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

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.

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.

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.

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)

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

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

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

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

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

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

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

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

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 – 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

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

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

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

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

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

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

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

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

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

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