Types of modulation for long-distance communication on VHF. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

 Comments on the article

Long-distance radio communication on VHF is no longer a rarity. Now a fairly large number of radio amateurs regularly conduct communications using the Aurora, reflection from meteor trails, various kinds of repeaters, etc. Therefore, posing the question of choosing the most effective type of modulation for long-distance communication on VHF seems to be quite modern.

The main factor determining the possibility of establishing a connection is the signal-to-noise ratio at the output of the receiver. Communication is possible only if this ratio is sufficient for intelligible reception of signals. The most advantageous from this point of view is the auditory reception of telegraph signals, which is already possible at ratios of 0,5-1 (from -6 to 0 dB). In addition, it allows narrowing the receiver bandwidth to 0,5-1 kHz, which somewhat improves intelligibility. Further narrowing is impractical due to the properties of human hearing: against the background of narrow-band noise, it is more difficult to parse the signal. For example, with a bandwidth of 100 Hz, the required signal-to-noise ratio already rises to 2-3 (6-10 dB).

For satisfactory speech reception, the signal-to-noise ratio must be higher than when receiving telegraph signals. On fig. Figure 1 shows a graph of the intelligibility R of a speech signal (in percent and conditional points of the RS scale) versus the signal-to-noise ratio at the receiver output. It can be seen from the graph that for the intelligibility of 50% of the signals (satisfactory reception), the required ratio is three (10 dB). Therefore, if we compare the telegraph and the widely used single-sideband modulation, it turns out that with equal transmitter power, the telegraph communication range will be higher. And vice versa, with the same communication range, the required power of the SSB transmitter will be 10-40 times (10-16 dB) higher. However, SSB can be brought closer in efficiency to the telegraph if the dynamic range of speech signals is compressed, which gives a gain of up to 10 times in power.

Ris.1

Telegraph and SSB receivers (with mixing detectors) are distinguished from receivers designed for other types of modulation by a characteristic feature - signal-to-noise ratios coincide in their IF paths and at the outputs, since it is not actually detection that occurs here, but a linear frequency conversion operation. For all other types of modulation, there is a threshold signal-to-noise ratio, below which the signal is suppressed by noise in the detector of the receiver. This can be seen from the graphs in Fig. 2, which show dependences relating the signal-to-noise ratios at the input and output of the detector for different types of modulation. The horizontal axis represents the ratio of peak signal power to noise power about a 3 kHz bandwidth at the input.

Ris.2

It is assumed that for AM and narrowband FM with index m=1 (deviation ±3 kHz) the IF bandwidth of the receiver path is 6 kHz, and for wideband FM with m=5 (deviation ±15 kHz) - 30 kHz. The threshold (inflection on the graph) for AM and narrow-band FM is observed at a signal-to-noise ratio at the detector input of 5-7 dB, for wide-band FM - much earlier. Therefore, if we compare AM, narrowband and wideband FM, we can conclude that narrowband FM provides a significantly better signal-to-noise ratio at the receiver output, and hence a greater communication range. When working with such an FM above the threshold, even a slightly better ratio is achieved compared to CW and SSB.

Since this type of modulation is still relatively uncommon among radio amateurs, it is worth dwelling on it in more detail. The FM transmitter is structurally simpler than the SSB transmitter, it does not require high powers of the speech signal for modulation (as with AM). Its output power is constant and equal to the peak, so it is much easier to design and set up such a transmitter (especially a transistor one). Crosstalk and impulse noise affect here much less. than with AM, since the detector does not respond to changes in signal amplitude. FM transmitters create less interference, in particular television interference.

If the FM transmitter modulator provides a uniform rise in high frequencies (approximately 6 dB per octave), and vice versa, attenuates high frequencies in the receiver's bass amplifier, the gain from correction (when operating above the threshold) can reach 10 dB. Dynamic range compression is just as effective as other types of modulation - it increases the average frequency deviation and prevents overmodulation.

It should be noted, however, that all of the listed advantages are manifested only when using a special frequency detector (limiter discriminator or ratio detector) in the receiver. If the detector responds to amplitude modulation, then narrowband FM is approximately equivalent to AM.

Summarizing the above, we can conclude that the most "long-range" is the telegraph mode of operation with auditory reception. In second place in terms of achievable communication range is SSB, narrow-band FM is approaching this type of modulation. AM and broadband FM are the least beneficial for long-distance communications.

Author: V. Polyakov (RA3AAE); Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Civil radio communications.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive New technology for optical imaging of nanoparticles 24.11.2020 Scientists from the University of Houston and the Cancer Center at the University of Texas (USA) have developed a new PANORAMA optical imaging technology that can detect nanoparticles as small as 25 nanometers. Experts note that the size of the smallest transparent object that a standard microscope can display today is from 100 to 200 nanometers. In addition to being so small, these objects do not reflect, absorb, or "scatter" enough light to allow imaging systems to detect their presence. Labeling is another widely used method; this requires researchers to know something about the particle they are studying—for example, that a virus has a spiked shell (like the "solar corona" of coronaviruses)—and develop a way to tag that feature with a fluorescent dye or some other method to make it easier to was to detect a particle. "Otherwise, it will appear invisible under a microscope, like a tiny dust particle, because it is too small to detect," the authors note. The PANORAMA tool works very differently: it does not rely on scattered light from nanoparticles or on markers. Instead, the system allows observers to detect a transparent target as small as 25 nanometers by monitoring the transmission of light through a glass slide coated with gold nanodiscs. By observing changes in illumination, they can detect nearby nanoparticles. At the same time, it is possible that PANORAMA can see the particles even smaller. "We settled on 25 nanometer nanoparticles simply because they are the smallest polystyrene nanoparticles on the market," said Wei-Chuan Shi, a professor of electrical and computer engineering at the University of Houston.

Other interesting news:

▪ Production of plastic bottles from sugar

▪ Smart bracelet Microsoft Band

▪ Xiaomi Lady Bei Portable Face Skin Humidifier

▪ Cardio watch will report an attack

▪ DPP-3 - TDK-Lambda three-phase DIN rail power supplies

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Wonders of nature. Article selection

▪ article Regrouping forces. Popular expression

▪ article Who supplies CO2 to the atmosphere? Detailed answer

▪ article The main ideas of the OSMS

▪ article A simple LF and HF signal generator. Encyclopedia of radio electronics and electrical engineering

▪ article Dirt through the hand. Focus Secret

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024