I enjoy homebrewing, and when it was time to calibrate the Stockton Bridge for measuring forward and reflected power in my QRP rig, I realized that I didn’t have a set of mismatches that could be used for that purpose. A set of mismatches is also useful for checking an SWR meter, or a nanoVNA. There are off-the-shelf mismatches that you can buy to test your nano, but they do not provide the power handling capability that this design does.
If you would like to get started with PCB design, this might be a perfect project to begin with. I am not endorsing any particular PCB design tool that you might find online, but I have found that EasyEDA is easy to learn.
The mismatches that I describe here can be used for QRP. All resistors in the design are 51-ohms and 2 Watts. Since we are not using 50-ohm resistors, this will result in a small error. Also, the layout is distributed (spread out), and this will result in a bit of extra capacitive reactance for the larger mismatches. SMA connectors were chosen because all of the RF interconnections within my QRP rig consist of RG316 terminated with SMA connectors.
Figure 1 is the schematic of what was built. It seemed pretty easy to construct the mismatches from a single value of resistor, but there is nothing to stop you from building mismatches from one or two parallel values of different resistors. What I have here seemed like a good idea because it made calculations simpler, and it resulted in power-handling capability large enough for any QRP project that I envisioned. Values of 3.0:1, 2.5:1, 2.0:1, 1.5:1 and 1.0:1 were chosen as data points for the Stockton Bridge that I was calibrating. For continuous operation at 5W, a cooling fan is recommended, particularly for the 1.0:1 load bank as it has the fewest number of resistors.
Figure 1. A Simple Set of Mismatches. Use of a single resistor value, 51-ohms and 2 Watts throughout, makes construction easy and economical. Use of series and parallel combinations result in higher power dissipations. Please click on the figure to enlarge it.
Figure 2 shows the virtual 3-D layout as provided by the EasyEDA PCB layout tool. The tool shows you what you are going to get once the PCB is assembled. The EasyEDA library is extensive, and it provides additional capability to import manufacturer’s symbols and footprints not already in the library. Although this set of mismatches was built as a PCB, there is nothing to stop you from building the same design on a piece of copper-clad perforated board.
Figure 2. Calibration Mismatches 3-D View. EasyEDA provides a 3-D viewer so that you can see what the final product will look like before the PCB is fabricated and before the PCB is populated. The mismatch values are shown near the SMA connectors. Please click on the figure to enlarge it.
Figure 3 shows the shows the final product after PCB fabrication and population. It closely matches what is shown in Figure 2.
Figure 3. As-Built Calibration Mismatches. The actual PCB closely resembles the 3-D model shown in Figure 2. The overall dimensions of the completed board are 6.50” x 3.60” including the connectors. Please click on the figure to enlarge it.
S11 values for the mismatches were measured from 1.8 to 29.7 MHz and stored on an old MFJ-226 Graphical Analyzer. The values were converted to rectangular form in Excel spreadsheets to facilitate calculations. Smith Charts were also plotted. In order to make this article more concise, the Smith Charts are provided in the Appendix that follows.
If you would like the S11 data in the form of Excel, please contact me. The spreadsheets contain all of the formulas required to convert S11 magnitude and angle to other useful forms including S11 rectangular, impedance rectangular, impedance polar, VSWR and return loss.
If you would like the Gerber file for PCB fabrication, you may also contact me. I will not be providing any bare boards, although you may wish to pool a PCB order to distribute the shipping costs among a few hams. For the JLCPCB supplier, the minimum number of boards is 5.
No, I’m not talking about short people! I’m talking about hams who may not have tall trees or the capability to put up a tower on their property. I want to tell you about a fascinating antenna design – a low-profile, high-performance solution ideal for those of us who might be challenged by restrictive antenna regulations or limited space. I’m referring to the Magnetic Radiator, specifically the Multiple-U (MU) design detailed in this article. This clever design comes to us from the inventive mind of Paul D. Carr, N4PC (SK) who had a column in CQ Magazine many years ago.
Now, you might be thinking, “Another vertical antenna? What’s so special about this one?” Well, let me tell you. This isn’t your typical electric radiator. This antenna operates on a fundamentally different principle—it’s a magnetic radiator.
What does that mean? Electric radiators, like your standard dipole or vertical, generate a strong electric field close to the antenna, leading to ground losses and less efficient radiation. This design, however, focuses on creating a strong magnetic field, minimizing those losses, and improving efficiency. Think of it as radiating power through the earth rather than into it. Some key advantages of the MU design are:
Low Profile: The vertical elements are less than 0.1 wavelengths high, making it perfect for locations with height restrictions. We’re talking about an antenna that’s practical for even the most compact locations.
No Loading Coils or Radials: No need for cumbersome loading coils or extensive ground radial systems. This simplifies construction and installation considerably.
Efficient Radiation: The design promotes efficient radiation, even at relatively low heights above ground. This magnetic radiation pattern offers surprisingly good performance.
Good Bandwidth: The MU design offers good bandwidth, which is important for modern digital modes and for those who like to cover multiple frequencies in the same band without retuning.
The article provides details design specifications and construction guidelines for various bands, from 10 meters up to 160 meters, with diagrams to walk you through the process. It even offers adjustments for different antenna heights above ground.
Now, let’s be clear—this isn’t a magic bullet. The performance will vary depending on the specific location, and like any antenna, there will be some directional favoritism. In the examples provided, there is significant performance in a certain direction. However, the overall design offers impressive performance, considering its low profile and simple construction. Remember that the measurements presented are based on real-world testing, demonstrating its practical effectiveness.
If you’re looking for an efficient, compact, and relatively easy-to-build antenna that performs well for long-haul contacts, I highly recommend taking a closer look at the Multiple-U magnetic radiator. The provided charts and diagrams will help you determine your optimal design based on your specific band and location.
Back in the 1990s, I built this antenna on my four-acre property in Boulder, Colorado. Boulder County’s strict antenna regulations prevented me from using a tower despite having ample space. After extensive research, I chose this design and started with a 10-meter version, using readily available parts from my “junk box”—speaker wire and RG-59 75-ohm coax for the matching network. I improvised support using a nearby bush and my garden fence and constructed the antenna, including the spreaders, in under an hour.
Connecting my 50-ohm feedline to the quarter-wave 75-ohm balun, I was pleased to see my ATU quickly achieve a 1:1 SWR with minimal tuning effort—always a good sign. Using my old IC-745, I tuned into a busy pile-up on 10 meters. I cautiously sent my callsign, fully expecting nothing, especially with my low power output of only 100 watts. To my astonishment, the DX station from Malta immediately answered who was the reason for the pile-up.
This unexpected success initially left me stunned. After confirming the contact with a 59 report, he responded that my signal was 59+20dB at his location. I explained my simple antenna. He compared my signal to a friend’s using a 50-foot high tri-bander in Illinois, noting that I was significantly louder. Propagation undoubtedly played a role, but switching to my vertical antenna resulted in a noticeable decrease in his signal strength (about two S-units) – this proved to me the design was effective. I was hooked and decided to build a larger version for 80 meters.
Using four 25-foot supports, I constructed a much larger 80-meter version of the antenna, requiring approximately 530 feet of wire. Bamboo served as the spreaders, and a quarter-wave 75-ohm line provided the matching. I oriented the antenna east-west for broadside radiation. That evening, I monitored an 80-meter WAS net and was amazed by the clarity of the signals. Typically, 80 meters is noisy, but this antenna exhibited remarkably low atmospheric noise, a characteristic benefit of H-plane operation, which minimizes noise typically prevalent in the E-plane. The longer “skip” characteristic of this antenna meant that distant stations came in exceptionally well, making it ideal for DX but less effective for closer contacts.
I replicated the antenna design for another ham who wanted a directional antenna specifically for 17 meters. He lived in a trailer park with antenna restrictions, so we needed a lightweight, easily repositionable solution. We constructed two supports using PVC pipe, with a central section and two horizontal PVC spreaders at the top and bottom. To ensure stability, the base of the vertical PVC support was encased in cement, allowing him to easily adjust the antenna’s direction simply by moving the cement-filled buckets at the base of the supports, effectively changing the broadside direction as he desired.
The unexpected success of my initial 10-meter antenna, built from readily available materials and achieving exceptional signal clarity, fueled my curiosity for this simple yet effective design. The subsequent construction of larger versions for 80 meters and a modified model for 17 meters further confirmed its versatility and adaptability. These antennas, built to overcome challenging site restrictions, demonstrated the principle of H-plane operation in minimizing atmospheric noise while maximizing the reception of distant signals. The experience proved that resourcefulness, ingenuity, and careful design could significantly enhance signal quality in challenging operating environments.
You can learn more about magnetic radiator antennas here.
During our weekly Sunday night VHF net, a question arose about the National Institute of Standards and Technology’s (NIST) time and frequency station, WWV. Net Control asked, “When did WWV move to Colorado?” While a few of us could answer, it became clear that many of the newer hams didn’t know much about the WWV station.
Myself, being a ham from Boulder, Colorado and now living in Nashua, New Hampshire, I saw this as a great opportunity to share information I’ve gathered over the years, both about WWV’s operations in Fort Collins, Colorado, and its move from Maryland in 1966.
WWV Site – Fort Collins, CO
WWV is considered one of the oldest continuously operating radio stations in the United States. It was first established in 1919 by the National Bureau of Standards (now NIST) and originally broadcasted from Washington, D.C. Its primary purpose has always been to transmit accurate time and frequency signals, which it continues to do today from its Fort Collins, Colorado facility. WWV’s long history of broadcasting time signals makes it a significant part of radio history in the U.S.
Boulder, Colorado, is home to the NIST (formerly the National Bureau of Standards, or NBS) Atomic Clock, which serves as the time and frequency standard for the United States and many other countries around the world. I’ve had the opportunity to view the Atomic Clock “in person” at the NIST Laboratory.
The NIST atomic clocks use cesium atoms to keep incredibly precise time. Here’s a simplified explanation of the process:
Cesium Atoms: The atomic clock relies on the natural oscillation of cesium atoms. Cesium atoms absorb and release energy at a very consistent frequency when they transition between two energy levels.
Microwave Frequency: The clock generates microwaves that are tuned to match the exact frequency of the cesium atoms’ oscillation. The frequency at which cesium atoms oscillate is exactly 9,192,631,770 cycles per second.
Tuning to Maximize Accuracy: The atomic clock continuously adjusts the microwave frequency to ensure it matches the cesium atom’s resonance as precisely as possible.
Counting Seconds: By counting these highly accurate oscillations, the clock measures time. One second is defined as exactly 9,192,631,770 oscillations of the cesium atom.
Disseminating the Time: NIST broadcasts the official time using radio signals (via stations like WWV), the internet (through NIST’s network time protocol, or NTP), and satellite systems. These signals help synchronize clocks around the world.
NIST’s time standard is crucial for GPS systems, telecommunications, scientific research, and other industries that require precise timekeeping.
In 2013, when I was serving as the ARRL Colorado Section Manager, we hosted the Rocky Mountain Division Convention (Hamcon Colorado) in Estes Park, Colorado. Given its proximity to the WWV radio complex in Fort Collins, our committee thought it would be a great opportunity to arrange a tour for interested hams. Since WWV is a secure government facility, we needed special permission. The WWV Chief Engineer, who was also a ham, informed us that they had never conducted a tour before and it might be impossible, but he would ask. To our surprise, permission was granted with some necessary security measures in place. Interest in the tour was high, and we chartered a school bus to take a large group of hams to the facility.
10 KW – 5 MHz WWV transmitter
The engineers at WWV went above and beyond, providing a comprehensive tour of the facility that included fascinating historical devices. We were able to visit the antenna sites and transmitters, with detailed explanations of their operations.
Historically, amateur radio operators played a key role in the technical development of the atomic clock and the WWV radio stations from their earliest days. Given that the atomic clock is housed in Boulder, CO, many members of the Boulder Amateur Radio Club (BARC) were among those who contributed to its development and advised on the WWV operations over the years.
Yardley Beers, W0JF
ne of the more notable BARC members was Yardley Beers, WØJF (formerly WØEXS and W3 AWH), who earned his MS in Nuclear Physics in 1937 and a Ph.D. in 1941 from Princeton University, where Einstein was in residence at the time. Beers was a pioneering scientist who first utilized cesium as the core of the aforementioned time standard oscillator. He was a dear friend whose boundless curiosity, humor, and deep expertise in all things radio-related made him a wealth of knowledge for our club.
At 0000 GMT on December 1, 1966, the veteran time and frequency station WWV in Greenbelt, Maryland, shut down permanently. Almost simultaneously, a new station with the same call letters and services began broadcasting from Fort Collins, Colorado. The decision to construct the new station and relocate was driven by several factors, primarily the obsolescence of the old facility and significant maintenance challenges.
WWV 15-meter antennas
In contrast, the new station utilizes the latest transmitter designs, offering significantly more efficient operation. The setup also provides greater flexibility, as the transmitters consist of identical units—except for some higher-powered transmitters, which include an additional amplifier stage—that can be tuned to any frequency. At the old station, only a few of the eight transmitters were identical. Unlike the old transmitters, the new ones apply modulation at low levels, with all subsequent stages maintaining precise linearity. This allows for a wide range of modulation options, including AM or single sideband, with either sideband and any desired degree of carrier suppression. These features mirror those found in modern amateur radio transmitters.
Lastly, the move brings the benefit of administrative efficiency. WWV is now co-located with two other NBS standard frequency and time stations, WWVB (60 kHz) and WWVL (20 kHz), at the same site. Additionally, it is more convenient to synchronize the station with the NIST atomic standards, which are based in nearby Boulder, Colorado.
WWVH began operation on November 22, 1948, at Kihei on the island of Maui, in the then
territory of Hawaii (Hawaii was not granted statehood until 1959). The original station
broadcasts a low-power signal on 5, 10, and 15 MHz. As it does today, the program schedule
of WWVH closely follows the format of WWV. However, voice announcements of time
weren’t added to the WWVH broadcast until July 1964. In July 1971, the station moved to its current location, a 30-acre (12-hectare) site near Kekaha on the Island of Kauai, Hawaii.
Today, the methods for calibrating frequency, synchronizing time, and assessing propagation have evolved significantly due to advances in technology, though some traditional methods (like using WWV) are still in use. Here’s a comparison of how these tasks were done in the past versus how they are typically done today:
1. Frequency Calibration
Before (Using WWV and Manual Tools):
WWV Broadcast: Operators tuned their radios to the exact frequencies broadcast by WWV (e.g., 5, 10, or 15 MHz) to verify or adjust their frequency dials
.Signal Comparison: Operators might use frequency counters or calibrate their equipment using signal generators. By manually adjusting their radio to match the WWV signal, they ensured their equipment was tuned correctly.
Crystal Oscillators: Some radios used quartz crystal oscillators that needed periodic manual adjustments to maintain frequency stability.
Today (Using GPS, Software, and SDRs):
GPS Disciplined Oscillators (GPSDO): Modern radio equipment can be calibrated with GPS, which provides ultra-precise time and frequency data directly from satellites. GPSDOs lock the radio’s oscillator to the exact frequency provided by GPS signals.
Software-Defined Radios (SDRs): SDRs can automatically lock to known reference frequencies or signals, often bypassing the need for manual calibration.
Digital Frequency Counters: High-precision digital frequency counters, often built into modern equipment, can accurately verify a station’s frequency without the need for an external signal like WWV.
2. Time Synchronization
Before (Using WWV or Manual Clocks):
WWV Time Signals: Operators would listen to WWV’s hourly time announcements and manually synchronize their clocks to the audio ticks or the minute mark. This ensured they had the correct Coordinated Universal Time (UTC) for logging contacts.
Mechanical or Quartz Clocks: Station clocks were either mechanical or quartz-based, requiring manual adjustments for drift.
Today (Using NTP and GPS):
Network Time Protocol (NTP): Computers, logging software, and transceivers are often synced to the Internet time servers using NTP, which automatically keeps time to within milliseconds of UTC. Many hams now use computers with built-in NTP syncing for contest logging and communication accuracy.
GPS Time: GPS provides highly accurate time synchronization. Many modern radios or station computers are connected to GPS receivers that provide time directly to within a fraction of a second of UTC.
Atomic Clocks: Although not widespread in amateur radio, some operators use atomic clock-based devices for extreme precision in timekeeping, often integrated with GPS.
3. Propagation Monitoring
Before (Using WWV and Beacons):
WWV Propagation Monitoring: Hams listened to WWV signals on different frequencies (2.5, 5, 10, 15, and 20 MHz). The strength of the signal provided a rough estimate of how well certain bands were propagating, helping operators decide which frequencies to use.
Beacon Stations: Operators tuned to beacon stations operating on different frequencies around the world. By monitoring when these signals were heard, they could get a sense of global propagation conditions.
Sunspot Numbers: Many hams used published sunspot data and predictions to estimate the effectiveness of different HF bands.
Today (Using Online Tools and Real-Time Data):
Real-Time Propagation Maps: Websites and apps like PSKReporter, DXMAPS, Reverse Beacon Network (RBN), and WSPRnet provide real-time data on where signals are being received and which bands are open. These platforms track signal reports and provide a visual display of current propagation conditions.
Solar and Geomagnetic Data: Many hams now use online services that provide real-time solar flux, geomagnetic indices, and space weather data. Websites like Space Weather Prediction Center (SWPC) offer detailed insights into how solar activity is affecting the ionosphere.
Cluster Networks: DX cluster networks provide real-time information on stations spotted around the world, giving hams direct feedback on current band conditions.
Software Tools: Advanced propagation software like VOACAP or HamCAP allows operators to model HF propagation based on real-time data, including solar activity, time of day, and location.
Summary of Key Differences:
While older methods like WWV are still valuable, modern technology has automated and refined many of these tasks, making it easier and more precise for amateur radio operators to ensure their equipment is accurate and their communication effective.
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Figure 1. A Simple Set of Mismatches. Use of a single resistor value, 51-ohms and 2 Watts throughout, makes construction easy and economical. Use of series and parallel combinations result in higher power dissipations. Please click on the figure to enlarge it.
Figure 2. Calibration Mismatches 3-D View. EasyEDA provides a 3-D viewer so that you can see what the final product will look like before the PCB is fabricated and before the PCB is populated. The mismatch values are shown near the SMA connectors. Please click on the figure to enlarge it.
