What is Shortwave Radio?

A short-wave radio station is a radio communication device that operates at a wavelength of 100 to 10 meters (with a frequency of 3 to 30 MHz). It is mainly used to transmit voice, equal amplitude report and frequency shift report. When transmitting telephone signals, amplitude modulation and single-sideband modulation are used. It consists of transmitter, receiver, antenna, power supply and terminal equipment. Generally divided into portable, vehicle-mounted and fixed radio. It has the characteristics of small size and light weight, usually using a whip antenna, and using ground waves for short-range communication, and the power is usually several watts to tens of watts.

Military shortwave radios are classified into portable, on-vehicle (or shipborne, airborne) and fixed radios according to the purpose and conditions of use. Portable radios are mainly used to ensure the communication of tactical units. They have the characteristics of small size and light weight. Generally, whip antennas are used to perform short-range communications using ground waves. The power is usually several watts to tens of watts. Vehicle-mounted radios are used to form command post communication hubs or for mobile communications. Their power ranges from tens of watts to several kilowatts. Whip antennas and dipole antennas are generally used. Stationary radios are mainly used for strategic communications. They usually consist of a centralized transmitting and receiving station. Their power ranges from several hundred watts to several kilowatts, and even to several tens of kilowatts. Generally, large antennas with good performance are used. To use ground wave communications, the frequency range of portable and vehicle-mounted radios has been extended to the mid-wave band, typically 1.6 to 30 MHz. ^[1]

Short-wave radios are generally used to transmit voice, equal-amplitude reports, and frequency-shift reports. Sending phone

Compared with AM radio, single-sideband radio has the advantages of spectrum saving, power saving, and easy multi-channel multiplexing.

There are two basic propagation paths for short waves: one is the ground wave and the other is the sky wave.

As mentioned earlier, ground waves travel along the surface of the earth, and their propagation distance depends on the characteristics of the surface medium. The conductivity of the sea surface medium is the most favorable for the propagation of radio waves. Short-wave ground wave signals can travel about 1,000 kilometers along the coast. The conductivity of the land surface medium is poor, and the attenuation of radio waves is large. Different land surface media have different degrees of radio wave attenuation (Slow attenuation on wet soil and large loss on dry sand and gravel). Short-wave signals can travel up to several tens of kilometers along the ground. Ground wave propagation does not need to frequently change the operating frequency, but obstacles must be considered, which is different from sky wave propagation.

The main propagation path of short waves is sky waves. After the short-wave signal is sent from the antenna, it is reflected back to the ground through the ionosphere, and it is reflected back to the ionosphere. But Tianbo is very unstable. During skywave propagation, path attenuation, time delay, atmospheric noise, multipath effects, ionospheric fading and other factors will cause signal weakening and distortion, affecting the effect of short-wave communications.

How do I listen to shortwave radio?

Most people are interested in shortwaves because shortwaves can listen to long-distance broadcasts and can directly listen to broadcast messages from all over the world. However, many people are confused because of the wrong way to listen to shortwaves, and finally have to give up. Here are some suggestions on how to start listening to shortwave radio.

What's the difference between listening to shortwave and listening to daily contact with MW and FM?

Everyday listening to MW or FM radio will rarely encounter the problem of finding radio stations, because the radio frequency of these radio stations is fixed, and many of them are broadcast 24 hours. For shortwave, it can be different. Except because there are many radio stations, seasonal broadcasting frequency and broadcast time change twice a year, and the quality of the received signal varies greatly every day. FM and FM are indeed a lot more complicated, but as long as you master the essentials, you can enjoy shortwave programs freely.

Listen to shortwave --- select radio station, frequency and time

For short-wave listeners, the biggest problem is that short-wave broadcasts are usually concentrated on a certain period of time? Broadcasting, resulting in a traffic situation similar to commuting time, appears unusually crowded. But you can make yourself not a crowded person, because usually the radio station will use the same frequency to broadcast the same program at different times. I can only receive very few radio programs, and even the background noise of the radio is reduced; it is difficult to listen to the radio clearly during the daytime under 7MHZ, but at late night, I can listen to the program very well, and the shortwave 9-12MHZ is all day You can receive the radio, but the best results are in the morning and evening. There are many radio stations and the sound is clear. Also, if you listen to the radio often, you will find that many radio stations regularly change the broadcast frequency every hour, so in order to facilitate listening to short-wave programs, it is necessary to make a schedule of your own listening time frequency (Schedule), of course You can also start by collecting the broadcasting time frequency table of each station.

In fact, short-wave radio stations usually use multiple frequencies to broadcast at the same time, but usually not every frequency can be heard well. The purpose of monitoring is to pick out the best sound signal from several broadcast frequencies and record them. After that, a schedule of broadcasting frequencies was made, and it was much more convenient to listen to the station's programs afterwards.

How to improve listening performance

Many people who just started to listen to shortwaves are greatly distressed by the noise of the radio and even give up listening to shortwaves. It is a pity. It is true that the sound quality of shortwave cannot be compared with the sound quality of FM high-fax broadcasting, but it is basically close to that of medium wave (MW). However, listening to shortwaves is often worse than midwaves because of many factors. In fact, if all factors are favorable, the sound quality of short-wave can be comparable to that of medium-wave broadcasting. The following points discuss the important factors that must be considered when listening to shortwave:

Ionospheric factors

Medium wave broadcasting (commonly known as MW), from the transmitting antenna of the radio to the reception of the radio, the distance is generally within a few hundred kilometers in diameter, and the medium wave wavelength is relatively long, and is not easily affected by obstacles such as buildings. Shortwave is not the same. In addition to the radio s transmitting antenna having a certain direction and elevation angle, the receiver's distance is usually thousands of kilometers, or even tens of thousands of kilometers. The radio waves transmitted by the radio must be near the surface of the earth. The ionosphere refracted at a height of 100 kilometers can be received at a distance. The ionosphere above the earth is like a multi-faceted mirror. Its ability to reflect short waves, the height at which they exist, and they change at any time. Therefore, short wave broadcasting Transmission becomes less reliable. ^[2] Nevertheless, there are some changes in the ionosphere that can be summarized, because the main factors for the formation of the ionosphere are ultraviolet rays from the sun and tiny particles with energy; therefore, the changes in the ionosphere will be affected by the following factors influences:

The strength of the solar activity: the so-called change about every 11 years.

The distance between the sun and the earth: the change throughout the year.

The amount of solar energy that passes through the earth when transmitted to the earth varies in thickness: from day to night, that is, from morning to dusk to night during the day, it varies. Therefore, the impact of solar energy on the ionosphere during the day and night is different.

In addition, due to the rapid changes in the ionosphere, short and long waves often appear as small waves when listening to short waves. This is a common phenomenon in short wave listening. Even in electronic circuits, automatic gain (AGC) is used to eliminate this. This phenomenon, but in severe cases, you will still feel the sound suddenly louder and louder, if you can get used to it, this is also a special feeling of listening to short waves!

Shortwave listening effect is different indoors and outdoors

Because the short-wavelength is much shorter than the medium-wave, buildings are a relatively large obstacle to short-wave, that is, the signal strength indoors will be much weaker than outdoor, so the best way to listen to short-wave should be: Outdoors use the radio's whip antenna to listen. When indoors, you must use an outdoor antenna to listen. According to experience, in addition to the irresistible natural environmental factors, setting up an ideal outdoor antenna is the best thing to improve the short-wave listening effect.

Various reasons to interfere with listening to shortwave:

Lightning interference in summer;

Indoor electronic fluorescent lamps, TRIAC dimming lamps, computers, televisions, microwave ovens, telephone lines, etc.

Radiated interference from neighboring factories using high-horsepower motors and transmitted through high-voltage power lines;

Radiated interference from spark discharges of tram line power lines and motors of various motor vehicles on the road

There are high-power high-frequency radio wave radiation interference near the listening place: such as pager launcher (BB); taxi 27MHZ radio intercom; professional short-wave communication radio, wireless mobile phone, FM and broadcast television with high transmitting power near the listening place Launch pad, etc ...

Set up short-wave outdoor antenna

When it comes to external antennas, this is the most confusing problem for short-wave beginners. Indeed, to set up a truly standard short-wave external antenna requires professional knowledge. For your convenience, here we only introduce a simple and practical external antenna for your reference: prepare a 5-15 m long ordinary wire, find a suitable place outdoors, and pull it horizontally at one end ; Pull the other end into the indoor rod antenna (about 7-10 turns) wrapped around the radio, and you're done.

The so-called appropriate location means that the higher place is better than the lower place, and the more open the surrounding, the better. For example, it is better to stay away from the wall than to stick to the wall. As for the length of the wire, if space permits, in principle, the longer the better (5-15 meters long). This wire does not need to be stripped from the beginning to the end, whether it is thick or thin. If there is no suitable space for horizontal drawing, then throw the wire out of the window and let it sag naturally, but it is better to tie a heavy object at the end to avoid blowing the wire when it is windy. High-voltage lines or other objects are dangerous.

Because outdoor antennas are pulled outdoors, we must pay attention to the problem of "lightning and lightning strikes", so during a thunderstorm, please be sure to loosen the wires that were originally wound on the radio and put them in a safe place (such as outdoors). To avoid danger.

Improve the effect and sound quality of listening to shortwave

In addition to the short-wave phenomenon mentioned above and the use of outdoor antennas to improve the listening effect, you should also pay attention to the interference of the surrounding listening environment, such as: fluorescent lamps, computers, televisions, microwave ovens, electric motors and various roads. Motor vehicles, sparks, and other external interference factors, of course, these interference will also occur in any band, but the short-wave signal is weaker and more susceptible to the impact, you should try to find the source of the interference and try to avoid it.

When listening to normal shortwave broadcasts, I still feel that the sound is not ideal. This is because the audio output power of small shortwave radios is generally not large. When the surrounding environment is noisy or because of other factors, a large volume is required, adjust the volume. Large, there will be a large distortion. Moreover, in order to improve the selectivity of the short-wave radio, the passband bandwidth of the IF amplifier has been narrowed, which also limits the sound quality. Therefore, if you can wear headphones or listen to a small external amplifier from the headphone jack Speakers can improve sound quality issues. Sometimes the sound quality is even comparable to that of a local MW station

About shortwave reception

The short-wave band is very wide, and the radio signals are also scattered. Acceptance requires certain skills.

1. Need a good receiving environment and a sensitive radio. A good acceptance environment can be open areas, high-rise roofs, and other places that are not blocked. In the room, especially in the reinforced concrete building, the receiving effect is very poor due to the shielding effect, and there are many disturbances. In addition, the radio needs to pull out the antenna when receiving short waves. Of course it is better if you have a separate outdoor antenna.

2. Find out the transmission time and frequency of the shortwave station. These can be obtained from the Internet, you can go to the broadcasting forum, there is a shortwave frequency table in the BCL area. Generally 19-meter, 41-meter and other band broadcasts are more concentrated. Or listen to these bands at will, and you can hear the strong folk music at the BBC VOA frequency. (Like our great party. Another whisper, really want to listen to the radio broadcast of these stations should carefully search the entire band, sometimes these stations will change the frequency, and these frequencies do not appear on the frequency table. If the radio by 18000 (Receiving frequencies above kHz can be searched between 18,000 and 23,000 kHz.)

3. Tuning of short wave. Be slow and patient! The mid-wave band is from 535 to 1605 kHz, while the short-wave band is 2700 to 18000 kHz, with one station every 9 kHz (though this is not the case, this is only a theoretical requirement), it is easy to know from the coverage situation. The position of each radio station on the short-wave band is very small. Although the radio divides the short-wave band into many areas (1234567890) for easy tuning, you still have to be careful and careful. Slowly turn the tuning handwheel. When listening, if you hear a sound similar to the broadcast, carefully turn the tuning handwheel left and right, and listen carefully to the broadcast sound to obtain the correct tuning.

4. Be mentally prepared. For ordinary radios, the sound quality of short-band radio broadcasts cannot be compared with FM or even medium-wave. And the short-wave propagation is far less stable than the mid-wave due to ionospheric fluctuations. There will be strong and weak fading. Although the radio has automatic gain control, it cannot be completely eliminated.

Of course, the best and easiest way is to find someone with a good technique to teach it, and writing so much may not be all clear

Shortwave radio

Traditional Pointer Tuned Shortwave Radio

If the type of radio is divided according to the received band:

Single-band medium wave radio: MW 525-1600 KHz

FM AM radio MW 525-1600 KHz, FM 87.5-108 MHz

FM / medium / shortwave radio ** MW 525-1600 KHz, FM 87.5-108 MHz

SW with only one short band: 3.9 --12.00 MHz (75-25 meters)

(Or 6.00-18.00 MHz, 49-16 meters)

(Or 9.00-16.00 MHz, 31-19 meters)

SW1: 2.2--7.50 MHz, SW2: 7.50-23.00 MHz

Or SW1: 5.9-9.50 MHz, SW2: 9.50-18.00 MHz

SW1, SW2, SW3, SW4, SW5, SW6, SW7 ...

Multi-band short-wave radio

(Each short-wave band covers an international short-wave meter band)

Traditional radios and radio cassette recorders usually have only one or two short bands, but each band covers a wide frequency range (several meters). The advantage is that the circuit is simple, but it is difficult to guarantee the frequency of each point in the frequency range covered. Sensitivity and selectivity are very uniform, so some meters often listen well, but others are poor. In addition, because of the wide frequency coverage, the stations appear crowded and inconvenient to receive, so some radios To improve by adding a short-wave fine-tuning knob.

There are also some traditional radios with well-designed short-wave circuits. The radios also have high sensitivity and selectivity, and they are accurate in production and debugging. They are also very convenient to use. Do nt be interesting, at least the trouble of changing the old band is eliminated. In addition, traditional radios mostly use 3-4 batteries and relatively large-diameter speakers. They sound very good. No wonder many old shortwave fans still like traditional radios.

Multi-Band Shortwave Radios by Meter Band

Modern short wave radios are often divided into 6-10 short wave bands, each short wave covers only one meter band (please refer to the international radio meter band table below). For such well designed short wave radios, sensitivity and selectivity are relatively easy to obtain Guaranteed, and the short wave is divided by the meter band. The interval between the radio stations seems to be widened. It is as convenient to listen to the short wave as to listen to the medium wave, especially for the 16, 19, 25, and 31 meter bands with the densest radio stations. .

If the short-wave radio is divided by the meter band, if it is not enough, it is because there are too many short-wave bands. For people who like different radio stations and programs, they often have to switch the short-wave band, which seems a little more troublesome.

In addition, designing a short-wave radio according to the meter band division. If you want to cover the entire short-wave frequency range, the optical short-wave band needs 13 bands, and each band must be designed reasonably. The electronic component materials used are many, making the circuit appear too complicated and The cost is too high. The imported brand-name short-wave radios that the author has seen, FM / Middle-wave / Long-wave / Short-wave all together add up to 15 bands, and the price is nearly 1,000 yuan.

It is worth mentioning that in the domestic market, there are also some short-wave radios, known as 18-band, 24-band, and the price is quite cheap. I do nt know if the designer is deceiving or deceiving himself! In addition, there are many short-wave radios in the 8 and 9 bands known as [Consumer Recommended Products]. Due to the vicious competition in the market, short-wave circuits have almost no components other than band switches. Rather than buying this type of radio, the author recommends: it is better to buy a traditional 3 and 4 band short-wave radio.

Secondary frequency conversion technology in short wave radio

Shortwave radios originally used direct amplification lines. Since the 1950s, a frequency conversion line has been used, which is usually called a superheterodyne radio. In order to further improve the sensitivity, selectivity and anti-interference ability of radio receivers, scientists have developed multiple frequency conversion technologies. Of course, they were first applied in the field of radio communications, and later they were transplanted into advanced radios, which greatly improved short-wave radios. Performance indicators.

Portable high-sensitivity short-wave radios generally use secondary frequency conversion, while more advanced professional short-wave communication receivers even use 3 or 4 frequency conversion technology.

Radio with phase-locked loop digital tuning technology (PLL)

The phase-locked loop digitally tuned radio is a high-tech product adopting contemporary microelectronics application technology. It combines advanced, practical and novel features.

1. A single-chip microprocessor chip is used as the core of the digital tuning system, and contains many advanced functions such as phase-locked loop frequency synthesis, frequency pre-selection, multifunctional digital clock control, and LCD digital display.

2. Using the high-precision and stable quartz crystal as the frequency reference, the frequency of the receiving station can be locked without drift.

3. With frequency memory function.

Generally speaking, the greater the number of digitally tuned radio storage stations, the better. Advanced digitally tuned radios should have direct input frequency digital and analog tuning knobs, and secondary frequency conversion technology is often used on electronic circuits to improve performance indicators.

The disadvantages of digital tuned technology radios are complex circuits, difficult design, strict requirements on components, high cost, and complicated production and debugging; due to the use of many components, the static power consumption is greater than that of ordinary radios. Tuning the radio's sensitivity and selectivity is not necessarily much higher than the good analog radio.

Radio with digital display frequency technology

This type of radio adopts traditional analog receiving circuit, the cost is not high, and it is easy to achieve high performance indicators. The difference is that the digital display has replaced the traditional radio pointer to indicate the frequency, and an electronic clock control function has been added; it saves power than digital tuned radios, and can be more compact and convenient in size. It has a higher price-performance ratio. Variety of practical radios.

The disadvantage of this model is that it does not have a memory radio function. Because it uses the traditional analog receiving technology, the frequency accuracy and stability are not as high as digitally tuned radios.