INTRODUCTION TO HF PROPAGATION for Ham radio or SWL
I translate from French to English
http://www.f4fjp.fr/propagationhf.htm?fbclid=IwAR3fBN25hS0Yt3I5HXcy0vtuWGUClHtur3ndKuR8Sp7NUUo6YY5d2QVqrLw
(the first part is a bit difficult to understand)
During a transmission, the transmitter sends HF energy through the antenna. The main energy concentration lobe presents an angle, above the horizon, which varies according to the antenna and its environment. Part of this energy is lost in space and the other part is guided, reflected or refracted in the various ionized layers of the ionosphere.
Between the antennas and the first point of return of the wave towards the ground, there is an area in which the signal is not received. The length of this zone depends on the elevation angle of the antenna. Depending on the bands, it is nevertheless possible to establish short-distance links by broadcasting the ground wave.
The ground wave, which only affects low frequencies, is a wave which propagates over a short distance (+/- 200 km) following the curvature of the earth; while the other waves are refracted by the ionosphere. On the amateur bands, we make very little use of ground waves.
DIAPER EVOLUTION DURING THE DAY
With sunset, the D and E layers disappear leaving room for the F1 and F2 layers to appear; whereas during the day, the ionization is significant and all the layers are present.
THE SKIP
It is the leap, the leap which separates the departure of the wave (antenna) and its return to the surface of the earth (after reflection or refraction). In this area listening to the transmitted signal is not possible. In this zone, the MUF is therefore much lower.
QSB
QSB is the fading that causes the signal to rise and fall at a more or less rapid rate.
On medium wave we have big problems with QSB or FADING
To join the F layers after having crossed the ionosphere, the signal can take several paths simultaneously and be refracted by layers of different refractive index. The signal you receive is therefore composed of several of these refracted signals arriving either in phase (high signal), or out of phase (low signal) or squarely in phase opposition (no more signal)
MULTI-HOP
A skip to contact the antipodes is impossible. In the case of a very long link, several hops are necessary. During an emission, part of the wave crosses the ionosphere and escapes into space (too large angle, critical frequency), another part is absorbed by the layers (collision of atoms and loss of energy), a third part is dispersed in several directions by the irregularities of the layers and finally the last part is refracted by the ionized layer, then after returning to earth returns to the ionosphere and the cycle begins again.
GREY LINE
The Grey Line is the line separating the surface from the earth
between the sunlit area and the night area. In reality, this line is not one, it is a fairly wide zone in which the transition between day and night is made. We have seen above that the ionosphere evolves between day and night. Some layers merge into one and others, with high absorption, disappear at sunset. Conversely, at daybreak, the F layer is reinforced before the appearance of the D and E layers. During this period, on the day side, the D and E layers have not yet appeared, while on the night side the F layer is still present. During these short moments (1 hour at sunrise and sunset) the propagation is very good.
https://dx.qsl.net/propagation/greyline.html
SECOND PART
Amateur radios use small antennas and powers compared to AM radios. On the shortwaves there are powers of 500 KW = 500,000 watts on very large antennas that are sometimes directive. The gain of the antenna can multiply the power of the transmitter by 100! In addition the radio turns its antenna towards the continent where it wants to be heard. So a radio that transmit to your country with 500 KW you are sure to be able to hear it!
Propagation 160 meter to 10 meter ( amateur radio have 9 bands )
160 meters ( or mediuw wave for SWL ) and 120 meter
During the day, contacts of less than 150 km benefit from reliable ground wave propagation; at the same times, the strong absorption of the D layer makes it very difficult to make contact over greater distances. At night, when the D layer disappears, waves can reach the F layer and be reflected. Greater distances are then possible.
Atmospheric noise can be very important and make communication very difficult. Mid-latitude thunderstorms generate a lot of static, especially in summer.
Better listening this band during the WINTER
80 meters
( or 90 meter and 75 meter for SWL )
The daytime absorption of layer D, even if it is less important than on the 160 meters, practically completely closes this daytime band; however it is still possible to practice contacts up to 400 km using a high angle. As soon as the sun begins to set, it becomes possible to make intercontinental contacts (up to the antipodes).
As for the 160 meters, the atmospheric noise is very present and the statics are very important in the summer.
Better listening Winter Evenings and Nights
40 meters
( or 60, 48 pirate, 41 meter for SWL )
The absorption of layer D is much weaker than on the lower bands, which has the consequence of maintaining an almost permanent opening depending on the mode of propagation. By day, the use of the E layer allows communications with a range of about 800 km in very stable conditions. At night, as soon as the ionization begins to drop, the F2 layer allows global contacts of very high reliability.
Atmospheric noise is minimal and static levels, even in summer, are generally lower than signal levels
Better listening Winter Evenings and Nights
30 meters
( or 31 and 25 meter for SWL )
This band shares the characteristics of the low bands (night opening) and high bands (day opening)
Atmospheric noise is minimal and static levels, even in summer, are generally lower than signal levels. During the day, the absorption of the D layer is insignificant making contacts possible over distances of up to 3000 km. At night, communications with the antipodes are possible. The use of the F2 layer is possible 24/24. MUF of certain area may decrease below this frequency.
The 30 meters band is the least subject to variation during the solar cycles. DX communications are therefore very stable at all times.
Best Listening the night
20 meters
( or 25, 22 and 19 meter for SWL )
This is the favorite band of the majority of OMs for worldwide communications. Dependent on the solar cycle, this band is always open at least a few hours a day for DX traffic via the F2 layer. It is also possible, from time to time, to establish short distance contacts via the E layer. During the maximum of the solar cycle, the band can even remain open 24/24. In winter, the band closes relatively early.
Atmospheric noise is negligible even during the day.
Best DX Openings: Days of Summer
17 meters
( 16 meter for SWL )
This band behaves like the 20 meter band, but it is more sensitive to variations in the solar cycle (of 11 years). In periods of low solar activity, the 17 meters are only open to DX during the day on a north/south axis and in latitudes below 50 degrees.
During periods of maximum solar activity, the band opens to long distance communications all day, early evening and even late into the night.
Atmospheric noise is negligible even during the day.
Good now because hight solar activity !!!
15 meters
( Or 16 meter for SWL )
This strip behaves substantially like the 17-meter strip, except that during low periods of solar activity, the strip can remain totally closed at all times.
Very dependent on ionization, the 15 meters band is only daytime during periods of low solar activity.
The traffic is very heavy via the F2 layer and very low, but possible, in ES (sporadic E).
Because high solar activity SWL is good in 2023
12 meters
( 13 meter band for SWL )
This band benefits from the advantages of 15 and 10 meters.
It is mainly a day band during periods of low or moderate solar activity.
In periods of strong solar activity, the 12 meters can remain open even at night.
In periods of low solar activity, the 12 meters are only open to DX during the day on a north/south axis and at latitudes below 50 degrees; but during these same periods the band can remain closed all day.
From 12 meters, ES contacts begin to be possible. ES openings are sometimes observable in winter, but their peak is between late spring and summer
10 meters
( 11 meter for SWL )
This band is very sensitive to variations in solar cycles and therefore very changeable.
It has a large number of propagation modes.
In periods of strong solar activity, the band opens at sunrise and closes a few hours after sunset.
During these periods, a power of a few Watts makes it possible to establish contacts of several thousand kilometers.
In periods of moderate activity, the band only remains open for low latitude transequatorial communications. During periods of minimum activity, DX communications are totally impossible.
The ES propagation begins to be important on 10 meters. It allows contacts over a distance of about 5000 kilometers. It reaches its maximum between the months of May and August.
For SWL the 11 meter band 25600 to 26100 is not use by many radio stations.
I make few articles about propagation on my blog
Look also at these links
Where are the tropical bands? According to the rules, there are three distinct ranges: 2300 - 2495, 3200 - 3400, and 4750 - 5060 kilohertz.
Free book in PDF
Aucun commentaire:
Enregistrer un commentaire
Please indicate in your comment your amateur radio callsign, swl, or your email
Remarque : Seul un membre de ce blog est autorisé à enregistrer un commentaire.