A Waterfall Display for TNC Users
by Charles Brabham, N5PVL
Many owners of TNCs and multimode controllers have wished at one time or another that they could have a waterfall display. This article shows how you can easily add this functionality to your equipment, at very little expense.
As users of soundcard modes with a waterfall display know, the visual display allows you to detect and identify signals that are difficult or impossible to detect by ear. - And it makes it easy to do so.
Waterfall displays are driven by receiver audio. They take that audio signal and convert it into a visual display, smoothly scrolling to show current activity, and recent history. This display of recent history is useful for detecting intermittent signals, as in the back and forth of a RTTY QSO. It is also useful for identifying many digital signals, as some have a characteristic shape that stands out on the waterfall display. Some Waterfall programs have RSID functionality, which will automatically identify digital signals that send an RSID signal. Most of all, a waterfall display is useful for detecting and identifying weak signals that are hard to pick out by ear.
The Hardware:Your TNC uses audio from your radio, most often from the radio's external speaker plug. Your waterfall display software needs to hear the same audio, so you need to make a two-into-one audio cable with appropriate plugs for your radio, TNC and computer.
Some may want to splice the cables with the soldering gun and some tape while other may prefer to patch cords together with a "Y" connector. - However you prefer to proceed, the end result should be as pictured below, where the TNC and the computer both get audio from the radio.
The Electronics:That was so simple, and it works! - But alas, many of us will notice that noise has been introduced into the audio signal. This is commonly known as a ground-loop condition, a problem which is addressed by electrically isolating the pieces of equipment from each other.
Audio lines are isolated by use of an audio isolation transformer. Packetradio.com has them, then there's Mouser.com and you never know, they might have one down at Radio Shack, or even at the local car stereo shop, or auto parts supply.
If you install one on each outgoing audio line as shown below, it should eliminate the annoying noise from a ground-loop, and give you clean signals to work with.
Note that splitting the audio line will attenuate the audio signal, and that installing audio isolation transformers will attenuate the signal further. You will probably need to bump up the audio drive ( radio volume ) a bit to compensate for all of that. Adjust it to make the TNC happy first, as the computer has its own software control for the input volume that you can adjust as necessary
Software:There are several ways that this can be approached. You could run the audio to an old spare computer for a large, dedicated display, or into the same computer that runs your terminal software for the TNC, for convenience and to save space.
The second method is illustrated below, with the terminal program in a window on the right, and MixW showing the waterfall display windowed on the left.
My ancient Win98 machine handles this just fine, and my little XP netbook, so it should be no problem with more modern computers.
Note the way I have eliminated or minimized everything on MixW except the waterfall display itself. You can do the same thing with DIGIPAN, and most other programs that include a waterfall display. - Just use whatever works best for you. In any case, eliminating all of that clutter of macro buttons, logs, etc. really makes a difference.
Applications:This article is about setting up a waterfall display for any user of a TNC, with some emphasis on how the waterfall allows you to detect and identify signals that you may not hear and that your TNC may not hear, either. This is a great advantage for TNC or multimode controller users who miss the benefit of having a waterfall display. Once you have this setup though, there are several interesting things that you can do with it.
Precise and Fast Tuning:
When you get a solid link going in QSO, you will be able to see your QSO partner's signals clearly on the waterfall display. Now note the scale at the top of the waterfall display. If you mark the position on the scale that is centered up on your partner's signals, then that will also show you where your signal will be, when you transmit. Now you can line up any received signal in that same mode with the mark you have noted - and you will be very closely tuned in on that signal.
The difference between doing this, and squinting at LEDs is like night and day. Once you've done it a few times, you'll be spoiled for life and will start to think of the LEDs as a primitive backup tuning system.
One way to mark the scale above the waterfall display is to use the program's point 'n click marker. You can also write down the apparent number on the scale for different modes, though in theory the center frequency should remain the same.
Read the Mail:
MixW allows you to monitor any of a number of digital modes, displaying the text and calls in that QSO. - I use it to monitor nearby QSOs, read W1AW, or catch Lids.
Catch Lids:
If some ham keeps crashing your QSO's with a particular digital mode, set up the waterfall program to monitor in that mode on that frequency and sooner or later you will get the callsigns involved. - You can't ask to guy to quit if you don't know who he is, or report him if he turns out to be a hardcore Lid who doesn't care.
At the present time, a properly adjusted waterfall display in conjunction with the human eye is the most sensitive signal detection system at our disposal. If you are both watching and listening, it is hard to miss any human activity that may be there. Waterfalls are also fun to watch at times, and it is always good to know what is going on near your QSO. Now users of TNCs and multimode controllers no longer need to feel left out, and can add this functionality to their systems fairly easily.
Good luck, and Enjoy!
