Waterfalls: The Band at a Glance

Once upon a time, we had VFO knobs. When you wanted to explore the bands you spun the knob for a voyage of discovery. You would gradually tune in stations, usually CW or SSB, with the filters wide so that you didn't miss anything. Many of us did the same thing outside the ham bands, often before becoming licensed, finding various military and commercial communications circuits and modes, broadcasters and much more. Spinning the big knob was a gateway to the magic of radio.

Now is the age of the SDR. Instead of spinning the knob, we can view a large swathe of spectrum at a glance. See something interesting? Click the mouse and there you are. But, in most cases, you must still listen to learn what you've found. If you integrate spotting networks and skimmers with your SDR that may not be necessary since the signals can be labelled on the spectrogram. Contest software like N1MM+ has this feature when coupled with a modern transceiver.

Has something been lost with modern technology? Certainly there was the magic of discovery before we had sophisticated receivers and displays, or the global internet. As Bob Locher W9KNI wrote in his seminal work, The Complete DX'er, that there is an art to listening: care, diligence and research to know what to expect. There remains a role for this style of operating, though it is far less common than it was. 

Despite the nostalgia I don't really miss the old ways. The reality could entail hours of drudgery scouring the bands for interesting stations, finding the rare ones, calling DX for a long time on an open band because no one stumbles across you, and not knowing what was there to be found or if there was propagation at all. I appreciate modern technology for optimizing the use of my time.

Early spectrum displays were not very good. The first were manually configured with knobs and buttons, the bandwidth was whatever the narrow IF could pass, the display was instantaneous only without a progressive view (waterfall), and there was no possibility of computer integration. An example is the SM5000 add-on to the FTdx5000. I have one and it is pretty well useless for spectrum monitoring.

That changed when I purchased the Icom 7610 transceiver. The waterfall display is a tremendous operating aid; that is, once you figure out how to configure it -- the user interface could use some improvement, yet some are worse (e.g. Yaesu FTdx101). Luckily I had my 7610 configured by a guest op familiar with the rig. I was annoyed until I saw that his choices were good ones. I've kept it the same ever since.

Many hams connect their 7610 spectrum scopes to an external display or to their computers. I prefer to leave it where it is since it's works well for my purposes and I strongly dislike the addition of more displays or the additional demand for display "real estate". In this article I'll talk about how I use the 7610 spectrum display (waterfall). My preferences may differ from yours, and that's okay since my operating interests may not be the same as yours.

This waterfall is similar to the one I showed in my first article about the 7610 (link above). During a busy contest the waterfall is an excellent way to find holes where you may be able to run. However, always send "QRL?" first! Even with the time axis of a waterfall you can miss a lot of activity that you might not hear at first, such as for signals that scroll off the bottom of the display. The 7610 has a coarse scroll adjustment that could be better.

A spectrum display without the time axis -- that is, a waterfall display -- is very poor for locating clear frequencies. Yet many try, and they do it without checking for occupancy before punching the CQ key. An instantaneous display, even one with time averaging, is inferior in comparison to a waterfall. Aside from the averaging time there is the problem of noise. A momentary broadband impulse can render the averaging display useless for 5 seconds or more. On a waterfall it's an innocuous horizontal line.

My contesting has benefitted since becoming a "big gun" because I run much of the time, and finding potential run frequencies can go slowly without a waterfall.

Not all of us have clean signals. There are key clicks on CW and splatter on SSB. Examples are shown in the panels on the left (14017 kHz) and right (14250 kHz). These are easy to spot in the waterfall. When interference is heard, all it takes is a glance at the display to know who is responsible. The ability to inspect the band all at once can be occasionally depressing due to the large number of poorly adjusted transmitters. 

Not everyone is aware since they can't hear (or see) their own transmitted signals. They may be unaware since they use rigs with poor transmitter IMD or fast CW rise times, or they don't know how to adjust them, merely accepting the defaults (often terrible) or what they believe to be correct practice. In many cases the rigs are fine but their amplifiers are over-driven.

The middle panel is more interesting. That is a CW signal if you can believe it. It was raspy and wide. My guess is that it is a home brew transmitter or an ancient and misbehaving boat anchor. Decades ago this was not such an unusual signal! It is a surprise when it is heard in the 21st century.

The SSB signal at right is perfectly clean. It drew my attention because it could be made better. Notice the large peak at low audio frequencies and relatively weak higher frequencies. This is typical of an adult male voice. Unfortunately it is not great for effective radio communication. 

Most modern rigs have audio equalizers and they should be used. A few tweaks of the equalization can attenuate that non-intelligence carrying and power robbing bass resonance and enhance the critical speech frequencies between 300 Hz and 2000 Hz. Notice that I receive with a slightly narrow filter on SSB since it removes splatter from adjacent stations without loss of readability. During phone contests I narrow the filter even more.

Many have noticed the increasing dearth of signals on our HF bands. What activity there is has concentrated on narrow channels for digital communication. This has attracted the attention of non-ham actors; that is, intruders. They have always existed, and not just on the amateur bands, it's just that they seem more common than before. It could also be because of the prevalence of SDR and waterfall displays -- with a large view of spectrum the intruders stick out more than they do with a VFO.

On the right is one example. It appears to be a dense digital signal of some kind. This type of intruder is quite common, both in our bands and just outside the band boundaries. They tend to avoid our spectrum during contest weekends, probably because the "interference" affects their operations. The intruders may be government actors, criminals or ordinary citizens.

Other common examples include OTH radar, SSB and AM commercial and personal communications, narrow band data modes and non-standard modulation. That only touches on the problem. HF still has value to many despite the global availability of the internet. Interfering with hams carries lower risk than operating elsewhere.

Waterfall displays on a relatively empty portion of an HF band can be disturbing when they show many intruders that you might not otherwise notice. Yet they're there and it's better to know about it than not. In most cases you'll have to work around them, unfortunately, and waterfalls help with that. I've used the 7610 waterfall to do just that.

There are many mystery signals to be found on our HF bands that may be intruders but are more likely electronic noise, test equipment, unintentional interference from conventional users (e.g. science experiments). The waterfall sees them all. Examples include an antenna analyzer or VNA sweeping an operational antenna, electronic sensors, RFI from devices in our homes (my heat pump does that when set to cooling), and so much more. I could not easily capture screenshots of them before publishing this article.

Other signals captured by the waterfall.are all kinds of "swishers" that quickly sweep across the band leaving only a momentary sound in the headphones. There are slowly drifting electronic signals (likely RFI), harmonics or spurious emissions from unknown transmitters. You can watch (mostly digital) signals gradually drift due to oscillator instability, especially on the higher bands like 6 meters. Again, I took no pictures for this article but you'll surely recognize these if you use a waterfall display.

In contrast to the disheartening information that waterfalls bring to our attention, there are many benefits, and not just for finding run frequencies. These are a few of the ways I've used the waterfall display:

• Propagation at a glance. I tune to a band, flip through the antennas pointed in various directions, and I can instantly learn the state of the propagation. That is, if there is any activity. 
• Locate and resolve noise and interfering signals.
• Discover the onset of aurora when signals experience Doppler spreading.
• Navigate a DX pile up by sight and not just by listening. I can see the holes where no one is transmitting, and those can be good places to drop my call.

You can likely think of other examples that you've used since acquiring a rig with a spectrum scope and waterfall feature. Now that I have one I can't imagine living without it.