Encyclopedia of radio electronics and electrical engineering / Civil radio communications

 Comments on the article

Ensuring the stability of the local oscillator frequency of amateur transceivers has always been an urgent problem. The requirements for this parameter have especially increased with the advent of digital modes of communication. Amateur designs of digital frequency synthesizers that completely solve the problem of frequency stability have not yet received wide distribution due to their relative complexity. However, there are more affordable options for solving this problem. One of them is described by the author of the article below.

The Digital Locked Loop (DAFC) device is intended for use in conjunction with the universal digital scale (DNS), which was described in [1]. The use of the DAC can significantly improve the stability of the transceiver tuning frequency.

The CACH scheme is shown in the figure. The frequency tuning of the GPA, which is supplemented by such a device, will be discrete in steps of 50 or 100 Hz, depending on its connection to the pre-divider on DD2, DD3 of the digital scale.

The operation of the circuit, with a tuning step of 100 Hz, can be represented in a simplified form as follows. If the value of the least significant digits (hertz) of the measured frequency lies in the range of 0 ... 49 Hz, then after the counting time has elapsed, the output of the pre-divider (pin 8 DD3.2) will be log. 0. With a further increase in frequency, a log appears at the output of the divider. 1. This property is used in the operation of the CAHR system. This principle is not new. It was used earlier in other constructions, for example, in [2].

Consider the case when the frequency "floats up". When the frequency of the transceiver's local oscillator increases, when the low-order bits of the frequency value fall into the range of 50 ... 99. Trigger DD1 of the CAFC circuit will fix this level and a log will also appear at its output 1.2. 1. A high level voltage will open the transistor switch VT1, which will lead to a gradual discharge of the integrating capacitance C1. The voltage across the local oscillator frequency adjustment varicap will decrease, and the GPA frequency will start to decrease until the log level appears. 2 at pin 0 of trigger DD1 of the CAPC node. Log.1.2 at this output closes the transistor switch, and the voltage across the integrating capacitance and varicap will gradually increase. The frequency of the GPA will also begin to rise.

From the description of the principle of operation of the system, it can be seen that it operates with a constant change in frequency - "ripples", which will be the smaller, the lower the rate of change in frequency under the influence of the CAFC system (in the speed limit of the CAFC and its own drift, the frequencies of the GPA will become equal). In this case, you can reduce the rate of change of frequency, either by increasing the capacitance of the integrating capacitor C2, or by increasing the value of the resistor R4. At the same time, it is necessary to ensure that it always exceeds the rate of frequency drift of the GPA itself, otherwise the CAFC system will be inoperative (there will be no capture and hold of the frequency).

The voltage on the integrating capacitance G2 can take values ​​from 0 to (0,7 ... 0,9) Upit (upper and lower limits depend on the ratio of resistors R4-R6). Depending on where the hour-thot "floats", the voltage will gradually decrease or increase in the specified range, keeping the frequency of the GPA. The frequency tuning range of the GPA with a change in the voltage across the capacitor C2 (within the limits indicated earlier) is the hold band of the TsAPCh.

If you analyze the work of the CAHR in the case when the frequency "floats down", then make sure that it works in a similar way.

To introduce the CACH system into the transceiver's GPA, a number of conditions must be met.

1. The frequency of the local oscillator must be fed to the input f1 (pin 1 DD1) TSSH.

2. GPA frequency detuning must be at least ±3,5 kHz.

3. Own drift of the frequency of the GPA should not exceed 200 ... 300 Hz for 5 ... 10 minutes.

Since the ongoing processes are very slow, the operation of the DAC does not increase the noise level of the GPA and does not degrade the electrical parameters of the transceiver.

The detuning of the GPA decreases with the introduction of CAPC by about 1,5 ... 2 times. If its preservation is essential, then before connecting the TsAPCh, it is necessary to increase the "stretching" capacitances in the varicap circuit.

When the detuning is enabled, an error occurs in setting the initial frequency, which is an inevitable consequence of the simplicity of this system. Therefore, in the enabled detuning mode, it is necessary to control the frequency using the CN. The frequency shift occurs sporadically without any control, but becomes unlikely with a small detuning - 200 ... 300 Hz. Really achievable "ripples" of the GPA frequency are 3 ... 5 Hz, which in most cases is quite acceptable.

Resistor R4 selects the time constant of the integrating circuit according to the minimum "pulsations" of the frequency when the DAC is running (it is controlled by a frequency meter in the hertz display mode). The values ​​of the resistors R4, R5 and R6 depend on the detuning band and the width of the retention band of the DAC. They are selected (within 1 ... 3 MΩ) according to the required detuning band, on the one hand, and according to the reliable retention of the GPA frequency for a long time, on the other hand (they are controlled after the transceiver has warmed up). During normal operation of the DAC, the HL1 LED (system operation indicator) should blink with a period of approximately 4 ... 15 s (depending on the GPA frequency drift rate). and the frequency of the GPA should not change by more than ±5 Hz.

The author's version of the TsAPCH GPA system has the following characteristics: the number of digital scale inputs used is 2; GPA detuning band after installation - ± 2 kHz (before installation of CAPC - ± 3.5 kHz); initial local oscillator frequency drift ± 1 kHz (depending on the range): the frequency stabilizes after 5 ... 10 minutes of transceiver warm-up; GPA frequency tuning step - 50 Hz (input D of trigger DD1.2 of the TsAPCh system is connected to output 5 DD3.1 of the scale).

The TsAPCh system works constantly (without shutdown). An error when setting the initial frequency with the detuning turned on is approximately 100 Hz for every 5 - 10 "reception-transmission" inclusions. With a detuning of 200 ... 300 Hz, an error in setting the frequency is unlikely.

Amendment. The upper output of the resistor R6 according to the diagram (see figure) must be connected to the GPA detuning circuit, and the lower one - to the GPA adjustment varicap.

Literature

1. Buravlev V., Vartazaryan S., Kolomiytsev V. Universal digital scale. - Radio, 1990, No. 4, p. 28-31.
2. Lapovok Ya. Highly stable GPA. - Radio, 1989, No. 3, p. 23-25; No. 7, p. 31.

Author: G. Lavrentiev (UR4QDF)

See other articles Section Civil radio communications.

Read and write useful comments on this article.

<< Back

<< 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 Spectroscopy in a cave 13.11.2011 French archaeologists, in collaboration with physicists from the University of Pretoria (South Africa), are studying wall paintings in caves, created about 3000 years ago by local Bushmen tribes. Scientists delivered a spectrometer to the caves located near the city of Durban to determine the composition of the mineral paints of ancient drawings. In the future, archaeologists hope to use a laser analyzer to find out which organic components were added to the composition of the paints for better adhesion to the stone. Presumably this is blood, fat, egg yolk and possibly snake venom.

Other interesting news:

▪ The resolution of smartphone screens has reached the capabilities of human vision

▪ World's largest XNUMXD printed building

▪ How to catch a graffiti artist

▪ A new solution for charging and backing up smartphone data

▪ Moth eyes help radiology

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Lecture notes, cheat sheets. Selection of articles

▪ Erwin Schrödinger article. Biography of a scientist

▪ article Can a person turn gray in a minute? Detailed answer

▪ article Carbon monoxide poisoning (carbon monoxide). Health care

▪ article Digital tachometer-watch. Encyclopedia of radio electronics and electrical engineering

▪ article Guessing a pencil. 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