Using the Wisconsin Network - Part 20

by Andy Nemec, KB9ALN

In the last couple of years, packet operators have been able to take advantage of higher speed packet operation at a more reasonable cost than in the past. TNC manufacturers are now accomadating the amateur radio market and have pre-packaged high-speed TNC's available. Although they have become much easier to set up than in the past, there are some things that you should know before you take the plunge into the magic land of 9600 baud operation and buy that new TNC.

First of all, how much good will it really do you? Under ideal conditions, 9600 baud data rates are 8 times faster than the 1200 baud operation that we have become accustomed to. In reality, a lot of factors affect data throughput and your results may vary considerably from the ideal. No question about it, 9600 baud packet operation is faster. In order to see a substantial difference, there are important things you have to deal with. Your radio is the first thing to look at.

What kind of radio do you plan on using? Most garden-variety FM Amateur transceivers are not adequate for the purpose, even the ones marked "9600 Baud Ready". Why? Modern radios use a method of modulation that is incompatible with 9600 baud operation. For narrow-band voice signals, this works acceptably. For the wide-band 9600 baud data signal, this modulation scheme will cause serious distortion of the data signal, making it impossible to decode. Not only that, a lot of these radios have a significant frequency error brand new, "out of the box". Another common affliction of these radios is the time it takes a transmitter to "settle" on frequency, and the time a receiver takes to recover from the transmit mode. These radios are often slow on both counts, causing retries and lost data.

Even if your station can send data fast, receiving it is quite another matter. What can be done? There are 3 alternatives. The first is a multi-mode radio. Why? These radios rely on a different modulation scheme, and they often have faster transmit-to-receive "turnaround time". Therefore, they not only transmit a cleaner data signal, the receiver recovers quickly, and can hear a response from a sent packet. They also feature a more precise tuning readout, which means that it is easier to get them on the proper frequency. The drawback is that these radios are often very expensive.

Another alternative is to buy a radio expressly designed for this purpose. Older Kantronics Data Radios are best avoided - I have heard little good about these radios. One radio that I hear consistently good reports about are the radios made by Tekk. There may be others as well. The important thing to look for is a crystal-controlled radio, or one that has a synthesizer optimized for 9600 baud operation.

The third alternative is to obtain a surplus commercial radio, such as a Motorola or G.E. We have had excellent success with Motorola Mitrek radios, they are crystal controlled, inexpensive on the used market, and very high quality. The disadvantage with getting any second-hand radio is the adjustment required to get it to operate correctly. it takes a little bit of technical skill and equipment to get everything set right. Unless you know a qualified technician, this may not be an option. Even some commercial equipment requires a small amount of modification to get it "just right" for 9600 baud operation.

Now that we have talked about the RF end of things, there is yet another thing to consider. Even if your station is 9600 baud ready, is your area ready for it? In other words, do you have access to a 9600 baud end-user node? In their eagerness to utilize this mode, some operators who do not have access to such a node rush out and buy a TNC, and get it almost working with some kind of radio. They neglect to find out if there is a 9600 baud end-user node and find themselves on a 9600 baud backbone node frequency. I can't stress this point enough to you - DON'T DO THIS!.

Why? A lot of these radio/TNC combos are not optimized for the backbone frequency. Remember, the purpose of the backbone is to handle a high volume of packet traffic, and these nodes are optimized for this purpose. They often have very fast response times, and communicate with nodes quite a distance away. This can disrupt the network in two ways.

The first disruption occurs from retries between a poorly set up end user and the local backbone node. The backbone node answers the end user quicker than it can deal with, and a packet has to be repeated very often. This slows data throughput between the end user and the local backbone node, as well as between the backbone nodes. The second problem occurs because of the "hidden transmitter syndrome".

Remember that backbone nodes may well be a considerable distance away, and are often located in high places with good paths to the remote node. The end-user station may not be so well blessed; it may be using a marginal antenna, or may not be in a good location. This means that it cannot hear the remote node. Consequently, this end user will transmit at the same time the remote node does. The local backbone node hears both of them, and hears a "double". Neither packet is decoded, and they have to be re-tried. Enough of these can seriously disrupt a network conection, and frustrate the end user. This will spoil it for everybody!

All of this may sound quite discouraging. Actually, it is intended as a guide to help you think carefully about your impending purchase. No doubt, 9600 baud packet operation will become the norm in a very few years. However, a lot of people may get discouraged if they make the wrong choice. What to do? If you don't have a 9600 baud LAN end-user node, thnk about what it would take to have one in your area. It can be done for less than $500, and if enough interested people in your area kick in a few bucks, that is not such a big pile of cash to generate. Node Operators often have enough cash stuck into their systems, and they often pull it out of their own pockets. Making it a community effort will not only make it a whole lot easier, it can help pull a radio club together and give it a project.

If you don't have a 9600 baud LAN frequency, contact the WAPR frequency coordinator and ask for one. He can assign one that is compatible with the bandplan in effect in your area. If you can't put an end-user node on the air quickly, at least you will have a place to park until you can. And it will keep you from interfering with the backbone operation. The bottom line in all of this is "do it right". Not only will you get more enjoyment from this mode of operation, you will be operating in concert with the rest of the Wisconsin Network.

On to Part 21 - Handling NTS Traffic via Packet Radio

Back to Part 19  - Using REQDIR and REQFILE on the MSYS BBS

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