How to read this
Local (NVIS) means contacts from next door out to about 300 miles: your signal goes nearly straight up and comes back down around you. It only works on the lower bands, and only below the critical frequency.
Skip / DX means everything farther away: your signal leaves at a low angle and lands hundreds to thousands of miles out.
Good is worth calling CQ on. Fair works but is weaker or comes and goes. Poor is a struggle. Closed means the ionosphere is not reflecting that band for that kind of contact at all.
Where the numbers come from
Solar flux, sunspot number, the K and A indices, X-ray flares, storm scales and the three-day forecast come from the NOAA Space Weather Prediction Center. Critical-frequency measurements come from the global ionosonde network (GIRO), by way of KC2G's propagation service.
Modes
Some modes get through with much less signal than others. The plain ratings are for phone (SSB): "Good" means a voice CQ should get answered. CW copies through signals 20 dB or so weaker than voice needs, and digital modes like FT8 and FT4 about 30 dB weaker. So a band that is "Poor" for voice can be "Fair" on CW or FT8, and FT8 often decodes during brief openings just above the maximum usable frequency. The Phone / CW / Digital switch on the band table re-rates it for that mode, and the strip under the summary shows the best band for each. These adjustments are rules of thumb that haven't been checked against what people actually hear on the air.
Forecasts
Next 24 hours runs the same estimate for every hour, using NOAA's three-day K-index forecast. Today's ionosonde reading counts fully for now and less for later hours. A flare in progress is only applied to "now", since flares are usually over within the hour. Coming weeks uses NOAA's 27-day outlook, which predicts each day's solar flux and largest K-index, largely from what the sun did one rotation (about 27 days) ago. It is good for spotting likely storm days and the general trend, not for exact conditions. Both follow the Phone / CW / Digital switch.
POTA Hunter
Lists the stations currently spotted at POTA parks and rates each one for your grid: the distance to that park decides which bands can reach it, and the spot's mode adjusts the rating the same way the band table's mode switch does. Every band has a skip zone, so a band can be wide open to a park 1,500 miles away and dead to one 200 miles away at the same moment. "Good chance" means the band should support that distance right now; "Unlikely" usually means it is skipping over you or is closed.
How much to trust it
The band ratings are a rule-based estimate, not a full propagation model. They are built from the numbers above, the sun's position at your location, and the nearest ionosonde reading when one is close enough to be useful. They do not know about your antenna, your power, your local noise, or sporadic-E. Treat them as a good first guess and let the band itself have the last word.
About
Strictly for amateur radio, educational, and hobbyist use. Everything is calculated in your browser.
Version · Created by Brandon Beeson KO6HWR · Buy me a coffee