radio surfers since 20050614.

This page presents basic VHF DX propagation modes and their properties with audio and graphic samples

Mode
Signal strength
Link to VAW
& graph
Sub types  Cause Annual variation Daily variation  Affects signal spectra Fading Usual
event
duration
Path distance Reflective media height Predic-
tability
Misc.
Tropo(-spheric)
Strong
Enhancement,
 ducting, troposcatter
WX related (as High moves away). Inversion layer
(prefers sea areas)
Yes, most: summer/fall,
depending on WX patterns
Yes, more often at night No In good condx:
slow if any
Hours to
days
Usually 500...~1000 km, but
ducting up to 4000 km
<450 m or
>450 m (<15 km)
Fair Better on higher freq.
Meteor scatter
Fair
Audio 1234567
Graph 123
Physically: relection or scatter Ionization of air by meteoric particles Yes, max.: fall & during
meteor 
showers, minima in spring
Yes, 1/2 to 1/4 ratio, max. in the morning, min. in the evening Head echoes: Doppler shift deep & fast with bursts Milliseconds to minute(s) 800...2350 km 80...120 km Fair Better on lower freq. Always present.  Path loss @ 50 MHz ~170 dB
Low latitude
sporadic E 
(Es)
Strong
Many, windshear&
???
No Yes, most around noon No Deep, semi-
irregular
Minutes to
 hours
600...2500 km + multi 90...120 km Unpredictable Better on lower freq.
Mid latitude
sporadic E (Es)
Strong
Graph
Many, windshear&
???
Mostly during summer months Yes, most: afternoons, evenings No Deep, semi-
irregular
Minutes to
 hours
600...2500 km + multi 90...120 km Unpredictable Better on lower freq. (path loss@50 MHz>140 dB)
High latitude
sporadic E (Es) = Auroral E
strong
Aurora related: energetic electrons frm magnetosphere No 15...06 LT, most during Harang-discont.  @ ~21 local time Flutter may occur Deep, semi-
irregular
Minutes to
 hours
600...2500 km + multi 90...120 km Unpredictable Better on lower freq.
D-region scatter
Weak
Ionoscatter,
PMSE (polar mesosphere echoes) @ high latitudes
Solar radiation induced turbulence (signal varies more at high latitudes) Peak: summer Max.: near noon, min.: evening. PMSE: flutter 0.1 to 3 Hz on 50 MHz PMSE: ~hours 900...2000 km daytime: 70 km, night 85 km (but weaker) Varies unpredictably, but is "always there" high path loss mode. Some times overrun by other E layer modes Better on lower freq.(path loss @50 MHz~225 dB)
Aurora
Strong
Graph
Audio
Afternoon, evening/night, (A1..3, E, S, types) Solar particle induced 2-stream plasma instability
(auroral zone only only)
Most around equinoxes Yes, most: afternoons, 
evenings/
nights
Strong Doppler spread & some shift Tens of minutes to hours 0...2300 km 80...120 km (110 km) Poor/fair Better on lower freq.(Path loss@144 MHz >175 dB)
FAI (field aligned irregularities)
Fair
(Mid lat.only) Related to radio aurora & TE(a) propagation. Called FAI when observed at mid latitudes Summer Yes, most:
day/evening
Doppler shift & spread & flutter (but not as much as aurora) <-- see Tens of minutes to hours <2300 km 95...130 km
TE (trans-equatorial= equatorial scatter)
Strong
F-layer scatter (a) during afternoon,
E-layer scatter (b) during evening. Across magnetic dip equator only.
 (a) Plasma instabilities.
(b) Iono acoustic waves by eqatorial electrojet.
Most around equinoxes and (a) solar maximas Yes, mostly
(a) 17-19 local time,
(b) 20-23 local time
 (a)  Doppler <4 Hz
(b) Strong Doppler spread & some shift <40 Hz.
(a) low QSB. 
(b) deep & rapid <15 Hz
(a) 6000...9000 km
(b) 3000...6000 km
(a) 250...1000 km
(b) 90...130 km
Unpredictable (a) better on lower (VHF), (b) better on higher frequencies (V/UHF)
F2
Strong
Mid & low latitude Solar particle ionization at F2 layer
(Prefers lower latitudes)
Most around solar maxima's & equinoxes Yes, most: afternoons, 
evenings/
nights
No No Tens of minutes to hours  3000..12000 km 250...400 km Mostly
unpredictable on VHF
Better on lower freq. (rare on 50 MHz, non exists >60 MHz)
Aeroplane reflection
Fair/Strong
Spectrograph
Artificial airborne
 metallic
objects
Acc. to air traffic Small +-Doppler shift Fast-slow
-fast pattern
Tens of seconds to minutes 0...600 km <15 km Yes, airline
schedules
Better on higher freq.
Lightning scatter
Weak
Audio
Lightning path ionized air Yes, WX
 patterns
Yes, least thunder in the morning hours No Under one second <600 km <15 km Same as predicting 
thunderstorms
Obs. path loss @144 MHz ~>225 dB)

 Notes: Main features of VHF DX propagation modes. Numeric values represent the usual situation and should not be taken literally.
Latitude may more often refer to magnetic latitude rather than geographic in cases related to magnetosphere related ionospheric radio wave propagation. (Low latitude~equatorial, mid latitude~temperate latitude, high latitude~auroral zone...~..polar area.)
Extended range propagation may occur through multiple hops (TX to ionosphere to ground to ionosphere to RX) or as successive ionospheric reflections from same or different layers (TX to F2 layer to Es layer to RX, or other combinations) which are marked on the table with "xxxx km + multi".

Audio & graph sample information:
Meteor Scatter audio 1: TV carrier on 85 MHz, unknown distance, mode CW, RX ant. 4-el. QTF 160°.
Meteor Scatter audio 2: 144 MHz high speed keyed CW, UT/DL2SDQ, 350W 17-el., KO39ER-KP30HV, RX ant. 4*15-el, 04-07-2000 1231 UTC.
Meteor Scatter audio 3: 62.213 MHz, Lopik, the Netherlands, mode CW, RX-ant. LPDA, QTF 260°, 12-08-2000 11-13 UTC.
Meteor Scatter audio 4: 85.260 MHz, TV carriers, mode CW, RX-ant. LPDA, QTF 170°, 12-08-2000 11-13 UTC.
Meteor Scatter audio 5: 88.800 MHz, mode FM narrow squelched, RX-ant. LPDA, QTF 225°, 12-08-2000 11-13 UTC.
Meteor Scatter audio 6: 144.100 and 144.200 MHz, high speed CW & SSB, RX-ant. 4*15-el., QTF 225°, 12-08-2000 11-13 UTC.
Meteor Scatter audio 7: 191.238 MHz, Russian TV carriers, mode CW, RX-ant. 10-el TV Yagi, QTF 150°, 12-08-2000 11-13 UTC.
Meteor Scatter graphs: TV carrier on 85 MHz, unknown distance, mode CW, RX ant. 4-el. QTF 160°, 12-08-1998.
Sporadic-E graph: TVcarrier on 48.250, station and distance unknown, RX ant. Discone, June 2000.
Aurora audio: SK4MPI on 144 MHz, JP70NJ to KP30HV, mode (keyed) CW, 1.2kW ERP, RX ant. 4*15-el., QTF 20°.
Aurora graph: SK4MPI on 144 MHz, JP70NJ to KP30HV, mode (keyed) CW, 1.2kW ERP, RX ant. 4*15-el., QTF 20°, 21-03-1998.
Aeroplane reflection spectrograph: Vuokatti YLE TV carrier on 61.873 MHz, KP33 to KP30HV, mode CW, 16-03-2000 1700 UTC.
Lightning scatter audio: SK4MPI on 144 MHz, JP70NJ to KP30HV, mode CW(narrow), RX ant. 4*15-el., 29-06-2000 2020 UTC.

Note: There are no audio samples on modes that do not change the detected radio signal significantly. Please note the possible modulation (or keying, if not carrier-only), has nothing to do with the effects caused to the signal by the propagation mode itself!


Unfortunately, the information within the table is not quite comprehensive, as there are lots of  poorly known aspects in radio signal propagation.

Thanks for Väiski (OH2LX) again for additional comments & corrections.


 
 
 



This page and the audio samples and graphs are © Ilkka Yrjölä, OH5IY, 2000...2016. All rights reserved.