ARE THE HF BANDS OPEN TODAY?
Updated: 3 days ago
If So to Where to??
By reading this blog you will learn that radio propagation is your friend as an amateur, the more you understand, the better you'll enjoy radio.
"Over the past +50 years, my primary passion in amateur radio has been the design, modeling, and empirical testing of large-scale, high-gain HF wire arrays—particularly rhombics, V-beams, and multi-element configurations. Because of the physical space required for these traveling-wave systems, the station has evolved into a comprehensive outdoor test range. For those interested in the technical side, I’ve published the complete far-field test data, antenna models, and construction logs openly on my Blog and QRZ.com. I always welcome connecting with fellow builders and engineers who share a fascination with classical HF propagation." Steve Walz. K0UO
K0UO now utilizes a highly modified version of Ace HF Pro, IONSUM, Proplab-Pro, highly specialized, secure, and ruggedized software systems for HF predictive mission planning and other programs with real time assistance, that employ the output from a private network & IONCAP prediction method to identify the most appropriate frequency band and necessary antenna gain under specific averaged conditions. IONSUM stands for IONCAP Summary.
We are actively collaborating with several groups on various designs in the areas mentioned below, and welcome additional partnerships.
Proplab-Pro HF Radio Propagation Laboratory https://shop.spacew.com/index.php/product/proplab-pro-hf-radio-propagation-laboratory/ Propagation predictions are crucial tools for managing HF communications with DX Stations. These predictions provide data to specify the types and operating frequency ranges needed to communicate with DX by adjusting the antenna's take-off angle to maximize signal strength in the desired direction. This approach is employed to contact DX stations using either long path or short path on the F layers, or to connect with North American stations during the daytime, when high D Layer absorption occurs (160, 80, 60, 40, and 30 meters). Some reflection can occur from the D region, but the strength of radio waves is diminished by absorption, leading to a significant reduction in the range of radio transmissions on lower bands during the daytime.
K0UO, is integrating AI-driven real-time analysis with a commercial private network of ionosonde data to enable full-spectrum HF propagation monitoring.
AI‑assisted real time propagation and SMART antenna optimization tools from a private ionosonde, or chirpsounder radar system for the Department of Defense, which refers to an ionospheric sounder operated by commercial companies, private research institutions, or private defense contractors rather than traditional public government agencies (like NOAA in the US or the Bureau of Meteorology in Australia).
While public ionosondes belong to global open-access networks, private systems are typically deployed to provide proprietary, hyper-local, or high-resolution data for specific defense, aerospace, or commercial communications needs.
Spectrum Coverage: By combining real time data and AI-driven MUF maps with the multi-point receive data, K0UO can now analyze the entire HF spectrum in near real time, identifying optimal paths and frequencies for any propagation scenario.
Geographic Propagation Advantage of Kansas at this rhombic station, with less than 5 to 10 degrees take off angles, K0UO is always the first to open to Europe, Asia and over the poles to western Asia & Mideast, and it is always open to North and South America on some HF bands.
Electron Density
Real-time profiles of ionospheric electron density featuring density error bars at various heights; vertical ionospheric total electron content (ITEC); and real-time classical ionospheric characteristics such as F2, F1, Es, MUF(3000), along with the IRI parameters B0, B1, and others.
SMART AI-controlled antenna switching and along with the lightning protection for site safety matrix: With real-time MUF, F layer, D layer absorption, and information on Sporadic E and other Solar & Aurora conditions, the SMART AI-controlled antenna switching matrix confidently selects the best available antenna. This selection is based on conditions, direction, and the necessary takeoff angle of attack for optimal signal strength to specific DX stations, and it can be automatically chosen.
Selection of any number of "null" frequencies or frequency bands where no RF power is transmitted during an ionogram scan.
This system accurately forecasts HF conditions over periods ranging from 1 minute to 24 hours. Together with live DX spots, it provides the operator with full control over the extensive arrays available, allowing for easy decision-making. Handling the vast arrays is simple and effortless.
Cutting edge technology: K0UO is undoubtedly one of the rew ham stations in 2026 utilizing large HF "Smart Antennas".
The K0UO Antenna Farm,
Real-time
Instantaneous E and F region drifts.
Immediate Internet data distribution.
Instant radio skymaps displaying ionospheric reflection points for both vertical and oblique Digisonde-to-Digisonde sounding.
K0UO (summer of 2026) now includes a GNU Chirp Sounder, a software-defined radio-based receiver designed for monitoring ionospheric sounders (ionosondes) and over-the-horizon radars. With the integration of an AI-assisted system, it represents a significant advancement, capable of making intelligent decisions based on real-time conditions of the D, F, F2 layers, Aurora, Sporadic E layer, and other factors to select the optimal antennas for communication with other stations. (As part of the DoD project)
SMART Adaptive Phased Array Systems
A SMART adaptive array (often called a fully digital or dynamic beam-forming array) continuously controls both the amplitude and phase of the signal fed to each individual radiating element in real time in now in use at K0UO. Where AI adds judgment to the automatic control system.
The new K0UO/R antenna site number 2 as part of this project additional site number 2
Using HamClock and ACE Real Time Data, Studio 3 K0UO uses real time ionosonde using AI (vertical HF RADAR ionospheric height-finder) data and ACE-HF Network, by Long Wave Inc which allows K0UO to analyze the entire HF spectrum using a single fixed transmitter location and multiple receive locations. The AI package provides high-frequency (HF) radio propagation, simulation, and visualization software package formerly developed by Long Wave Inc.. It used the VOACAP engine to predict signal strength, path reliability, and real-time antenna patterns, creating animated coverage maps for HF communication systems.
K0UOs new AI application has enhanced ACE-HF features which uses Google Earth and Google Maps to provide detailed HF Area Coverage Maps. K0UO uses, and has been part of real time GPS observables network to measure properties of the electron density such as the total electron content (TEC). The TEC is a measure of the total number of electrons that would be contained in a cylinder that extends up vertically above a given point on the earth all the way through the ionosphere.
K0UO recent developments integrate real‑time ionosonde data into ACE‑HF Pro via a commercial or private network. Ionosondes measure the ionosphere’s electron density, which is critical for HF propagation modeling. By feeding this live data into the ACE engine, the software can dynamically update its predictions, reflecting current ionospheric conditions rather than relying solely on historical or forecasted data.
An ionosonde is a vertical radar that transmits radio pulses upward and measures the echoes reflected by the ionosphere. By varying the frequency, it determines at what height and intensity different frequencies are reflected.
The ACE HF Pro, by Long Wave Inc and AI with real time commercial private network of ionosonde data, now allows K0UO to analyze the entire HF spectrum using a single fixed transmitter location and multiple receive locations. The K0UO now uses the ionosonde (vertical HF RADAR ionospheric height-finder) in real time, not data that is incomplete and hours old, like comes from GIRO, NOAA, and SWS.
Automated High Frequency Communications Planner (AHFCP) HTZ Warfare is a comprehensive radio network planning and spectrum engineering tool for the deployment, optimisation and real-time analysis of mission-critical communications.
HF Propagation modeling for stationary TX with positional RX sites
K0UO has the ability to create a circuit probability area coverage map
VOACAP and IONCAP can still be used for Ionospheric Model data
Now: Antenna Performance Analysis capability is available for all of K0UO's systems, including LPDA, Rhombic, V-Beams, Curtain Array, Four Squares, and Beverage receive antennas with preset models. The station utilizes real-time AI for array switching.
Chirp Sounder Equipment at the K0UO Antenna Site Number 2 Old amateur operators really never die.
They just fad away (QSB)
AI‑Enhanced Propagation Prediction Tools
Used for:
HF band‑opening prediction
Gray‑line optimization
Contest strategy modeling
Tools in this category include:
VOACAP AI‑assisted models (machine‑learning enhanced versions of VOACAP datasets)
HamSCI ML propagation models
Solar‑data neural AI predictors (e.g., models trained on SFI, Kp, MUF trends)
These tools help plan DX and contest operating windows.
A good antenna can make a weak signal usable.
A SMART antenna can decide, moment by moment, how to make that signal better.
HEAR it, WORK it, LOG it.
THE BIG PROJECT STARTING SPRING 2026
K0UO's Major Initiative for 2026 is collaborating with a Department of Defense group, utilizing the Flex ML-9600X/FPA-5K and FPA-10K (not affiliated with Flex Corp) for diversity in transmission and reception, utilizing an AI platform.
Also some antennas on site are currently assisting a group with a project using TDoA (Time Difference of Arrival ) Direction Finding (DF) checking integrated statistical localization algorithm which allows the localization of HF transmitters based on AoA (Angle of Arrival).
DOD Seeks Self-Healing Capabilities: All systems are employing AI self-healing technology to automatically address issues with malfunctioning radios, faulty rotor boxes, and the arrays and station controls as necessary.
ACE‑HF Pro is a high‑fidelity HF propagation simulation and visualization tool that models the 1.8–30 MHz bands, predicting coverage, circuit quality, and best frequencies for any transmitter‑receiver pair. Traditionally, it has been used by amateur radio operators and DoD military clients for planning DX contacts, and optimizing HF circuits.
Dynamic Path Optimization: AI can now adjust transmit frequency and power in real time based on ionospheric conditions, improving DXing and contest performance.
Practical Impact
K0UO 's new AI Adaptive Sounder Input Prediction (ASIP) module setup transforms ACE‑HF Pro from a static planning tool, into a live, adaptive HF spectrum analyzer. For K0UO, it could mean:
Faster DX contact planning.
Better coordination of multiple receive sites.
Enhanced resilience in changing propagation conditions.
Integration with secure, mission‑critical networks for joint operations.
In short, the combination of real‑time ionosonde data, AI‑driven ASIP, and ACE‑HF Pro’s visualization capabilities allows K0UO to “analyze the entire HF spectrum” from one fixed TX location, with dynamic, network‑supported updates for all receive points.
Geographic Propagation Advantage of Kansas at this station, with less than 5 to 10 degrees take off angles, K0UO is always the first to open to Europe, Asia and over the poles to western Asia & Mideast, and it is always open to South America.
The"chirp" or "zwoop" sound if intercepted on a regular single-sideband (SSB) receiver Sweep Rate: The most common standard rate is 100 kHz per second. At this rate, it takes exactly 280 seconds (4 minutes and 40 seconds) to clear the standard 2 MHz to 30 MHz range. Other systems may use faster rates, such as 200 kHz/s or 500 kHz/s. [1, 2]
Repetition Intervals: These sweeps are generally synchronized to GPS time and repeat at highly structured intervals, usually every 5, 10, or 15 minutes (and sometimes every 1 minute during active space weather events). [1, 2]
The system is MIL-STD-188-141 compliant, using a framework for both 3G ALE (STANAG 4538 / Appendix C) and 4G ALE (Wideband HF / Appendix G)
Remember, "The Best antenna is one that is, In the Air and On the Air"!
Real-Time AI Assistance During Contests
Running a DX or Contest station is intense. You’re juggling logging, band changes, propagation monitoring, and more. AI can act like a co-pilot, offering real-time suggestions that keep you ahead of the game. For example, AI can analyze propagation data on the fly and recommend when to switch bands or modes to catch the best openings.
I remember one contest where my AI assistant alerted me to a sudden opening on 15 meters that I would have missed otherwise. Jumping on that band netted me a bunch of new multipliers and boosted my score significantly.
Here’s how AI helps during contests:
Dynamic band management: Suggests optimal bands based on current conditions.
Call sign recognition: AI can help decode callsigns faster, speeding up logging.
Error checking: Real-time log validation to avoid costly mistakes.
Propagation alerts: Notifies you of sudden openings or changes.
A DX or Contest operator implemented an AI system that monitored band conditions and automatically switched frequencies to avoid congestion. This increased contact rates by 15% to 20% during the event
Private, commercial and DoD ionosonde owners include Lowell Digisonde International customers, SpacEarth AIS users, GIRO network participants, and various private research observatories worldwide. Many are in academia or government, but some are operated by private companies or independent researchers for specialized ionospheric studies.
K0UO has an Adaptive Sounder Input Prediction (ASIP) module for the old ACE HF Network™. ASIP:
Incorporates worldwide sounder inputs to continuously update the frequency tables used by ACE‑HF Pro ant others.
Uses AI to refine predictions, improving accuracy and responsiveness to rapid ionospheric changes.
Distributes updated tables to tactical networks like the Battle Force Tactical Network (BFTN) and Resilient Command & Control (RC2) systems, enhancing network availability and mission‑critical HF communications.
Ionosonde Fundamentals: Ionograms provide unbiased plasma density measurements up to the F2 peak, forming the “ground truth” for HF propagation models.
In essence, K0UO’s setup merges AI analytics with global ionosonde data and multi-receive HF monitoring to create a closed-loop, real-time HF propagation system — enabling full-spectrum analysis from one fixed site, with adaptive frequency selection for optimal communication.
K0UO leverages AI extensively to control the main station, optimizing performance across antennas, frequencies, band conditions, and contests. AI functions act as advisory and automation tools, enabling operators worldwide to engage with the station efficiently and effectively, even when transmitting from the K0UO remote.
D Layer overview
After researching over the past few years, and now with the chirp sounder we have found that "D layer" is more that just absorption in the day time.,
Sitting at the bottom of the ionosphere between roughly 60 and 90 km altitude. Because the neutral-gas density is still high here, electron-neutral collisions occur far more often than the wave oscillation, so energy coupled into free electrons is dissipated as heat mort more than re-radiated ( but it can definitely occur under the right conditions. The layer is created by solar Lyman-alpha and soft X-rays, which is why it dominates daytime ionospheric propagation losses and then collapses within an hour of sunset. Its main effect is to attenuate lower-HF skywave, raising the lowest usable frequency and narrowing the daytime skip zone behavior of long-distance circuits. HF communication improve at night when the D-layer disappears with in a few hours or sooner.
While the 20-meter band and higher frequencies are not significantly attenuated by D layer energy absorption due to their smaller wavelengths, absorption at lower frequencies is usually too severe for long distance contacts during the daylight manifestation of the D layer.
However, the Near Vertical Incidence Skywave (NVIS) technique causes lower HF signals to travel through the D layer in the shortest dimension, nearly at a right angle to the layer’s spherical shell overhead. As a result, absorption of low frequency signals is minimized and NVIS regional communications is often viable during daylight hours, particularly on the 40 and 30 meter bands.
Lower HF Range (approx. 2 MHz to 5 MHz): Research and propagation models show that direct D-region reflection can become a dominant daytime mode for oblique propagation in the lower-most HF spectrum (such as around 2 to 5 MHz)
The Transition Zone: Above ~5 MHz and extending toward 10 MHz and higher, the electron density gradient in the D-layer is generally too gradual or too heavily dominated by collisional absorption to reflect signals very cleanly. Instead, waves in these bands are either heavily attenuated (absorbed and turned into thermal heat via electron-neutral collisions) or pass through the D-layer entirely to reach the E and F layers for true refraction (yes E layer on 80, 40 and 30 meters).
NVIS: The D-layer does not bounce the 5 MHz signal. Instead, your signal passes through the D-layer and continues upward until it hits either the E-layer (~100 km) or more commonly the F-layer (~250–300 km). These higher layers have a much lower atmospheric density, allowing the electrons to vibrate freely and cleanly refract (reflect) the 5 MHz signal back down to Earth. Because NVIS requires sending signals almost straight up (at a 75° to 90° angle), your radio wave takes the shortest possible path straight through the D-layer.
Think of a D layer as a sponge for lower frequency signals like 5 MHz
On the way up: The signal passes right through the D-layer. Because 5 MHz is a relatively low frequency, the D-layer saps a noticeable portion of its energy through collisional absorption.
On the way down: After reflecting off a higher layer, the signal must pass straight through the D-layer a second time before it reaches the receiving antenna on the ground.
The Upper Limit (Critical Frequency / foF2): If your frequency is too high (e.g., 14 MHz), the wave passes straight through the F-layer and into deep space.
The Lower Limit (Lowest Usable Frequency / LUF): If your frequency is too low (e.g., 1.8 MHz or 3.5 MHz), the D-layer absorption is so brutal during midday that your signal is entirely smothered and turned into heat before it can ever return. Ground wave of course is still possible up to and just beyond line of sight.
The E layer is often over looked on lower HF frequencies most think it's a 6 or 10 m phenomena for communications.
Technically, there is no physical "lower limit" where the E-layer plasma stops being able to bend a radio wave. Instead, the lower boundary is dictated entirely by whether a signal can pass through the D-layer and how much power is lost in the absorption
D layer, with a huge catch: it can only do so at night, because of the D layer absorption sponge.
Other Projects at the RSI K0UO test range
However still in use by DoD and others like K0UO
K0UO/RSI Corp has several ongoing DoD projects using the test range site
Long Wave Inc. is a defense contractor based in Oklahoma City that specializes in:
Strategic Communications: Installing and maintaining VLF, LF, and HF systems for the U.S. Navy, Air Force, and Coast Guard.
Antenna Infrastructure: Managing shore-based broadcast systems and providing tower engineering and repair services worldwide.
Software Development: Developing simulation, training, and operational software for mission-critical command and control.
1. The E-130J "Doomsday Plane" Program
Long Wave is a key partner in a $3.5 billion Navy contract led by Northrop Grumman to develop the E-130J, the next generation of airborne nuclear command and control aircraft.
Oklahoma City Free Press +1
Company Impact: Long Wave’s portion of this contract is valued at $350 million, which is more than ten times its typical annual revenue of $30 million.
Role: They are responsible for the systems engineering and training systems for the pilots and aircrew. They are developing high-tech virtual simulators—similar to advanced gaming environments—that allow crews to certify on the aircraft before they ever step foot on it.
2. High Frequency Global Communications System (HFGCS)
The company was recently awarded a $112.6 million Air Force contract for antenna program support.
U.S. Department of War (.gov) +1
Scope: This is a seven-year project (running through 2030) that involves maintaining and installing high-power, high-frequency antenna subsystems across 13 global locations, including Guam, Japan, Italy, and Puerto Rico.
Mission: These systems are essential for strategic military command and control, ensuring global communications remain active during wartime
3. Fixed Submarine Broadcast System (FSBS)
Long Wave holds an $84 million Navy contract to provide engineering and maintenance for the ashore Fixed Submarine Broadcast System.
Long Wave Inc
Focus: They support VLF (Very Low Frequency) and LF (Low Frequency) antenna sites worldwide that communicate with U.S. submarines operating deep underwater.
Status: Long Wave acts as the In-Service Engineering Agent (ISEA), meaning they are the primary technical support for the Navy’s entire high-powered submarine broadcast transmitting system
RSI Corp
Defense Technical Information Center (DTIC)
Training and assessment services for the United States and other governments Us!
The Defense Technical Information Center is RSI's central facility, see https://www.rsicorp.com/dtic
A Map of just one of the real time ionosonde networks, Digisonde® network
Historic Preservation: The K0UO station diligently preserves and uses components and insulators from renowned, historic radio arrays, including those from W6AM (Don Wallace), W7YRV Roy, BBC, Voice of America (VOA), and many others.
"Over the past years, my primary passion in amateur radio has been the design, modeling, and empirical testing of large-scale, high-gain HF wire arrays—particularly rhombics, V-beams, and multi-element configurations. Because of the physical space required for these traveling-wave systems, the station has evolved into a comprehensive outdoor test range. For those interested in the technical side, I’ve published the complete far-field test data, antenna models, and construction logs openly on my Blog and QRZ.com. I always welcome connecting with fellow builders and engineers who share a fascination with classical HF propagation."
"The K0UO station is unlike any other ham station globally," making it truly unique as a Big Gun Mega Station. It is one of the few capable of constructing and utilizing very large Rhombic and V Beams, along with a variety of other antennas and AI. K0UO features the largest ham radio operational HF wire antenna in the world.
The K0UO & RSI Corp antenna test range site utilizes the 4KS Walz airport and its surrounding area as an effective learning environment for STEM (Science, Technology, Engineering, & Mathematics) antenna projects in a real-world outdoor setting. If your group is involved in a university aerospace or antenna research STEM program, please contact me.
The KØUO Rhombic Antenna Farm and Antenna Test Range: Home to the World's Largest amateur radio (ham), High Frequency (HF) Wire Arrays still in use, with miles of wire operating daily.
SEE ALL BLOGS Here, & Just Skip the first few pages, and go to the Blog List
AI for Ham Radio: Contest Planning, DXing, & Station Design Automation
See the ARRL news letter featuring K0UO SMART Station Nov. 5 2026, https://mailchi.mp/arrl/the-arrl-letter-for-october-1-20253411?e=43e56aab26
For all the other Blogs see https://www.k0uo.com/k0uo
TIP: It is a Blog, so just SKIP the Blogs HEADER and go right down to the blog.
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Bài viết đọc dễ vào, cảm ơn bạn đã chia sẻ; đoạn nói về nạn sao chép đúng phần mình đang thắc mắc. Mình thì hay theo dõi thống kê XSMB mỗi ngày nên tự gom lại thành một trang tổng hợp để tra nhanh cho tiện, khỏi phải lục nhiều nơi. Ai cũng quan tâm số liệu cập nhật theo ngày thì ghé xem thử https://www.tizmos.com/Soicauxsmbpro?folder=Home
Love this site, have always wanted to build a "Rombic" now for the first time we have a couple acres maybe I might be able to fit one in my small area. Thanks for allowing me to drop in. 73 from k0css Rick