The HF Bands

1. The HF Bands For HF Beginners Gary Wescom – N0GW

2. The HF Bands • The HF bands can be mysterious • Some work at night, some during the day • Some seem to be good for long distances • Some seem better for short distances • Even worse – they change tremendously from hour to hour and day to day.

3. The Ionosphere • Communications beyond a few miles on the HF bands occurs because of the Ionosphere. • Extends from roughly 35 miles to 300 miles up in the atmosphere. • Atmosphere is ionized by solar radiation. • Ionization process absorbs most of the harmful solar radiation making life on the surface of the earth possible.

4. The Ionosphere (cont) • The actual operation of the Ionosphere that allows HF communications is very complex. • Air pressure about a thousandth surface normal at bottom, about eight orders of magnitude lower at top. • Different wavelengths and kinds of solar radiation effect different heights • Several Ionospheric layers have been identified. The D, E, and F layers are what we care about.

5. F2 F1 E D The Layers The path through D, E, F1, and F2 layers (Not to scale)

6. The D Layer • 35 to 50 miles up • Strongest in daylight and mostly an absorber of radio signals • Absorbs lower frequencies more than higher • D Layer is why 160 and 80 don’t work very well during the day • Ionization drops off rapidly as sun sets because of relatively high atmospheric pressure

7. The E Layer • 50 to 100 miles up • A wild card in radio propagation • Sometimes present, sometimes not. • Sometimes absorbs • Mostly reflects • Sometimes it reflects very well, even up into the VHF region

8. The F Layer • Does the real work bouncing radio signals around the county and around the planet • Is primarily a reflector • Radio sounding identified F1 and F2 regions • F1 – 100 to 130 miles up and exists mostly during daylight hours. • F2 – 130 to 300 miles up – very low atmosphere density causes very slow ion recombination so remains largely intact through the night

9. The Sun Spot Cycle • Solar radiation ionizes air molecules at very high altitudes • Solar radiation follows the 11 year sunspot cycle • 2007 is bottom of cycle – next peak 2011-2012 • Upper HF band operation will improve gradually as peak is approached. • Peak of cycle is turbulent but higher sunspot count generally mean better HF propagation

10. Sunspot Count and Solar Flux • Two different measures of solar activity • Sunspot count is visual count • Solar flux Index (SFI) is measured 10.7 cm microwave radiation level • SFI values above 200 are high, below 100 are low • Openings become common on 10 meters when SFI reaches about 180

11. Night and Day • Obviously if the sun is important to radio propagation, day and night must matter • Each layer reacts differently • Higher pressures in the lower layers allow their ions to recombine more quickly • D layer absorption drops at night • F1 layer fades but F2 hangs in there

12. Summer and Winter • Winter improves lower frequency nighttime bands, reduces operating time on higher bands • Summer reduces operating time on lower bands • Summer lightning storms sometimes make 160 and 80 meters nearly useless • 160, 80,60,40, and 30 meters best during winter • 20, 17, 15, 12, and 10 meters best in summer

13. The Skip Zone • Above some critical frequency, signals sent straight up will not be reflected • Angle must be lowered for reflection to occur • Skip zone is area around your station which cannot be reached via Ionospheric reflection • Acts like there is a hole in the ionosphere over your station • Skip zone increases with frequency

14. The HF Bands • 160 Meters (1.8 – 2.0 MHz) Night • 80 Meters (3.5 – 4.0 MHz) Night • 60 Meters (5.3 – 5.4 MHz) Day/Night • 40 Meters (7.0 – 7.3 MHz) Day/Night • 30 Meters (10.1 – 10.15 MHz) Day/Night • 20 Meters (14.0 – 14.35 MHz) Day • 17 Meters (18.068 – 18.168 MHz) Day • 15 Meters (21.0 – 21.45 MHz) Day • 12 Meters (24.89 – 24.99 MHz) Day • 10 Meters (28.0 – 29.7 MHz) Day

15. 160 Meters • Primarily nighttime regional band • Nighttime range is usually very good from next door out to about 500 miles with full size horizontal antennas • Worldwide DX possible with tall vertical and extensive radial system • Nearly useless during summer because of lightning storms

16. 80 Meters • Primarily nighttime regional band with coverage extending out to 1500 miles • Morning and afternoon operation out to 200 miles common • Worldwide DX more likely – smaller antennas than 160 meters • Badly impacted in summer by lightning storms

17. 60 Meters • Better daytime coverage than 80 meters • Because of 50 watt power limit, range usually limited to about 750 miles even at night but transcontinental operation possible • Band is not available on many older rigs so activity is sparse but friendly

18. 40 Meters • Daytime regional out to about 300 miles • Nighttime coverage often worldwide • Part of band is a short wave broadcast band in other parts of the world – difficult to find empty spot to operate when DX conditions are good • Summer lightning noise is a problem but not nearly as much as lower bands

19. 20 Meters • This is the King of DX bands • Usually open daytime even at bottom of sunspot cycle • Usually has low D layer absorption • Usually has a Skip Zone extending out 300 to 500 miles • Good frequency for F2 layer operation so band may stay open until late at night – especially to the west

20. 17 Meters • Lower keyed version of 20 meters • Opens later than 20 and closes sooner • Skip zone typically 500 miles • No contesting on this band so good for both DXing and rag-chewing

21. 15 Meters • A good DX band once it starts opening up a couple years after the sunspot cycle minimum • Skip zone commonly 500 – 1000 miles • Suffers less D Layer absorption than 20 meters so provides good signal levels when band is open

22. 12 Meters • A combinations of 15 and 10 meter characteristics • Contesting not allowed on this band so is clear for rag-chewing and DX even on weekends • Provides good DX opportunities during high part of sunspot cycle

23. 10 Meters • Sits on the threshold of VHF • When this band is open, even low powered radios and modest antennas can make world wide DX contacts • Skip zone sometimes exceeds 1000 miles though E Layer will sometimes allow closer contacts • To perform at its maximum potential, sunspot count must be high

24. So what band should I use? • Each band has it advantages and disadvantages • In low part of sunspot cycle, most activity found on 17 meters and lower in frequency • At bottom of cycle, 40 meters during day and 80 meters at night would provide many contacts • Highest likelihood of DX contacts would on 20 and 17 meters • As sunspot cycle improves, the upper bands will become active