Mel - N7GCO - Cheney, WA

HF Radio Propagation

Key Measurements

Mel Ming (N7GCO) & Randy Crews (W7TJ)


I am trying to increase my effectiveness at DXing. In the next phase, I am focusing on two areas: 1) Receive Antennas for 80 and 160 and 2) Better understanding of propagation. For both of these I have reached out to mentors (Elmers) to help me.

For Propagation I reached out to Randy Crews (W7TJ) who has a special interest in propagation. What follows is mostly his insights, so I want to give him the credit. It was a great help to me and I hope it is helpful to you to. If you want it as a WORD Doc or PDF, I would be glad to send it to you.


”Sunspots are the KEY to HF Radio Propagation as the radiation they emit turns the Earth's ionosphere into a big [ electrical mirror ]  this ionization along with help from the Sun opens the high bands during the day, and the allows outstanding propagation on the low bands during the night once the D layer decays. Both of these trends are absent today due to solar activity ( sunspots being too low ) The real key to successful DXing in today's environment is a quiet geomagnetic field ( no storms) plus low A and K indices along with low solar wind. Even with low or NO sunspots, you will be successful if you pick a period with very quiet conditions. The Solar Flux is a measure of the degree of ionization in the Earths ionosphere (the higher the better).” RC


Solar Flux

               Scale: 50-300  -- For HF propagation the higher the number the better.


< 70: propagation potentially bad.                           

-(67-75) The workhouse bands will be: 160,80,40, nights, and 20M Days.


80-90: propagation potentially are somewhat low


90-100: propagation tend to be average


100: this is a key threshold - 17 Meters opens and stronger signals on the previous Bands.

125:  15 Meters opens stronger signals on the previous Bands.

140:  10 Meters opens stronger signals on the previous Bands.


100-150: propagation will tend to be good


>150: propagation will tend to be ideal


Solar Flux above 200: Six Meters opens and most the high bands are open 24/7.


 “Here are links to two websites that I believe are the best predictors of sunspots and the conditions they predict - one short term this one is by the Norwegians and is loaded with data: 

This is a link to the Space Weather Prediction Center in Boulder, Colorado ( SWPC ) and a screen shot follows:   (updated weekly)”


If I had only one Propagation Website to pick, it would be this one:   VE3EN does an outstanding job - more information than most of us need. I'll point our they key things which you need to focus- a screen shot to ease the explanation: Please Focus on the upper left portion of the screen for now -

Pictured is our sun with a lone sunspot tracking across. Below the Sun is the key data to watch:

Solar Flux (SF) A index, and K index along with Solar Wind.  The <absolute key> in todays low period of solar activity is a QUIET Sun... K indexes of 1 to Zero, A index less than 10, and low solar wind (Less than 400 Km/sec.


Here is the last website to monitor current conditions:   Solar Flux, A and K indexes are neatly displayed along with the Solar Wind (Velocity). The Author gives a short term prediction on solar flux and A index along with the Earths aurora bands, grey line and MUF maps.  - Randy Crews


A & K Indices measure magnetic field

Generally the lower the number the better


A Index (Scale: 0 (quiet) to 400 (severe storm).

  • A = 0 - 7 Quiet
  • A = 8 - 15 Unsettled
  • A= 8 - 15 Unsettled
  • A = 16 - 29 Active
  • A = 30 - 49 Minor storm
  • A = 50 - 99 Major storm
  • A = 100 - 400 Severe storm


K Index (Scale: 0-9)

  • K = 0 Inactive
  • K = 1 Very quiet
  • K = 2 Quiet
  • K = 3 Unsettled
  • K = 4 Active
  • K = 5 Minor storm
  • K = 6 Major storm
  • K = 7 Severe storm
  • K = 8 Very severe storm
  • K = 9 Extremely severe storm



Sun Spots

Higher sunspot numbers indicate increased ionizing radiation from the sun which enhances the ionosphere's ability to refract HF signals, The sunspot number can vary from zero to over 200 during the peak of the 11-year solar cycle.


< 50: propagation conditions potentially very bad

50-75: propagation conditions attenuated Understanding HF propagation reports

75-100: propagation conditions might be good

100-150: propagation conditions should be ideal

>150: propagation conditions possibly exceptional


If you have additional information that you think is helpful for DXing, please send it my way.





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