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Ground-mounted verticals are all the rage these days in portable HF operations. This is particularly true in POTA activations. We all like to get extra mileage out of our verticals in terms of their frequency range and efficiency, no?

One method is to add an inductor to the radiating element to extend what its length looks like for RF resonance. Some versions of this are to bottom-load the vertical (Wolf River Coils does this with their Sporty Forty coil) as well as center-load it (as does Chelegance does with some of their JPC line of verticals). There are top-loaded designs, too.

An issue the portable HF operator might face if they create their own vertical antenna system is determining the value of the inductor coil. I’ll walk through this briefly to illustrate one problem that many vendors create for them in their product offerings.

Shown above is a center-loaded vertical that I’ve designed. It’s called the Eiffeltenna because of the similarity to the Eiffel Tower from the tripod legs. The details will be forthcoming once it is fully tested but the focus in this article is is that it is center-loaded as the inset photo illustrates.

What inductance value should I use? It all depends on the band, height before the coil’s insertion, and the total height of the vertical itself. Oh, and the ground and counterpoise element can play a role as well. Here, I’m using a 42″x35″ sheet of Faraday Cloth on a washed gravel driveway next to my garage. While this is far from good ground conditions, it functions very well as shown in an RF sweep below.

There are a number of calculators to help hams answer these questions. One is from 66pacific.com. I’ve placed a screenshot of the calculations for this test antenna below. The design goals are for the 40 meter band (7.0 MHz). But I also want to get 20 meters available, too. The total height of the antenna is specified as 16.75′. The coil is inserted at 7.5′ so what is the value of the required inductor to make a 20 meter vertical resonant on 40 meters here? According to this calculator, we need a coil that measures 12.1 micro-Henries.

One option is to simply build a fixed (non-adjustable) coil for this value. There are many online coil calculators for this. It is a desirable option unless there might be another band or the ground counterpoise system is very different or something else that changes things here. The other option is to purchase a coil from a number of vendors. One gotcha: very, very few actually tell the customer the inductance value for their coil (or the range if it’s an adjustable one)! They usually just say it’s “for 40M” referring to their own commercial antenna product for which it is an accessory.

Since I have several coils like this, I used one of my calibrated bench LCR meters (HP 4275a @ 200 KHz) to measure the value or range of values for several commercially available inductor coils. The results are in the table below. I have included three adjustment settings for the variable coils and the Q value. One definition of Q is “The quality factor (Q factor) is defined as the ratio of reactance to resistance, indicating efficiency at a given frequency.” For us, the importance of Q is “A higher Q value signifies lower losses and better suitability for high-frequency applications, as it implies a smaller ratio of resistance to inductive reactance.” So Q is an additional measurement about that inductor’s value that shapes how effectively it works.

While the MFJ open-air coil is no longer being manufactured, it is in wide circulation in the amateur radio community. It has a wide range, from 0.4 to 17.1 uH with corresponding Q values of 0.5 to 5.8. While the Mad Dog adjustable coil (sturdily built, I might add) has a wider range (0.73 to 28.3), it has somewhat low Q values (0.3 to 0.6). The Chelegance JPC-7 also has a wide range of inductance settings, from 0.5 to 22.8. Like the Mad Dog coil, the JPC-7 Q values are not great at 0.33 to 0.18 (double checked this figure). Here’s where one coil, larger than the rest, shines in this table. The Wolf River Coils Silver Bullet 1000 has values from 2.73 to 80.3, allowing a larger frequency range for loaded vertical antennas. Equally impressive is that the Q values range from 4.3 to 13.5 at the same time. All of these adjustable coils would fit the requirement of adding a 12.1 uH value at the center point of the vertical antenna shown above.

I included another coil from Wolf River, their fixed value Sporty Forty. They don’t tell the buyer what value it is, just that it’s an accessory for their ground-mounted whip antennas to get them to also work on 40 meters. I have two and they’re well built. Their value is 8.3 uH. There is a clone from China that is also 8.3 uH. Perhaps because of different manufacturing processes, the WRC coil has a much higher Q value at 8.6 than the clone from China has at 2.5. For these fixed value coils, it is key to realize what inductance value they have because neither would work in the center-loaded vertical example used here.

There is a very neat “bypass” trick created by Michael KB9VBR, published on his Youtube Channel. My version is shown at left. It’s simply a set of pigtails attached at the top and bottom of the coil with Power Pole connectors on each end. Plug them together, the coil is bypassed. Unplug them, and it’s in the driven element. Takes about 15 minutes or so with materials that you likely already have it you’re an antenna builder. If not, these parts are very inexpensive via online vendors.

This bypass trick can be used with any inductor coil so keep it in mind if you build a center-loaded vertical like I’ve done here. I don’t have to bring down the full vertical whip by unscrewing it, physically removing the coil, and replacing the whip. I can just reach up, plug or unplug the pigtails, and the vertical is either on 20 or 40 meters. This assumes that I’ve already done two things in the case of the Eiffeltenna center-loaded vertical.

Getting it tuned spot-on for 20 meters is fairly easy using the Faraday Cloth for the counterpoise field. It is a precursor for switching in the adjustable coil, such as the JPC-7, as shown above in my driveway. This is so that the coil can than then be adjusted to the correct uH value to load the antenna for 40 meters using an antenna analyzer. Once this is accomplished, marking the coil makes the process almost automatic during setup in the field. Checking it with an antenna analyzer, though, is always a good thing (ask me how I know, lol).

These vertical antennas can be configured in many ways but I hope that this article is useful to the portable operator who wants to operate with multiple band options using a quick setup vertical antenna. The Eiffeltenna, inspired by a tripod experiment published by Jim W6LG on his popular Youtube Channel, and further work by Jason VE5REV, fits that bill. Extend the tripod, add the coil and whip, placed it on the Faraday Cloth rectangle, connect the ground wire to the Cloth and the coax, and you are largely ready to go.

I’ll be publishing more about this very portable antenna once I’ve completed testing it. However, getting a load of the principles in this article applies to many, many vertical antennas. Get a the load of the coil you’re buying before the purchase!

The work that Rob Sherwood NC0B has contributed to the public over the past decade is unique and an amazing service to hams worldwide. I’m talking about, of course, his summary Table of receive bench tests published at this Sherwood Engineering website. He is independent so no one can think that advertising dollars could skew his assessments or how he presents them. As a CW contest operator, he is very clear that he sorts his table on the basis of what his experience and training has shown him to be the single most important measurement in his table: the narrow dynamic range.

I am not a CW operator or accomplished contester (lol) but enjoy the latter with my small team of fellow hams. But I am a statistician who likes to focus on problems where analytic tools can help foster a wider understanding of the data surrounding the problem area. So, working with Rob NC0B, I’ve created a set of “Sherwood Tools” to visualize his data as well as link them to a couple of other critical aspects of a rig purchase: market-entry price, consumer satisfaction, and the year the radio entered the market. These four vectors of data drive all of these tools, now available over at foxmikehotel.com.

The tools include a sortable Sherwood list where you can sort on any of the nine tests he publishes as well as the composite index of them that I created and included in my two-part NCJ articles in 2021. A set of 3D data visualizations are available to simultaneously view radios on four data elements (that does make it 4D, technically). Several graphs illustrate key aspects of the data, including how to not get tripped-up in the “ranking” of radios where the bench measurements are just not appreciably different. Seeing how the past 50 years of radios appearing in Rob’s Table have made a remarkable and clear progression toward the best receiver performance that modern test equipment can detect is in another tool. In addition, how the trend in getting a receive bang-for-the-buck has progressed over this 50 year period is there, too. Finally, I’ve used the industry-standard tool by Gartner, the Magic Quadrant, to help isolate radios in Rob’s Table that perform and are rated above average at various price points. I call these the Golden Quadrant Lists.

Rob NC0B has not endorsed these tools and neither have Scott K0MD or Bob K0NR. But all three have given advice and suggestions for how I’ve designed them for which I am very grateful. None should be held accountable for any mistake or result that the viewer may find there. I hope these Sherwood Tools are of use to viewers who are evaluating rigs. (They have been to me over the past two years of doing this research during which I’ve purchased two new HF rigs.) Making a written set of must-have features is a critical complement to these tools. Just like Smokey the Bear says: only you can put out forest fires. Only you can determine the feature-set and ergonomics to satisfy your use-case for a new radio!

I’m outlining a talk on the use of these tools should clubs wish me to visit with them via Zoom. See my contact tab above. I’m good on QRZed.

One of the most valuable tools for amateurs worldwide to use when evaluating HF rigs is the set of bench tests that Rob Sherwood NC0B has provided for quite a number of years now. He ranks the receive tests by his favorite metric: narrow dynamic range in dB. It’s a key for CW contest operators (pun intended) which he is in spades. But it is a frequent question from readers of Rob’s table: why can’t I sort it on another criterion? Especially if I’m not a CW contest operator?

Well, now you can! Working directly with Rob NC0B, I’ve taken his latest receive test data and made a sortable table for the Sherwood Test Results. They are circa March 5, 2022. It’s at my companion site, foxmikehotel.com at this link. I plan to update it when Rob adds new radios to his Table.

I’ve also added sub-pages to illustrate some facets of the data. Based on my work over the past couple of years with adding price and consumer satisfaction data for each rig in his Table, I’ve learned that it’s important for readers to better understand both Rob’s tests and his ranking metric. In that research published in the ARRL’s National Contesting Journal, I created a composite of all nine of Rob’s bench tests which I called the Sherwood Performance Index (SPI). It is a broader assessment of receive performance than the narrow dynamic range. But it is not intended to be a replacement for Rob’s preferred metric, only a complement.

Thus far, I’ve added two interactive charts that will help the viewer better understand Rob’s table results. More may come.

One chart shows how the reader can “out-rank” themselves by ONLY focusing on how a rig is ranked on the narrow dynamic range measurement. Rob tells readers not to take the exact ranking as the only aspect of a rig for the top ten rigs are all very good on receive. This interactive graphic will allow the viewer to see how some rigs “bunch” together with almost identical narrow dynamic range but are, indeed, sequential ranked because of numerical differences that simply do not make much difference as realized in the rig’s actual performance. But, ever hear an athletic team cheer this after a game? We’re Number 10! We’re Number 10! I didn’t think so. But Number 10 might be just as good as Number 1 on the metric determining the ranking. You have to look at the data behind the ranking. This chart makes it easy.

A second chart demonstrates how Rob’s ranking variable, narrow dynamic range, relates to the composite SPI. You’ll find some interesting results from that chart, seeing how narrow dynamic range is important but there is more to some rigs than that. Especially if you’re not a contest operator, CW or otherwise.

As he has stated in various podcast interviews (including mine on the ICQ Podcast and recently on the Ham Radio Workbench), he started these bench tests for his own use as a CW contest operator. Rob disagreed with the ARRL’s tests as published in a review of the classic Drake R-4C receiver. So he created what he thought was a suite of appropriate bench tests. And the rest is history. For transceivers and receivers (“rigs”) over a 50 year period!

Here’s a trend line for the SPI by year over the horizon of rigs in his Table, circa November 2019. We are in the best period yet for receive performance in terms of Rob’s test suite. But now you can sort the Sherwood Table on any of his tests including the composite SPI that I added to asses your rig of choice.

Rob codes his website in conventional HTML. He recently had to suddenly change hosting providers. So he’s had enough on his plate with all of the other engineering contributions he makes almost daily to various email lists and groups. So while he could alter the HTML code to provide the ability to sort his table, I appreciate his spending his retirement time continuing to assist the amateur radio community as he does now. I hope that this offering of a Sortable Sherwood Table on my companion website will help the reader better understand this terrific tool as well as help Rob, too.

We hams often resort to the common claim to choke the “life” out of RFI on feed-lines or other wire carrying electrical current in our shack environment (and nearby) by using ferrite materials in various forms. So it’s just a reflex action to buy those ferrites to install or to make chokes. Wind-em tight. A lot. Pour on the ferrite beads. If one is good, five should be better, especially if they’re cheap. And we like cheap. Right?

Hardly! That jig can be terribly misleading, expensive or, heaven-forbid, make noise worse! That’s a jig that needs to be up.

We do it without knowing because of the genuflection to the folklore of the hobby. Without putting a meter to it to more fully understand just what the ferrite(s) we install are doing. And what we want them to do. But that is the dominant behavioral pattern of many ham operators. Add K4FMH to the list of guilty parties.

It is much easier with that handy-dandy NanoVNA that you got for not much money. IF you know how. Yes, you could read Dunsmore, Witte or Bonaguide & Jarvis. And you should. Or, have someone give you a more practical tutorial. That may well lead you to study the Masters of the VNA as shown below. As Lord Kelvin once said something like: it ain’t science if you ain’t measuring it. Sort of.

Definition of the jig is up: —used to say that a dishonest plan or activity has been discovered and will not be allowed to continue.

Merriam-Webster

It was an honor to get to do a sneak-peek at one of this weekend’s QSO Today Virtual Ham Expo talks on this very subject. Mark Smith N6MTS is giving a talk entitled, Measuring Common Mode Chokes Using a NanoVNA, at 8:00 AM – 9:00 AM: 1500 UTC, 15.08.2021. This talk is worth the price of admission alone if you work HF!

I found it highly engaging, practical, informative, and he’s got the plans to build a test jig (get my title now?) to measure your own chokes before just “hoping” they will do the trick. Mark plans to post those on the Ham Radio Workbench podcast website soon. There are a lot of what look to be great talks scheduled for this weekend. But I know this is one of them because I got the chance to see it already and to share comments with N6MTS.

After you watch Mark’s talk, take a look at one or more of the online NanoVNA groups I am a member of which are listed below. Very helpful and (most always) nice members. Then take a look at Bob Witte’s book if you’re not familiar with it. It’s the preferred gateway drug to the ones by Bonaguide & Jarvis then Dunsmore. Measurement is addictive. And there’s no Twelve Instrument path for withdrawal.

Cited Books:

The VNA Applications Handbook by Gregory Bonaguide and Neil Jarvis.

Handbook of Microwave Component Measurements: with Advanced VNA Techniques 2nd Edition by Joel P. Dunsmore.

Spectrum and Network Measurements, 2nd Edition by Robert Witte.

Online groups on NanoVNAs:

https://groups.io/g/nanovna-users

https://groups.io/g/NanoVNAV2

https://groups.io/g/nanovna-f

https://groups.io/g/nanovna-f-v2