Subtitles of the Movie

Now, finally, talking about, uh, the science involved with radio frequency, let's [`00:00:06] look at range and speed. Now, the range or distance that an RF signal can travel [`00:00:11] depends upon several things. The three main things, though, are power, frequency [`00:00:16] and interference. And essentially the, uh, an increase in power will give you an [`00:00:20] increase in range. Kind of makes sense. More power, the farther it can go. A [`00:00:24] decrease in power results in a shorter range. Now, you might be tempted to say, [`00:00:27] well, if I need it to go farther, I can just increase the power. But the problem [`00:00:31] with that is, is transmit power is regulated in the United States by the Federal [`00:00:35] Communications Commission or FCC and it's regulated in other countries as well. [`00:00:40] It's also regulated which frequencies you can be on. Each manufacturer of wireless [`00:00:44] devices have to stay within those regulations, so each device has limits to the [`00:00:48] maximum amount of power they can put out. Now, I have heard of people tweaking [`00:00:52] devices and the, and making them transmit a little bit more than they're, uh, [`00:00:56] designed to do or even legally allowed to do, but I don't recommend this. You [`00:01:00] can get in serious trouble for one thing, but you can also destroy your [`00:01:03] equipment if you don't know what you're doing. Now, frequency also effects range [`00:01:06] and, uh, essentially higher frequencies are shorter waves. Now, remember back in [`00:01:11] an earlier part of the course where we saw our purple and our red waves that the [`00:01:14] lower frequencies have longer waves and the higher frequencies, the more cycles [`00:01:19] in a given piece of, uh, of radio waves have shorter waves. Now, normally the [`00:01:25] longer waves will travel farther. Now, assuming the same amount of power is [`00:01:30] applied, the lower frequencies will travel farther because they have longer waves. [`00:01:34] The higher frequencies have shorter waves and they will not travel as far. So [`00:01:38] frequency effects range. High frequencies, short waves means less range. Lower [`00:01:43] frequencies, long waves, greater range. Ok? A good illustration of this point is [`00:01:48] that the 802.11B and G standard has a farther range than 802.11A. Now, why is this? [`00:01:55] Basically because 802.11B and G have a 2.4 gigahertz frequency range and 802.11A [`00:02:01] has a five gigahertz frequency range. So you can see that 2.4 gigahertz, the [`00:02:06] lower frequency range, longer waves, travels farther. One more thing that can [`00:02:13] interfere with range is interference itself. Now, interference can be a wide [`00:02:18] range of things. Interference can be electrical noise, such as lightening or [`00:02:22] electrical noise from a magnetic device or another electrical device that's near [`00:02:26] the transmitter, for example. Or the receiver. Weather can interfere with, uh, [`00:02:30] range. Uh, lightening strikes, but also clouds, rain and other things can [`00:02:34] interfere. Other transmissions can interfere. If you have two devices near each [`00:02:39] other that are both transmitting or transmitting near the receiver, that can [`00:02:42] create interference that can, can reduce the range. Now, how do you mitigate [`00:02:47] some of that? Well, you could use RF shielding. You could use more power. You [`00:02:51] move devices away from each other. If you try to limit the electrical noise that [`00:02:54] you have. Now, weather, there's not much you can do about. I don't think there's [`00:02:57] been a solution for controlling the weather just yet that could effect limiting [`00:03:01] the range of your wireless networks. Let's look at speed of networks. We talked [`00:03:11] about distance. Now, how about speed? Normally speeds of wired networks are [`00:03:15] traditionally measured in bits per second and with wireless networks, that's no [`00:03:18] different. Wireless networks use the same speed measurements as wired networks. [`00:03:23] Bits per second or BPS. Now, from our older network days when we used just old [`00:03:28] modems, telephone connections, they were measured in kilobits per second and [`00:03:33] some of the ranges that you might have, depending upon how fast the modem was, [`00:03:36] could have been 14.4 kilobits per second, 36.6 kilobits per second or even the [`00:03:42] old, big, fast, whopping 54 kilobits per second as some of the top of the line [`00:03:47] modems had. We don't measure LAN speeds that way anymore because we have faster [`00:03:51] speeds, Ethernet and networks. Modern local area network speeds are measured in [`00:03:56] megabits per second and some of the even low-end common speeds are ten megabits [`00:04:01] per second. But usually the middle-way point is a hundred megabits per second. [`00:04:05] Uh, we even have a thousand megabits per second, which is a gigabit. We call that [`00:04:10] gigabit Ethernet. But that's how LAN speeds are measured these days and wireless [`00:04:14] networks are also measured in terms of those speeds. Of course, faster is better. [`00:04:24] Now, how do we effect speed? Again, electrical interference, weather, faulty [`00:04:28] equipment, uh, even saturated bandwidth, those are all some of the things that [`00:04:31] can reduce your network speeds. And there are things you can do to prevent those [`00:04:34] uh, things from interfering with your network speed. Reduce electrical [`00:04:37] interference using shielding like we talked about. Moving electrical devices [`00:04:41] away from each other. Replacing the faulty equipment or upgrading older equipment. [`00:04:45] You know, upgrade those old 10100 cards to, uh, gigabit Ethernet cards. Even [`00:04:49] saturated bandwidths. If you have devices on a network that are over [`00:04:52] transmitting or someone is just, uh, you know, doing a lot of file sharing or a [`00:04:56] lot of network use, that can reduce your bandwidth, which in turn can effect [`00:05:01] your network speed. [`00:05:04] [`00:05:05]