Presentation on theme: "For HF Beginners Gary Wescom – N0GW"— Presentation transcript:
1For HF Beginners Gary Wescom – N0GW The HF BandsFor HF BeginnersGary Wescom – N0GW
2The HF Bands The HF bands can be mysterious Some work at night, some during the daySome seem to be good for long distancesSome seem better for short distancesEven worse – they change tremendously from hour to hour and day to day.
3The IonosphereCommunications 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.
4The 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 heightsSeveral Ionospheric layers have been identified. The D, E, and F layers are what we care about.
5The path through D, E, F1, and F2 layers The LayersThe path through D, E, F1, and F2 layersF2F1ED(Not to scale)
6The D Layer35 to 50 miles upStrongest in daylight and mostly an absorber of radio signalsAbsorbs lower frequencies more than higherD Layer is why 160 and 80 don’t work very well during the dayIonization drops of rapidly as sun sets because of relatively high atmospheric pressure
7The E Layer 50 to 100 miles up A wild card in radio propagation Sometimes present, sometimes not.Sometimes absorbsMostly reflectsSometimes it reflects very well, even up into the VHF region
8The F LayerDoes the real work bouncing radio signals around the county and around the planetIs primarily a reflectorRadio sounding identified F1 and F2 regionsF1 – 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
9The Sun Spot CycleSolar radiation ionizes air molecules at very high altitudesSolar radiation follows the 11 year sunspot cycle2007 is bottom of cycle – next peakUpper HF band operation will improve gradually as peak is approached.Peak of cycle is turbulent but higher sunspot count generally mean better HF propagation
10Sunspot Count and Solar Flux Two different measures of solar activitySunspot count is visual countSolar flux Index (SFI) is measured 10.7 cm microwave radiation levelSFI values above 200 are high, below 100 are lowOpenings become common on 10 meters when SFI reaches about 180
11Night and DayObviously if the sun is important to radio propagation, day and night must matterEach layer reacts differentlyHigher pressures in the lower layers allow their ions to recombine more quicklyD layer absorption drops at nightF1 layer fades but F2 hangs in there
12Summer and WinterWinter improves lower frequency nighttime bands, reduces operating time on higher bandsSummer reduces operating time on lower bandsSummer lightning storms sometimes make 160 and 80 meters nearly useless160, 80,60,40, and 30 meters best during winter20, 17, 15, 12, and 10 meters best in summer
13The Skip ZoneAbove some critical frequency, signals sent straight up will not be reflectedAngle must be lowered for reflection to occurSkip zone is area around your station which cannot be reached via Ionospheric reflectionActs like there is a hole in the ionosphere over your stationSkip zone increases with frequency
15160 Meters Primarily nighttime regional band Nighttime range is usually very good from next door out to about 500 miles with full size horizontal antennasWorldwide DX possible with tall vertical and extensive radial systemNearly useless during summer because of lightning storms
1680 MetersPrimarily nighttime regional band with coverage extending out to 1500 milesMorning and afternoon operation out to 200 miles commonWorldwide DX more likely – smaller antennas than 160 metersBadly impacted in summer by lightning storms
1760 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 possibleBand is not available on many older rigs so activity is sparse but friendly
1840 Meters Daytime regional out to about 300 miles Nighttime coverage often worldwidePart 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 goodSummer lightning noise is a problem but not nearly as much as lower bands
1920 Meters This is the King of DX bands Usually open daytime even at bottom of sunspot cycleUsually has low D layer absorptionUsually has a Skip Zone extending out 300 to 500 milesGood frequency for F2 layer operation so band may stay open until late at night – especially to the west
2017 Meters Lower keyed version of 20 meters Opens later than 20 and closes soonerSkip zone typically 500 milesNo contesting on this band so good for both DXing and rag-chewing
2115 MetersA good DX band once it starts opening up a couple years after the sunspot cycle minimumSkip zone commonly 500 – 1000 milesSuffers less D Layer absorption than 20 meters so provides good signal levels when band is open
2212 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 weekendsProvides good DX opportunities during high part of sunspot cycle
2310 Meters Sits on the threshold of VHF When this band is open, even low powered radios and modest antennas can make world wide DX contactsSkip zone sometimes exceeds 1000 miles though E Layer will sometimes allow closer contactsTo perform at its maximum potential, sunspot count must be high
24So what band should I use? Each band has it advantages and disadvantagesIn low part of sunspot cycle, most activity found on 17 meters and lower in frequencyAt bottom of cycle, 40 meters during day and 80 meters at night would provide many contactsHighest likelihood of DX contacts would on 20 and 17 metersAs sunspot cycle improves, the upper bands will become active