radio surfers since 20040701. Update 2001-12-25.

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 12 3 4 5 6 7 Graph 1 2 3	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!

Radio Aurora, FAI (Field-Aligned-Irregularities), TE (Trans-Equatorial-propagation type b) are all field aligned irregularities, where Earth's magnetic field lines must be properly oriented for signal to be reflected to the receiving site (propagation geometry). The reflected signal is attenuated by 10 dB/° if the angle of the incident ray is more than 3 degrees off from being perpendicular to the magnetic field lines. This angle decreases when frequency increases.
All these modes are closely related magnetic/electric field generated plasma instabilities. In such conditions the electric field excites the electrons to speeds exceeding the speed of sound and metric scale instability waves form. At lower electron speeds nothing happens. The visible light of the Aurora is not part of the process that causes two-stream Farley-Buneman instabilities, though they may co-exist.
Most VHF DX propagation modes suffer more or less often from multipath fading.
Multipath propagation delay spread can be observed by using a TV receiver (such as smeared F2 pictures) on most ionospheric VHF propagation modes, but it does not hamper slow 'data' rate narrow band communication modes.
The Aurora's Doppler spread makes SSB, and specially FM and TV signals usually unreadable.
In real life, specially on VHF low band, propagation path may often be a combination of TE to Es, or F2 to Es, but the real situation may be impossible to say for sure.
Back or side scatter (which are merely descriptions of propagation path geometry) may be observed (besides Auroral back scatter) on some propagation modes (at least on F2, FAI and meteor scatter) where the single reflection or scattering losses are not high. They might also consist of combinations of reflections from ionospheric layers (F2 and E) and/or ground.
There surely exists some un-listed propagation modes such as rainscatter, or other high path loss, or microwave propagation modes that have also been observed on VHF, but which are not considered of importance.
Principally, when the reflecting media is ionization, lower frequencies are usually preferred, with the exception of meteor head echoes, b type TE, etc. Technical differences, noise environment and other such biasing issues must be taken in to account when doing frequency band comparisons. Tropo and Aeroplane reflections are not part of this ionization-based group and with them propagation loss decreases on higher frequencies.
A detailed look into propagation modes reveals there are numerous listed sub-types for each mode (except for aeroplane and lightning scatter). However, comprehensive descriptions of all of them are beyond the scope of this page, but can only be found from scientific papers mostly, in which they might be conclusions of the individual scientist/author.

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.