8o meter 8 element Sterba Curtain @ 200 feet
- skylarkcolo
- Dec 26, 2022
- 5 min read
Updated: 1 day ago
Roy W7YRU had a 8 element full size Sterba Curtain at 200 feet in AZ,
http://w7yrv.blogspot.com/2013/10/8o-meter-8-element-sterba-cutrtains-on.html
He also had six 20 meter sterba curtains at 120' high in
12 directions
The Sterba Curtain Array (invented by Ernest J. Sterba in the 1930s for Bell Labs) is one of the most powerful, high-gain directional wire antennas ever conceived for high-frequency (HF) communication. This innovative design has played a significant role in advancing radio communication technology, particularly during a time when effective long-distance communication was crucial for both military and civilian applications. The Sterba curtain antenna is renowned for its ability to provide enhanced signal strength and clarity, making it an invaluable tool in various communication scenarios.
Unlike the rhombic antenna—which projects its signal along its horizontal length—a Sterba curtain is a broadside array. It hangs vertically like a massive curtain between two or more masts and beams its energy perpendicular to the plane of the wires. This unique configuration allows the Sterba curtain to achieve high gain in a specific direction, significantly improving transmission and reception capabilities. The design consists of multiple parallel wires that are carefully spaced and tuned to optimize performance across a range of frequencies, particularly in the HF band where atmospheric conditions can greatly affect signal propagation.
The Sterba curtain's construction typically involves a series of vertical wires supported by a framework that maintains their alignment and tension. This setup not only enhances the antenna's durability but also ensures that the radiating elements are positioned optimally to maximize their effectiveness. The antenna's ability to focus energy in a specific direction makes it particularly advantageous for point-to-point communication, where clarity and distance are paramount. Furthermore, the Sterba curtain can be designed to operate effectively in various environments, adapting to the specific needs of the user, whether for amateur radio, military operations, or other applications requiring reliable HF communication.
Many people mistakenly refer to the HRS, USIA, or Distribution fed curtains as a Sterba or Bobtail Curtain. These are not the same. A Sterba doesn't even achieve 25% of the gain of a standard HRS.
There are notable differences in performance and construction between broadcast curtain arrays, such as horizontally polarized Distributed Fed Curtain arrays or USIA arrays, and lower gain antennas like the Sterba curtain or Bobtail antenna used by some amateur radio operators. A common misconception among RF engineers is labeling a modern HRS (Horizontal Dipole with Reflector and Slewing) or Distributed-Feed VOA Curtain as a "Sterba Curtain," which is incorrect. Although both are large, wire-rigged broadside arrays that hang vertically like curtains, their electrical architecture, physics, and feeding mechanisms are completely different.
The Takeaway: Calling a VOA-type HRS curtain a "Sterba" is like calling a modern active electronically scanned array (AESA) radar a "rotary radar dish" just because they both scan the sky. Ernest Sterba did also invented a brilliant series-phased loop; the VOA/HRS arrays perfected parallel-phased, wideband distributed networks.
Here is a breakdown of how the Sterba curtain functions, its unique design mechanics, and why it became a staple of early international broadcasting and military operations.
1. How It Works: The Continuous Loop
The hallmark of a classic Sterba curtain is its construction from a single, continuous loop of wire folded back on itself in a particular geometric design.
The Elements: It comprises several vertical and horizontal sections, typically spaced half a wavelength apart.
The Phasing: The brilliance of Sterba's design lies in the folding technique. The current in the wire reverses direction at each fold. Due to the spatial arrangement of the wires, the currents in all the vertical elements flow in the same direction simultaneously (in-phase).
Cancellation of Horizontal Radiation: The currents in the horizontal connecting sections move in opposite directions, causing their radiation to cancel out. This results in only the substantial, synchronized RF energy of the vertical elements being emitted.
2. High Gain and Sharp Directivity
With numerous vertical elements connected, a Sterba curtain functions as a large RF "lens."
Bi-directional Beam: In its natural, free-hanging state, a Sterba curtain projects a highly focused beam of energy from both the front and back.
Unidirectional Modification: To direct all the energy in one direction, engineers often suspend a second, identical curtain a quarter wavelength behind the first to serve as a parasitic reflector. This reflects the rear-facing beam forward, creating a single, extremely narrow, high-power beam.
Gain Performance: A large Sterba curtain with a reflector can achieve 12 to 15 dB of gain. This performance is on par with or superior to a large rhombic array, but it accomplishes this with a much smaller horizontal land area.
Footprint: A Sterba curtain attains its 12 dB gain by hanging vertically between two masts over a narrow strip of land. In contrast, a Rhombic requires acres of land to extend its wires horizontally to achieve the same signal strength.
The Catch: Bandwidth vs. Directivity
Given the Sterba curtain's superior efficiency and compact design, why did engineers like Grigory Ayzenberg opt for the expansive steel-wired Rhombics throughout the USSR?
The Rhombic's Superpower: The Rhombic is an exceptionally broadband (traveling-wave) antenna. One Rhombic can deliver high gain and stable input impedance over a 2:1 or even 4:1 frequency range (e.g., operating seamlessly from 7 MHz to 28 MHz). As the ionosphere shifts during the day, simply adjust the transmitter frequency.
The Sterba's Critical Weakness: The Sterba curtain is a highly resonant (narrowband) antenna. Its elements must stay precisely in-phase, limiting its effectiveness to one specific design frequency (with a narrow 5% to 10% bandwidth range). Any frequency change disrupts phase coherence, causing element interference and a complete loss of gain.
Many hams attempt to use their Sterba on other bands with an antenna tuner, which might load up, but it falls out of phase, potentially resulting in negative gain.
Summary
For a single, fixed-frequency, point-to-point pipeline, a Sterba Curtain delivers a stronger, more efficient signal using minimal land (Gain per Acre). However, if your communication needs span multiple HF ham or shortwave bands throughout the day, the robust, wideband capability of the Rhombic is unparalleled.
Wow, this is a 200' tower built by Roy and pulled up with a 90' gin pole. Roy W7YRV/SK, Roy told me in 2019 "I did this all by myself with a hand winch and I had to get a picture to prove that I got it this far up in case of a mishap."
See Roy's Six 20 meter Curtains
SEE K0UO's CURTAIN PAGE https://www.k0uo.com/post/current-distributed-feed-system-as-used-on-sterba-curtains-will-be-utilized-on-the-new-antenna
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