THE SOUND OF SILENCE - Arctic Amateur Radio Club Propagation Oct 2017.pdf · THE SOUND OF SILENCE AND OTHER MYSTERIES OF HF ... • Sound of signals ... 10 times the numberof disturbed

THE SOUND OF SILENCEAND OTHER MYSTERIES OF HF PROPAGATIONLarry Ledlow, Jr. N1TXn1tx@akradio.net

AGENDA

• Basic HF• Ionization• The ionosphere• The geomagnetic field• Solar wind

• Polar Propagation• Data

THE BASICS

”Two atoms are walking along…”

One atom stops and says, “Oh no, I’ve lost an electron!”

“Are you sure?”“I’m positive!”

In the upper atmosphere, the main source of ionization is the sun: X-rays, UV, charged particles.

The ionosphere extends across multiple layers of the atmosphere.

INC

REASIN

G D

ENSITY

The rarer the atmosphere, the more ionized a gas will be.

There are fewer opportunities for electron-ion re-combination.

Some layers exist only during daylight.

Radio wave interaction with the ionosphere depends on the frequency and degree of ionization. D absorbs medium wave transmissions, but long distance is possible at night.

Daytime DX on higher frequencies via F layers

Hams enjoy DX on 20, 15, and 10 meters during day.At night the F1 and F2 layers are no longer so distinct.

Solar activity follows 11-year cycles.Low bands are favored during lulls.

THE NOT-SO BASICS

”But seriously, folks…”

A Quick Re-cap1. The sun ionizes the atoms in the upper

atmosphere.2. The amount of ionizing radiation from

the sun varies constantly.3. Some ionospheric layers disappear at

night – no solar radiation for ionization.4. Low bands (160-40m) are favored at

night. DX is possible on 20-10m during daylight.

5. But it’s more complicated than that…

GEOMAGNETIC FIELD

“Aurora’n good time!?

The earth’s magnetic field simplified, but…

…is not actually uniform due to solar wind.

The measure of geomagnetic disturbance is the planetary K index (Kp), ranging over 0-9.

The solar wind constantly buffets the earth and distorts the magnetic field. See animation here.

The solar wind streams off of the Sun in all directions at speeds of about 400 km/s (about 1 million miles per hour)

The resulting turbulence in both the ionopshere and magenetosphere cause propagation problems.• Absorption• Multipath• Flutter/rapid fading• Skewing

You need to learn to read the “tea leaves” to know what is happening.• Sound of signals• Sound of noise• Space weather indicators

FUGGETABOUTIT!

A lot of what they teach you in radio school is bunk when it comes to polar propagation.

Why are conditions at high latitudes special?

• The geomagnetic field becomes nearly vertical in the high latitudes.

• Magnetic field lines connect the high latitudes to the outer part of the magnetosphere, which is directly impacted by solar wind.

• That also means the ionosphere is tilted as well as more complex and turbulent.

• The atmosphere is thinner near the poles, and the active regions of the ionosphere are nearer the ground.

• Arctic radio wave coupling to the ionosphere is inefficient.• Paths are not necessarily reciprocal! Direction can be

significantly skewed.

In short, polar propagation is far more sensitive to solar-induced disturbances than any other area on the planet.

• Rapidly changing conditions may force a change of antenna, frequency and/or mode.

Conditions you will encounter

Long-term, “flat” fading – slow changes in signal strength across a band. Often accompanied by increasing noise.

Conditions you will encounter

Selective fading – A narrow band of frequencies fade

Conditions you will encounter

Multipath and Aurora flutter

OH1ML - LB1AH QSO on 10 meters via aurorahttps://www.youtube.com/watch?v=gB1nTxxkkbw

Conditions you will encounter

Higher absorption on the path out of Alaska.

EXPECT YOUR SIGNAL TO BE 6-10 DB WEAKER AT THE OTHER END (1-2 S-UNITS) UNDER “NORMAL” CONDITIONS.

Specific effects are highly localized. Two stations close together can endure completely different propagation.

RX LEVEL AT WA7LNW

http://reversebeacon.net/analysis/

Conditions you will encounterSkewed paths

NORMAL PATH

ACTUAL

Special CircumstancesSporadic E (Es)

Occasionally, patches of the E layer become highly ionized. At high latitudes, Es tends to occur in the fall and spring.Contacts on 10 and 6 meters and higher is possible.

Special CircumstancesGray Line Enhancement

As sunrise and sunset occur, signals on any HF band can be enhanced between two stations near the day/night terminator. Openings are usually +/- 2 hours before sunrise/set.Try short and long paths. “Follow the sun” is a good guideline.

DX

In practical terms

• Try changing antennas• Receive diversity is a powerful tool• The best rx path is not necessarily the best tx path.

• Be patient.• If the Kp is 3 or higher, you will be able to hear stations,

but they won’t hear you. Openings occur periodically, so keep trying.

• Try changing bands.• Lower is not necessarily better. 15 meters can open

before 20m.• Try changing modes.

• CW is easier to receive than SSB in many conditions• Use a digital mode with good error correction; e.g.,

JT65 vs. PSK31

REAL-TIME TOOLS

Handy data to assess conditions

Websites• NOAA Space Weather Prediction Center

http://www.swpc.noaa.gov/communities/radio-communications

• Space Weather dot com http://spaceweather.com/

• Australian Space Weather Serviceshttp://www.sws.bom.gov.au/

What some of the numbers mean• A index (Ap): Used to compute daily

average of geomagnetic activity.

• Sunspot number (SSN): an arbitrary numerical value that is used to describe the sun's spottedness, is the number of individual spots plus 10 times the number of disturbed regions.

X-Ray Measurements from Spacecraft

Proton Measurements from Spacecraft

More on the solar wind

Interplanetary Magnetic Field Orientation (Bz)NEGATIVE = BAD

Solar wind speedHIGHER = BAD

Solar wind densityHIGHER = BAD

Solar wind temperature

IMF angle PhiRAPID CHANGE = BAD

The interplanetary magnetic field (IMF) is a part of the Sun's magnetic field that is carried into interplanetary space by the solar wind.

IonogramsStations worldwide regularly probe the ionosphere with ionosondes.The outputs are ionograms showing ionospheric profiles.

Recommended Reading and Viewing

Three Wrong Assumptions about the Ionosphere, by Eric Nichols KL7AJMAR 2012 - QST (PG. 40)

Understanding Propagation with JT65, JT9, and FT8, by Carl Luetzelschwab K9LAOCT 2017 - QST (PG. 45)

More Links to ARRL articles here:http://www.arrl.org/propagation-of-rf-signals

Sentinels of the Sun: Forecasting Space WeatherBy Barbara B. Poppe, Kristen P. Jorden (2006)

Tamitha Skov – Space Weather ForecastsYouTube Channel: https://www.youtube.com/user/SpWxfx

N1TX@AKRADIO.NETQUESTIONS?