Free technical library

Universal frequency modem for 300/600/1200/2400/4800 baud. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment

 Comments on the article

The modem is intended primarily for use in packet radio systems, but can also be used in general purpose radio systems and wired systems.

The modem does not require a mandatory hardware packet communication controller, it works with any software controllers such as L2, TFPCX, TFX. When using the Kiss-mode emulator, TFKISS can use the TNC software controller of TCP / IP programs such as KA9Q, TNOS, JNOS. When using in the ISO OSI standard (X25/AX25 protocol) the fuel dispenser subscriber program and the Host mode program

(click to enlarge)

FBB speeds are doubled due to 2x software compression. Similarly - when working according to the ARPA standard (TCP / IP protocol). The modem includes 3 domestic microcircuits of the 561 and 1401 series (K561GG1, K561IR2, 1401UD2B). In total - 59 elements. Functionally, the modem consists of two completed parts-blocks: a receiver and a transmitter. The receiver and transmitter sections operate completely independently. The total current consumption of the entire modem does not exceed 3,2 mA in the +5 V circuit. The modem on the TCM3105 chip contains two cases and has 419 parts. With almost the same number of elements in both modems, the undoubted advantage of a modem based on a domestic element base is the possibility of obtaining higher nominal rates for broadband voice frequency channels.

At speeds of 2400/2800 Baud, the proposed frequency modem is also close in characteristics to the duplex FFSK, GMSK, 4-L FSK microcircuits FX469, FX589, FX909, FX919. It has high sensitivity and high failure rate statistics in interference conditions. But unlike the listed single-chip radio modems, it does not require a direct current connection to the transmitter varicap and from the output of the receiver's frequency detector. This limitation is a major barrier to working with radios that do not have these modem pins. In addition, the modem does not reproduce scrambling errors, as in the GMSK modem, which does not allow the latter to work with signals below 8...9 points on the S-meter.

The presented frequency modem can have five regulators:

• transmitter medium frequency regulator;
• transmitter deviation regulator;
• receiver average frequency regulator;
• receiver deviation controller;
• receiver duty cycle control and reception band switch (2,5/5 kHz).

The modem scheme is shown in the figure. The receiver is built according to the PLL scheme. At the input, a zero detector of the D1.1 microcircuit is installed. From the output of the zero detector, the signal is fed to the frequency detector of the PLL of the D2 chip. The output of the PLL is fed to a second-order low-pass filter on the D1.2 chip. At the output, a threshold device is installed on a D1.3 chip. The PLL loop constant is determined by the R4 C4 chain. Capacitor C7 determines the frequency. Resistance R11 sets the center frequency, and R12 sets the frequency deviation.

The receiver requires the threshold element to be adjusted by setting the resistance value R14 to obtain a duty cycle of 2. The transmitter is based on continuous phase FM modulation. There may be the following types of ratios without phase break: 0,5/1; 0,75/1,25; 1/1,75; 1/2 subcarrier cycles.

The resistance R23 and the diode VD2 provide the key mode of operation of the control element of the transmitter VCO (microcircuit D1.4.), which is the transistor VT2. The resistances R26 and R17, together with the capacitors, determine the frequency parameters.

Resistance R24 and capacitors C11, C12 determine the frequency parameters of the transmitter.

Speeds and frequencies are shown in Table 1, where FH is the lower frequency, Fcp is the average frequency value, FB is the upper frequency.

Table 1

The table is compiled in such a way as to ensure minimal switching when going over 1200/4800.

At 300/600/1200/2400 baud the modem operates in a typical voice frequency channel, at 4800 baud - in a non-standard voice frequency channel (double width).

The VCO of the transmitter is made on a D1.4 chip. Its output signal goes to a ring counter. The ring counter performs the functions of forming a stepped sinusoidal signal modulated in frequency with a continuous phase (16-step sinusoid without phase break at the output of the resistive adder). The spectrum of the output signal thus obtained has a minimum width of 1,15 of the deviation band. The VCO operates at 16 times the deviation frequencies listed in the table and is controlled by the input bit stream.

Transistors VT3 and VT4 are used to shunt the output signal and control the transmitter on. On the elements VD1, VD3, VBW'eor, a parasitic power supply circuit from the computer's RS232 is used, and on the DD4 chip, a voltage regulator of 5 V is used.

The LED VD1 (AL107A) is an indicator of the hangup of the RS232 port, an indicator of the reception and transmission. The indication is carried out on the basis of a partial change in the luminosity of the diode. The following display modes are available. If the program is unloaded from RAM, and the indicator is on, then the port is hung. A general glow means that the modem is working and the TNC resident program is loaded into RAM. When transmitting, the brightness of the diode VD1 decreases by 50%, and when receiving - by 30%. By changing the parameters of the resistances R11, R12, R24 smoothly or discretely using switches, it is easy to obtain the required transmission rates in a conventional voice-frequency channel or in a double-width channel. To obtain five speeds, these resistances can be made in the form of a line of three to five resistances mounted on a hinged switch or on a board. It is most convenient to perform a number of these resistances based on the resistances of SP 19-1. The inaccuracy of setting the nominal frequencies of 20% does not have a significant impact on the operation of the circuit.

Reducing the capacitance value of capacitor C8 by half gives double the bandwidth. The design of the modem may be as follows. The modem runs on a two-way board 75 mm wide and 78 mm long. The board is soldered into the ends of two 25 pin connectors. The case has a U-shape and covers the height and length of 3 mm connectors. The lower flat part of the housing is inserted between the thrust flanges of the connectors. The case is fastened without screws due to latches from below into the sidewalls of the U-shaped case. Switches and variable resistances are installed on the underside of the board. For access to them, holes are provided in the lower flat part of the body.

RSC Energia,
head of the collective radio station RZ3DYK,
V.BATUKHTIN (RV3DGA),
Ph.D. S.STREKALOVSKAYA (RA3DQE),
141070, Kaliningrad, Moscow region,
Kalinina st., 15, PO Box 15.T./F. (095)5133738.

Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Nodes of amateur radio equipment.

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 AmberSemi digital chip for direct AC to DC conversion 14.03.2023 Amber Semiconductor (AmberSemi) announced that it has completed the design of a digital chip for direct AC-to-DC conversion. The patented technology represents a huge global opportunity to revolutionize the way energy is delivered to every end electrical device. One tiny chip will replace the large transducer block and free up that space for something more useful. Today, a variety of devices from simple smoke detectors to consumer and computing electronics rely on AC power for power. Each time, bulky AC/DC converter circuits are created to convert AC to DC, which is necessary to power low-power electronics. The AmberSemi chip greatly simplifies the circuitry of such blocks, reducing the number of sufficiently significant discrete elements by at least half. The freed up space can be used either to reduce the size of devices, or to increase its capabilities by adding new functions. The new chip has not yet been released in silicon. Only its digital design is ready. Now the company is engaged in the production of photomasks to launch the solution in mass production.

Other interesting news:

▪ Paper against coronavirus

▪ Edible coating to extend product shelf life

▪ Universal wireless charger from Samsung

▪ Superbread for weight loss

▪ Panasonic is the greenest electronics brand

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Acoustic systems. Article selection

▪ article Grab fate by the hair. Popular expression

▪ article Why was a disabled dog awarded the rank of sergeant in the US Army? Detailed answer

▪ article Production of letterpress printing plates. Standard instruction on labor protection

▪ article Symmetric multivibrator. Encyclopedia of radio electronics and electrical engineering

▪ article Find the intended coin. 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