfa web site and found some specs for the unit, their specs show this unit has different output levels for different modes of modulation! For OFDM modulation the RF output is rated at +24 dBm which is 250mw or a quarter of a watt/.25 watt. When using CCK modulation the output is rated at the full +30 dBm output which is 1000mw/1 watt. So, you don't really get a full watt of output in some modes of operation! From what I've been able to find on the net regarding these two kinds of modulation is that the Alfa is rated at less power for OFDM because the efficiency of its built in power amplifier is fairly low due to requiring the amplifier to operate in a highly linear manner which is less efficient producing less output power where CCK modulation does not require the amplifier to be linear and thus more efficient producing more output power. I am still trying to determine if CCK is a short burst of data and OFDM a longer or continuous transmission which would also explain why one mode allows more output power over the other, if the shorter bursts allow the amplifier to transmit a higher peak of power without overheating. I have not found what I'm looking for on this yet, when I do I will update this review. (More on CCK and OFDM at the bottom).

According to law, in the USA when the unit is transmitting with CCK modulation (fast pulsed short duty cycle) producing 1000 milliwatts or 1 watt of output at 2.4 GHz the highest gain antenna you can legally use is 6 dBi which produces an effective radiated power (reference to isotropic radiation pattern) of 4 watts, that's the maximum power you can legally radiate which is higher than many other countries if not all. When the modulation uses OFDM producing 250 milliwatts of output the highest gain antenna you can legally connect and transmit with is 12 dBi which will produce an EIRP of 4 watts. The highest gain antenna you can legally use in the CCK mode of modulation producing 1000mw/1 watt of RF output at 2.4 GHz is 6 dBi which also produces a EIRP of 4 watts of EIRP. What does EIRP mean? It is the abbreviation for "Effective Isotropic Radiated Power" which means the combination of RF power input and gain of the antenna you are using (when measuring the area of its maximum radiated power) will equal the same amount of signal level that a antenna which radiates equally in all directions would produce when being fed with the same amount of RF power at its feed point (not counting feed line or coax and connector losses along the way to it).

If the above doesn't make sense there are plenty of web sites you can Google which better explains EIRP but in short, it just means how much signal level your antenna can produce... some antennas have such high "gain" that they can make a very low power signal seem like a very large amount of power due to squeezing most of the transmit power into a very tight and narrow bream width. In the case of a collinear Wi-Fi whip antenna which has several dB of gain the design of the internal elements of the antenna cause the area of reception as well as transmit power to be squashed down into the shape of a doughnut so that little power is wasted strait above or below the antenna and radiated outward in a pattern which is more useful for line of sight point to point communications but omni-directional as a whip.

Want more receive and transmit gain than a collinear whip can produce? Try a flat panel, Yagi or parabolic dish antenna. The flat panel antennas are really a phased array of dipoles in the form of "slot" antenna which give gain, the more which are phased together inside the panel the higher the gain and consequently the larger the panel. High gain Yagi antennas are very long and bulky, not so good for high winds but can produce good gain too. A parabolic dish or paraflector type of antenna has very high gain and is mechanically stable but the more gain you want the larger they get. As a general rule, every time you double the diameter of a dish you get six dB more gain or equal to four times more effective power output or higher receive gain, at a given frequency. Double the frequency instead of the size of the dish and you get the same, 6 dB more gain. That said, every time you double the diameter of a dish there is four times more surface area... thus, 6 dB more gain which is 4 times more power! Why? When receiving the larger sized dish is collecting more signal and focusing it into the feed point, when transmitting the surface of the dish is concentrating the transmit power into a much smaller beam width of RF power so less of it is wasted going out into directions you don't want the power to go, as a point to point antenna.

Regarding the Alfa's coaxial RF connector:

I am not yet sure why the unlicensed (not requiring a license to transmit) Wi-Fi industry did so, but the RF connectors used on their equipment are non-standard and because of this won't fit together with normal coaxial connectors. The antenna connector on the Alfa, at a distance without viewing carefully enough looks just like a normal SMA RF connector but it isn't! That connector would normally be called a female connector which you would screw a male SMA connector on to but they made a change to the center pin, instead of a female center receptacle which a male pin slides into the manufacturers reverse it by making it a stub instead of a hole, or in other words there is a pin coming out of the center. Yes, it's reversed inside but the outside looks like a normal connector. I've wondered why they did this and I could research this more but my bet is that it was a regulatory action placed on them or something the industry decided to do to make it harder for people to find ways to illegally use the equipment by hooking up high gain antennas which have the same connector, but made for F.C.C. licensed point to point communication systems. If you are breaking the law by using a antenna which has a gain which is a little too high I wouldn't worry about the F.C.C. knocking on your door too much as the agency is severely under-funded, have been for their entire history except in the hay day of CB, and don't have very many employees and very few offices which are scattered around the USA many hundreds of miles apart. There is just too much Wi-Fi for them to chase after those complaints and users are left to solve problems themselves. Of course, if you were interfering with a licensed station they could drag the F.C.C. into it but the Wi-Fi spectrum these units use is unlicensed so how likely is that to happen? It can happen but I'd expect to be hit by lightning first.

Back to the technical issues of the "RP" or reverse polarity RF connectors. It seems the whole unlicensed Wi-Fi industry is using RP/Reverse Polarity RF connectors on their equipment. I've looked at the RF connectors on a LinkSys wireless router, the type used in most homes to produce an in home Wi-Fi system and the model I took apart uses a RP TNC connector which is much larger than the SMA connector used on the Alpha, so again more of these special coax connectors which have their center pins backwards. Why they call it reverse "polarity" I don't know, this has nothing to do with electrical polarity, it is merely that the center pins are physically opposite of what normal RF connectors of the same type use, except in the unlicensed Wi-Fi industry. If you want to find an adapter just search the net for "RP SMA" or "reverse polarity coax connectors" etc and you will find vendors who sell them, including several here on Amazon.com.

Want to run a length of regular coax which already has a normal RF connector (not RP) on it to remote your antenna further away or hook up to a bigger one?

You can certainly do so all you need is a "RP" coaxial adapter which will allow you to use it with this units RP SMA connector but you must choose coax which was made for the high frequency these units receive and transmit. 2.4 GHz or 2400 MHz is microwave frequency, the same part of the radio frequency spectrum your microwave oven uses so don't place your antenna near one because whenever someone heats something in that oven you will likely lose your wireless internet connection until it is done cooking.

Choosing the right coax may take some study if you aren't a techie type familiar with such but with what I've written here shouldn't be too difficult to discern. If you ask a vendor to choose coax for you make sure you specify it is for the 2.4 GHz spectrum (which these Alfa's use for both transmit and receive). Also, no matter what length you choose I'd make sure the total attenuation or loss is no more than about 3 db at 2.4 GHz or you will lose half of your transmit power before it even reaches the antenna, as well as your receive strength too. However, there are some exceptions to this advice, if you were to use a very long run of high quality CATV cable which had loss of 10 dB that loss would become moot if you were able to use a high enough gain antenna on the end of it to allow you to have wireless connectivity to the internet. Who cares how much loss the coax has if inside the building you can't reach the internet but when running 100 feet or more of coax with a high enough gain antenna you can? Doesn't matter, you have internet. However, it is best to use as short a length of coax you can or the lowest loss coaxial feedline possible but what is best is having both, the lowest loss coax as short as possible. With low loss coax such as 1/2 inch diameter foam dielectric Heliax made by Andrew/CommScope, product identifier LDF 4-50A you can have a 100 foot long run with only a little more than 3.5 dB of loss at 2.4 GHz. If you use a high gain antenna on the end of that hundred foot length with a gain of 12 dBi you have an equivalent of using a 8.5 dBi gain antenna directly connected to the Alfa without any feed line at all but having the antenna where it isn't obstructed by the walls in your building, etc.

If the run of coax must be long you should as a rule use the lowest loss coax you can afford to buy. What are examples of fairly low loss coax? Most CATV coax which uses a foam dielectric inside to insulate the center conductor from the outer shield wrapping is fairly low loss but the lowest loss coax you can buy is air dielectric or in other words, no insulator between the center wire of the coax and its outer shield, using only small non conductive spacers every few inches to keep the two from contacting. Who manufactures that coax? Andrew Inc. (Now CommScope Inc.) makes extremely high quality coax with either a low loss foam dielectric insulation or what is considered air dielectric, even though this coax really isn't 100% air because it has a plastic spiral running throughout its length it is about as low loss as you can get (for a specific diameter) as a feedline except for hollow waveguide which would be far too costly and fairly large at 2.4 GHz. Their coax has the trademarked name of Heliax® and in my opinion is the best you can buy but expensive, even for the smaller half inch diameter coax it is more expensive than most people would want to buy new but you can sometimes find this coax for sale at much better prices used. Heliax can last for decades without degradation so if you can find it that way don't be afraid of it unless it has significant dents in it or has been malformed by bending or crushed which will change it from the characteristic 50 ohms impedance to who knows what at that point in the line where the damage is. Many ham radio operators use this kind of coax and if you know one they can help you locate a place to find some fairly cheap but even then not nearly as inexpensive (per foot) as normal CATV cable used for cable television, even if new. So, that's what I'd recommend, high quality cable television coax but be sure to check the specifications for loss at 2.4 GHz, not all manufacturers CATV coax are equal.

What kind of coax should you stay away from at 2.4 GHz? Any of the types which start with RG such as RG-213 with a hard or solid center insulator or dielectric, it is very lossy at these frequencies, even a short 10 foot long length of high quality RG-213 can have close to the same amount of loss a 100 foot run of quality CATV/cable television cable has. The RG-types of cable have been around my entire life and they are good for lower frequencies, but not so good for these frequencies but I've seen people use it! For example, 10 feet of RG-213 has a loss of close to 2 dB at 2.4 GHz and that's for the best you can buy, some of the low quality RG-213 far more, twice as much or more. You can't always believe what is stamped on the coax, some of the manufacturers specs don't hold up to what they are claiming. That said, one manufacturer I know you can believe is Belden Cable, if they say their coax has a loss of such and such at a certain length for a specific frequency you can believe it.

Decibels/dB, how to understand their relationship to power loss:

1 dB loss: 80% of power remains.

2 dB loss: 63% of power remains.

3 dB loss: 50% of power remains.

6 dB loss: 25% of power remains.

9 dB loss: 12.5% of power remains.

10 dB loss: 10% of power remains.

12 dB loss: 6.25% of power remains.

20 dB loss: 1 percent of power remains.

30 dB loss: .1 percent of power remains.

60 dB loss: One millionth percent of power remains.

Decibels in relation to power gain:

60 dB is an increase of 1,000,000X in power

30 dB is an increase of 1000X in power

20 dB is an increase of 100X in power

10 dB is an increase of 10X in power

6 dB is an increase of 4X in power

3 dB is an increase of 2X in power

2 dB is an increase of 1.6X in power

1 dB is an increase of 1.25X in power

0 dB is no increase or decrease in power

Alfa Specifications from the manufacturers web site:

IEEE 802.11g/b, WPA/WPA2 Compliant, Attachable Antenna

Connects at a full 54Mbps via USB 2.0, up to 8 times faster than a USB 1.1 adapter

High gain upgradeable

Compact size for greater flexibility

Also compatible with USB 1.1 desktop and notebook computers

Plug-and-Play Compatible with windows 98SE, 2000, Millennium, XP and Linux

High security 64/128/256bit WEP Encryption, TKIP, WPA, 802.11

Specification :

Model AWUS036H

Standards Wireless: IEEE 802.11b/g

USB 2.0 standard

Data Rate 802.11b: UP to 11Mbps

802.11g: 54Mbps

OS Supported Windows 98SE, Windows ME, Windows 2000, Windows XP, Linux 2.6, Mac 10.4

Interface USB 2.0 mini USB

Antenna Type 1 x 2.4Ghz SMA connector

Chipset Realtek 8187L

One LED

Power/Status, Wireless Act.

Frequency Range 2412~2462 MHz (N.A)

2412~2472 MHz (EU)

2412~2484 MHz (Japan)

Channel

1~11 channels (North America)

1~13 channels (General Europe)

1~14 channels (Japan)

Emission Type DSSS/OFDM

Output Power 24dBm (OFDM), 30dBm (CCK)

Sensitivity for 802.11b

1, 2 Mbps (BPSK, QPSK): - 96dBm

11 Mbps (CCK): -91dBm

(Typically @PER < 8% packet size 1024 and

@25ºC + 5ºC)

Sensitivity for 802.11g 54Mpbs (64QAM): -76dbm

48Mbps (64QAM): -71dbm

36Mpbs (16QAM): -78dbm

24Mbps (16QAM): -80dbm

18Mbps (QPSK): -81dbm

12Mpbs (QPSK): -82dbm

9Mbps (BPSK): -85dbm

6Mbps (BPSK): -91dbm

(typically @PER < 10% packet size 1024 and @25ºC + 5ºC)

Frequency Stability within +25 ppm

Data Modulation Type BPSK,QPSK, CCK and OFDM

Power Voltage: 5V+5%

Security WEP 64/128

802.1X support

Wi-Fi Protected Access (WPA)

WPA-PSK

WPA II

Operating Temp 0°C ~ +50°C

Storage -10°C ~ +65°C

Humidity 5%~98% non-condensing

Dimention 8.5*2.2*6.3cm

Weight 38.5g

- - - - - - - -

"Complementary Code Keying (CCK)

Is a modulation scheme used with wireless networks (WLANs) that employ the IEEE 802.11b specification. In 1999, CCK was adopted to replace the Barker code in wireless digital networks.

Complementary codes, first introduced by Golay in 1961 are sets of finite sequences of equal length, such that the number of pairs of identical elements with any given separation in one sequence is equal to the number of pairs of unlike elements having the same separation in the other sequences.

The complementary codes first discussed by Golay were pairs of binary complementary codes and he noted that when the elements of a code of length N were either [-1 or 1] it followed immediately from their definition that the sum of their respective autocorrelation sequences was zero at all points except for the zero shift where it is equal to K*N. (K being the number of code words in the set).

CCK is a variation and improvement on, M-ary Orthogonal Keying and utilizes `polyphase complementary codes'. They were developed by Lucent Technologies and Harris Semiconductor and were adopted by the 802.11 working group in 1998. CCK is the form of modulation utilised when 802.11b operates at either 5.5 or 11 Mbit/s. CCK was selected over competing modulation techniques as it utilized approximately the same bandwidth and could utilize the same preamble and header as pre-existing 1 and 2 Mbit/s wireless networks and thus facilitated interoperability.

Polyphase complementary codes, first proposed by Sivaswamy, 1978, are codes where each element is a complex number of unit magnitude and arbitrary phase, or more specifically for 802.11b is one of [1,-1, j,-j].

Wireless networks using the 802.11b specification employ CCK to operate at either 5.5 or 11 Mbit/s in the radio-frequency (RF) band at 2.400 GHz to 2.4835 GHz. Networks using the 802.11g specification employ CCK when operating at 802.11b speeds. At higher speeds (up to a theoretical maximum of 54 Mbit/s), 802.11g WLANs use a more sophisticated modulation scheme called orthogonal frequency division multiplexing (OFDM). This is the modulation method used by 802.11a WLANs in the RF band at 5.725 GHz to 5.850 GHz."

- - - - -

Orthogonal frequency-division multiplexing (OFDM)

Essentially identical to coded OFDM (COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access.

The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to handle time-spreading and eliminate intersymbol interference (ISI). This mechanism also facilitates the design of single frequency networks (SFNs), where several adjacent transmitters send the same signal simultaneously at the same frequency, as the signals from multiple distant transmitters may be combined constructively, rather than interfering as would typically occur in a traditional single-carrier system.

Пича и за антените е писал http://www.amazon.com/gp/cdp/member-reviews/A1R7RPHXBZVWDJ?sort_by=MostRecentReview&x=15&y=11&display=public

Редактирано 16 Февруари, 2012 от NetworkPro

[gbdesign]

едно добро ревю : http://www.amazon.co...0#RC5VNTAI7GJV0

и сега едно такова питане : тая 2W usb пи*ка как се храни с 500mA от USB порта ?

0.5A X 5V = 2.5W възможна консумирана мощност... та те така.

[111111]

0.5A X 5V = 2.5W възможна консумирана мощност... та те така.

има едни кабелчета за външни хардове и cd/dvd които ядат ток от 2 USB порта

[pavlan]

0.5A X 5V = 2.5W възможна консумирана мощност... та те така.

правилно смятаме колега , но изходна != от консумирана мощност

[zahranvane.com]

В предвид класа на работа който има усилвателя. КПД 8-15%

За USB порта, телефоните не дърпат по-малко от 2W

По темата: http://www.overclock.co.uk/product/Edimax-EW-7711USN-WiFi-nLite-150Mbps-Wireles-USB-Adapter-3dbi-detachable-antenna_25462.html

Това използвам. Хваща много добре и стабилно. Пробвах да му сменя антената с външна, уви не случих на кабел.

Сега е със запоена директно на платката неговата си антена.

През по-вече от 3,5м USB кабел само свети и не може да направи контакт.

Редактирано 17 Февруари, 2012 от zahranvane.com

[dtmf]

Какви са подходящите кабелни удължители за мощни USB консуматори?

2 ватовата алфа карта след 3 метра USB удължител не работи, докато 0.5 ватовия ТП линк си работи без никкави изменения и спокойно го изкарвам на терасата. USB кабела с който пробвам е екраниран високочестотен с филтър .

Едит : под 2 вата се разбира не консумираната мощност , а заявените от производителя 33 dB в определени модулации, и съответно 27 dB за TP link.

Редактирано 17 Февруари, 2012 от dtmf

[Велин]

ако проблема наистина е в захранването в смисъл пад на напрежение , или му прекъсни + и го захрани с външен 5в адаптер или дублирай захранващите кабели паралелно с по-дебели