↑ HF Propagation Indices

By Doron Tal, 4X4XM

Understanding the influence of HF propagation indices (indexes) on propagation conditions can help radio operators, amateurs, and professionals to find the best frequency to make a reliable conact.

  1. Propagation Indices - What Are They?
  2.  

    Propagation indices are numerical values that describe the current state HF propagation conditions. They provide insight into how the ionosphere affects HF radio wave propagation.

    The propagation indices used for HF propagation are:
    1. SSN - Sunspot Number is a count of the number of dark spots seen on the sun.
      Higher SSN values indicate improved conditions on 14 MHz band and above: SSN <50 poor propagation     SSN >150 ideal propagation.
    2. Solar Flux Index (SFI) measures the sun's radio emissions at a wavelength of 10.7 cm (2800 MHz). A higher SFI generally indicates better HF propagation conditions. A typical range is 60 to 400. Higher values correlate with improved long-distance HF communication.
    3. The solar indices: SSN, SFI
      condBADLowAverageGoodBetterBest
      MUF< 15 MHz> 21 MHz> 24 MHz> 28 MHz> 50 MHz
      SSN0255075100125150175200250
      SFI6783102124148172196219240273
      Reference to the conversion between SSN and SFI.

      High SSN and SFI values are good for daytime propagation on all HF bands. Best for higher frequency bands (20 meters and up). Provides better long-distance communication opportunities.


      The geomagnetic indices: Xp, Ap
    4. A-Index represents geomagnetic activity. It measures disturbances in Earth's Magnetic field caused by solar events like solar flares or coronal mass ejections (CMEs). A low A-Index (0-7) suggests quiet geomagnetic conditions, which are favorable for HF propagation.
    5. K-Index is another measure of geomagnetic activity, ranging from 0 to 9. A lower K-Index indicates calmer geomagnetic conditions, which are more favorable for HF propagation. It's usually calculated from data recorded every 3 hours.
    6. Interference due to geomagnetic activity
      HF Propagation conditionsBestAveragePoorBAD
      Geomagnetic activity index (log-scale)K0123456789
      Geomagnetic activity index (linear)A 0  4  7  15 27 48 80132207400
      Low A-Index and K-Index are favorable for HF propagation.

    7. The solar flare index: X-Ray bursts may cause blackouts.
    8. Solar  Flare  Class A  B  C MX
      Radio Blackout ScaleR0R1R2R3R4R5

    The above five indices, SSN, SFI, A, K, and X-ray, are known as "propagation indices."


     
  3. Tools for Monitoring Propagation Indices: Stay updated on propagation indices using various online tools and resources:
  4. Space Weather Prediction Center (SWPC) provides real-time solar and geomagnetic data, including SFI, A-Index, and K-Index.

    DX Cluster Websites: Many DX cluster websites display current propagation conditions and include propagation indices.

    Propagation Prediction Software: Use dedicated software like VOACAP (Voice of America Coverage Analysis Program) for detailed HF propagation forecasts based on propagation indices.


     
  5. Adjust Your Operating Strategy:
      Based on the propagation indices, adapt your operating strategy:

    1. Select Appropriate Bands: Choose HF bands that match the current SFI and geomagnetic conditions.
    2. Optimal Times: Plan your HF operations during daylight hours when the SFI is higher.
    3. Monitor for Changes: Keep an eye on the indices, as they can change rapidly due to solar activity.
    4. Experiment: Try different bands and times to maximize your chances of successful HF communication.

  6.  
  7. Continuous Learning:
  8. HF propagation is a dynamic field, and propagation indices can vary daily. Stay engaged with the amateur radio community and learn from experienced operators to refine your understanding and skills in using propagation indices for HF propagation.

    By grasping the basics of propagation indices and their impact on HF propagation, you can enhance your ability to make effective long-distance HF contacts and enjoy the exciting world of amateur radio and shortwave communication.

Read more about propagation indices & Ham Radio Propagation


The project "Understanding HF Propagation" provides a detailed overview and tutorials on HF propagation.

flags of visitors!