Frequency synthesizer for VHF radio station. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Frequency synthesizer for VHF radio station. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Frequency synthesizers

Comments on the article

The proposed frequency synthesizer (MF) for a radio station in the range of 144 ... 146 MHz with the first intermediate frequency of 10,7 MHz is distinguished by simple circuitry and good repeatability.

The tuning step is 25 kHz, two decimal position switches are used for tuning in the range, at the output of which there are signals in the code 1-2-4-8. This MF uses the principle of mixing VCO frequencies and an additional high-frequency oscillator to obtain a low IF (0.3 ... 2.3 MHz) supplied to a variable division ratio divider (CVD). More details about such MFs are written in [1].

The low IF of the midrange allows the use of CMOS microcircuits in the DPCD, which are economical and do not worsen the noise characteristics of the midrange.

Schematic diagram of the synthesizer (part 1)

Schematic diagram of the synthesizer (part 2)

The DPCD of the described synthesizer is taken from [2] (tnx EU1 DQ). Its main advantage is a small number of chips (only 3) and the ease of obtaining "repeater" and "inverse" receive/transmit shifts.

The analog part of the midrange uses simple and successful circuit solutions [1]. It consists of a VCO and two identical channels (for receiving and transmitting) for generating fixed RF voltages for MF mixers. Each channel contains the following nodes:

- quartz oscillator: for RX - VT2 at a frequency of 44,333 MHz, for TX - VT1 at a frequency of 47,9 MHz;

- frequency tripler with a band-pass filter (PF) - (respectively VT5 and L5, C28, L7, C31; VT4HL4, C17, L6, C27);

- FET mixer with two insulated gates (VT7 for RX, VT6 for TX);

- shaper of rectangular pulses on the chip DD1 (DD1.4...DD1.6 for RX, DD1.1...DD1.3 for TX).

The VCO is assembled according to the capacitive three-point scheme; to change its frequency when switching to transmission, a KD409 diode is used, which shorts out part of the turns of the coil. In the receive mode, the generation frequency is 133,3 ... 135,3 MHz, while transmitting - 144 ... 146 MHz. Due to the fact that the midrange was originally developed for Storno radios, the supply voltage of which is -24 V, the VCO is powered by this voltage through the parametric stabilizer R23, VD3. The VCO coil is wound on a frame of high-frequency "Stomo" coils and is closed by a screen; a switching diode KD409, a decoupling capacitor C12 and a current-limiting resistor R10 are also soldered here.

The supply voltage to the frequency triplers and mixers is constantly supplied, to the quartz oscillators, the supply voltage is supplied through the switches on the transistors VT12 (RX) and VT11 (TX).

After the shaper of rectangular pulses, signals with frequencies of 0,3 ... 2,3 MHz (depending on the division factor of the DPKD) arrive at the DPKD through a switch on the DD2 chip, i.e. from the receiving (transmitting) frequency formation channel. Due to the high sensitivity of the driver on the DD1 chip, the use of relay K1 is required to bypass the input of the driver that is not working in this mode (RX or TX).

DPKD consists of a counter DD4 and two adders DD5 and DD6, the inputs of which are fed from the frequency code from the tuning switches and from the mode switch (to pins 2 DD5 and 4 DD6) a mode signal: simplex, repeater or inverse. The imported microcircuits used in the shaper and DPKD are inexpensive and available through companies that supply imported components on order.

The signal from the output of the DPCD is fed to one of the inputs of the phase detector (PD) of the DA1 microcircuit, the second input of which receives pulses with a frequency of 25 kHz, obtained by dividing by four by the DD7 microcircuit of the frequency of 100 kHz of the generator on the DD3 microcircuit.

From the output of the FD, the mismatch voltage through the filter R57, C54, R58, C55 enters the VCO varicap, closing the PLL loop. Through the chain R 17, C 14, a modulating voltage is applied to the same varicap in the transmission mode. The required frequency deviation is set by adjusting the amplitude of the modulating voltage in the microphone amplifier.

The power supply of the analog and digital circuits of the midrange (with the exception of the VCO) is +9 V from the DA2 K142EN8A stabilizer. The consumed current is about 50 mA.

Construction and details. As already mentioned, the midrange was developed for installation in the Stomo radio station. Most of the details of his circuit are assembled on a printed circuit board (with the exception of the 100 kHz oscillator and the DD7 divider). VCO and PF coils are wound on frames from the contours of "Storno" radio stations and have tuning cores. The VCO coil has 4 turns of silver-plated wire with a diameter of 0,7 mm, the tap is 0,75 turns from the pin connected to the case. PF coils also have 4 turns of PEV wire with a diameter of 0,6 mm. The generator coils have 9 turns of PEV wire with a diameter of 0,2 mm. When repeating the MF for other radio stations, the contour can be made using the data given in [1]. If there is no -24 V voltage in the radio station, then from [1], in this case, the VCO is also used, the frequency change of which during transmission is carried out by disconnecting an additional capacitor from the VCO circuit [3]. It is convenient to use the RES60 relay for this purpose (instead of the applied RES15), one pair of contacts of which closes the input of the idle shaper of rectangular pulses, and the other connects the capacitor to the VCO circuit in the receive mode.

Setting

You can easily and quickly adjust the midrange using an oscilloscope with a wide bandwidth and a frequency counter with an upper limit of at least 150 MHz. The following order may be recommended:

1. By shunting the quartz resonator of the 44,333 MHz generator with a capacitor of 2 ... 10 nF and controlling the frequency on the collector of the transistor VT5, tune the generator to this frequency by rotating the tuning core of the coil L2. Unsolder the shunt capacitor and, by rotating the tuning core, achieve maximum oscillation frequency stability. If this maximum is not at a frequency of 44,333 MHz, it is necessary to turn on either an inductance (at a generation frequency above the required one) or a capacitor (at a generation frequency below the required one) in series with the quartz resonator and select their values. This operation may take quite a long time, but it is necessary to perform it - the stability and accuracy of the midrange frequency setting depend on this.

2. Tune the tripler PF to a frequency of 133,0 MHz.

3. Perform the operations described in paragraphs 1 and 2 for the transmission channel by closing the PTT point of the DD2 switch to the case. The corresponding frequencies are 47,9 MHz and 143,7 MHz.

4. Disconnect the PTT point from the case, apply -24 V to the VCO, connect a frequency meter to the output of the VT10 source follower, unsolder the resistor R57 from terminal 13 DA1 and, by applying an external constant voltage of 1,3 ... 7 V through this resistor, adjust the trimmer VCO core at frequencies of 132,5 ... 135,5 MHz, respectively. Do not set the VCO frequency overlap step. If the overlap is noticeably different in one direction or another, it is necessary to select the capacitor C1.

5. Set the voltage at which the VCO frequency is about 133,3 MHz, i.e. the beginning of the 144 MHz band for the receiver.

6. Reconnect the PTT point to the chassis and check the VCO frequency. The frequency value should be about 144 MHz, otherwise it is necessary to select the connection point of the KD409 diode to the VCO circuit. To achieve the desired result, the operations of points 5 and 6 should be done several times.

7. Measure the frequency at pin 14 DA1. If necessary, use capacitors C49, C50 to set the value to 25 kHz ± 1 Hz.

8. Connect resistor R57 to terminal 13 DA1.

If the parts used are in good condition, and there are no errors in the installation, the midrange is set up and ready for use. The table below shows the correspondence of the set frequency values to the position of the switches. The table shows that the repeater channels start with the decimal digit 4, and the units digit corresponds to the channel number, i.e. 43 - 3rd repeater channel, 45 - 5th repeater channel.

Frequency, MHz	Switch value	Frequency, MHz	Switch value	Frequency, MHz	Switch value	Frequency, MHz	Switch value
144,000	00	144,500	20	144,000	40	144,500	60
144,025	01	144,525	21	144,025	41	144,525	61
144,050	02	144,550	22	144,050	42	144,550	62
144,075	03	144,575	23	144,075	43	144,575	63
144,100	04	144,600	24	144,100	44	144,600	64
144,125	05	144,625	25	144,125	45	144,625	65
144,150	06	144,650	26	144,150	46	144,650	66
144,175	07	144,675	27	144,175	47	144,675	67
144,200	08	144,700	28	144,200	48	144,700	68
144,225	09	144,725	29	144,225	49	144,725	69
144,250	10	144,750	30	144,250	50	144,750	70
144,275	11	144,775	31	144,275	51	144,775	71
144,300	12	144,800	32	144,300	52	144,800	72
144,325	13	144,825	33	144,325	53	144,825	73
144,350	14	144,850	34	144,350	54	144,850	74
144,375	15	144,875	35	144,375	55	144,875	75
144,400	16	144,900	36	144,400	56	144,900	76
144,425	17	144,925	37	144,425	57	144,925	77
144,450	18	144,950	38	144,450	58	144,950	78
144,475	19	144,975	39	144,475	59	144,975	79

Switch SA1 must be in the "repeater" position. When switching switch SA1 to the "inverse" position, reception / transmission is carried out at the frequencies of the repeater.

Literature:

1. Radio. - 1990. - N6. - P.23-29.
2. Funkschau. - 1990. - No. 5.-C.107-108.
3. Radio amateur. - 1992. - No. 4.-C.16.

Author: G. Pechen (EW1EA), Minsk; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Frequency synthesizers.

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

Ricoh AM S3P 5500D printer 24.11.2015

Ricoh, one of the world's leading suppliers of printing equipment, has introduced a 3D printer of its own production, which is aimed at the industrial segment. Perhaps in the future we will see models for home use.

Ricoh has joined the global trend and also launched 5500D printers. The presented model Ricoh AM SXNUMXP is an industrial printer, which is built on the basis of SLS additive technology, which allows you to create complex objects of high strength as a result of laser sintering of polymer powder.

The Ricoh 3D printer can work with nylon and polypropylene, which are widely used in modern industrial production, including the automotive industry. Due to the large area of the working field, which is 55x55x50 cm, Ricoh AM S5500P is able to simultaneously create several different objects and quickly produce large parts.

The manufacturer does not plan to stop at the release of one model and in the future is going to expand the range of products offered in the field of 3D printing. Perhaps we are waiting for the emergence of printers for home use, which at the moment are of great interest among ordinary users.

Other interesting news:

▪ Modular Robots ElectroVoxel

▪ Scarecrow can run and swim

▪ Trees help with the city heat

▪ Gaming smartphone Sony Xperia 1 IV

▪ Self-learning photonic computer

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Medicine. Selection of articles

▪ article A million torments. Popular expression

▪ article When were bricks first used? Detailed answer

▪ article Gun-vacuum cleaner. home workshop

▪ Article LDS is battery powered. Encyclopedia of radio electronics and electrical engineering

▪ article Organization and operation of electrical installations. Electrical management. Operational management. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

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