SM6EHY on PROPAGATION (below 10 MHz mainly)

After beeing active some few 10 years on especially 80 and 160-meters having used directional antennas one cannot neglect to comprehend something about the band behaviour or propagation towards distant locations.

Most of the papers written on this subject is made due to direct orders from the BC-industry.
They had to know where their transmitters could be heard with reasonable readability and for how long at dayhours mostly. A radio amateur is not only interested in this phenomenon, rather is it how far out one can reach at each time (evening or nighthours mostly) on a given band.
Using a non directional antenna one can only notice different signalstrengths and cannot decide from which azimuth sector the particular signal is coming from. Ofcourse one can hear from what country a station is coming from but this does not indicate the azimuth direction for certain.
One can quite easily decide however if the signal travels trough an area where the Aurora Boralis is active, due to the signal quality: Selective fading and flutter are signs of auroral affection.

Communication parameters
Most commonly (nowdays) this is a matter associated with microwave communication links. These parameters are (seen from the transmitter / receiver all the way towards the ionsphere):

Transmitter

Receiver

Modulation type

Demodulation

Transmit bandwidth

Demodulation bandwidth

Power

Sensitivity

Feeder loss

Feeder loss

Antenna gain

Antenna gain

Clear view in direction

Clear view in direction

Fading, Multipath, Background
energy from the sun at the
bouncing area.

Fading, Multipath, Statics, QRM,
Background energy from the sun at
the bouncing area.

If You increase Your transmit power by a factor of 4, You will be heard at twice the distance, when You are in the linear portion of the graph.
If You have gained enough number of dB's, for the path of interest, You will notice that You will get out twice the distance for LESS than 4 times (6 dB's) the power. The graph can be almost flat, meaning that You can count with to increase Your distance twice by only increasing Your power a fraction of a dB !
It is quite obvious that it is desireable to reach for this "super-conducting"-level. In order to gain it, Your antenna radiation lobe has to be in the very right spot, both in azimuth and in elevation. The specific installation is more responsable than the antenna itself.

The transmit energy excites the atoms at the bouncing mass in such a way that they cause a chain reaction. If the transmit energy is high enough it seems like the electyrons are lifted one or more energy "levels". On very rare occations the transmit energy can set such a stress at the mass, that the reflection coefficient rather gets worse with increased level for a specific angle. The reflection starts at other angles, and a spread reflection takes place. Too much background energy from the sun has the same effect.

Read the A-index from WWV i Boulder; if under some 4 or over some 10, indicates disturbed conditions. The A-index is a 24 hours average, and the K-index is a 3 hour index. For the ionsphere layers to be best for low frequencies (some 2 to 10 MHz), the K-index has to be low (<2 ); the longer the better. It indicates that the bouncing mass is uniform enough in order to enhance bouncing. With values a bit higher, the upper HF-bands gets better, hence the uniform unit is in wavelengths.

As the activities of SM6EHY reveals, we have no less than 8 different propagation modes on the 80m-band:
 

Propagation mode

Takeoff angle

Maximum occurance 

Duration

Distance

1.
Groundwave path

High

Always
Consistent

No DX

2.
Normal Skywave path
(only ONE bounce in the
ionsphere and back)

High
(Rarely low) 

Almost always
Almost consistent

No DX

3.
Short path 

High and
low

Nights / Twilight
Nights / Twilight

DX

4.
Long path

Mid high

Depends upon DX location
Mostly BOTH stations at twilight
and ONLY some 1% of time

DX

5.
Trans Equatorial path

High

Summer
Around midnights

DX

6.
Polar Cap path
(for stations located within the Auroral cap
at the time)

High and
low

Both highly dependant upon
the auroral activity at the time

DX

7.
Skewed Short path

High
(rarely low)

The dark half year
When the direct short path is closed
due to auroral activity

DX

8.
Skewed Long path

High

Depends upon DX location
Mostly BOTH stations at twilight
some 99 % of time

DX

How to determine if the condx are good or bad ?

It is highly a matter of what You think of !
    Is it the signalstrength or the readability at one or both ends ?
  2   Is it to be able to get as far away as possible?
  3   Is it to be able to talk with Your friend in VE1 (N.Foundland)[in the European point of view]?
  4   Is it the number of DX-stations You can work per hour ?

1: Signalstrength: You have to decide what time of night that is best, considering the equipment used at both ends. If both stations are using DX-wise poor antennas (a simple InvVee or a Dipole at some low height ; < 15 meters AGL) the maximum occurs when both are in TWILIGHT or both are in darkness and have equal distance to a twilight zone.
Readability: Not only to have the above in mind, but also consider Local Noise (QRN=static crashes from thunderstorms nearby). For example if You are located in the Mexican Gulf or in Indonesia You have some 15 times more statics than the guy up in Scandinavia. In a low noise area it is common knollege that if You hear a station from a high noise area, he must be at least S9+ before it is worth calling him, because he has a local noise level of some S9... . Choose a low noise period or yet better a special low noise reveiving antenna at the high noise end. The QST-magazine has an article almost anually about this matter.

2: First of all, get yourself a DX-edge calculator or a computer model visulizing the grayline around the globe (Miller projection). By means of this tool You will be able to determine how far away You can reach. The poorer Your efficiency is at the low take off angles, the closer to the exact sunrise/sunset-line You get.
You can use the grayline info to determine how efficient your antenna is for Long Haul DX-ing.
The following figures regards 80 meters:
for a latitude close to the equator you can get some 40 minutes grayline-effect for a good antenna. The poor antenna will only give you some 10 minutes. At 57° you can get up to 2.5 hours (and even more...) and down to 30 minutes, not counting the 3 summer months when the entire (quite short) night will give you a grayline-effect.

3: The signalstrength maximum occurs when both have equal distance to midnight and a dark sky. The takeoff angle is quite high, and You must use a high angle radiating antenna such as an average dipole or a horisontal polarized loop, broadside to the other stations great circle sector. Under severe conditions the Aurora can wipe out a contact. Using a vertical with good efficiency at low angles will often make a contact possible at these severe conditions.
If the readability is the mayor concern use a vertical antenna with good and long radials in the other stations great circle sector. You can count with to have a contact up to some 1.5 hour BEFORE sunset in VE1 and some 1.5 hour after sunrise at Your end.

4: Here we encounter some more factors other than pure wave propagation. We have to include what the usual operators habits are like.
When in the evening hours are most of them active on the radio ?
What do they do around their sunset / sunrise ?               What do they do around their midnight ?
At sunset the operators usually; drive home from work; eats their dinner; watch their television news; socializing with their family e t c.
At sunrise they either; sleeps; eats their breakfast; drives to work e t c.
The operating experience tells that we are mostly active from some 2100 to 2300 hours local time. At this time we have high radiation angles active. To be able to contact a stateside station for a station in Eu, the operating time shall be chosen to be 2100 + 6 = 0300 CET.

SKEWED PATH
This phenomenon is not mentioned in many other papers (if any ?). The occurance is maximized around the Spring / Autumn equinoxes and are generally active when the usual direct path is closed. Most often this means that the Aurora is active.
As can be seen in the table above, this path involves HIGH take off angles, almost disregarding the distance. The actual bouncing from the ionsphere takes place higher up above the earth than usual.
How come ?     To explain the bouncing mass, we have to recall that our mother Earth is bombarded by the Sun-storm of particles. During daylight the height of the ionsphere is depressed towards ground, and the opposite during the night, when the storm tends to drag it out from earth.
See an example picture of one of the equinoxes here.
As can be seen we have an oval highly dark area, with a twilight area surrounding it. In the middle of this dark oval we have a peak height of the ionsphere. It is highly assumtious that even the highest take off angle signals will sooner or later come close to the bouncing layer in a smaller angle than necessary for to be totally reflected. The incoming bounce-angle is the same as the outgoing angle, which means that on the other side of this oval the signal will be reflected again down to earth, in order for some station to hear it.

If the signal path is skewed within the night oval, it is also quite possible for the signal to be bouncing around in ovally shaped circles, with a certain height angle transfer for eatch turn. This means that the signal can be delayed up to a few seconds, before eventually dropping down to earth again.

Propagation analysis are made in almost every countries national magazine. There is but one significant thing that is overlooked in ALL predictions. It is the "common knowledge" every active Ham has.
The analysis programs; IONCAP, ICEPAC, Minimuf e t c are NOT dealt with in view of the active Ham operator. These analyses are based upon the BC-industry; Good antenna and POWER at the transmit end, and poor efficient antenna whip at the receiving end. This way the prediction has little effect for us, telling us when a band is open.
As the investigation of SM6EHY reveals, we have to take off some 70 dB of attenuation in order to be able to see the actual openings we hear on the bands.
That is due to that the amateur can rely upon some  6 dB signal to noise (s/n)-ratio, and NOT 70 dB the programs ,by default, puts in; the Rx-antenna is far better than the default used "whip" and the Rx-bandwidth is much smaller.
When such attentuation is taken off, we can see the following over a given path.
In a typical winter month, Gothenburg (Sweden) - Delaware (USA) in sunspot minimum.
 


© Björn Waller, SM6EHY 1998, 1999