Using the Wisconsin Network - Part 13

by Andy Nemec, KB9ALN

In the last edition of "Using the Wisconsin Network", we started looking at the network from it's beginnings, your station. We discussed in basic terms, just how these pieces work together. In this installment, we will continue this discussion and look at setting up your radio and TNC so that your station becomes more "friendly" toward the network, and to other stations operating on your LAN frequency. And we will start in that order, with the radio.

Many people forget that packet radio is radio. The computer and associated boxes you have may all be working just fine, but useless if your radio is not properly set up. Remember that your data ultimately gets transmitted and received as audio tones, so the first place you have to look at packet performance is at your radio. First, let's look at transmitting.

Your transmitter has to be on frequency, have the proper amount of deviation, and has to have clean audio. No Buzzes, no P.L. tones, and no RF getting into the microphone audio circuitry. Frequency error is often overlooked when people are trying to diagnose a bad packet connection. If you have any doubt, try checking it with a frequency counter. You will need absoloutely NO audio into the mike circuitry when you do this, and don't forget to turn off your P.L. Assuming that you find your radio on frequency, you can go on to the next step, checking out your transmitter deviation.

Your audio level from your TNC directly effects this, so you will need to hook your TNC back up and send some packets. To accurately measure deviation, you need to look at the signal on a Service Monitor. This handy test gear is out of the range of most Amateurs, but ocassionally you will find someone who has one. If you have access to one of these, your peak deviation should be approximately +/4 KHz. If you are like most of us and don't have access to one, you can come close with an oscilloscope and another radio to listen on. If you don't have a 'scope, then your ears will have to do. The trick to these two methods is to have a reliable reference to compare your signal to.

This would probably be the local node for most people. You adjust your transmit audio level (On the TNC) so that it matches the volume level of the station you are using for a reference. That is why you will need to listen on another radio. It is easier and more accurate if you use an oscilloscope hooked to the speaker terminals of the other radio. It is even more accurate if you hook it to the discriminator of the other radio, and have it calibrated. This is not usually the case with most people, so you will probably be hooking it up to the speaker.

Once you have your transmit audio level set, you may wish to look at the cabling to the TNC. Use high-quality shielded cable for your connections to the microphone circuit (or Data connector, if your radio has one). There is also one final part of the transmit system you should pay attention to. That is what kind of antenna you are using, and where you have placed it in relation to your computer and TNC.

First, using a rubber-duck antenna is not a preferred setup for packet. Not only does it not work very well when receiving or transmitting, but it also hears stuff you don't want it to hear. Keeping a rubber duck in close proximity to the computer and the TNC will insure the reception of computer hash from both of them. It also has the nasty property of radiating a signal into your electronics, which can distort your transmit audio and possibly cause damage to your system. Best to have an antenna on the roof, or at least a good distance away from the rest of the equipment.

Now on to the receiver. There are 2 simple adjustments here. You don't need too much volume to get the TNC to decode properly, so setting the volume at 10 to 11 O'Clock is generally quite enough. More is not better here! The squelch may require a bit of tinkering with. Generally speaking, the squelch should be set about 1/8th turn past the threshold of quiet. Sometimes lower noise levels will open up your squelch. This is not good, because in most cases this will cause your DCD light on your TNC to come on, and will prevent your station from transmitting (it thinks someone else is transmitting). Don't overlook this if your station does not want to transmit!

Now that we have looked at the radio end of your station, we will move on to the TNC. As was said earlier, this is important as it affects the way that your station interacts with others using the network and the LAN. The North East Digital Association (NEDA) has set up guidelines for the real world of packet radio that make sense in today's packet radio environment. They make a great deal of sense when you look at it, and we will use their guidelines as a basis for setting up our TNC's. Below is a list of the more important parameters, what they do, and what is a realistic setting for them. Remember, most factory defaults were set in a day when packet radio was not as well populated as today, so it makes sense to change them to match today's packet radio world.


Turn off your beacon. There is no need to have a beacon unless you have important information to disemminate. Your idea of a good joke of a clever saying is not a good reason. If people need to know that you are out there, they can look at their "Heard" list. "Mail For" and ID broadcasts are legitimate beacons. Every Amateur radio publication relating to Packet Radio tells us that Beacons are a waste of spectrum. Let's end this practice!


Turn off your digipeat feature, unless you have no node in the area, or it is absoloutely necessary for some reason. Nodes do a much better job of repeating your packets, and keeping the Digi on will often override other features of your TNC that govern timing.

FRACK = 6 to 12 (seconds)

This is the "FRame ACKnowlegement" timer. It governs how long your TNC waits for an acknowlegement from the other station you are connected to. In croded areas like Milwaukee, for instance, you may want to use 10 to 12.


This governs how many Data frames are sent with each transmission. Too many frames will keep your transmitter up too long, and not allow others to share the channel. Also note that the more frames sent, the longer the packet. The longer the packet, the more chance of errors, and this means poor throughput of data.


This allows the TNC to wait a random amount of time before transmitting. You must have the Digipeater turned off for this to function. This gives other stations a chance to transmit, too.


This generates a random number to be used in conjunction with SLOTTIME to calculate the time it waits before transmitting. The lower the PERSIST, the longer it waits. Though 64 is suggested, you may use 128 if yours is not a busy packet LAN frequency.

SLOTTIME = 20 (in ms)

This is used with the PERSIST setting and again, governs the time the TNC delays before transmitting a data packet to the receiving station. Note: MFJ calls this "deadtime".

RESPTIME = 10 to 15

This is a timing parameter that controls how long the TNC waits to acknowlege a received packet. This differs from the above PERSIST in that PERSIST is involved in sending a data packet. RESPTIME is only effective in the acknowlegement of a received packet.

RETRY = 10

This is the maximum number of retries allowed before a station sends a disconnect. You may also consider setting this to 6 or so. If you can't get to somebody in 6 tries, someone has problems!

Note that some TNC manufacturers may use slightly different command names than we have used here (especially Multi-Mode controllers). Take a good look at the TNC manual and see if any of the commands have a similar description. While this all may seem to be more trouble than it is worth, it will make a pronounced difference in throughput if you take the time to change a few settings. And anytime you can improve efficiency and channel usage, it is certainly worth the time.

If everyone on a LAN can cooperate and use the same settings, life will be easier for everyone. And if life is easier on the LAN, then it will be easier on the network. And that will help you use the network more effectively.

On to Part 14 -  BBS Basics with emphasis on the MSYS BBS

Back to Part 12  - Setting your TNC Parameters for better Network operation

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