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Everything posted by Hibby

  1. For actual RF analysis, we're having fun in the labs with a Rohde & Schwarz FSW26 for the moment, but for wifi analysis, we've got a fleet of Flue Optiview XM tablets that go out. There's more stuff too but it's not as shiny, and that's all that matters :)
  2. Further to this, antennae don't exclusively increase the range of your signal, specifically what they do is focus signal akin to a reflector behind a bulb in a torch. Some types, referred to as omnis, will give you a more toroidial pattern, like a squished doghnut, as their gain (or, more accurately, directivity) increases. Others, known as directional, will focus the beam as the reflector mentioned earlier - yagis fall into this class... They won't increase your throughput or magically give you more power (don't confuse antenna gain for amplifier gain), but they will increase your range in a single direction. As the others have said - this range increase is manifested in a higher throughput at greater distances, yes, but it doesn't increase the maximum throughput and, vitally, it decreases performance in all other directions apart from the beam direction. The trade off for a high gain omni is vertical performance - you get a large, flat, horizontally wide beam pattern but poor vertical performance. For measuring your RF performance, your adapter will offer you a dBm output figure - that's decibels referenced to 1mW. The closer to positive dBm (negative dBm is a fraction of 1mW -> -3dBm == 0.5mW, positive dBm is a multiple 1mW -> 3dBm == 2mW) the better your performance. This is, however, influenced by your receiver - specifically it's antenna's characteristics and receive sensitivity, so make sure you use the same one with the same physical orientation (90 degrees from horizontal/etc). So it's a bit like bars, but with numbers attached :). To get into the proper RF analysis tools that I use in work, you're looking at thousands of USD/GBP/Local currency - it's not cheap to properly map an RF field, and not 100% accurate given the sheer number of variables. Proper systems and antennas are analysed in an Anechoic chamber, with the RF nearfield analysed with hundreds of sensors. The power is then turned down and done again to map far-field, with some clever maths done to extrapolate the full field as close as is possible. It's a good fun process that one! In short, antenna choice depends on the application and the location - both an omnidirectional or a directional will have advantages, but these come at a cost - there's a tradeoff to consider which varies between situations. So... Tell me more about how you want to increase your range...
  3. On top of this, suggesting that hak5 should break your local laws to get a pineapple to you is somewhat unnecessary. The device itself is for personal research, development and experimentation on the 2.4GHz ISM RF band using common technologies, and for learning about common IP technologies as well. There's no need to break the law to get such a tool, and there's no reason that you would have to go to such great lengths to hide the tool. I've imported millions of dollars of high power, obscure, custom RF equipment and analysers into many countries around the world. What you've undergone is a minor inconvenience. Being interviewed by customs, have your personal purchases and company purchases reviewed down to the penny with the accusation of purposefully importing equipment under the wrong harmonised tax codes and not properly declaring all goods on international packing lists is an invasion of personal privacy. It's also terrifying. By suggesting, on a public forum, that you do feel the need to hide things from customs, break the law to import things, you've done this in the past and having a potentially personally identifying image as your avatar, you've probably done more damage to yourself in future than a knowledgeless customs officer saying "oh, it's one of those router-modem thingamabobs, $35 tax please". Let's just be a little bit sensible and not get upset at hak5 for not breaking your local laws in the way you like to do, or for not giving you what you feel is an appropriate heads up on your local import laws.
  4. It's like I tell my clients. Always know your wavelength, so you can have optimum separation when you wave it with others. Actually, usually I say "What do you mean you moved the antennas closer together than what I designed?"
  5. Riiight so... Generally, your antenna directivity isn't directly drawn from the type, but the type and method of construction - while you can get 18dBi yagis, you can also get 22dBi (big) and 12 (small) and suchlike. Antennas are passive equipment - they add no power and/or strength to your signal, only focus it, if that's how they've been built. It's exactly the same as a lightbulb - hanging from the ceiling, it lights all corners of the room. Put the same bulb in a torch with a reflector and it forces all the light forward to give you a clear path ahead at night. If you have a wander through my post history, you'll spy that I write quite a lot about antennas, so I'll boil it down to a couple of points: One from ebay for wifi // 2.4GHz shouldn't do your equipment any damage - they seem to be cheap enough about 18dBi as you suggest. My preferred option is building them. It's not hard or an exact science - antenna performance relies on lots of variables we can't control so a slight quirk in build isn't going to kill it. I highly recommend either building a cantenna or an axial mode helical antenna. The first one is a tin of pringles, the latter one is some wire wrapped around a piece of plumbing pipe. If your google fu for them is weak, give me a shout on irc - I never disconnect, so you can leave a message and I'll get back to you. I should warn you - I can talk about these things all day and all night!
  6. I learned most of my commandfu by getting a free shell account over @ www.silenceisdeafeat.com - taught me ssh, mutt, screen, irssi, nano then vim.... all the useful basics. Then I took a step further and got a headless vps, ran servers in my house. I learned logs, networking, vim all over again, security and all sorts. That's what I did!
  7. Right, so - There's a few things here to look at. There's a couple of types of matching that you cover. First off: Electrical. The alfa should have an antenna out port. You can assume, because I tell you so, that it's output impedance is 50 ohms. The laws of electromagnetism state that conductance is most efficient when the load is matched with the source. In english, this means that your antenna has to be at 50ohms, or close to 50 - not doing so will cause you to lose transmit power and receive sensitivity. The background on this is: The impedance value is frequency dependent - this is why we don't call it a resistance. Your antenna has a certain frequency at which it transmits most efficiently, and at this point the impedance happens to be 50 ohms. By ensuring your output, transmission line and antenna are all matched, you minimise your losses and maximise your potential output and efficiency - in real English, you lose less power to the magic power eating pixies. When the load, line and source aren't matched, you get waves reflected from the antenna back to the transceiver and standing waves in the transmission line, in this case the alfa card - this can possibly damage your card and further reduce overall transmit efficiency. (There's an excellent, visual experiment you can do to prove this using an oscilloscope and small power supply that I'll explain another day if someone desires). Electrical matching is important as you're minimising your losses. Remember, though, that we're working at really low power here - 1W. A 3dB loss really isn't that bad. I work with systems that are often hundreds of W and sometimes in the kW region - shitty standing waves and a 3dB loss there is really fucking bad news for the hardware and financial bottom line! Secondly: Signal Matching. You talk about summing dB - yes, it's very important, but be careful when you do it! Remember dB are a dimensionless number - they indicate a ratio, nothing more. Ensure you consider what 'type' of dB you're using. Antennas are often measured in dBi - decibels relative to an isotropic antenna (a theoretical 'point source' that radiates in a perfect sphere. impossible), but can be measured in dBd, decibels relative to a dipole (the simplest antenna) and less frequently dBq, decibels relative to a 1/4 wavelength 'whip' antenna. Watch out for dBm - this is a power level relative to 1mW and not to be used calculating proportional losses. The key things you're interested in are line loss - the loss, in dB per meter, of your coaxial cable / transmission line. Multiply that by your output power: Power out = Power in * 10^(loss/10) and you get your power inserted into the antenna - we'll call this insertion power for the next section! Thirdly: Antenna Gain! Always, always, always remember this: Antenna gain is passive. Repeat after me: Antenna gain is passive! Antenna gain is passive! What does this mean? It means that by using a directional antenna, you are not gaining any power. You are focusing the beam, and the output of: (antenna gain * insertion power) is called the EIRP: "equivalent isotropically radiated power", but for short we can call it ERP or Effective Radiated Power, and is measured, like all power, in watts, W. Note the word Effective. That means that the power 'is like' the output of the isotropic antenna at that insertion power. Remember the isotropic antenna? The impossible perfect sphere of radiation? All you're doing with a directional antenna is focusing your beam to give the effect of a higher power transmitter and higher sensitivity receiver. You calculate your ERP with: Insertion Power * antenna gain = ERP. And antenna gain == 10^(antenna_gain_dB/10) for all intents and purposes. Transform the gain in dB into a proportinal number by un-logarithming it. It's worth noting that I get all concerned about these things and have to consider them because at the high powers I work with, and with the transmission line lengths I work with they really, really, really fucking matter. At your 1W output (maximum legal output for 2.4GHz ISM band, also known as "wifi"), the effect is drastically minimised, and it will only be equivalent to -1dB or -2 dB total loss, about 15-30%, which isn't that much. If I lose that much, it could be 300-400 watts, which is a lot of money to waste, and a lot of heat to generate! If you're really, really interested, I'll go into more detail with actual proper maths on my blog. But I'd advise, if you're still here dear reader, to get an Amateur Radio license with your local Ham Radio club. You will learn how radio works, and be legally entitled to build high power transmitters, antennas and all sorts of groovy shit. It's not just about talking to lonely old men late at night - you can build every part of your data transmission system from modem to radio to antenna and communicate with people on the other side of the globe. How cool is that? I learned everything I knew about RF there from some of the smartest, most creative people I've ever met at my local radio club, until I became a radio professional. Then I realised I knew more than most folks in the building anyway! I got distracted. Did I even answer your question?
  8. Live and work in Aberdeen now, but I was based in Glasgow and grew up in Ayrshire. And yourself?
  9. I think you'll find we speak the best English in the uk up here in the far North. :)
  10. Give it your best shot - it'll be great to see wha the community can come up with. While I'm here and I've had a wee gin... Dear boy, the apostrophe is used in error - it isn't there to be used to indicate something is plural - it's there for indicating possession (Guy's new bicycle) or contraction (is not -> isn't). Guys will suffice here. Guy's won't. .... I can see why some don't like the irc.
  11. There be educatin' goin on right now.
  12. You have to be very careful when asking for a stronger signal with regards to antennas - they don't amplify, they focus - it's almost exactly the same physics as a flashlight with mirrors behind the bulb to focus the beam. (Admittedly, this can be confusing as both amplifiers and antennas use gain, but they represent different things) Be careful with using dBi as well - that term means decibels over (an) isentropic radiator (antenna) - effectively a 'point source' which radiates a perfect sphere of signal - any deviation from that sphere incurs a change in the rated dBi of the antenna - you can get a 9dBi directional antenna - a cheap 2-3 element yagi, for instance, and you can get a 9dBi 'omni' - a folded dipole or a 1/4 wave whip antenna or similar - both have the same gain, but entirely different radiation footprints. As it so happens, people pay my company lots of money to install these kind of systems - We used to use an antenna called a 26T-2400 by a company called Andrews - it had about 23dBi gain and wasn't mad expensive, but it's been discontinued. You want to look for a '2.4ghz parabolic grid antenna' on the internet - there's a few on ebay amongst other sources. Looking at what you've got already - the yagi - I don't understand what you mean by it not having as much power as the alfa unit: The antenna will focus and direct the signal with it's 18 dBi gain - not add output power. The alfa has a maximum output power of 1W / 1000mW / 30dBm (dBm is decibels relative to 1mW) depending on the modulation scheme you're using. In the real world, 802.11a/g uses OFDM and as such the alfa 'throttles back' to 250mW. 802.11b, however, uses CCK - the alfa will tx at 1W in CCK mode. This comes with a warning, however - you have legal limits that vary from country to country about the maximum Effective Radiated Power (EIRP) on the unlicensed (ISM) radio bands, of which 2.4GHz is one. EIRP is a function of antenna gain * output power - by attaching an 18dBi antenna to a 250mW transmitter, it's likely you're breaking the law... Something else worth considering: "- Impedância de entrada: 75 Ohms" (from the yagi antenna webpage) Could be causing you issues - as far as I'm aware, the alfa has an output impedance of 50 ohms - matching a 50 ohm transmitter to a 75 ohm antenna causes standing waves to form in the transmission line - in other words, you lose power and possibly damage the output of your transmitter (alfa). Neither design of antenna will have a stronger signal, particularly. Parabolic Grid antennas are great as they handle inclement weather much better in permanant installations (wind passes right through them) but are expensive because of the fact that they're designed for this. Yagis are great as they're light and cheap and perform well, but not as well as the parabolic reflector that's intended to be permanant. Have you ever considered making your own? For about 10 Euro, you could build an axial mode helical antenna out of plumbing pipe and wire - here's a design that'll get you about 18-19dBi depending on construction. You get that old-school "Did it myself" hacker feeling too when it all works. I designed an array of these (4 in parallel) that didn't cost a ton and I used for satellite tracking (stepper motors/etc) with roughly 24dBi gain (diminishing returns after 1, really) Maybe you could try a cantenna - they're cheap and well documented! Research, read, hack and ask dumb questions! If all else fails, give me a shout on IRC. I can talk about this all day. The guys in #hak5 know it all too well.
  13. 1) Calm down, it's only the internet! In the grand scheme of things, it doesn't matter. If it still matters to you, read all the text below. Don't skip it, or I'll be forced to educate you. You won't like me when I'm educating you. 2) First off, you should check this before deciding we don't like you: Are you root user?We have a blanket ban everyone that connects as root@ - change your user details and you'll get in no bother. Usually your nick is fine, unless that's root too. 3) Have you been banned from #hak5 and you don't understand why? First off, make sure you understand the network rules (displayed when you join the server and here - you can definitely go back and look at them) - Rule #7: "No intentional ignorance" means that not knowing the rules are there will not help your case if you've been naughty and want unbanned. Join #help and ask to discuss it politely with whomever is available. Screaming requests (read: all caps or pestering), wild accusations or abuse of Ops will be ignored or result in a kick from either #help or the server itself. If no one's about - just hang around. The ops are spread around the planet and all work & sleep, so someone most likely won't be available to service your request instantly, but there will be a response. If you can't stick around, leave an email or pm it to a mod asking for a response - we're nice guys and probably will get back to you! DO NOT REJOIN #hak5 UNDER A DIFFERENT USERNAME AND COMPLAIN. This will result in the ban being extended or yourself being dealt with in a less timely/polite/balanced manner - this is classed as ban evasion and is often dealt with a permaban from the server. 4) Have you been banned from the server? I direct you to our contact form to discuss directly with the admins. Again, the above applies - be polite and sensible and things will more than likely go your way. Still having problems? Send me (or another op) a /msg - I'm eternally connected and will respond in a short period, as are most of the others. Simple! Much Love, Hibby xx
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