very so often, we find the need to set up a relatively small radio-based data network. This could be to provide coverage for a smaller event like the local town picnic, or something (geographically) larger, like a fireworks display or 5k race. We ve had the ability to do this on, say, 2 meters since the 1980s using TNCs and AX.25 packet, but that is far too slow for anything but the most rudimentary of text-based messages. Transferring a 1-MB spreadsheet or photograph would take hours at 1200 Baud. For greater data capacity, we can turn to Wi-Fi, also known by its IEEE designation, 802.11 networking. The 802.11 refers to the IEEE standard that ensures everyone is using the same protocols and methods, so things remain compatible. The first popular version, known as 802.11a, operated at up to 54 Mbit/sec on the 5-GHz band. Later common standards include 802.11b (11 Mb/s on 2.4 GHz), 802.11g (54 Mb/s on 2.4 GHz) and the current commercial standard, 802.11n (up to 150 MB/s on 2.4 and, optionally, 5 GHz). There are newer standards that run much faster, but these are not in the popular mainstream just yet. Today, it takes some effort to buy anything other than an 802.11n device, although these are backwards-compatible all the way to 802.11a. Also, 802.11n devices are said to have a slightly greater range expectation about 820 feet line-of-sight outdoors. To help in your understanding of our project this month, be aware that there are several different kinds of network devices you can get. Let s start with wired networking devices: Most common is the, which serves as an interface between two networks and directs data within each of those two networks. This intelligently routes traffic to the network and to the client (user) to whom the traffic is addressed. A typical use is for your home network (LAN or Local Area Network) on one side and the Internet (WAN or Wide Area Network) on the other. All traffic on your home network stays on the LAN, but if traffic for the Internet is seen, the router automatically acts as a or to the WAN (usually a cable or DSL modem connecting to the Internet). A bridge connects two networks, but does not have any switch capabilities (see below). It is a way to keep two networks separate, but allow them to communicate with each other. Similar to a router is a, which routes traffic within a single network. A router can be thought of as two switches with a bridge between them. Like a router, a switch is intelligent, sending traffic only on the channel on which it knows the destination can be found. As an example, a switch is like a series of old-time speaking tubes in your home: You speak your message only down the tube to the room with which you wish to communicate. This avoids having to use data channel time for another device s data.
Then there s the. A data hub somewhat difficult to find these days is a little like a switch in that you can connect several devices together, but it has no intelligence: Every station connected to the hub hears all the data traffic. This is not very efficient, but what it lacks in efficiency is made up in simplicity. Much like everyone being in the same room (or a non-tarpn Packet Radio 1 User Port ), everyone hears everything, but all that data means channel throughput is limited, and falls off rapidly as more stations are added. Now let s add in the radio port Wi-Fi. Here we basically have two devices: The (often with bridge capabilities) and the. The access point (AP) is basically a hub on the radio side, with a wired Ethernet port for connection to a switch. Your wireless router has a built-in access point for Wi-Fi, along with (usually) a multi-port wired (Ethernet) switch and a router. Many APs also have bridging capability, which separates the RF and wired networks into two different networks, sometimes a useful feature. A repeater, also known as a range extender, is just that it takes what it hears and retransmits it, allowing the RF signal a somewhat greater range. The disadvantage here is the loss of bandwidth: All the data has to be sent twice, first by the originating station, then again by the repeater. If data speed or channel capacity is not an issue, this can be a reasonable choice. Now let s take a look as some networking cases and how we can handle them. In the case where we have a small outdoor area say, a 200-foot diameter circle to cover, setting up a Wi-Fi network becomes trivial: Just place one router in the middle and everyone can connect to Wi-Fi. You have a few wired ports for the command center, and a WAN port on the router if you need Internet connectivity. This is exactly like setting up your home network. (We ll talk about security in just a moment). In the case where we have a larger area say, a half-mile by quarter-mile area we have a few choices. The first, and simplest, is to set up a router at one point to cover part of the area, and one or more repeaters to extend to the rest of the area. Sure, your data rates are limited, cut in half for every repeater, but even with three repeaters you can still see well over 1 Mb/s, which is usually plenty fast. Just beware of HTS (Hidden Transmitter Syndrome) where repeater B transmits and interferes with repeater A s transmission because they cannot hear each other this can drop throughput to zero, so be careful. The second, and almost as simple, option is to use a router at one point, and one or more wired access points to cover the rest of the area. This requires running a few hundred feet or more of Ethernet cable, but 1,000 feet of cable can be had for under $50. Category 6 Ethernet cable can easily go about 700 feet before an active device (such as a hub or switch) is needed to re-form and boost the signal. If the situation supports running wires, this is the way to go for speed and cost. Some devices have a feature called (PoE), and it is just what it sounds like: You inject DC power onto the Ethernet cable, eliminating the need for a separate power supply at the distant device. The third, more complex (and costlier) solution is to use a pair of access points as a wireless bridge between your two (or more) local networks (which can also be wireless). This can be thought of as a wireless Ethernet extension, but not every AP has wireless bridge mode available. Note that this backhaul link is not accessible to regular wireless users; its
only purpose is to transmit data between two or more points, not to serve general users. You can have more than two stations on a single wireless bridge channel, but of course, this cuts into the available bandwidth. In any case, this is where we need to use high-gain antennas to get sufficient range between wireless bridge stations. A mile is about the upper limit for an 802.11 link. Wi-Fi sends an acknowledgement (ACK) for each data packet, and expects it within a certain time. If it doesn t get the ACK in time, it assumes the packet was lost, and retransmits it. At distances greater than about a mile, the speed of light is such that the ACK won t be received in time to prevent a retransmit. Thus, the link stops functioning. In such a case, we need to employ some other kind of radio modem designed for longer distances. Or, perhaps, a bunch of cellphones in Wi-Fi Hotspot mode, sadly dependent on non-amateur infrastructure (and possibly costing several tens of dollars in data fees). Considering the three cases above, the first is trivial and the last is troublesome at best, so we ll focus on the middle case: Two thousand feet of coverage, using a wireless bridge to span the distance between APs and provide a wide area of Wi-Fi coverage. For this setup example, I am going to use a pair of 5-GHz long-range wireless access points such as these at Gridconnect <http://bit.ly/1k4qg48>. These $350-a-pair items are a bit pricey but have external antenna capability, PoE, and can span well over a mile out of the box. Of course, any AP or router that has wireless bridge capability can be used, and you surely can find something in your price and performance range. The first step is to connect to the AP over Ethernet and configure it as a wireless bridge. If you don t know how to do this, find and read the operating instructions, since different APs have slightly different setup screens. Basically, you open a web browser, type in the AP s default IP Address (something like <http://192.168.1.1>) as the web address (URL) to connect to, and a simple web server in the AP displays the setup screens as web pages. Your AP may have a default password (which might be a blank) be absolutely sure to change it. To configure the wireless bridge channel, first select the Wireless tab and under Basic settings set the Wireless Mode to Bridge. Then select WDS settings and type in the MAC addresses of the distant wireless bridge(s) in the Remote AP MAC Address fields, as shown in. You should
then set the other AP(s) the same way, but using the other AP MAC addresses, so each station knows about all the others. (What s a MAC address? Just a unique 12-character hardware identifier, looking something like 00:19:70:00:f6:76. You ll find it on a label on the device, and pre-filled as the Local MAC address ). While you re in Setup, go through each setting and pick whatever s necessary. Mostly the defaults are fine, but some might enhance performance. For example, Output Power is an obvious choice, but Channel Mode (bandwidth) is more subtle. Lower bandwidth reduces speed, but also boosts noise immunity and range. Take some time to understand the myriad settings, do some research, and pick intelligently based on your desired outcome. Oh yes, don t neglect security. More on that in a moment. Now we need to set up local user access. Since the wireless bridge channel is on the 5-GHz band, and more devices are compatible with the 2.4- GHz Wi-Fi band, it is best to operate only on 2.4 GHz, in Wireless-G (802.11g) mode. Configure all your wireless routers the same (meaning network SSID and password), but set them to separate RF channels if they can hear each other. There are 11 channels available in the U.S., but only channels 1, 6, and 11 do not overlap, so try to avoid interference. Every device must have its own unique IP address, so be sure to change the defaults and keep track of which is which in case you need to reconfigure something wirelessly. With the routers set up, connect them with an Ethernet cable to a wireless bridge, so they act as wireless access points and switches. These should use the standard antennas, which often have an omnidirectional pattern, for best coverage and convenience. What you end up with is shown in. Please understand, however, that there are other settings on the LAN and Wireless side of the routers and wireless bridges that will need to be adjusted for everything to inter-operate. It is not possible to cover every situation here. But what I ve described are the basics, which will get you very close. The very first thing you absolutely must do is set a unique and strong password on every device, so only you (and trusted others) can get into the setup pages of any device on your network. Some devices use a default user name of admin (which is OK) and a default password of either password or just a blank. Fail to change this and you are just asking for trouble any kid with a cell phone can shut you down in 12 seconds. The next thing you ll want to do is limit access to your network. You only need this for the user ports, since the wireless bridge ports are not accessible to devices not listed in the MAC Address table. If you are running under 802.11 rules basically, unmodified equipment then set up a shared key password and some level of encryption for closed access. You may even want to suppress the transmitting of the SSID, making it harder for the casual user to see your network. This is essentially the same as what you should be doing for a home network. If you are running your network under Part 97 perfectly legal for WiFi-G Channels 1-6, as long as you follow the rules then, well, follow the rules. Setting the SSID to your callsign satisfies the station ID rule, but encryption might be a gray area, entirely dependent upon the purpose of the encryption. Keep using a password for users to connect, but simply switch encryption off. The issue is that someone monitoring the network not a trivial task though can see the password being sent unencrypted. So, passwords keep the casual users out, but a determined hacker can still get in. As a second layer of access control, we turn to MAC Address Filtering to limit which wireless devices can successfully connect into the network. Every device has a MAC address for the Wi-Fi radio. It may be on a label, or you might need to type in IPCONFIG into a Command prompt window to find it. Depends on the device. By setting up MAC filtering, only the devices listed in the table will be allowed to connect into the network. Beware: MAC filter tables can be either Include or Exclude, the former granting permission to those devices, the latter specifically prohibiting those devices. Don t ask how I learned that one... If you change the antennas probably a good idea for the Wireless Bridge if you expect to cover a distance of more than a few hundred feet you may again be operating under Part 97. Ask the supplier about antennas that allow you to operate under 802.11 rules, but if you need to, use a high-gain Yagi or dish antenna. The wireless bridge has a 16- dbi antenna, but an antenna like that
shown in can dramatically increase range. Just remember, 2.4 and 5 GHz are line-of-sight frequencies, so if you can t see the other antenna (even through trees), you may have difficulties. In most cases you will have electrical power for your network, but there will be occasions where AC mains power simply is not available or convenient. In these cases, first know that most Wi-Fi equipment runs off 12 volts DC. This means a deep-cycle marine or gel-cell battery can operate the network for hours or days. Second, a DC-to-AC power inverter can be your friend. A small 150-watt inverter was recently found at RadioShack on sale for $24. This can power a laptop and network device (that needs other-than-12 volts ) when connected to a 12-volt battery, often for quite a long time. Finally, when operating on microwave bands at nearly a watt with high-gain antennas, consider what that energy might do to a person, and make a good effort to keep RF away from people. Put your wireless bridge antennas up high, on a pole, so nobody can touch them. Fence off the area to prevent someone from knocking down your pole, or somehow getting near to it. And, of course, any time you are using mains AC voltage (even from an inverter), take pains to avoid a shock hazard. In conclusion, now we know about the many networking devices we might use to deliver high-speed data access by radio for several users. Wi-Fi is really only useful for about as far as you can shout, but with some tricks, we can extend that range to about as far as 10 people can shout, if the night is quiet. We ve used portable FM radios for so many years, and they are still a great way to communicate, but sometimes the event calls for data. There s nothing as ubiquitous as Wi-Fi OK, maybe cell phones beat that but Wi-Fi is a great choice for interoperability and convenience. You can even set up your own web server on your network, or provide Internet access if that s necessary. No matter what, I hope this gets you thinking about a use for all this technology. Now go do it! 1. For more information on TARPN, see previous "Digital Connection" column in July 2015, pages 82-85. - COAX WIRE TC-12 TC-18 TC-20 TC-22 TC-24 - - - - RF Transformers Type U 2 to 300MHz For 50 years our volunteers have endured long hours and tough working conditions for no pay. And 9 out of 10 would do it again. HF Power - - - - - TO FIND OUT WHY contact REACT International, Inc. (301) 316-2900 (866) REACT-9-9 P.O. Box 21064, Glendale, CA 91221 REACT.HQ@REACTintl.org www.reactintl.org