1. For HF Beginners Gary Wescom – N0GW
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. The path through D, E, F1, and F2 layers
The Layers
The path through D, E, F1, and F2 layers F2 F1 E D
(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 of 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
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
60 Meters (5.3 – 5.4 MHz) Day/Night
40 Meters (7.0 – 7.3 MHz) Day/Night
30 Meters (10.1 – MHz) Day/Night
20 Meters (14.0 – MHz) Day
17 Meters ( – MHz) Day
15 Meters (21.0 – MHz) Day
12 Meters (24.89 – 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