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Nashua Area Radio Society Field Day 2022

August 1, 2022 Nashua Area Radio Society

Nashua Area Radio Society Field Day 2022

Field Day 2022 is over, creating great memories for all who joined us. We have 47 names on our guest log, including members and visitors. Add to that number our helpful volunteers, and over 70 people participated in Field Day with us. This year we returned to Hudson Memorial School, the site of some of our most ambitious past Field Days. Our current effort was more modest, we would be class 3A, with four radios and antennas to cover 6, 10, 15, 20, 40, and 80-meter bands. Our primary tower was 40 feet tall and held a tri-band Yagi and two dipoles, one each for 40 meters and 80 meters. For 6 meters, we had a loop-fed array on a push-up mast. All of our radios were configured to support all modes, SSB, CW, and Digital. Each station incorporated a laptop PC to run our logging application and support digital modes.

Planning

Our Kick-Off Meeting for Field Day was on March 9. There is lots of planning and training to do before the day of the event. Many of our volunteers have participated in Field Day with the club in past years, but this year some of them would become the leaders of their teams for the first time, myself included. Fred, AB1OC, and Anita, AB1QB, would represent the ARRL in their new roles during Field Day and leave their past roles in NARS Field Days for other members to fill. I volunteered to lead the effort this year, and both Fred and Anita generously gave their time and advice to our team to assist with planning and training for the event.

My first efforts went towards finding a group of volunteers who would commit to the project and to securing a venue for the event. In recent years we had successfully held Field Day at Keyes Memorial Park in Milford, NH, but this year it was booked for Field Day. We also had great success with Field Day at the Hudson Memorial School in Hudson, NH so I inquired with them about returning to their site. The school is a friend of NARS, we have done many activities with them, including an ARISS contact, so they made it easy for us to engage and obtain approval to use their field. Special thanks to Principal Keith Bowen for making this painless.

The Field Day 2022 Teams

We had 20 members volunteer to support our Field Day effort from planning in the beginning to putting the last bit of gear back into storage on Sunday night after the event. Other members assisted as they could during planning or the during the event itself. While NARS owns a lot of the gear we used for Field Day, we do not own any radios or peripherals. We are very fortunate to have members who generously lent their radios and other gear to the cause. In our first few planning meetings, we took stock of our team’s skills, experience, and preferences and sorted ourselves into functional teams. We were fortunate that each team leader had the basic skills and experience needed to assume their role. We would arrange training where needed and documentation from past field days to take advantage of hard-won knowledge from past efforts. The teams broke down as follows:

Transport Team

NARS has a storage trailer where we keep all of our gear that does not require a climate-controlled environment. Much of this gear is only used for our Field Day activities. On Field Day, our day begins here, the Transport Team gathers, and the other Team Leads make sure that all of the material they will need at our Field Day site is loaded onto the trucks. We are fortunate that we have many members with pickup trucks, and we also have a number of trailers available. We spent around 2 hours at the trailer on Friday morning loading the trucks with our gear. This year our Field Day site was only a 15-minute drive from our store. Murphy loves Field Day, so we did make a return trip to the trailer to pick up additional material before the day was done.

Once we arrived at Hudson Memorial School, we were able to unload and stage our equipment on the field prior to beginning setup. Most of the team members from the other functional teams were there to assist, and the job was done very quickly.

Shelter Team

On March 15th, 7 members of the Nashua Area Radio Society met at BOB, our storage location for club gear, to do an initial gear test and evaluation to begin our hands-on preparation for Field Day.

This gave the Shelter team a chance to set up all of the tents we would use and confirm that everything was in order and identify any gaps. We also inventoried tower and antenna components to prepare for future training. A more detailed article about this is here:

Gear Test and Evaluation for Field Day 2022 – Nashua Area Radio Society (n1fd.org)

Tower Team

As we met each week and worked out our upcoming tasks and responsibilities, we also uncovered areas where we needed to fill gaps in knowledge and skills.

One such area was in the Tower team. Everyone on the Tower team had experience from past Field Days, but all had worked under a team leader who was no longer going to be active with us in our efforts this year. Fred, AB1OC, led the team in the past and offered to provide us with hands-on training for erecting the tower and antennas in May. This would give us the perfect opportunity to actually raise the tower, assemble the antennas and confirm that we had all of the assembly steps properly documented and that we had all of the required parts and materials available as well. We met at BOB on May 11 and had a full-scale dress rehearsal for the Tower and Beam teams. You can read about this event in this article:

Hands-On Tower and Beam Antenna Training for 2022 Field Day (n1fd.org)

Beam Team

The Beam Team is responsible for assembling the antenna and making sure it is properly in tune for each band prior to raising the tower. Our antenna is from 2014 and has been assembled and disassembled many times over the years. There are many small parts, so the team performs the assembly on sawhorses placed on tarps. This allows for easy retrieval of any parts that may drop during assembly. When the beam is completed, they sweep it with an SWR meter to confirm it is in proper tune. This beam antenna covers 10, 15, and 20 meters.

Once tested, the assembled antenna is carefully mated to the mast on the tower and the coax is attached.

Station Team

The Station Team also had a complex task to complete. As a 3A Field Day station we would have 4 radios in operation. We were going to have each radio setup in a separate tent with a laptop computer for logging and digital modes, and a Winkeyer and paddles for CW. Each radio is limited to specific bands and the coax to the antennas would be routed through band pass filters and/or a multiplexer and antenna switch on the way to the relevant antennas. Figuring this out on the day of the event was not an option, so we planned on creating a full-scale test setup of the configuration prior to the event. I had experience with this area and had been a station master in a past 14A Field Day with NARS so could help out. Joe, AC1LN volunteered to lead the team and Lee, KC1GKJ joined in to assist. We were able to consult with documentation created in past years and that formed a good base of knowledge for us. We arranged with Fred, AB1OC to have a focused training at his QTH for some of the details of setting up the IC-7300 radios, N1MM+ logger and WSJT-X software along with the Winkeyers and paddles. The goal of that training was to properly configure one radio and laptop and use that setup as a reference to roll out to the other radios. Shortly before the training, I caught Covid-19 and could not attend. Joe and Lee worked with Fred and accomplished the initial goal of setting up the first radio.

Joe volunteered to do the trial setup at his QTH and was able to set up an area in his basement that we could work in. We were able to gather the gear we would borrow for the event and set it all up in the test lab at Joe’s. Thanks to Fred AB1OC, Lee KC1GKJ, Jamey AC1DC, Jack WM0G, Dave K1DLM, and Jon AC1EV for generously loaning their gear to the cause.

Joe, Lee, and I took multiple passes at completing the full setup of the IC-7300s along with the laptops and software to get everything configured properly. There are levels and levels of settings to manage, and we were able to get them ready in advance, so set up at Field Day was just a matter of assembling all of the labeled components. We used the Super Antenna MP1, seen in the background for testing on 20 meters, and Jerry AE7KI, an old friend from Tennessee, gave us an excellent report.

Media, Publicity, and Food

While all of the above activities were underway, John W1SMN was working behind the scenes to promote our Field Day activity. He worked to contact various government officials, news media, and others to invite them to join us on Field Day. He also worked with local businesses to obtain support from them for our efforts. Here are the major donors to our event.

Sponsors on Food Tent — Sponsors of Food Tent

Nashua Area Radio Society is grateful for the support from these businesses, and we presented a certificate of appreciation to each of them to say thank you for supporting us.

Here John W1SMN and I present Bill Wilson, owner of Donna’s Donuts in Tewksbury, MA, with a certificate of appreciation from the club.

Ready to begin

Here is a diagram of our proposed setup at Hudson Memorial School in Hudson, NH. We have done much larger Field Days here in the past, even as large as 14A, so there is plenty of room for our setup this year. As you can see from the following pictures, we were able to make the diagram above into a reality.

Operating

This year NARS is operating in class 3A. This means we are a club and have 4 radios. In addition to our 4 radios that can contribute to our QSO count, we also had another radio setup as a GOTA station. GOTA stands for Get On The Air. This station allowed our visitors to make contacts and join in the fun. No license is required as there is a Control Operator present under whose authority the visitor can operate.

Some of our members came with their children and they were very enthusiastic about making contacts. Day or night, the GOTA station had lots of use. Each GOTA operator received a certificate to commemorate their participation.

Club members also operated day and night. Each station was configured to cover all modes, so the operator could choose from Phone, CW, or Digital modes. To maintain social distancing in this time of COVID-19, we only had one radio per tent. Here is how each tent was setup. We had an IC-7300, power supply, Winkeyer, paddles, laptop, mouse, and external monitor. The laptop was connected to the IC-7300 and was running N1MM+ and WSJT-X software. All Laptops were networked together including a 5^th laptop in our information tent, so we could track our cumulative QSO score in real time.

This being Summer Field Day it was hot during the day. Propagation was good at night, so we had many members operating at that time. Each operating station included a fan and light so we could see what we were doing and stay cool.

Field Day operations last for 24 hours and after that it is time to break down the setup and return everything to its place. We learned in past years that effort spent during this time to stay organized pays extra dividends next year when we do it all over again. Our members really put in extra effort for this, after a few long hot days and even with everyone tired from Friday and Saturday’s work, had enough energy and effort to complete the task. From the end of operations at 2:00 PM on Sunday to the last items stored at BOB and the 6-meter antenna and mast returned to Hollis only took around 4 ½ hours. There are a dozen people in this picture helping with breakdown and others out of view.

Field Day 2022 – How Did We Do?

Lots of people had loads of fun! In addition to operating the radios we also learned from every aspect of the event. Field Day is a complex endeavor; we began planning in March and acquired new skills as we progressed towards the day of the event. We worked together and depended on each other. We shared our skills and now those skills are an asset to the club. This year we took training on things we didn’t know and next year we may give training in those same areas to others who follow us. Experienced Hams know that Field Day isn’t a contest, but we do keep score! Here are some of our stats.

Summer Field Day is the highlight of the year for many hams. It is a big part of the history of the Nashua Area Radio Society. It is also a lot of work. When I first joined NARS as an inexperienced ham, I witnessed a very ambitious FD effort with 3 40’ towers, a 60’ tower, a 40 meter V Beam, VHF, and satellite antennas as well. I was very impressed and decided that I wanted to participate in the event the next year. The following year, the club had a similar effort, I think it was 14A and our score reflected our size. Since then, with Covid-19 restrictions and changes in club membership we scaled back our operation. We are fortunate that many of the volunteers who participated this year had experience in past years and were able to assume leadership roles. Our new members are now experienced too, and the club will benefit from the expanded skill sets of its members. We all had fun and working together has given many of us the basis for lasting friendships. We will take advantage of this year’s event to learn from it and apply those lessons to next years Field Day. That’s it for now, 73 and best wishes from

Jon AC1EV

Antennas, Featured, General, Newsletter

Differential and Common Modes on Transmission Lines – Part I

July 25, 2022 Martin Blustine

Introduction

In Part I of this three-part series, we discuss what is meant by differential and common modes on RF transmission lines. Part II will discuss the construction of the Joe Reisert, W1JR, 1:1 balun [1] that may also be used as a common mode choke. Part III will present some test results for the common mode rejection of two common mode chokes, one constructed with #31 ferrite material and another constructed with #43 ferrite material.

Differential Mode

Two familiar balanced transmission line types that will support differential mode operation are open wire line and waveguide. This section will focus on open-wire lines. An ideal model of an open-wire line is shown in Figure 1. Current from the transmitter or other matched source enters the transmission line from the left. The transmission line may be thought of as an infinite number of distributed inductors and capacitors. Each infinitesimal length of the transmission line is made up of two tiny inductors, and each infinitesimal pair of lines forms a capacitor between them. All transmission line types, not only open wire lines, are characterized by values for inductance per unit length and capacitance per unit length.

Figure 1 Idealized Model of Open Wire Transmission Line. An open wire transmission may be modeled as an infinite number of distributed inductors and capacitors.

In reality, the conductors will have a resistance per unit length. If there is a dielectric present, as there might be in a window line, twin-lead or open wire line (the dielectric would be the spreaders and air), there will also be a leakage conductance through the dielectric between the conductors.

Consequently, all transmission lines are characterized by an impedance, Z_0, that is defined by,

where,

Z₀is the characteristic impedance in ohms

R is the resistance of the wire per unit length

G is the leakage conductance through the dielectric per unit length

L is the inductance of the transmission line per unit length

C is the capacitance of the transmission line per unit length.

Years ago, it was quite common for roof-mounted television antennas to be fed with 300-ohm twin-lead. Twinlead is a parallel wire transmission line in which the conductors are spaced apart with plastic dielectric. The dielectric fills very little of the volume around the conductors. There is just enough plastic to cover the conductors and space them a small distance apart. Consequently, twin-lead will be treated as though it were an open-wire line. If we assume that the resistance of the wire and the leakage conductance are negligible, we can make the approximations that,

As a result, the impedance of the transmission line may be simplified to,

By making further approximations that the wire diameter, d, is much smaller than the center-to-center spacing of the conductors, D, and that the value of the dielectric constant filling the volume around the conductors is close to unity,

it is possible to approximate the values of L and C from,

where,

and,

where,

from which we get,

Furthermore,

Thus,

Substituting the numerical values, we have,

So, by making reasonable approximations, our estimate is very close to 300 ohms.

When driven by and terminated in its real, characteristic impedance, the currents and voltages anywhere along the open wire transmission line will be mostly uniform. Assuming that the wire transmission line is well made, dissipative losses in the conductors and leakage conductance will account for any nonuniformity. Since the currents in the transmission line conductors are equal and travel in opposite directions, the transmission line is said to be operating in differential mode. Simply stated, the transmission line operates in a single mode, and what you put in one end is mostly what you get out of the other end. The transmission line will not radiate signals, nor will it receive signals and noise.

Figure 2 is greatly oversimplified, but it is adequate to explain what is meant by differential mode. We note that if we take a snapshot of the currents on each half of the dipole, i_1, and i₂, they are in the same direction as are the currents, i₁ and i₂, in the open wire transmission line. From this, we may conclude that the transmission line is operating in differential mode while the antenna is operating in common mode, and that is what is causing the antenna to radiate RF in the first place. At least for this case, we have demonstrated that we may associate common mode currents with antenna radiation (and reception, too).

Figure 2. Balanced Open Wire Transmission Line Feeds a Dipole Antenna. The unbalanced transmitter or transceiver is transformed to a balanced transmission line with a balun. The transmission line operates in a single, differential mode because the currents are opposite while the antenna operates in a common mode because the currents are in the same direction.

Common Mode

For completeness, let’s begin by calculating the characteristic impedance of an unbalanced coaxial transmission line. Coaxial cable was first employed to prevent interference between transmission lines in transatlantic cables used for telegraphy prior to 1860. It was Oliver Heaviside who first described its theory of operation.

Let’s determine the characteristic impedance of RG-400/U since our common mode chokes were constructed using this type of coax. RG-400/U was chosen because of its high power handling capability and small outer diameter. If the inner diameter of the coax shield is much greater than the diameter of the center conductor,

where,

d is the diameter of the coaxial transmission line center conductor
D is the inner diameter of the coaxial transmission line shield,

the inductance per unit length and capacitance per unit length for coaxial cable are approximated by the formulas,

where,

from which we obtain,

As before,

Substituting the numerical values, we have,

Again, reasonable assumptions lead us to the expected result.

When we speak of common mode for transmission lines, we are discussing signals that may enter or leave the conductors in the same direction. The most common cause of common mode current is an unbalanced transmission line. Imagine, if you would, a dipole antenna being fed by the coaxial transmission line of Figure 3. The currents inside the coax will be opposite. Now, suppose that the currents in the coax reach the antenna. If we take a snapshot of the currents on each half of the dipole, i_4, and i₂, they correspond to the directions of the currents, i_3, and i₁, on the inside of the transmission line (but not their amplitudes). From this, we may conclude from the currents on the antenna that the antenna operates in common mode, as before.

However, we also notice that there are currents, i₅, on the outside of the coax shield and the current, i₁, on the center conductor that are in the same direction. These currents operate in common mode. The outside of the coaxial cable shield operates as a single conductor transmission line, a distinct mode. This mode operates separately from the mode represented by currents i₃ and i₁, which operate in, essentially, differential mode. Thus, we have a transmission line system that operates in two distinct modes. The outer cable shield will radiate upon transmit and will be susceptible to receiving signals and noise upon receive.

Figure 3. Common Mode Currents on Unbalanced Coaxial Transmission Line. Because of its construction, there is no way to keep the current i₃ from dividing into currents i₄ and i₅. Since currents i₁ and i₅ are in the same direction, they operate in common mode. Since the currents i₁ and i₃ are in opposite directions, they operate in differential mode. Thus, we have a transmission line system that operates in two distinct modes. The common mode conductor will radiate and also be susceptible to receiving signals and noise.

To reiterate, since one side of our dipole antenna is connected to the shield, any current that is traveling inside the shield may split between the antenna and the outside of the shield. In this configuration, there is nothing to stop this from happening. Now, we have a center conductor and the outside of the shield acting like a pair of conductors with currents traveling in the same direction. This is very much like a single wire transmission line, and the outer shield will radiate and receive power quite nicely in common mode. Another observation is that the currents on the antenna halves are asymmetric, and this asymmetry will corrupt the antenna pattern. Notice that the current on the outer shield may be returned to the chassis of the transmitter. This can become very unpleasant for the operator.

A remedy for this is to convert the unbalanced coaxial line to a balanced line where it feeds the antenna and provides a means to suppress current i₅. This is done with a device called a choke balun (balanced-to-unbalanced). The choke balun effectively disconnects the inner shield from the outer shield so that most of the current will no longer flow on the outer shield. Can there still be common mode currents on the coax? The answer is yes. The shield can still couple some of the antenna’s radiated emission back to the shack, or signals and noise on the shield may originate from elsewhere. Either or both may occur because it’s not unusual to place a choke balun at the feedpoint of the antenna. RF can still couple to the coax beyond where the choke is located. For this reason, it is not unusual to place another choke at another current maximum on the coax outer shield where it may be effective and at a location that is close to the entrance to the shack. This point on the transmission line may be found with a clip-on antenna current probe like the MFJ-854 [2], or by modeling the antenna in something like EZNEC [3]. It is incorrect to assume that the placement of a common mode choke is arbitrary. If we want the common mode choke to work, it should be located near a voltage null on the outside coax shield. Another effective way to reduce the common mode signals and noise on the outer shield from reaching the shack is to bury at least some of the coax.

Baluns may be constructed from sections of coax or from wire or coax wrapped on ferrite cores. Baluns constructed from coax alone, rely upon the electrical length of the coax to work, so they tend to be narrow band. Baluns constructed from coax are more practical for UHF and VHF because of the short length of transmission line required. Coax baluns do not possess the same choking properties that ferrite baluns have.

Part II of this three-part series will discuss the construction of a Joe Reisert, W1JR, 1:1 balun that may also be used as a common mode choke.

References

Reisert, Joe, Simple and Efficient Broadband Balun, Ham Radio, September 1978, pp. 12-15. https://worldradiohistory.com/Archive-DX/Ham Radio/70s/Ham-Radio-197809.pdf
https://mfjenterprises.com/products/mfj-854
https://www.eznec.com/

Antennas, Featured, General, Newsletter

DIY 6m Moxon Antenna

July 17, 2022 Aron Insinga 1 Comment

The ARRL book Magic Band Antennas for Ham Radio by Bruce Walker N3JO has the plans for a 6m Moxon Antenna that I found interesting because, instead of wire or tubing, it uses 3/4″x1/8″ aluminum stock available in hardware stores in 4′ or 8′ lengths. No bending, just drilling! I’ve worked on it bit by bit over the last few months or so, and the CQ VHF contest this weekend gave me the extra push I needed to get it up into the air!

I got 8′ sections of the aluminum stock, but I cut the center of the parasitic element (the longest piece) into 2 pieces of less than 4′ each, in case I want to pack the antenna into a car.

The boom is PVC pipe, and for the spacers between the active element and the parasitic element, I used a 1-1/2″x3/4″ vinyl substitute for wood used for trim, which is also available in hardware stores. I cut it down to 3/4″ wide strips for the insulators between the ends of the elements. Unlike the book, I used the full width to attach the elements to the boom so that the U-bolts could be attached beside, instead of under and through, the elements. (It was not at all clear to me from the book’s drawing — no photographs — how the parasitic element was attached to the boom given the bolt positions as drawn. Also, I may have misunderstood if the author meant 1″ ID or 1″ OD pipe; since it is Pipe, I assumed it was ID.)

I made a coil balun as described in the book, and the UHF connector is mounted on a right-angle piece of plastic cut from an inexpensive outlet box which is a trick suggested in the book.

I put Noalox on the stainless steel nuts and bolts to prevent them from “welding” themselves together and also to protect the aluminum from the stainless steel.

I changed my ideas on how to get it up into the air a couple of times, and today I finally just went and got an MFJ-1911 lightweight fiberglass mast and a set of MFJ-2830X guy rings at our local “candy store.” (I wish there were a ring in the set with an even larger center hole.) I did not extend it to the full 20′ (yet, anyway) because I was concerned that the antenna was too heavy, so it is only about 14′ up in the air now.

I used hose clamps (threaded through a water drain tube, so the clamps don’t cut into the mast) above each exposed joint in the mast to give added protection against the “twist lock” mast unlocking and collapsing into itself. I put another one around the base with loops of paracord through it that I can hold down with tent stakes, in addition to putting the base of the mast against one of the raised garden beds to keep it from slipping. (I’m sorry, I don’t recall which video blogging ham I learned those hose clamp tricks from.)

The 6m Moxon Antenna ended up being tilted slightly (actually, rotated around to be almost upside-down!), but I’ve got some U-bolt saddles on order to fix that. (They’ll be the two pieces of metal besides the aluminum elements that aren’t stainless steel. Unfortunately, I used a smaller size U-bolt than what seems to be the “standard” for antenna masts of about 2″ inside diameter for the U-bolts.) I made an extension that screws in above the vertical piece of PVC pipe through the boom so that I could add support ropes for the insulators far out from the center of the antenna, but I haven’t put it on yet to save weight. (I may replace the mast with a heavier-weight product from MFJ to allow this and to raise it higher.)

As you can see below, the minimum SWR is 1.0 at about 52,140 MHz, not the point in the 6m band where I would like it for FT8, but at least it is in the lower half of the band. (I haven’t thought about how to tune it or if I need to. But I do know that I want to replace the thin coax feeding the antenna now with LMR-400.)

SWR curve hitting 1.0 at about 52,140 MHz

With much-appreciated help from my XYL Merle W1MSI, I was able to get the DIY 6m Moxon Antenna up late this afternoon and try it out before the band closed for the day. The “magic band” did what it does, and I was able to make 27 QSOs on VHF with FT8, from my shack in FN42 (southern New Hampshire) to as far as EL98 (Florida) and EN52 (Wisconsin). So I think the antenna is working pretty well. It is the first beam antenna at my shack.

For a while there, I was happily collecting DXCCs and US states on HF with SSB, but then I discovered FT8, and after that FT4, and now I’ve got grid squares to collect on VHF — so I have even more paper to chase!

Aron, W1AKI

Nashua Area Radio Society Field Day 2022

Planning

The Field Day 2022 Teams

Transport Team

Shelter Team

Tower Team

Beam Team

Station Team

Media, Publicity, and Food

Ready to begin

Operating

Field Day 2022 – How Did We Do?

Introduction

Differential Mode

Common Mode

References

Radio Amateurs Developing Skills Worldwide