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.

Superfox and DXing

The Superfox name is not unique to WSJT-X. I didn't know that until I did an internet search for sites and images related to it. Although it isn't true that there's nothing new under the sun, this is so obvious a name for many reasons that I should not have been surprised by its commonality. 

I included an appealing image that my search uncovered. Considering the public availability of AI image generators it is surprising that these tools aren't used more often by hams as a way to create icons for our increasing software-centric hobby. If nothing else, it adds levity to discussions about new technology entering our hobby.

After I used the FT8 Superfox mode for the first time it spurred a few thoughts that I'd like to share. In this case it was to work N5J on 80 meters.

Although I prefer to work new DXCC countries on CW, that isn't always easy or convenient since most DXpeditions now devote more time to digital modes. Whatever you might think of it, digital has become more popular for HF DXing than CW and SSB. DXpeditions quite sensibly devote time to the modes and bands where there is demand. Digital is also beneficial to lightweight DXpeditions such as N5J, and to the majority that have small stations and are chasing them.

One night last week I happened to wake up before dawn. Instead of going back to sleep I padded down to the shack to see if N5J was active on CW on the low bands. With my 160 meter antenna unavailable during the summer, my objective was 80. But they were on FT8 instead. I got up to leave and then thought, what the heck. So I sat down and gave superfox mode a shot.

It was a simple matter to activate superfox since my version of WSJT-X supports it. I tuned to 3567 kHz and saw this:

On the spectrogram/waterfall their signal makes very little impression. If you listen, it sounds like the soundtrack of a 1950s sci-fi movie with its staccato series of seemingly random tones. The software decoded N5J, the superfox, however, the mode seemed vulnerable to noise. When it couldn't decode it couldn't decode any of the multitude of messages transmitted. That's unlike multi-stream FT8 where each stream is independently decoded.

I waited a minute for the noise to disappear -- probably software misconfigured by a caller -- and they were quickly logged. The 3-element vertical helped even though I limited myself to 100 watts. A friend with a smaller station was calling at the same time and got through a few minutes later.

It was easy. Was it too easy? Have DXing awards become a participation pin for just showing up rather than a sign of skill and achievement? With superfox, "verified" foxes will also reduce the risk of working pirates, something that often happens on FT8 and CW.

I don't know how to answer those questions, and I doubt the glib answers of the self righteous. But consider the progression we've made in the DXing art in the past 10 or 20 years:

• Local and then global DX spotting networks
• Real time communication by DXpeditions of their operating frequencies
• Real time log confirmations
  
• Large, well-financed DXpeditions that exceed 100,000 contacts
• Digital modes to level the playing field: pile-up opportunities for smaller stations
• Multi-stream and superfox for high digital rates
  

These advancements call into question the value of a QSL or DXCC certificate. After all, if everyone can work 'em, does the value of a DX award decline? Superfox mode accelerates the trend in two ways: more stations can be worked within the same time and resource budget, faster than CW or SSB, and getting those coveted band slots requires only a modest station investment and a few clicks of the mouse. FT8 ain't so slow any more.

I am not a curmudgeon: superfox is a marvel of logistics and technology. I applaud the technological advancements in our hobby. It's inevitable and will only continue. But I have to wonder whether DXing and station building are skills that have reached an inflection point. When reaching the stratosphere of DX achievement is far less difficult than it once was, is it a worthwhile endeavour?

Many (most?) hams enjoy working DX yet have no desire to build a big station or to devote a lifetime to reach DXCC Honor Roll. Technology brings it within reach. Does it matter that it takes far less time and effort than in years past? Probably not if the participants are enjoying themselves. It appears that they are.

One old timer of long acquaintance is using digital modes to close the gap to earn the 2500 endorsement for the DXCC Challenge award. Working N5J on FT8 superfox brought him a little closer. Most older DXers that I know have adapted very well to digital modes, often with enthusiasm. Digital modes are not being shunned by older hams, it is just that a hostile minority speaks loudly.

I've become a reluctant superhound.

U-bolt Threads and Strength

This is a topic that is not one of the most exciting that I've written about in this blog. Yet it is important since fasteners of all kinds are found in our stations. Even if you never build your own towers and antennas, a little knowledge can go a long way. That said, I'll proceed to bore most of you.

Cutting threads onto a blank bolt shaft weakens the bolt by removing material. The effective cross-sectional area has been reduced approximately in proportion to the new minimum diameter measured at the bottom of the threads. The amount of material removed depends on the bolt size and thread standard. Since a bolt without threads isn't too useful, we need to learn how to take their effect into account when choosing bolts.

A chain is only as strong as its weakest link...

...is an old saying that we use for subjects as diverse as industrial supply chains, military forces and marriages. It can also be applied to threaded bolts.

The weakening of the bolt due to the threads is not a problem in itself since you must calculate the required fastener strength (cross section and material grade) for your application. In our case the most common applications are towers and antennas. Since few of us design and construct the towers in our stations (we only assemble and erect them) that leaves us with antennas. A far larger number of hams design and build yagis, and that entails selection of many kinds of fasteners.

The style of bolt pictured above is very common. For shear applications, such as the bolts for splicing (joining) tower sections, the load is carried by the short blank shaft under the head. The threaded shaft carries no load other than that needed to keep the nut in place. Threads are more important for axial loads.

There are many styles of specialty hardware where the thread size is greater than the shaft size. For example, the guy yokes for my large towers have ½" shafts and 9/16" threads. This keeps the fastener strength that of the ½" shaft throughout since the diameter across the thread bottoms is approximately ½".

I was reminded of u-bolt specs when I was recently shopping for small stainless u-bolts for my latest antenna project: a 40 meter reversible Moxon. I ordered online from a vendor I hadn't dealt with before. The company was reputable and the specifications and price looked good. I had a close look at them when they arrived, as one should when dealing with a new supplier.

Compare the photos of the hex-head bolt and u-bolt. In the former, notice that the shaft tapers down towards the threads. For the u-bolt the opposite occurs. The reason is that on the u-bolt the threads are raised. On these u-bolts the threads are ¼"-20 (UNC) and the unthreaded shaft is less, measuring roughly 3/16".

The axial tensile strength of the u-bolt is largely determined by the diameters of the unthreaded shaft and the inner thread diameter. Although the threads are ¼", the minimum cross-sectional area is determined by the minimum diameter, which is that from thread valley to thread valley. The table (extracted from this source) contains data for most of the UNC thread sizes we are likely to encounter.

The effective cross section (Tensile Stress Area) for ¼-20 bolts is 0.032 in². We can rearrange the well-known equation A = πr² and solve for the diameter (2r). That equates to a diameter of 0.2", in agreement with the Minor Diameter in the table. That's slightly more than the 3/16" I got from my quick measurement. The shaft diameter is therefore appropriately sized. A larger shaft does not increase the axial strength of the bolt.

A second example is this large galvanized u-bolt with ⅝"-11 threads. The calipers show that the shaft is about 9/16". This is approximately the minor diameter so the shaft diameter is, again, appropriately sized. This is typical of the all the u-bolts (including muffler and saddle clamps) you are likely to encounter.

All of this is very interesting (well, I think so) but how does it help us to select hardware? There is no simple answer and there can be no simple answer. Shear strength is in some respects easier to calculate, which I did when I custom built guy hardware for one of my big towers. However, u-bolts are typically placed under axial load; that is, load along the direction of the shaft/threads axis. 

The axial load for typical antenna applications is the sum of the dead and live loads on the antenna section being supported and that from tightening of the nut against a rigid plate and tube/pipe. Use of a saddle distributes the load over more of the tube surface so that the tube is less likely to be crushed (e.g. excessive nut torque) or rotate.

Consider the following two methods for using u-bolts to support the large capacitance hats on the element tips of the reversible 40 meter Moxon that I am currently building. They may look alike until you take into account what sits on or hangs from what. In both cases the element takes the load of the capacitance hat.

In the top picture, the capacitance hat is underneath the element. The hat hangs from and is held by two u-bolts. The weight of the capacitance hat loads the u-bolts. The hat and plate both place an axial load on the u-bolts hanging from the element.

In the bottom picture, the capacitance hat is on top of the plate and the plate sits on the element. The load of the hat on the element is the same (as it must be) but the u-bolts have a lower axial load for the same nut torque. (Note that for this fitting work that I omitted lock washers or nylocs.) The u-bolts hold the tubes in place, but the only axial load is from the torque on the nuts.

Does that matter? Yes, but not by a lot. I find that hams that design and build yagis tend to stick to one method of connecting yagi elements to booms, either sitting or top or hanging below. Despite the axial load difference, I haven't heard many good arguments about which is superior. 

In a marginal case with u-bolts that are of minimum size it might make a difference. However, bolt grade, material and durability are more important in most cases. Axial and sheer strength of u-bolts become increasingly important for high load applications such as boom-to-mast clamps and rotator mast clamps. 

A failure under unanticipated stress is something you really want to avoid if you can. Size your u-bolts  by the application and fundamentals if you can, or do your best to mimic the size and grade in similar applications that have proven durable in commercial products. That is, lean on the engineering done by an engineer.

My Labrador Adventure

Blog activity has been below average due to other priorities and activities. In particular, I was travelling. But what a wonderful trip! This was my first visit to Labrador. The purpose of the trip was directly related to amateur radio and contesting. Vlad VE3JM and I drove to Happy Valley-Goose Bay (FO93) with Chris VO2AC/VE3FU to help him prepare his new remote station.

One of the astonishing aspects of the trip was that it could be driven. It wasn't so long ago that the vast expanse of land was only accessible by canoe or float plane. Once you head north from the St. Lawrence River the population density falls precipitously. There is no cell service; those that work in the vast spaces between towns rely on satellite services. Settlements in the northern interior exist to support mining and hydroelectric power generation. There are few roads; railroads and transmission lines carry the land's bounty south.

That's me standing at the western end of the Trans-Labrador Highway, between Fermont (QC) and Labrador City (NL). The more than 500 km to Happy Valley-Goose Bay is paved. There is still about 150 km of road on the Quebec side that isn't. That expensive job is an ongoing multi-year project. Chris regaled us with stories of the bumpy unpaved road his family had to navigate when he was young.

This is the hydro-electric dam at Manic 5, one of the largest of its kind in the world. It's a lot bigger than it looks in the picture, which you only appreciate when you drive close to the dam. Chris gave us a closer view of the installation at Churchill Falls, Labrador where he once lived and worked. Even from the outside the scale is impressive, as you'd expect from a facility that generates more than 5000 MW of power. That'll drive a few amplifiers.

We also had the opportunity to watch, from a distance, mining of iron ore and other minerals in the vicinity of Fermont, Quebec (Fermont translates to iron mountain). I have pictures but I'll spare you those and return to amateur radio.

Our trip was delayed for a week due to the wildfires that came within a few kilometers of Labrador City and nearby Wabush. Both communities were evacuated, with many temporarily sheltered in Happy Valley-Goose Bay. Happily both communities were unharmed and the evacuees returned. During the drive we saw the effects of previous fires and recently constructed firebreaks.

One of the evacuees was Naz VO2NS. I took this picture of him at the Labrador City club station when we passed through after everyone moved back. Driving around town everything looked so ordinary that it was hard to believe it was empty a few day earlier. There are fewer than 30,000 people living in Labrador so there are not many hams. Only a few of them are active on HF. Naz is one.

We continued east to Happy Valley-Goose Bay. Chris's parents and family friends hosted us during our stay. Labrador (and Newfoundland) hospitality is really something. All I can say is that we were treated very well and fed sumptuously. We had to watch ourselves not to overdo it -- that would have impacted our ability to work and climb.

When we arrived the new tower was nearly complete. He transported and planted the Trylon tower on two previous trips. We topped the tower, constructed and tuned the yagis then raised them. Low band wires and 40 meter vertical were raised, tested and tuned. By the time we left he had antennas for 160 through 6 meters. His remote station with SO2R capability was previously built and installed, and only needed reconfiguration to use the new antennas.

There were numerous difficulties along the way. With three experienced hams and tower climbers we resolved almost all of them. We had to be self-sufficient with parts and tools since only ordinary construction material and hardware could be bought locally.

With just the one tower there are inevitable interactions to be dealt with. We did the best we could when faced with space constraints. The picture shows the installation partially constructed, with Chris working to the left of the tower.

There were two difficulties more difficult to overcome: heat and flies. The temperature was far in excess of the normal 21° C for late July. The first day broke records with 33°, and a couple of later days were nearly as hot. The black flies for which Labrador is infamous were constantly swarming. Bug dope helps but is unpleasant. I chose to cover up as much as the heat allowed. 

The carnivorous pests soon covered our exposed skin with tiny scabs from their innumerable bites. I've always liked this song which expresses the experience pretty well:

And the black flies, the little black flies

Always the black fly, no matter where you go

I'll die with the black fly a-picking my bones

In North On-tar-i-o-i-o, in North On-tar-i-o

An eastern view with the JK tri-bander raised but not yet attached to the mast shows a little of the town and the Churchill River in the near distance. The 6 meter yagi was placed on the mast before it was raised to its final height and the rotator installed. Although the mast is strong it is not suitable for climbing, and therefore unsuitable for raising yagis to the top after the mast is in place, which I typically do for my own large towers and antennas.

Acting as tour guide, Chris showed us the numerous points of interest in and around town. On the adjacent Goose Bay AFB is one site of the SuperDARN network for ionospheric research. I counted 16 LPDA in the array. The photo of a section of the array shows Vlad VE3JM (left) and Chris VO2AC.

In the end...

...was it worth it? It was a week and a half of my time, working up to 10 hours a day and a grueling 4000 km on the road. I'm not young anymore. 

I find that as I age and mellow out that my urge to help others grows. It's a great feeling to see another ham smiling when their station dream is fulfilled and they begin their new journey. Chris was eager enough that he operated (remote, as usual) for an hour in NAQP CW from the hotel where we stayed overnight on the drive home. There is more work to be done, but with what was accomplished on this trip he'll be able to do the rest by himself during future trips. I think it is fair to say that you can expect a larger presence from Labrador and zone 2 in upcoming contests.

We didn't come home empty handed. Some of that Heliax followed us home. Scroungers gonna scrounge.