Propagation VHF and Above

2003-08-30 RAC Forum and Technology Update

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Propagation VHF and AbovePropagation VHF and Above(an overview only)

Rick Bandla (VE3CVG)


Slide 2

Radio WavesRadio WavesElectromagnetic Waves composed of equal

electric and magnetic power levelsTravel in straight lines more or less like lightChange direction if/when encounter atoms,

molecules, ions, electrons.Wave movement takes place by stimulation of

electronsCoherent electron activity re-enforces wave


Slide 3

The Ground The Ground – info from OZ1RH– info from OZ1RH

Low angle of radiation usually desirable Vertical antennas need perfect ground to give low angle of radiation Radiation angle of a horizontal beam is a function of its height over

the ground. Quality of ground has minimal effect Antenna on a hill (land slopes down) will have a lower angle of

radiation than flat land.

Height on Flat Gnd Ground Gain Max Radiation @

1/2w -1.7dB 13 degrees

1 +2.6dB 11 degrees

2 +4.8dB 7 degrees

5 +5.5dB 3 degrees


Slide 4

IonizationIonization

Atoms are usually electrically neutral with a +ve nucleus surrounded by some quantity of electrons

If electrons become separated we have free electrons and positively charged ions

Ionization occurs as a result of bombardment by charged particles, UV, X-rays, gamma rays

Radio waves are non-ionizing radiation


Slide 5

When Radio Waves meet MatterWhen Radio Waves meet Matter Refraction – change in direction of wave

Refraction due to ionization looks like reflection Reflection – some fraction of a wave is turned back Scattering

wave encounters objects smaller than a wavelength. Over-dense scattering resembles refraction and reflection. Under-dense scattering from objects with order, may result in

useable propagation (meteors, aurora) Absorption – energy converted into heat Diffraction

obstacle removes part of a wave front. Causes propagation into the shadow of the object

Loss increases with scattering angle and frequency (clear takeoff more important at higher frequencies)


Slide 6

Refractive Index or NRefractive Index or N

N is the radio wave velocity in free space/velocity in a new medium

Calculation: N = 77.6 (pressure in millibars/temp in kelvins) + 3.73 (105 (water vapour pressure in millibars/temp2)) which is typically about 324

N is Independent of frequency In normal atmosphere, air temp and dew point decrease

with height above ground therefore N also decreases


Slide 7

TroposphereTroposphere This is where our weather lives Tropopause is upper boundary and is the temperature

inversion layer (about 10 km depending on lat and conditions)

No significant ionization Physical properties of the air may vary radio refractive

index or N N decreases linearly for first 2-3km (particularly after a

rainstorm). Rate of decrease reduces with altitude Refraction within the troposphere is what extends the

optical horizon to the radio horizon (4/3 earth)


Slide 8

Tropo ScatterTropo Scatter

Point to point communication on radio horizon is typically 50km max, S9 signal strength Workable distance is d1(km)=4.1( h1 + h2)

Troposcatter Ts is always possible, independent of frequency 50Mhz – 10GHz

Range up to 800km is realistic Troposcatter loss increases with the scatter angle Note: there is also Back Scatter and Side Scatter


Slide 9

Tropo DuctingTropo Ducting Caused by radio waves reflected and refracted between layers Waveguide in the sky, with very little loss

Often one opening and one exit May be multiple ducts through the same area Often excellent signal strength. Ranges of 2500km or more May last a few minutes or several hours Typically 144MHz and above

Surface Ducting If temp increases with height, we have a temperature inversion. N

decreases more sharply at the boundary, bending radio waves downwards and trapping them between earth and boundary

Usually occur over water, generally between 15m and 400m deep Elevated ducting formed by double discontinuity in N.

.5 – 2 km above ground or sea & shallow compared to surface ducts


Slide 10

Atmosphere Chart


Slide 11

IonosphereIonosphere MUF or Maximum Usable Frequency is highest freq returned to earth D Region at 60-90km

Absorbs HF but almost transparent to VHF and above Contributes to VHF and above forward scatter during intense solar

activity E Region at 90 to 120km

Ions predominate neutral atoms Sporadic E, Aurora, Meteors capable of reflecting VHF and above

F region F1 – some refraction at 50MHz F2 at about 350km elevation, between 100km and 200km deep

World wide communication at 50MHz but insufficient ionization to effect 144MHz and up


Slide 12

Sporadic E (Es)Sporadic E (Es) Range 500-8000km on 50MHz (multi hop) Range 800 – 4000km on 144MHz (double hop) Occasional openings to 222MHz Openings last a few minutes - few hours Higher frequency = shorter openings Geographically selective Work several stations all in one or 2 grid squares Signals are often very strong Types

Temperate Zone Es – solar driven, summertime, 50-200MHz Auroral Es – see Aurora slide Equatorial Zone Es – 50-100MHz, around the magnetic equator


Slide 13

Sporadic E (Es)Sporadic E (Es) Some Temperate Zone predictability/probability:

50MHz Apr-Sept, between 6am and 10pm 144MHz May-Aug, between 11am and 8 pm mid-morning peak & larger peak at abt 6pm Tends to occur repeatedly between same spots

Es layers contain high concentrations of ionized metal, which gradually fall to earth

Constantly being replaced by meteor debris No definite relationship between solar cycle and E layer Possible relationship with thunderstorms Theory: Wind shear causing ion concentration


Slide 14

Aurora (Ar)Aurora (Ar) Complex! Charged particles emanating from sun in the solar wind

become trapped in earth’s magneto tail which streams behind earth away from sun. Increase in solar flux stretches magneto tail until it snaps and reconnects into a more stable configuration. Some snapped particles eject into space, retained particles collapse back to earth. These collapsing particles somehow pick up enough energy to penetrate the E region.

Auroral effects are in E layer Daily rotation of magnetic pole about geographic pole & solar wind make

the auroral zone approach and recede twice daily Usable from 50-902MHz but mainly 50MHz and 144Mhz Visible aurora (400km high) & radio aurora (100km high) not consistent Both stations point antenna at aurora High power helps Range is about 2000km (usually less because of lack of stations) Region where auroral contact is possible is referred to as the “boundary

fence”. Oval 2000km to your east and your west and 1000km to your north (forward scatter) and south (back scatter).


Slide 15

Auroral EsAuroral Es Follows time and location of aurora 50-200MHz Higher latitudes, night or day, other times besides

summer Ionization originates from auroral particles Usually formed from ionization remaining after

auroral storm Ion concentration probably due to wind shear Usually northern latitudes but can spread south to

mid latitudes


Slide 16

Aurora MapAurora Map

See http://www.sec.noaa.gov/SWN/


Slide 17

Meteor Scatter (MS)Meteor Scatter (MS) Propagation is actually from trails of ionization as high velocity

fragments (grains) burn up at about 100km. Trail (tail) 20 – 65km long 1m in diam Meteors are random, any time works, but midnight to dawn best for MS Meteor “showers” are very predictable.

Quadrantids 3-4 Jan Arietids 8 June Nu Geminids 12 July Perseids 12-13 Aug Geminids 13-14 Dec

Pings are abrupt and rapidly fades (semi-coherent scatter) Bursts are much longer and may come from over or under dense trails Bursts from over dense trails increase in strength & oscillate then fade MS significantly easier on 50MHz than on 432MHz


Slide 18

Meteor Scatter – What Works?Meteor Scatter – What Works?

High ERP an advantage, horizontal polarization at both stations

“Point a not too directional beam along the great circle path at the other station and hope for meteors”

With meteors at 88-100km high max range is 2100 – 2250km

Longer contacts probably single hops assisted by other modes

WSJT software by K1JT makes MS much easier


Slide 19

Summary of Propagation ModesSummary of Propagation ModesMedium Mode Abbrev 6M 2M 70cm Above

Troposphr Refraction Tropo X X X X

Ducting Tropo X X X

Scatter Ts X X X X

Ionosphere Sporadic E Es X X

Auroral E Ar-Es X X

Aurora Ar X X X X

F2 F2 X

Meteor Scatter MS X X ? ?

Iono Scatter X ?

Obstacles Diffraction X X X X

Moonbounce EME ? X X X

Reflection X X X X


Slide 20

PolarizationPolarization Refraction and reflection of a wave is more

probable when polarization of the wave and the surface are in the same plane. (less loss)

Horizon, Ionosphere, clouds, various layers are horizontal with respect to the surface of the earth.

Horizontal polarization more successful for DX propagation at VHF and above frequencies.


Slide 21

So What Mode Was That?So What Mode Was That? Sometimes it’s obvious from frequency or characteristics

of the signals Sometimes more than one mode contributes to a path Short Es and long MS sound the same Very short tropo ducts sound same as Es (same time of

day, same season) Important to know whether a burst of signal is a prelude to

an Es opening Tools include weather maps, books, beacons, broadcast

signals, fm repeater behavior, DX spots, web sites, sun stats, aurora stats, celestial patterns, discussion and info sharing

Listen a lot! Experience!


Slide 22

What You Need to Succeed on VHF/UHF & UpWhat You Need to Succeed on VHF/UHF & Up A transceiver that covers the desired bands & has reasonable

performance Extra power useful but not mandatory Good Antennas are mandatory!!!

Horizontally polarizedRotatorThe more gain the better

Low loss feed lines very desirable Clear uncluttered horizon (there are other options) Flat or elevated site very desirable Antenna height very helpful Computer and some software in the shack helpful but not

mandatory Internet access in the shack can be useful


Slide 23

When’s A Good TimeWhen’s A Good Time??


Slide 24

Methods and ModesMethods and Modes

Point-to-point Meteor Scatter Moon Bounce

Voice on SSB CW JT44 & JT6M FSK441 PSK31 Other


Slide 25

WSJT by K1JT Joe TaylorWSJT by K1JT Joe Taylor Windows PC software (freeware) which uses a computer sound card

connected to a transceiver for: Tropo propagation using JT44 or JT6M Meteor Scatter using FSK441 EME (moon bounce) using modified JT44

Excellent way to learn about propagation See http://pulsar.princeton.edu/~joe/K1JT/ to download a copy of the

software See http://www.chris.org/cgi-bin/jt44talk for co-ordinating JT44

contacts. See http://www.pingjockey.net/cgi-bin/pingtalk for co-ordinating

FSK441 contacts.


Slide 26

ReferencesReferences

The VHF/UHF DX Book Vol#1 RSGB – Editor Ian White G3SEK

See the list of web sites


Slide 27

Web SitesWeb Sites Bill Hepburn’s VHF UHF Tropo Ducting as well as links to MUF, Aurora,

Meteor Scatter, F2 Skip http://www.iprimus.ca/~hepburnw/tropo.html Space Weather Now (solar, aurora, etc) http://www.sec.noaa.gov/SWN/ Gary Kronks Meteor Observing Calendar

http://comets.amsmeteors.org/meteors/calendar.html Weather Related Interference

http://www.bbc.co.uk/reception/factsheets/docs/reception_weather.pdf VHF UHF and up Spots http://dxworld.com/ IW9CER Spots and info http://www.iw9cer.com/ Paul Kelley N1BUG - VHF and Above http://www.n1bug.net/ Palle Preben-Hansen (Denmark) OZ1RH http://www.qsl.net/oz1rh/

Propagation VHF and Above

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