simply RED
May 10th, 2006, 06:49 AM
Short Waves (3 - 30 MHz), anyway 1,8 is often included...
Here is the bandplan for frequencies used by amateours.
The best place for interference is very near these frequencies.
http://www.bfra.org/cgi-bin/index.cgi?bandplan.html
Here is the bandplan used for broadcast.
http://ibb7-2.ibb.gov/ibbeng/shtwave1.htm
These bands are 24/7 crowded with international broadcast services. Some exotic radio stations are presented there.
Consider everything else military bands and do not interfere there!
Modulation: Usually SSB or some kind of encoding is used in HF communication.
Antennas: "T" and "G" are common listening antennas. 1/4 vertical dipole is a good choice for the upper bands.
Yaggies and other sophisticated antennas are used for both receiving and transmitting.
Information for the bands:
The 1800 kHz (1.8 MHz or 160 metre band) band suffers from extreme daytime D-layer absorption. Even at high radiation angles, virtually no signal can pass through the F layer and daytime communication is limited to ground-wave coverage. At night, the D layer quickly disappears and world- wide 160m communication becomes possible via F2-layer skip. Atmospheric and man-made noise limit propagation of this band. Tropical and mid-latitude thunderstorms cause high levels of static in summer, making winter evenings the best time to work long distance at 1.8 MHz. A proper choice of receiving antenna can often significantly reduce the amount of received noise while enhancing desired signals.
The 3500 kHz (3.5 MHz or 80 metre band) is the lowest HF band, which is similar to 160 m in many respects. Daytime absorption is significant, but not quite as extreme as at 1.8 MHz. High-angle signals may penetrate to the E and F layers. Daytime communication range is typically limited to 400 km, primarily via ground-wave propagation. At night, signals are often propagated halfway around the world. As at 1.8 MHz, atmospheric noise is a nuisance, making winter the most attractive season for the 80 m.
The 7000 kHz (7 MHz or 40 metre) band is useful for daytime communication up to a distance of 800 km via E and F layers. Long distance world-wide communication takes place in this band through F2 layer.
10 MHz BAND
The 10 MHz or 30 metre band is unique because it shares characteristics of both daytime and night-time bands. Communication up to 3000 km is typical during daytime, and this extends halfway around the world. The band is generally open via F2 o n a 24-hour basis. The International Telecommunication Union (ITU) has allotted 10,100 kHz to 10,150 kHz to the radio amateurs in Region 3 countries.
14 MHz Band
14 is a typical daytime band.
This is the most useful HF part. Long distance transmission is possible via F layers (up to 4400 km for a single hop). And short distance via E (several hundred km). With multiple hops and combination of F and E reflection sometimes the whole world is covered.
Majour drawback is the expensive apparature and the sophisticated antenna systems.
21 and 28
Consider these to have UHF properties.
21 has too high frequency to be useful for long distances. 28 is absolutely useless for more than 50km...
Anyway there is a citizen band there that is available without any permission and nobody watches near this band.
Despite the fact that the introduction of artificial communication satellites for long distance radio communication made communication more reliable and there is very little role left to be played by the ionosphere in the professional telecommunication networks, it still draws the attention of communication enthusiasts, arm forces and spies. Ionosphere is a gift of nature. Unlike the costly artificial satellites, we need not subscribe to anybody to get access to a facility, which can transfer our radio messages to distant parts of the world. It is worthwhile for a radio user to learn more about the ionosphere.
"Skip Zone"
Under the action of solar radiation and the hail of meteorites, an ionized layer is formed in the upper part of the Earth's atmosphere. In this layer, the neutral air molecules are decomposed into ions and electrons and the whole layer presents a chaos of charged particles.Short wave radio signals are reflected from this layer just as light rays are reflected from the surface of a mirror, or sound from a barrier.Likewise, this layer can be compared with the edge of billiard table: if the ball does not go straight into the pocket, it can be sent o n rebound. In a situation, a radio receiver set located at a distance of 200 kilometres (say) away from the wireless transmitting station can not receive signals from the transmitting station. This is because the ground waves are stopped by the Earth's curvature and the sky wave will not reach the receiver, because it bounces again more than 200 kilometres way. So some 'blind zones' are formed and if the receiver is located in that blind zone it will receive no signal or very weak signal. In such a situation, another station can relay the message to the target station. The distance of the intended receiver from the transmitter is then termed as 'skip distance'. So it is not always necessary that a receiving station located nearer (than a station located further away from the transmitting station) to the transmitting station will be able to receive its signal.
Fade-out
It is the gradual phenomenon, that take place with the change of time of the day. Fadeout of radio signal is related to the ionization gradient of the ionosphere, which decreases in absence of sunlight. Since ionization is intense during day light hours, higher frequency (like 14 MHz and 21 MHz) of the short wave spectrum can be used during daylight hours. As the night approaches, signal strength at that higher frequency decreases. Using a frequency at the lower edge of the HF spectrum (e.g. 7 MHz) will yield satisfactory result against this fadeout.
Fading
As distinct from fade-out, fading is the constant variation of the received strength of radio wave. To the listener it appears as gradual rising and falling of the volume. The signal waxes and wanes and at times even drops below usable values. This phenomenon is manifested chiefly in long-distance transmission. It is caused by multiple reflections from the ionsphere which cause two or more waves from the same transmitter travel over different paths of different lengths and hence differ in phase and amplitude when they arrive at the receiving aerial.
Propagation:
Most of the long distance communication results from ionisation of the F layer, the most applicable radio bands in the High Frequency being 3.5 MHz, 7 MHz, 14 MHz and 21 MHz. The layer height may vary from a little over 200 km to as high as 400 to 500 km depending o n the time of the year, latitude and time of the day and particularly the amount of sun-spot activity. During the peak period of the 11 year maximum sun spot activity cycle, propagation via the F layer extends up to around 30 MHz
For ranges up to 800 kms use 7MHz. For every 160 kms of range above 800 kms add 1 MHz to the frequency.
Radio waves travel at the speed of light i.e. 300,000 km per second and because wavelength and frequency are related you can easily translate from wavelength to frequency by the relationship:
Frequency in MHz = 300/Wavelength in metres
For example,a wavelength of 25 metres gives: 12 MHz
Conclusion:
HF could be fun for experimenting or last resort backup - but is generally useless if modern communication is available. Modern short wave radio transceivers covering the "amateour" frequencies are available on the maket - but there is a need for simple construction - that could be made at home - to be "created".
For now such simple and effective solution is missing...
Here is the bandplan for frequencies used by amateours.
The best place for interference is very near these frequencies.
http://www.bfra.org/cgi-bin/index.cgi?bandplan.html
Here is the bandplan used for broadcast.
http://ibb7-2.ibb.gov/ibbeng/shtwave1.htm
These bands are 24/7 crowded with international broadcast services. Some exotic radio stations are presented there.
Consider everything else military bands and do not interfere there!
Modulation: Usually SSB or some kind of encoding is used in HF communication.
Antennas: "T" and "G" are common listening antennas. 1/4 vertical dipole is a good choice for the upper bands.
Yaggies and other sophisticated antennas are used for both receiving and transmitting.
Information for the bands:
The 1800 kHz (1.8 MHz or 160 metre band) band suffers from extreme daytime D-layer absorption. Even at high radiation angles, virtually no signal can pass through the F layer and daytime communication is limited to ground-wave coverage. At night, the D layer quickly disappears and world- wide 160m communication becomes possible via F2-layer skip. Atmospheric and man-made noise limit propagation of this band. Tropical and mid-latitude thunderstorms cause high levels of static in summer, making winter evenings the best time to work long distance at 1.8 MHz. A proper choice of receiving antenna can often significantly reduce the amount of received noise while enhancing desired signals.
The 3500 kHz (3.5 MHz or 80 metre band) is the lowest HF band, which is similar to 160 m in many respects. Daytime absorption is significant, but not quite as extreme as at 1.8 MHz. High-angle signals may penetrate to the E and F layers. Daytime communication range is typically limited to 400 km, primarily via ground-wave propagation. At night, signals are often propagated halfway around the world. As at 1.8 MHz, atmospheric noise is a nuisance, making winter the most attractive season for the 80 m.
The 7000 kHz (7 MHz or 40 metre) band is useful for daytime communication up to a distance of 800 km via E and F layers. Long distance world-wide communication takes place in this band through F2 layer.
10 MHz BAND
The 10 MHz or 30 metre band is unique because it shares characteristics of both daytime and night-time bands. Communication up to 3000 km is typical during daytime, and this extends halfway around the world. The band is generally open via F2 o n a 24-hour basis. The International Telecommunication Union (ITU) has allotted 10,100 kHz to 10,150 kHz to the radio amateurs in Region 3 countries.
14 MHz Band
14 is a typical daytime band.
This is the most useful HF part. Long distance transmission is possible via F layers (up to 4400 km for a single hop). And short distance via E (several hundred km). With multiple hops and combination of F and E reflection sometimes the whole world is covered.
Majour drawback is the expensive apparature and the sophisticated antenna systems.
21 and 28
Consider these to have UHF properties.
21 has too high frequency to be useful for long distances. 28 is absolutely useless for more than 50km...
Anyway there is a citizen band there that is available without any permission and nobody watches near this band.
Despite the fact that the introduction of artificial communication satellites for long distance radio communication made communication more reliable and there is very little role left to be played by the ionosphere in the professional telecommunication networks, it still draws the attention of communication enthusiasts, arm forces and spies. Ionosphere is a gift of nature. Unlike the costly artificial satellites, we need not subscribe to anybody to get access to a facility, which can transfer our radio messages to distant parts of the world. It is worthwhile for a radio user to learn more about the ionosphere.
"Skip Zone"
Under the action of solar radiation and the hail of meteorites, an ionized layer is formed in the upper part of the Earth's atmosphere. In this layer, the neutral air molecules are decomposed into ions and electrons and the whole layer presents a chaos of charged particles.Short wave radio signals are reflected from this layer just as light rays are reflected from the surface of a mirror, or sound from a barrier.Likewise, this layer can be compared with the edge of billiard table: if the ball does not go straight into the pocket, it can be sent o n rebound. In a situation, a radio receiver set located at a distance of 200 kilometres (say) away from the wireless transmitting station can not receive signals from the transmitting station. This is because the ground waves are stopped by the Earth's curvature and the sky wave will not reach the receiver, because it bounces again more than 200 kilometres way. So some 'blind zones' are formed and if the receiver is located in that blind zone it will receive no signal or very weak signal. In such a situation, another station can relay the message to the target station. The distance of the intended receiver from the transmitter is then termed as 'skip distance'. So it is not always necessary that a receiving station located nearer (than a station located further away from the transmitting station) to the transmitting station will be able to receive its signal.
Fade-out
It is the gradual phenomenon, that take place with the change of time of the day. Fadeout of radio signal is related to the ionization gradient of the ionosphere, which decreases in absence of sunlight. Since ionization is intense during day light hours, higher frequency (like 14 MHz and 21 MHz) of the short wave spectrum can be used during daylight hours. As the night approaches, signal strength at that higher frequency decreases. Using a frequency at the lower edge of the HF spectrum (e.g. 7 MHz) will yield satisfactory result against this fadeout.
Fading
As distinct from fade-out, fading is the constant variation of the received strength of radio wave. To the listener it appears as gradual rising and falling of the volume. The signal waxes and wanes and at times even drops below usable values. This phenomenon is manifested chiefly in long-distance transmission. It is caused by multiple reflections from the ionsphere which cause two or more waves from the same transmitter travel over different paths of different lengths and hence differ in phase and amplitude when they arrive at the receiving aerial.
Propagation:
Most of the long distance communication results from ionisation of the F layer, the most applicable radio bands in the High Frequency being 3.5 MHz, 7 MHz, 14 MHz and 21 MHz. The layer height may vary from a little over 200 km to as high as 400 to 500 km depending o n the time of the year, latitude and time of the day and particularly the amount of sun-spot activity. During the peak period of the 11 year maximum sun spot activity cycle, propagation via the F layer extends up to around 30 MHz
For ranges up to 800 kms use 7MHz. For every 160 kms of range above 800 kms add 1 MHz to the frequency.
Radio waves travel at the speed of light i.e. 300,000 km per second and because wavelength and frequency are related you can easily translate from wavelength to frequency by the relationship:
Frequency in MHz = 300/Wavelength in metres
For example,a wavelength of 25 metres gives: 12 MHz
Conclusion:
HF could be fun for experimenting or last resort backup - but is generally useless if modern communication is available. Modern short wave radio transceivers covering the "amateour" frequencies are available on the maket - but there is a need for simple construction - that could be made at home - to be "created".
For now such simple and effective solution is missing...