The HF Bands
For HF Beginners
Gary Wescom – N0GW
The HF Bands
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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
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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)
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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 Layers
The path through D, E, F1, and F2 layers
F2
F1
E
D
(Not to scale)
The D Layer
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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
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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
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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
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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
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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
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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
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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
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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
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160 Meters (1.8 – 2.0 MHz)
80 Meters (3.5 – 4.0 MHz)
60 Meters (5.3 – 5.4 MHz)
40 Meters (7.0 – 7.3 MHz)
30 Meters (10.1 – 10.15 MHz)
20 Meters (14.0 – 14.35 MHz)
17 Meters (18.068 – 18.168 MHz)
15 Meters (21.0 – 21.45 MHz)
12 Meters (24.89 – 24.99 MHz)
10 Meters (28.0 – 29.7 MHz)
Night
Night
Day/Night
Day/Night
Day/Night
Day
Day
Day
Day
Day
160 Meters
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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
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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
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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
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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
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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
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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
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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
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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
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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?
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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