Series Xc Antenna Tuning

Earlier this year I was helping a friend install and tune a 40 meter vertical that he had purchased at a flea market. It was made from large aluminum tubes of constant diameter and was therefore a fixed length (height). It was mechanically sound but required rope guys and a post for support.

He had prepared 16 radials of about 10 meters length -- about ¼λ -- which we stapled to the ground. It was directly fed with coax, without a matching network. The match was poor. The antenna resonated about 300 kHz too low, well outside the band. I suspected that the radials were too long, but cutting them was not an option.

Not being allowed to cut the radials or the vertical, there were still a few options. I studied the antenna with an analyzer for a few minutes to characterize its impedance. At resonance (outside the band) the impedance was approximately 37 Ω (I don't recall the exact value). This is typical for a vertical with low ground loss. However, as the frequency increased the R value also increased, along with the inductive reactance X. R was close to 50 Ω between 7.0 and 7.1 MHz (again, I forget the exact values).

This was a blessing and a curse. A blessing because only a series capacitor was needed to cancel the inductive reactance to provide a good SWR curve across most of the band, but a curse because I didn't have suitable capacitors on hand, fixed or variable. To my surprise, my friend had a large supply of ancient mica transmitting capacitors. All I needed to do was find the right one.

Rather than guess, we did the simple math to calculate the capacitor value that would equal the measured inductive reactance near the centre of the spectrum that of interest: 7.1 MHz. The value came to 400 pf. 

The equation, which all hams ought to know, is Xc = 1/(2πfC). Look carefully at that equation if you are unfamiliar with it: the smaller the capacitance, the greater the reactance. Large values that have a very low reactance (at the design frequency) can be found in lightning arresters and bias-T circuits to block DC while passing RF.

I rooted through the box until I found a capacitor that was suitable for 1000 watts and close to the desired value. That was a beefy 330 pf mica capacitor. I connected it in series and measured an excellent SWR curve. We made the connection more permanent and left my friend to add a weatherproof enclosure later. The antenna continues to work well.

This approach to antenna matching is similar to that for gamma matches where you find the tap point on the element where R is close to 50 Ω and then use a series capacitor to cancel the inductive reactance, resulting in a 50 + j0 Ω match at the selected centre of the operating bandwidth. There are other potential applications. 

Consider the SWR curves for two antennas resonant (X = 0) at 3600 kHz, for CW and digital modes. The vertical has a "perfect" ground, or one simulated with an extensive radial field, and the inverted vee is 30 meters above EZNEC medium ground.

Now suppose that you want to also have a low SWR for SSB high in the band, say 3900 kHz. You have several choices, and you can probably think of more:

• Make it a fan dipole/vertical, with the parallel element tuned for higher in the band.
• Cut the antenna for 3900 kHz and have a switchable coil at the base or partway along the element (each half-element of the inverted vee).
• Switched L-network or similar to match the antenna at 3900 kHz.
• Switched series capacitor to improve SWR in the SSB segment, if the R value is suitable.

Note that both antennas are not a perfect 50 Ω match for CW, though the SWR is close enough in most cases, especially when an antenna tuner is used. The vertical is more broadband than the inverted vee (or dipole), which is typical. Although the omni-directional mode of my 80 meter yagi (driven element as a simple vertical) has a reasonably low SWR up to 3800 kHz, I included a switched L-network to lower it further for SSB to "future proof" it in case I purchase a broadband solid state amplifier.

Getting back to those two example antennas, SWR curves are inadequate to determine whether it is possible to insert a series component to match the antenna for the SSB segment of 80 meters. We need to calculate or, better, measure R and X across the operating range. For reliable measurements you should use a modern single-port antenna analyzer or VNA of known accuracy, especially for large deviations from the nominal 50 + j0 Ω impedance. I use RigExpert but there are other excellent products on the market.

For this exercise I'll stick with calculations by EZNEC. Although I mostly used the NEC5 engine for the models in this article, NEC2 is perfectly good for these simple antennas, and it comes free with EZNEC. Below is a plot of the R and X values for both antenna models.

One striking difference is that the inverted vee's X (reactance) changes more rapidly with frequency. That's the reason for its narrower SWR bandwidth. Also, notice the slow change in R for both antennas, which increases with frequency. Finally, there is an excellent linear frequency relationship of both R and X. However, that is only true for small percentage frequency ranges. Other antenna types will have different curves.

The relationship scales: the chart is for 80 meters but the same is true for my friend's 40 meter antenna. It should be clear why I was inspired by the antenna feed point's measured R and X.

We can cancel the inductive reactance with a series capacitor to shift the SWR curve higher in the band. Of course it isn't quite that simple. First, since R will remain the same, that will determine the minimum SWR in a 50 Ω system. On the chart you can see that the vertical is more promising than the inverted vee. Second, the quality of the capacitor is critical. It must have a high Q so that very little power is dissipated by the devices ESR (equivalent series resistance) or it will fail with high power. Good transmitting capacitors (see the earlier article reference) should have a Q of at least 1000 so that the ESR is low enough for high power. Solve for R in Q = X / R and then use that in P = I²R to calculate the power dissipation. Unlike coils, capacitors are small so their construction and surface area to conduct heat away can be critical if the loss is more than a few watts.

For the vertical it is easy to find the correct capacitor value by calculation or trial and error in EZNEC. To bring X to zero at 3900 kHz the capacitor value is 835 pf. There are no commercial capacitors with that value so it would have to be done with a combination of capacitors or a variable capacitor, with or without a parallel fixed capacitor. EZNEC also helpfully calculates the power dissipation if you provide the ESR. For a capacitor with a Q of 1000 the calculated loss is almost exactly 1 watt for a transmitter power of 1000 watts.

We are not so lucky with the inverted vee due to that high R of about 94 Ω at 3900 kHz. This is a case where a two-component L-network is preferred in order to transform both R and X to achieve a better SWR. The same is true for an inverted vee tuned to resonance at 3900 kHz and brought down to 3600 kHz with coils.

It should also be noted that since the inverted vee is a balanced antenna, a series capacitor in each leg is required to preserve balance. In this case the capacitance reactance in each leg must be less because they are in series. That is achieved with a higher value capacitor of 550 pf versus about 280 pf if a single capacitor is used. You can use one capacitor but should not because the antenna becomes unbalanced and common mode current is more likely and a CMC choke with a higher impedance is needed to avoid excess heating.

At this point I'll reveal that I have an underlying motive other than what I've discussed. On my list for new projects is my longstanding desire to make my 80 meter 3-element wire yagi a yagi on SSB. It is only a yagi in the CW segment at present. A 4-square on 80 meters works from 3.5 to 3.8 MHz (the 80 meter segment of interest to me) while a yagi is too narrow band, only covering 3500 to 3650 kHz. Shifting the antenna upward 150 kHz would achieve my objective.

I won't get it done this year, so there is time to consider alternatives. A series capacitor in all 5 elements is one of the options. The approach has several advantages:

• High efficiency: High Q capacitors are easier than high Q coils.
• Small size: A capacitor and relay will fit inside the existing PVC electrical boxes.
• Switching: SSB relay lines to the parasitic elements is already installed. The SSB selector line at present is only used to modify the L-network for the driven element in omni-directional mode.
  

Until now my plan was to place two coils in the parasitic element switch boxes. With the element tuned as a director for SSB, one coil would shift resonance downward to make it a reflector (as is currently done) and the second to move resonance downward from SSB to CW.

As a CW reflector there would be two series coils. That would further reduce the already low radiation resistance (due to the T-shaped parasitic wire elements) and incur loss in the coils. Getting coil Q high enough to avoid significant loss would require new enclosures to fit two of them in a manner that avoids stray coupling.

By using a series capacitor these difficulties can be largely circumvented. The new difficulty is finding enough of the needed low loss, high RF current capacitors of the required value. But first, let's determine the capacitor value and its performance using an EZNEC model.

For yagi operation from 3500 to about 3650 kHz the director is tuned to 3680 kHz and the reflector to 3450 kHz. By opening the shorting relay, the series coil shifts resonance downward by 230 kHz. For use between 3650 and 3800 kHz, the parasitic resonances shift 150 kHz upward to 3600 and 3830 kHz. 

The height of the driven element (tower + stinger) is difficult to adjust so an L-network tunes the antenna for yagi mode (all 4 directions) and for both CW and SSB omni-directional modes. In any case, feed point R is quite low for yagi mode and below 35 Ω in omni-directional mode.

My first question was how much the parasitic element's R would change when inserting the appropriate value of series capacitor at the feed point. For the required 150 kHz upward shift the capacitor value is 1400 pf. R increases from 21.4 Ω to 23.8 Ω, or about 10%. That's for perfect ground. When ground loss is added the percentage change is less since it is in series with the feed point. 

The percentage change is less when it is made a reflector by switching in the 2.1 μH coil. R is 23.9 Ω at 3450 kHz (CW) and 25.8 Ω at 3600 kHz (SSB).

That's promising since the impedance is roughly the same for parasitic elements tuned to either CW or SSB by the series capacitor. If the same can be done for the driven element, a fixed L-network can be used for all yagi and omni-directional modes. That can now be tested in the model.

I pulled out my old EZNEC model of the completed 80 meter yagi. There were several design iterations before construction began, and this is the one that was built. In the EZNEC view, the antenna direction is to the right.

I used NEC2 since NEC5 introduced small differences that I didn't want to spend time on even though the result is certainly more accurate due to the acute angle on one side of the T-shaped parasitic elements. Continuing with NEC2 does not substantially affect the present study. I'll switch to NEC5 when I am ready to proceed with the project.

The L-network for the yagi modes was refined to make the SWR curve as good as it can be. When I built the antenna, I used the model as a guide but built the matching networks based on measurements. The two were pretty close. 

SWR curves for CW were calculated and then 1400 pf series capacitors were inserted at the base of the 3 active elements (the inactive elements are floated) to, hopefully, shift the array to the SSB contesting part of the band, which is roughly 3650 to 3800 kHz. 

The driven element reactance is not the same as the reflector and director so I manually adjusted the capacitor until the SWR curves were roughly alike. The capacitor for the driven element is 3000 pf (less inductive reactance to cancel).

The curves are almost identical. I expected them to be close but not this close. The impedance change for the 150 kHz upward shift is quite modest so the same L-network at the driven element feed point works very well for both CW and SSB. 

However, we have not yet demonstrated that the yagi's performance is similar. I did that next.

To my eyes they're identical. In fact, the SSB performance is marginally better. Performance lags in the top 50 kHz for both CW and SSB, which was already known from the original design. Yagis, which are high Q antennas, are challenged on 80 meters where the percentage span of the operating range is high, in this case over 4%. That's equivalent to 300 kHz on 40 meters and 600 kHz on 20 meters.

The low gain is due to near field and far field ground loss, typical of verticals. It's worse with yagis since the radiation resistance is low. 4-squares perform better. I have plans to improve antenna performance, which I hope to implement next year. 

Series capacitors to support SSB appear to be a good technique to apply to the current and future version of the 80 meter yagi. It's simple, efficient (with the right capacitor) and predictable. All I have to do now is scrounge those 5 capacitors.

Fall Maintenance

It should not be surprising that there is more maintenance for a large station there is for a small one. That means that I have a lot of work ahead of me this fall. I am prioritizing some jobs so that I am ready for the major contests that are rapidly approaching.

Despite all the problems, there are so many antennas that I have been able to continue operating. But that's for casual operating; in a contest I want all of the antennas to be available. That is especially important for multi-op and SO2R where the antennas must be shared among two stations.

In addition to repairs and other maintenance, I have new projects underway or planned. To give you an idea of what's involved to keep my moderately-sized "big gun" station going, I'll show you my to-do list for this fall. First the repairs and then the new projects.

Repairs

20 meter 5-element yagi: The upper rotatable yagi in the 20 meter stack began exhibiting intermittent behaviour in the spring. By midsummer the failure was complete and the antenna became unusable. There is very little that can go wrong in a simple, if large, antenna like this so I knew the repair would be easy. Unfortunately, after testing the entire antenna system in stages, the fault was determined to be at the feed point. It is unreachable from the mast so it had to come down. It is now sitting in the hay field. The repair was indeed simple and I hope to raise it soon. I'll have more to say about the faults and their repair in a future article.

80 meter wire yagi: Deer continue to molest the antenna. One enterprising individual tore apart the "temporary" protection on the southwest parasitic element and proceeding to chew and tug the wires until it pulled off the switch box. When other projects are out of the way I would like to build metal cages for the box and wires, and perhaps replace the bottom 2 meters of the wire element with tubing.

40 meter 3-element yagi: The capacitance hats need to be replaced. It's a complicated job since the antenna is so large and heavy. The replacements have been ready for quite some time. I haven't been in a rush since no more capacitance hat arms have broken and the antenna performs well. I may have to defer this job (again) to next spring.

Side mount rotator: Intermittent operation was found to be a cold solder joint on the Hy-Gain Ham M motor phasing capacitor. I have it mounted on the tower to eliminate loss and eliminate two wires. It currently turns an XM240 40 meter yagi. I had to inspect the capacitor on the tower, determine the fault, bring it down for soldering and then return it to service. Even a simple fix like this takes time due to the climbing. I took the opportunity to replace the enclosure with UV-resistant plastic.

Trees: Half a dozen large dead trees need to be taken down since they threaten Beverage antennas and, in one case, my workshop/garage. Beverages and feed lines will have to be temporarily moved since they're in the fall zone. There are no trees threatening the towers or guys at present, which are mostly well away from the trees. That was by design. Threatening trees are marked with blazes so that they can be identified this winter when all trees have no leaves.

Software: The 160 meter mode of the 80 meter vertical yagi can now be used. This had been a limitation of my antenna selection software that I delayed fixing due to its relative complexity. Along with that, several bugs have been resolved that are related to antennas that are multi-band or on the same port, with an auxiliary switch. Full SO2R and multi-op testing needs to be completed before CQ WW.

Beverages: Ants cut through the taped weep holes of the remote switch so I had to once again evict them. I caught them early so there was no damage. However there is an intermittent in the one or more of the RF paths that occasionally cuts the signal path. Switching appears to be fine. I suspect the RG6 connectors. I will have to open all of them to clean the conductors and ensure that all threads are coated with dielectric grease. Failure of the short east-west Beverage in September was due to the centre conductor of the RG6 breaking off inside the F connector.

Antenna interaction: The side mounted XM240 and TH6 have an interaction on 40 meters that impacts the XM240 when it is pointed approximately west. In that direction it is at right angles to the south pointing TH6. It is not often appreciated that a 3-element yagi has a "hidden" resonance at the next lower band, where it behaves like a short dipole with large capacitance hats (the parasitic elements). I will model the antennas and decide if I can reduce the interaction by raising the TH6 several feet.  It can't go much higher since it'll get too close to the next higher set of guys and the risk of increased interaction with the lower yagi of the 10 meter stack.

160 meters: My failed attempt to broaden the bandwidth of the shunt fed tower with a wire cage for the gamma rod was aggravating. I gave up when the weather got too cold for further attempts, especially as contests approached and the 160 meter season was well underway. I will try again this month once the 20 meter yagi is back on the tower. I don't roll out the radials while I have ground crew helping me with tower work since they are a safety risk. Breaks in the radials due to critters must also be mended -- wire nuts served as temporary repairs.

Prop pitch motor controller: There was no lightning damage this year but I diagnosed and repaired damage from last year. The motors turned slowly and the current draw was high. One motor was affected more than the other so I suspected a motor problem. The motors are fine. I mistakenly relied on the current measurement when I ought to have measured the voltage. The old controller I am currently using (it will be replaced) only produces 24 VDC under no load. Under load that drops 2 or 3 volts even with a large filter capacitor, and is lower still at the motor due to wire resistance. When I measured it this summer it was between 17 and 19 volts at the power supply. I discovered that the bridge rectifier was damaged by lightning. Semiconductor devices can partially fail when they are hit by a voltage spike. A new 50 amp bridge rectifier fixed the power supply. I ordered several; they're inexpensive.

New projects

Although repairs receive the highest priority, this station is constantly changing and growing. The changes are mostly incremental now that the station is mature. This is a list of new projects that I am working on. Most won't be completed this winter, but all are being worked on as time allows.

40 meter reversible Moxon: Mechanical construction is mostly complete. The half elements are too long to keep in the workshop so they've been moved outside along with the boom. Dimensions and component values have been fine tuned using NEC5. The elements are not yet mounted onto the boom and the switching system isn't built. With luck it'll go up in late fall.

Stubs: Although a simple addition to the station, I have yet to do it. This is a job that is easy to do during winter so I have deferred it. I really should have done it last winter. The easiest stubs are for 80 and 40 meters, to suppress harmonics on the second and third harmonics, because the antennas for those bands are connected to their own auxiliary switches instead of separate ports on the 2×8 switch.

Antenna selection software: The UI (user interface) has not stood the test of time. Operators select the wrong antenna, don't know which are available and, for SO2R and multi-op, one UI is difficult to use and confusing. Design for its replacement is well advanced, although development has yet to begin. It will feature separate UI windows for each station, which can be networked on different computers, and limit the display to the availability of the antennas for only the current band, including receive antennas. I plan to write the software over the winter. The Arduino switching system does not need to change, although I'd like to migrate PC communication form USB to wireless.

80 meter wire yagi: There are several electrical and mechanical improvements on my list. I've been deferring them as the solar maximum has waxed since 80 is less important than the high bands for the time being. I intend to add SSB yagi modes (it is currently only a yagi on CW), install concrete bases, replace the tower with a taller one (to remove the troublesome stinger), decrease ground loss, improve critter protection (see above), and a few other changes. I will do what I can this fall and winter as the weather and other projects allow. Most will wait until at least 2025.

New prop pitch motor controller: I am well along in the construction of an Arduino-based controller for the two prop pitch motor rotators. The first step is direction indication, followed later by rotation controls. The project has been idle for several months due to lack of time and some confusion over non-linearity in the op amp circuits. Eventually I will interface it to a PC for software control. An article will follow once the controller is complete.

6 meter Moxon: The Moxon is on the small tower bracketed to the house. There is no rotator or coax! I haven't yet decided how to proceed, whether to fix the direction or make it rotatable. My objective is rapid propagation checks in different directions.

Small is beautiful?

It should be obvious that a big station is not for everyone! There's always work to do so it has to be something you enjoy. I do, most hams do not and I can't fault them. Dreaming of a big station is far less stressful than owning one!

Between good DX conditions on 6 meters, DXpeditions and station maintenance, fall is a busy time. We've had unexpectedly mild weather which is very welcome to getting the work done. However, good weather is good for other outdoor activities competing for my time. Somehow I have to do both.

6 Meters Recap 2024

There is evidence that sporadic E incidence declines during solar maxima. I haven't looked into the research but I do know, from this part of North America, that last year's 6 meter sporadic E was poor and this year was worse. I delayed writing a season recap in the hope that fall equinox propagation would add some spice to a dull year but that hope is fading. 

Although there is a good chance of F-layer DX propagation this fall, now seems to be as good a time as any to summarize the season. Maybe by writing the season summary now the DX will subsequently start rolling in!

My hopes earlier this year for a significant increase in my DXCC count were entirely squashed. I expected at least 10 new ones and ended up with just two: E51EME and FR8UA. I heard a few others that I failed to work. Sometimes it was a matter of timing, such as when I was doing a chore when HD8M was worked by several locals. My stretch objective of 20 was absurd in retrospect. 

I was confident that an average sporadic E season combined with additional F-layer propagation due to the high solar flux would carry me to my DX objective. Although solar flux dramatically increased, boding well for the remainder of the current solar maximum, and 10 meters has been very good, it didn't carry to 50 MHz. It isn't easy for the MUF to bridge that frequency gap of close to an octave.

Those at lower geomagnetic latitudes did better. Although FN24 is almost exactly midway between the equator and north pole, the same is not true of our geomagnetic location. Follow the lines of constant magnetic inclination (isoclinics) and all of Europe below Scandinavia and northern Scotland are further "south". Since envy is not an effective strategy we can only do the best with what we get.

That is not to say it was all doom and gloom. We experienced periods of fascinating and tantalizing  propagation. That it didn't always translate to DX in the log does not diminish my interest. Fleeting propagation due to as yet only partially understood natural phenomena is one of the attractions of 6 meters.

• Propagation to Europe was well down. We had only one widespread opening, and the rest were marginal or to parts of west and south Europe that are routinely heard here. 
• Openings to South America were brief, and in any case I have pretty well worked out that continent. 
• Other than 7Q, which was in with surprising regularity, and the usual west African islands like EA8, Africa was nearly absent this year. 
• There were a couple of likely F-layer openings to the Indian Ocean during which I worked FR and heard 3B8 and 3B9 stations that I worked before.
• There were several marginal and brief openings to Japan which netted a total of 4 contacts along with several partials. The rest of east Asia was not heard, however I did hear at least one Maine station work DU.
• West and Central Asia were marginal several times, with stations in OD, TA, and UN heard. One tantalizing message from 9N is of uncertain veracity. More on this below.
• Pacific stations were absent other than a brief opening to Hawaii and regular appearances by E51EME (ZL1RS) during his two DXpeditions in June and September, along with 3D2 and FK. VK9DX was briefly and weakly heard late one evening.

A lot of the marginal openings are mostly notable due to being caused by the high level of activity. Without the prevalence of capable stations around the world and their willingness to periodically call CQ DX on 50.313 MHz (FT8) many (most?) openings would have been undiscovered. It is very interesting to see those orphan (single) messages from around the world when the band seems to be otherwise dead. True, they do not result in QSOs, but the possibilities excite the imagination.

I don't miss much on 6 meters. During the sporadic E season, and now beyond that with the improved propagation prospects, I usually monitor 50.313 MHz whenever I am not using the station. If there's an opening or one is likely (W1/VE1 hears DX, DX spots or occasional decodes) I will often CQ in the direction of the opening and then check for any flags on PSK Reporter.

The following are a few highlights of openings or at least near openings.

East Asia: There were quite a few openings to Japan though only occasionally good enough to work anyone. I worked a total of 4 JA stations on two separate openings. No other east Asia was heard.

Central Asia: UN (Kazakhstan) had numerous openings though none very workable from here. I called a few and worked none. Other central Asia were heard in northeast NA but not here. Examples include EX. 

On the same path (compass bearing) there were repeated marginal openings to Ukraine and Scandinavia. One time when eastern UN was heard, the following message appeared on my screen:

The path is the same and, on inquiring on ON4KST chat, 9N7AA was working Europe at the time. I did decode a few messages of Europeans working him. Out of curiosity I reached out to him by email to ask if this message was legitimate but he did not reply. It remains an intriguing mystery.

West Asia: Numerous countries were copied, including TA, OD and 4X. None of the openings was persistent enough to sustain a QSO. It takes at least 2 continuous minutes to have an FT8 QSO once the station is heard. On the other hand, hearing a station on CW or SSB during a fleeting opening is very unlikely. You accept the bad along with the good on the digital modes.

Arctic: There were a few workable openings to Scandinavia. QSB was deep with signals cycling from strong to unheard every several minutes. One interesting QSO was with LA in the far north that was in daylight while it was night further south. OX and TF were also heard and worked.

Europe: There are many openings to Europe that are easily noticed due to the high level of activity. Most openings were not widespread; they were brief, narrow in coverage and weak. One spotlight opening worth mentioning was to Greece in July. From the discussion on ON4KST chat, it seemed that I was just about only one on this side of the Atlantic to experience the opening. It took patience and some coordination on the chat to log several SV stations. The opening eventually faded without having extended outside the spotlight zones.

Aurora: There was one good aurora opening in May that netted many CW contacts including western Canada and the US. Other aurora sessions were not as far ranging. Aurora is more common during a solar maximum so we can expect more for the next two years. It isn't DX but I enjoy it nevertheless.

Central America: While not rare, it was nice to be able to work TI on both CW and SSB. These days I don't often bother with the traditional modes but when propagation is good these modes easily outperform digital. The QSOs are fast and they're fun. If F2 propagation really gets going, you can expect to find me on CW and SSB more often.

West: There were a surprisingly large number of openings to western NA, including one to Hawaii. I only worked one KH6 but a large number of W6, W7 and VE7 stations were worked this season. I don't think I've ever worked so many west coast stations in previous sporadic E seasons. It was great for grid hunters, which I am not, yet it was difficult to resist calling several of the rare ones.

South America: Every second or third day for the past few weeks we've heard a few weak SA stations in the late afternoon. This is typical equinox propagation. It was poorer than expected for the high solar flux. I enjoy working SA even though I've worked all the easy ones. As noted earlier, I missed HD8M. CB0ZA was never heard here.

The CY9C DXpedition was an easy shot from here. I worked them on a previous DXpedition so I stayed out of the pile ups. The path was more difficult for many others. Of course there are countries and DXpeditions that are difficult for us and relatively easy for others to work on 6 meters.

Arras, C. & Resende, Laysa & Kepkar, Ankur & Senevirathna, Gethmini & Wickert, Jens. (2022). Sporadic E layer characteristics at equatorial latitudes as observed by GNSS radio occultation measurements. Earth, Planets and Space. 74. 10.1186/s40623-022-01718-y.

Where do we go from here? What are the prospects for better DX? There are readers closer to the equator (the geomagnetic equator) who are already experiencing good propagation and may be wondering what I'm complaining about. It isn't just high-MUF but also sporadic E. Compare the above chart of global sporadic E incidence with the earlier one showing geomagnetic isoclines. Do you see the similarity?

My primary interest on 6 meters is DX. My DXCC total now stands at 139 worked and 128 confirmed (LoTW) since my return to the magic band in 2017, and I am reaching the point of diminishing returns. I want more, but it won't be easy.

As I write these words the solar flux is 275 and there was a suspected F2 opening to western Europe occurred earlier in the day. I will keep monitoring 50.313 MHz for signs of openings, turning the yagi throughout the day to the most likely directions for DX openings. October and November are excellent months for F2 propagation in the northern hemisphere, so I am hopeful. I recall the pattern from the 1989/90 solar maximum.

6 meter DX has been poor so far this year but there could be fireworks ahead.

Not Reporting Contest Operating Time

Right up front I'll say that most readers won't find this article of the slightest interest. I've been busy with travel, tower work and family responsibilities and I've hardly even operated recently. After a brief and casual effort in SAC (Scandinavia Activity Contest) CW last weekend and reporting my results to 3830, this topic came to mind as I perused score submissions alongside my own. So why not a brief article on one my observations.

The subject of reporting raw scores during and immediately after contests has long been tainted with controversy, although most contesters pay little to no attention. They don't care, and that's fair. For the most part neither do I. I report my results promptly after contests, and typically submit my log to the sponsor at the same time. 

Opportunities for competitive comparisons have gone further. While I have only participated once while using and monitoring the contest online scoreboard, its popularity is growing. Participation is optional and you can control how much detail is shared. Soon we may have real time scoring. These developments are changing radiosport in many ways and have the potential to make it better and more interesting.

Where's the controversy to which I alluded? Certainly there are some that object to increasing dependence on the internet during the contest, or consider their operating tactics private. However the specific topic of this article has nothing to do with the internet or real time tactics. Rather, it's about disclosure, and how that information can be used by other contest participants. 

It comes down to: how much about your performance and objectives should be available to others? Should early (even real time) disclosure be an option or mandatory, and how can it help or hurt you in the current and future contests? There are major contests like CQ WW where your submitted log becomes public after the final results are published. So if you enter you must agree to this. Others can analyze your log for insights, but only long after the contest is over

Disclosure and public logs are not the norm for the majority of contests. Many choose not to disclose anything. As mentioned, real time contesting will greatly increase disclosure, and that can help or hurt your competitiveness. Do you want others to know that you are doing poorly on 80 meters, that you can't maintain a high rate during big openings, when you take off times, or what category you've entered?

I have no answers. All I can say is that more disclosure is the trend. Get ready for it since, if you contest, you will be affected. If not today then soon.

That's a long preamble for a short article. So let's get to the one aspect of disclosure I want to talk about today: hours of operating time in a contest. At a glance it discloses your rate by simply dividing QSOs by hours. Or does it?

An important measure of your performance in a contest is rate. At it simplest it is the ratio of QSOs to time, typically average contacts per hour. Higher is better if you are competitive. But too great a focus on rate can hurt if you spend less time hunting for multipliers. It's just one metric in a complex calculation of performance.

It can be very illuminating to compare your rate to others with similar or better stations in your area. If you're that station, your on time disclosure helps them to assess their relative performance. The comparison can help you, and other participants, to address shortcomings in future contests, if that's your objective.

This is a screenshot from 3830 a few hours after SAC CW ended Sunday morning. Most operators reported their operating time. I did not. Am I avoiding disclosure of my performance from other participants to give myself an edge? After all, I now know something about their contest performance that they do not know about mine.

The answer is: no. Lack of disclosure can have non-nefarious reasons. My reasons for not reporting operating time in this particular contest are as follows:

• I don't know
• I don't care
• It doesn't matter

This is typical when I operate casually in non-major contests.

Why don't I know? On time is calculated by pretty well every contest logging application. I use N1MM+ and it is easily selected from a drop down menu. The answer to the question is that I didn't look. Which brings me to the next two points in the list.

I didn't look because I didn't care. That requires an explanation. Even during a casual contest operation it is useful to look at the rate and to select operating hours when propagation and activity is best. I do that in some casual contests but not all. When I do I usually report my on time, since I monitor it and use it to measure my performance. It can provide useful feedback during casual and part time efforts even though a full time effort will typically result in a lower rate since, eventually, you run out of stations to work or you need to move to bands where contacts are more difficult.

The issue is that on time has a common meaning in addition to the definition specified in the contest rules. For example, if I operate for 15 minutes, step out of the shack for 20 minutes and then operate another 40 minutes, by the common meaning I operated for 55 minutes. In almost every contest there is a minimum off time period, typically 30 or 60 minutes. Therefore, per the rules, my on time was 75 minutes; the 20 minute break counts as on time. N1MM+ and other contest loggers use the definition in the contest rules.

That's how I operated SAC: operating for a bit, wandering out of the shack to do other things, then do a bit more operating. I did this without paying attention to on and off times. Therefore the software would calculate a time that does not represent my chosen pattern of activity. That time calculation is not personally useful to determine rate or anything else of consequence. 

The contest sponsor will calculate an on time from the submitted log in accordance with the rules. That calculation should match the time calculated by the software. Therefore it, too, is of no use to me. I ignore both.

Even if I had been competitive the on time calculation does not impact ranking in the contest results. In a contest like SAC where you can operate for the full 24 hour period, your choice to operate less is irrelevant. Rate doesn't enter into the ranking determination; only your score matters. That is why my third reason is that it doesn't matter.

In contests like NAQP and CQ WPX where single ops are limited to 10 out of 12 hours and 36 out of 48 hours, respectively, on time does matter. I pay close attention in those contests, seeking to maximize on time without exceeding the limit. Indeed, selection of off time is determined by contest strategy.

In major contests like CQ WW where there are no time limits it is still very useful to know your on time since endurance is a factor in participants' performance. The contest is 48 hours but if I can only physically tolerate operating for 42.5 hours, that matters. Therefore I track the time and report it.

I am not shy about disclosure when it matters.

I know contesters that deliberately hide whatever metrics about their contest entries that they can. Or they will wait until the log submission deadline. As more contest sponsors publish submitted logs after adjudication and publishing results, disclosure can be delayed but not prevented. 

I know a few of the reasons some do this but that's a topic I am not prepared to delve into. I've heard what I consider both good and bad reasons, keeping in mind that these are matters of personal judgment where there can be a diversity of opinions.

QRG.000

In the old days we had technology called "analogue". Our radios depending on it. Oscillators oscillated and ruled dials marked where we listened and transmitted. Or so we hoped. Calibration was mandatory, but with calibration standards of varying reliability we mostly just crossed our fingers when a rare DX station showed up near the band edge. With less stable oscillators, our VFOs might drift out of band while our attention was on the business at hand.

Analogue is mostly gone, pushed out by digital. Gone are the ruled dials and the frequent need for calibration. When the VFO says "21.033.91", we believe it. Indeed, if I arrange a schedule with you on 24.938500 MHz, we can both spin our VFOs to that frequency (or type in with a keyboard) at the appointed time and we'll find each other. We probably won't even have to twiddle the knob to make our voices recognizable on SSB.

Modern technology is a marvel. But being able to set up a sked at 24.938500 MHz is awkward; there are too many digits to remember. So most hams round it off to 24.938 or even 24.940 MHz to get rid of those pesky rightmost digits -- zeros are useful for doing that. Frequencies are much easier to remember when you can mentally ignore the trailing zeros of a precise frequency. 

Of course that reduces the available sked (or DXpedition) frequencies but, well, the bands aren't as crowded as they one were. If you run into QRM you QSY 5 or 10 kHz, precisely, and carry on.

That may be fine for skeds and DXpeditions, but what about other activity that isn't on repeaters, nets, digital watering holes, etc.? What should I do when I call CQ? Many hams will very carefully adjust their VFOs to, say, 28450.00 (or 28450.000) kHz and make their call. Only rarely will that least significant zero flicker, suggesting a drift of ~0.03 ppm or, more likely, a stray pulse from the optical encoder.

When you click a DX spot on the band map you are almost assured that you will hear the station if propagation cooperates and the spotter didn't make an error when manually typing the frequency. But few do that anymore, letting the software read the frequency, automatically round it to nearest 100 Hz and then broadcast the message around the globe. 

Even if the frequency is slightly wrong, you can assuredly wager that the majority of the click-and-call stations will all be zero beat, defying the DX operator to pull a call out of the bedlam. Oscillator calibration is that good. It's so bad that some software applications apply a random offset to the spot frequency to prevent zero beating.

That's one negative consequence of digital precision and there are others. Consider the station choosing a frequency on which to call CQ. An excessive zeal to punch in all those rightmost zeros can have unexpected effects. Most receivers inherently have spurious signals (birdies) and many stations must deal with RFI sources. Birdies are usually not on exact kilohertz frequencies, but many RFI sources are. These can come from various electronics or from commercial transmitters (e.g. AM broadcast), the latter of which do often operate on round number frequencies such as 910 kHz.

Notice that last frequency -- its second harmonic is within the CW DXing sub-band at 1820 kHz. Many of us have weak or strong signals on frequencies like that. Call CQ on exactly 1820 kHz and many station will hear you zero beat that AM carrier harmonic. It happens more often than you might believe. The smart operators deliberately choose a frequency that is not an exact kilohertz. They know that they will have better "luck" being heard.

I wonder, as do many others, why so many hams choose to "channelize" themselves when it is completely unnecessary? Is there an aesthetic to the practice that lesser mortals are incapable of comprehending? Are zeros pretty? I suppose beauty is in the eye of the beholder.

It's gotten so bad that I tend to do the opposite, deliberately. I'll pick a frequency like 21249.12 kHz to call CQ. A surprising number of stations will call me at 21249.00 kHz and then wonder why they are having difficulty copying me. I shrug and dial in the RIT when necessary.

The practice of channelizing is uncommon in contests. When the band is packed with signals you rarely have the luxury of choosing a round number to start your run. You narrow the filter and squeeze your way in between a couple of big guns to make your call. Those non-zero least significant digits are ignored for those 24 or 48 hours.

In our technological society we build exceeding complex devices and use them to improve our lives. Hams are no different. It is perhaps not surprising that the way we operate is influenced by that same technology, just as much as a pedestrian who blindly stumbles into the roadway with eyes fixed on their phone.

We can precisely set our frequency, and for many that means we must precisely set the frequency. Round number are attractive to many. I enjoy watching how technology affects people. It can be amusing. It's a guilty pleasure of mine.

40 Meter Wire Inverted Vee Reversible Moxon

My 40 meter rotatable reversible Moxon project is progressing well. However, it is not an antenna that most hams could contemplate building and raising. Recently a friend decided to build a fixed direction version of the antenna with inverted vee wire elements. It can be a good choice since it's lightweight and the two most important directions for contesting in this part of the world are northeast (Europe) and southwest (US). I therefore thought it worthwhile to spend some time evaluating its performance, in at least one configuration.

Years ago, I worked through the performance and construction of a variety of 40 meter wire yagis. This is an opportunity to add one more design concept to that old pile. I've avoided modelling this antenna in the past because the 90° corners are not accurately modelled with NEC2. It's close but it would require adjusting wire lengths after construction. NEC5 does better, and I will be using it throughout this article. It integrates very well with EZNEC.

Before we start, it may be helpful to mention general points about 2-element yagis with a reflector. These include wire yagis, Moxon rectangles and rotatable aluminum yagis, with loaded or full size elements.

• Maximum gain occurs below the lowest frequency within which the SWR and F/B are optimum. For most 40 meter antenna designs intended for CW use, the target frequency for maximum gain is typically between 6.950 and 6.975 MHz.
• Gain bandwidth is narrow. Although the maximum gain looks good -- typically around 7 dbi in free space -- gain in excess of, say, 6 dbi is typically less than 100 kHz on 40 meters. It is a pet peeve of mine that this is rarely mentioned when compared to yagis with 3 or more elements.
  
• Gain is reduced when the elements are not straight and parallel λ/2 lengths. This applies to Moxons, yagis with loaded elements (coils, capacitance hats, etc.) and elements with any bends. It is equally true of the antenna presented in this article.
  
• Inverted vees have a higher angle of radiation and greater ground loss than dipoles with the same peak height, including when they are incorporated into yagis. 
• 2-element yagis "see" the ground more strongly than yagis with more elements at the same height because there is more radiation directed up and down. A height of 20 meters for all parts of a 2-element 40 meter antenna reduces ground interaction to near negligible, but elements that bend downward, closer to ground, such as inverted vee elements, affect antenna performance.
  
• Copper wire elements have more loss than aluminum tubing. Depending on the antenna design, wire yagis have 0.2 to 0.3 db less gain due to resistance loss. The loss is higher at frequencies near maximum gain where the radiation resistance is especially low. For 2-element yagis with a reflector (including Moxons) that is at the bottom of the frequency range.
  
• Tuning of wire yagis is sensitive to wire gauge, material, insulation, proximity to obstructions and metal used for utilities and house infrastructure, and height of the element ends.

To simplify the design process I will begin with an ordinary Moxon rectangle in free space. It will be symmetric. which is necessary to reverse it and preserve performance. There is an implied switching system at each element centre, which will be described further below. Once that antenna model works as intended, the elements will be rotated to form inverted vees, and the required adjustments made. Only then will ground be added to the model. Proceeding in steps may take longer but typically leads to more predictable and better results.

Modelling the antenna with inverted vee elements and ground from the start complicates the process. Scaling elements that are not parallel to the X, Y or Z axis can make it difficult to maintain desired angles, lengths and see the impact of ground. Doing it is stages really takes no longer and we get to see the impact of bending the elements and the ground on performance. For a similar 40 meter wire "diamond" yagi, I wrote a spreadsheet to simplify the process. Here I'll do it differently, as will be described below.

The model at this point has the following parameters, which are in range of what is typical for Moxon rectangles:

• Boom length: 5.6 meters (0.13λ at 7.1 MHz)
• 12 AWG (2 mm) bare copper wire
• Element length: 15.04 meters
• Each right angle leg: 2.65 meters
• Gap between element ends: 30 cm
• Reflector element coil inductance: 1.25 μH
• Gain at 7.0 MHz: 6.33 dbi (free space), which falls to 4.6 dbi at 7.3 MHz
• F/B: 10.5 db at 7.0 MHz; 30 db at 7.1 MHz; 20 db at 7.2 MHz and 9.5 db at 7.3 MHz
  

The SWR is pretty good, but it could be better. I did a little optimization -- coil, boom length and element tip gap -- and I was able to lower the SWR slightly, at the expense of 0.1 db of gain. However, these changes are negligible and we can expect greater effects once the elements are folded into vees. The exercise was interesting but arguably inconsequential. Note that I calculated the SWR down to 6.95 MHz to highlight the impact of a low radiation resistance where gain is maximum.

Overall, the measured performance is about what one can expect from a wire Moxon. Making it symmetric and reversible has little impact. That's good.

I split the elements at the centre to make it easy to fold them into a vee shape. It is not my intent to try every possible interior angle, settling on 120° as the most common choice and one with typically good performance. Angles of 90° and less are strongly discouraged for any inverted vee or yagi made from them since the fields between element legs increasingly cancel. The interior angle will be less than you expect due to wire sag, so keep that in mind when you lay out the antenna on your property.

The lower radiation resistance reduces gain and can make matching to 50 Ω more difficult. This is a Moxon so we don't want a matching network at all!

The first change was to rotate the elements by 30°. There are significant differences. First, the SWR curve improved slightly. However, as expected, the operating range shifted upward by about 50 kHz. Also expected, the gain and F/B declined. At the bottom of its range, which shifted upward to 7.05 MHz, gain fell to 6.05 dbi, a reduction of about 0.3 db. F/B bandwidth remains wide, typical for a Moxon, but it never gets as good as for the rectangle. (You can scroll down if you want to see the performance comparison in a chart.)

A slight gain improvement of 0.05 db was achieved by decreasing the coil inductance to 1.2 μH, at the expense of a slightly worse SWR. Increasing the coil to 1.3 μH did the opposite, decreasing gain by 0.05 db and improving the minimum SWR to almost 1.0. Leaving it at 1.25 μH seems to be a good compromise. That said, environmental interactions will likely have a greater impact than small adjustments such as this.

Scaling a Moxon rectangle is not trivial. Each dimension has a unique role, and those roles must be respected when the scaling is performed. Yes, you could simply scale every dimension but the results might not be what you expect. Consider these points:

• The gap between element ends is critical to the Moxon rectangle's unique performance. I try to keep this dimension constant once I've decided on the geometry for a particular frequency. Small changes are okay but there can be surprises.
  
• Radiation is from the long parallel sides of the rectangle. Longer is therefore better. The fields of the symmetric and opposite inward legs largely cancel. Proper scaling requires that the ratio of their lengths is kept constant, but doing so requires changes to the boom length, element tip gap or both. Again, small changes usually have small consequences.
• The wire gauge also must be scaled for an accurate result. However, for small changes the effect of wire diameter is negligible and can be ignored.
  

For this design I kept the gap of the Moxon rectangle (gray) constant (green circle): 30 cm. Note that the scaling options have been exaggerated in the diagram. All show an increase in the size (lower frequency), but the opposite scaling should be obvious. Since this antenna is a reversible Moxon with symmetric (identical) elements, one scaling calculation applies to both elements.

In option A (red) the boom length changes but not the rectangle's long sides. In option B (blue) all dimensions are scaled equally. Both change the basic geometry of the rectangle, which can be detrimental when referenced to a fixed frequency. My preferred option is C (orange) since the boom length and inward legs are kept constant. 

All that said, it is reasonable to argue that this is much ado about nothing since the scaling factor in this case is small and therefore so is the potential performance impact. In practice the scaling option is more likely to be driven by construction and environment constraints, and that's perfectly fine.

You could bend the long sides inward as I did for the 2-element diamond vee yagi that I referenced earlier but that, too, alters performance, and not for the better. It is an option that may be appealing when the dimensions must be adjusted once the antenna is in place. The boom length may be more difficult to change.

Shifting the antenna's frequency range downward by 50 kHz requires lengthening the element by approximately 0.8%. The length was therefore added to the long sides. Adding 1% is even better since we are not changing the lengths of the inward legs; that is, the wire length changes are made in the long sides. 

The long side half-elements were increased from 7.52 to 7.59 m. A small increase of the reflector coil inductance to 1.3 μH slightly improved the free space SWR and put the frequency range where I wanted it, and equal to that of the horizontal (conventional) wire Moxon.

Gain and F/B of the inverted vee Moxon are lower. The gain reduction was expected but I was unsure how the F/B would be affected. The SWR bandwidth is roughly equivalent, which is one of the main attractions of the Moxon rectangle.

The reason for the gain reduction in free space is dominated by field cancellation due to the bending of the elements. That is expected behaviour for inverted vees. There is a small but negligible increase of wire loss. I did not delve deeper into the calculation to determine why the F/B declined. It has approximately the same shape across 40 meters but with lower numbers.

The differences are not huge. Gain of the inverted vee wire Moxon increases towards the top of the band but is otherwise within 0.5 db of the horizontal wire version. F/B is even closer except for 100 kHz mid-band where the horizontal wire Moxon excels.

Out of interest, I added figures for the rotatable reversible Moxon that I am currently building (T-hat in the charts). Its gain compares favourably while the F/B is little better than the wire inverted vee Moxon. This is despite the negligible wire loss of aluminum tubes. Performance of the rotatable reversible Moxon is also somewhat reduced by the large T-shaped capacitance hats that keeps the elements short in comparison to the copper wire Moxon antennas modelled here. 

The SWR curves for all 3 antennas are close enough that I did not bother to plot them.

Those performance figures are for free space. When placed above real ground, the impact will be about the same for the rotatable Moxon and the horizontal wire Moxon. However, that is not the case for the one with wire inverted vees. 

The elevation plot compares the wire reversible Moxons at a height of 20 meters (λ/2), which is a good height for a 40 meter yagi. They are more similar than might be expected from the free space figures. Ground in these models is EZNEC medium ground.

Expect the relative performance of the inverted vee Moxon to decrease at lower heights and to approach that of the horizontal rectangle at greater heights as the influence of ground increases or decreases, respectively.

Let's move on to several construction details. These are suggestions rather than rules so feel free to improvise. First up is the boom. 

If the antenna is mounted on a tower, the approximately 5.6 meter long boom could cause problematic interaction with other antennas on the tower. A non-conductive boom is preferable but difficult to make strong enough, even with a rope truss. A stiff fibreglass joint between aluminum tubes will halve the conductor sizes and greatly reduce interactions with all but 6 meter antennas. Alternatively (as one friend of mine has done), use a short aluminum boom with ABS tips (or other non-conductive materials.

The second item is tying down the ends of the inverted vee elements. Although the antenna is mechanically complex compared to a conventional wire yagi, there is at least one method that is quite simple. A rope connects insulators at the element tips. The outward tension of tie-down ropes from the rectangle corners stabilizes the geometry and is as strong as the ground anchors. Trees or other convenient supports can be used to keep the ropes out of harm's way.

Finally, there is the switching system. A total of 3 DPDT relays are required, one on the boom and one at each element. SPDT relays cannot be used since both conductors of each coax section must be switched. The boom relay switches the 50 Ω feed line to what is the driven element for the selected direction. The default direction for the Moxon should be the one that is used the most. The lengths of the coax to the elements are not critical and do not need to be equal. The element relays select a series coil (to make the element a reflector) or the 50 Ω coax to the boom relay. 

Coil Q is not critical since its inductance is small. Even so use a coil design program such as K6STI's Coil to ensure a Q of at least 300. That's a reasonable design objective. For example, a coil that is 1.5" long, 1.5" diameter, 7 turns and 10 AWG copper wire, with 1" leads, has an inductance of 1.3 μH and a Q over 400. It should be enclosed to prevent rain and ice from affecting its characteristics.

In the default direction all relays are idle, using the NC (normally closed) positions. When the antenna is reversed, all the relays are energized so that the NO (normally open) positions are used. The control cable may be able to use the common ground (coax shield and/or tower), depending on how your station is wired. It can be dispensed with entirely using a bias-T circuit. Be sure to use relays adequate to the power level in use and never hot switch the relays.

A common mode choke can be integrated in the enclosure for the boom relay, or you can place one at each feed point on the short connecting coax runs to each element. The former should work well since the less than 3 meters of connecting coax is likely to have a high common mode impedance at 7 MHz.

I hope that this article has given you a few ideas to consider should you want a reasonably simple antenna with gain for 40 meters. As I mentioned at the beginning of the article, a friend of mine is building this antenna and I am curious to learn how well it works. The boom and switching system are installed but he might have difficulty fitting the wires within the property lines.

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.