Transcript Slide 1 - Sumter Amateur Radio Association`s

VHF
Propagation
NOTE: This is only an introduction. Further
personal propagation study is highly
recommended. Many of these propagation modes
are also active on 10 meters. Hint: Get on the air.
Introduction (1/2)
• Inverse Square Rule
• ρP=1/r2
– Doubling the distance from a transmitter
reduces the power density to ¼ the original
value
– If at 2 miles the power density is 4 watts/square
meter, at 4 miles it drops to 1 watt/square meter
– Kind of like paint coming out of a spray can
Introduction (2/2)
• D=√2h
– D=Distance in miles
– h=Antenna height in feet
• 4/3 Rule - Radio waves propagate to 4/3 visual horizon.
• Explanation
– Speed of radio waves in air
– At Altitude it’s colder, less water molecules to attenuate signal
– Higher wave portion moves faster through upper air, so go
farther
• Like walking in water up to your knees – your upper body in the air can
move faster than your legs in the water.
– This bends the radio waves (Refraction)
Visual Cues
• Light waves also refract like radio waves
• Super refraction – Objects over visual horizon
are visible (commonly called a “mirage”).
• Ground mirages on hot, calm days
– Also bends radio waves
• Example – California-Hawaii path.
• Look for enhanced propagation on hot, still, hazy
days
• Es usually around longest/shortest days of year
Troposcatter (1/3)
• Signals refract off of particulate matter or
objects in the atmosphere
– Moisture, dust, buildings, etc.
• Two stations may be beyond line of sight, but still
able to communicate
• We use this all the time
– Simplex HT use in open areas outside line of sight (i.e.
On opposite sides of a small rolling hill)
– Hitting the repeater with no direct line of sight
Troposcatter (2/3)
• Think seeing car headlight beams in the air
before you see the car come around the curve or
over the hill
– Microwavers bounce off thunderstorms,
precipitation, airplanes, etc.
– N4VBV – W4CRZ 1/2w 70cm path
• Military/Commercial Troposcatter use
Troposcatter (3/3)
Airborne Particulate Mass
Hill
Station A
Station B
Actually works better if the highest particulate concentration is near
one end of the signal path.
High Pressure (Inversion) Tropo (1/2)
• Calm high pressure system
• At approx 1000’ up the air gets warmer/dryer with
increased altitude vs cooling.
– Ever drive up a mountain and the air gets warmer as you go
up, causing your windows to fog on the outside?
• This sharp change in temperature, moisture and
pressure changes the air’s refractive index
• This ducting condition may refract VHF/UHF signals
for hundreds or thousands of miles
– Has nothing to do with the ionosphere
High Pressure (Inversion) Tropo (2/2)
• This is called “instability” by weather folks
– Steve’s SKYWARN brief
• Commonly caused by frontal layers and morning
radiational cooling of lower air layers
– Like when the temperature drops just after sunrise
• Duct thickness is important
– Some ducts will conduct 70cm but not 2m
• Don’t necessarily have to be “in” the duct
• Ducts may appear quickly and fade quickly, but may
last quite a while
Low Pressure Tropo
• Storm fronts approaching
• Usually shorter lived than high pressure tropo
(May need SSB/CW)
• Watch the barometer – as the main front meets
your location the duct will probably drop
Tropo Ducting
Cold Air
Warm Air
Cold Air
Earth’s Surface
Station B
Station A
Station A
Warm Air
Station B
Cold Air
Sporadic E (Es)
- Charged E-Layer clouds reflect VHF
(mainly 50 and 144 MHz) signals.
- Multiple hops possible.
Other Modes (1/3)
Es Cloud
Multi-Hop Es:
Es Cloud
Station A
Es – F2 - Es
Station B
F2
Station B
Station A
Es – High Altitude Duct - Es
Station B
Station A
Can also have combinations of above.
Other Modes (2/3)
Trans-Equatorial Propagation (TEP)
- Between stations equidistant from the “radio”
equator (Also called “chordal hop”).
- Signals enter F2 layer, propagate across
equator, exit same distance on other side of
equator.
Earth-Moon-Earth (EME)
- Bounce signals off the moon.
- High power, long antennas, new digital modes.
Other Modes (3/3)
Aurora Scatter
- All stations point beams north.
- Bounce signals off auroral curtain.
- Usually use CW/digital modes due to the
“flutter” of the moving aurora.
- Higher power, “mostly” northern stations, BUT
remember when aurora was active in SC in
October/November 2003.
The Practical Part (1/3)
• Listen
– Propagation beacons (Usually CW)
• 6m – 50.060-50.080 (Also 10m beacons 28.170-28.300)
• 2m – 144.275-144.300
– Only one 2m beacon listed for SC – JT on 144.277 (CW)
• 70cm – 432.3 - 432.4
– NOAA WX Radio stations
– 146.52 Simplex
– Distant Repeaters
• Raleigh is ~ 130Miles straight-line distance, but not over
flat ground; not normally heard.
– Distant FM radio stations on an empty dial freq.
The Practical Part (2/3)
Calling Frequencies
– 6m: 50.125 (50.110 for DX) (SSB/CW);
• 52.525 FM Simplex (10m: 28.400 SSB; 29.600 FM for General and up)
– 2m : 144.2 SSB/CW; 146.52 FM Simplex
– 70cm: 432.1 SSB/CW; 446.0 FM Simplex
– Hint: Program 29.60, 52.525, 146.52, and 446.0 into
an old scanner and leave it on
• Can also program active 10m/6m/2m/70cm repeaters at
various distances/directions around your station that are
not normally heard
– Some enhanced propagation may start at the lower
bands and move up, or the other way around
The Practical Part (3/3)
– For other VHF/UHF bands, check:
http://www.arrl.org/FandES/field/regulations/bandplan.html
• Listen/CALL on 29.6/52.525/146.52/446 FM
• Use the repeater directory to try distant repeaters along
the estimated ducting path
• May be able to get hundreds or thousands of miles when
ducting is active
• Most long distance operators use SSB/CW with
horizontal polarization, but if you only have vertical
antennas and FM give it a try anyway
• Even though you may not physically be “in the duct”,
your signal may be able to get in
Raleigh-Sumter
- 147.015 repeater output (same as ours)
- 130 mile path
- Just after sunrise
- 800’ Antenna height
- √2*800=√1600
- 40 miles under normal conditions
over flat terrain
- Over 3 times longer reception when
ducting active
- Happens regularly
Sumter - Laurens
- 90 mile path (146.52 simplex)
- Just after sunrise
- 5’ Antenna height/25w mobile
- 20’ Base antenna
- √2*5 (√10) +√2*20 (√40) = 9.5
- 9.5 miles under normal conditions
over flat terrain
- 10 times longer reception when
ducting active
Sumter-Athens, GA
- 144 mile path
- Near Sunset
-800’ Repeater antenna height
- 50’ Base antenna
- 47 miles under normal conditions
over flat terrain
- 3 times longer reception when
ducting active
JT’s 1000 mile 2m/5W Beacon
Grid
Latitude
Longitude
Your Station:
EM93TW
33.93750°
-80.37500°
DX Station:
EM10GC
30.10417°
-97.45834°
Distance:
1035 miles @ 259°
Run Anothor Calculation
From: [email protected]
Date: Tue, 5 Jan 2010 22:54:05 EST
To: <[email protected]>
Subject: Reception of W4CRZ/B into EM10gc
Hi, Mike, N4VBV,
It's good to hear from the guys behind the BCN's CW. There are a lot of unknowns about that
reception, and about the propagation that night.
I've asked around to several of the locals
who were on that evening, and having the time of their lives with the DX opening. So I've
incorporated some of their observations in this, too. The concentrated on working stations
above 144.100. I may have been the only station who looked below 144.100 for BCNs.
As you recall, there was a long and fairly straight cold front stretching SW-NE. Before it the
winds were relatively warm humid Gulf air out of the S and SE. The winds were riding along
over a fairly chilled ground, and this probably caused the inversion(s) and odd ducts. Before
the front passed them, stations in KS, MO, and OK were working into central Texas. The
spectacular ducting, however, was occurring between here and points NE, into LA, MS, AL,
GA, and TN.
And they were ducts for sure. Local stations 50 miles apart here had markedly different paths
to the NE. Over the approximately 1/2 hour I was hearing your BCN it was in there all the
time. The announced altitude of the BCN may be a confirmation of some of the recent
discussion about ducts and inversions being higher AGL on their E ends and lower on the
W. The only other stations I worked around the time I was hearing W4CRZ/B were in the
mountains N of Atlanta, and in the mountains of TN. I don't know if there were just no other
stations on over your way, of if the duct was a pipeline between us.
With great conditions 5 W and a loop obviously can do wonders. Thanks for getting it on, and
maintaining it. I certainly will be looking for it (and the guys behind it) the next time things
break open.
73,
Bill, W5GVE
EM10gc
Online Sources to Check (1/4)
• http://dxworld.com/144prop.html
Online Sources to Check (2/4)
• http://mountainlake.k12.mn.us/ham/aprs/path.cgi?map=na
Online Sources to Check (3/4)
• http://www.dxinfocentre.com/tropo.html#hour48
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7
8
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Online Sources to Check (4/4)
www.dxmaps.com
Weather Effects Example
• See next 2 slides
The Bad Part of Ducting
• Repeater Interference
– Repeaters coordinated based on normal conditions
– May require PL to be turned on when not normally needed
– May cause problems in emergency situations
• Microwave link problems
– Hap’s ETV microwave link discussion
– Satellite Signals
• Cell phone issues
– Ever notice no/spotty reception near sunrise/sunset where it’s
normally good?
Ducting “Head Scratchers”
• Ducts usually form at 800’-1000’, but may be at
different levels
– Near the surface
– 30,000 Feet
– Sometimes you might head for high ground looking for a duct
and pass right through it
• A 2m duct may not work for 6m
– Same for 70cm and 2m
– Think duct thickness as related to wavelength
• Sometimes the repeater may sound “poor”, but actually
be working fine
– Repeater antenna is in the duct but you’re not
Ducting Prediction
Actual WX
Actual 2 Meter Propagation
References
• 2006 ARRL Handbook, Chapter 20,
“Propagation”
• CQ Communications “VHF Propagation, A
Practical Guide for Radio Amateurs”
• Any internet search