Methods for improving the characteristics of PRPU R-399A, R-381. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / radio reception

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The first "finished" amateur radio transceiver design (then still based on R-399A boards) appeared in 1984. The receiving path had a sensitivity of 0,15 μV and a dynamic range for intermodulation of the 3rd order (measured by V. Skrypnik's instrument, UY5DJ) - 84 dB, which exceeded factory products. Work to improve the characteristics of "Katran" did not end there. So, a modern PRPU can have a sensitivity of 0,03 μV with a dynamic range for intermodulation of the 3rd order - 94 dB and a dynamic range for clogging - more than 100 dB. Over the past years, more than 150 advice points have been accumulated to improve the performance of the PRPU. We would like to bring some of them to all users of R-399A, R-381. Having experience in the manufacture of transceivers (about 250 pieces were made), give recommendations in this direction. So!

1. Do not be afraid to "climb" into the apparatus! He, like everyone else, is made by human hands. It is made qualitatively, for the decision of professional tasks. But it has a number of shortcomings and shortcomings, some of which can be eliminated in amateur radio conditions.

2. First of all, it is necessary to control and adjust the supply voltages. When monitoring the voltage at the power source, we recommend setting the following values: +27,5V, +12,5V, +5,4V.

3. In the PRPU of early releases, the preselector boards (K1104) are interconnected by signal inputs and outputs with a low-frequency cable, which gives significant losses at low signal levels. It is necessary to disconnect the signal wire of the cable from the boards K1104, K1104-1, K1104-2 and connect them with an "overhead" line (solid wire 0,8-1,0 mm). Ideally, in all PRPUs, such connections should also be made with the K1104-3 board. Connect the K1103 and K1104-3 boards with a cable with lower RF losses, such as RK75-2, RK75-4. Replacing the cable and laying "overhead" lines do not require mandatory adjustment of the preselector circuits.

4. With a frequency response meter, you can achieve better preselector performance on amateur bands. The use of series-connected low-pass filter and high-pass filter circuits led not only to small losses, but also to large unevenness in the preselector passband. So, for example, the amateur range of 20 meters falls into the dip of the frequency response of the band filter (Fig. 1). By adjusting the cores of the preselector coils, you can achieve better performance on amateur bands (gain up to 2 dB).

Ris.1

5. If your PRPU has a balanced 1st mixer (K1201), we do not recommend trying to check the balance of the bridge (R22.R25) without skills. This is a rather complicated process, and the imbalance of the bridge significantly worsens the dynamic characteristics of the PRPU.

6. On the K1201 board, it is necessary to check the correct setting of the L6 coil. This can be done even by ear or by a dial indicator. By applying a signal of an RF generator (10 μV) to the input of the PRPU on any range and rotating the L6 core, achieve the maximum signal level at the output of the PRPU. If the core has to be completely screwed in, we recommend rewinding the bobbin. After adding 3-4 turns, adjust again.

7. Quartz filters of the first IF are assembled in a bridge circuit on 4 harmonic quartz resonators (Fig. 2).

Ris.2

Resonators B1-B4 have a resonant frequency of the 3rd harmonic equal to 34805 kHz, B2, B4 - 34765 kHz. It is known that quartz resonators, no matter how high quality they are, are subject to aging. This process affects the resonant frequency and quality factor. Experience has shown that the resonators used in the FP2P1 -457-34785-45V filters can change their resonant frequency down to 1 kHz per year. So, for example, a copy of the filter produced in 1983, which was in operation, had in 1993 the frequency response shown in Fig. 3.

Ris.3

The frequency drift of quartz resonators significantly worsens the characteristics of the PRPU. The easiest way to check and adjust the boards K1202, K1203: according to the maximum signal at the output of the PRPU, adjust the circuits L2, L3C8 on K1202 and L1C5, L2C7 on K1203. However, we do not recommend this method. The most correct will be the adjustment of the path of the first IF with a spectrum analyzer (type SK4-59). The methodology is described in the documentation attached to the PRSP.

8. The end of 1991 was marked by another modernization of the R-399A by the manufacturer. Users received a product with a new 1st mixer, assembled according to the scheme used in PRPU R-309A "Jump". This is a good solution that improves the dynamic characteristics of the PRPU. However, immediately after this, the quartz filter disappeared from the K1203A board ... Now, in the amateur band of 20 meters, with good transmission, you can hear broadcast stations, usually located somewhat higher.

From fig. 3 shows that one quartz filter has an attenuation beyond the passband of less than 40 dB. Thus, the harmonic of the second IF (2nd local oscillator ±215 kHz), which is 430 kHz higher from the fundamental frequency, is received by the PRPU with an attenuation of less than 40 dB. We hasten to upset the owners of "fresh" "Katrans": such a device, if it suits you in terms of reception, can produce an excessively high level of spurious emissions (+430 kHz) for transmission in transceiver mode. There is only one way out: install a second quartz filter.

9. Resistors R1, R8 on the K1205 board only reduce the already low quality factor of the L1C4C5C6 circuit. We recommend replacing them with jumpers.

10. Resistors R1 - R5 on the K1206 board are used to equalize the frequency response in the EMF passband. These resistors should be replaced with others with a resistance of 2,4 - 2,7 kOhm. This will reduce losses by 1,5 - 1,8 times with passband unevenness of no more than 3 dB.

11. Let's dwell on the most significant improvements. On the K1207 board, the values ​​​​of resistors R19, R29 should be selected in the range of 8,2-10 kOhm. The same ratings should be resistors R6, R11, R24 on the K1208 board. The signal "Output TLG" should be removed from output 12 of the K1208 board, and output 15 should be used for transmission.

12. In a narrow circle of amateur radio, we call the K1209 board "Error" (Hi). You can somewhat improve the operation of the 3rd mixer by placing source followers at the signal inputs and the 3rd local oscillator (Fig. 4).

Ris.4

Resistors R2, R3 should be removed from the board. Diodes 2D503A in the mixer should be replaced with D311, GD507. This will reduce the power at the mixer and increase the linearity of the detection. In the mode of receiving signals A1, A3, we recommend turning off the AM detector not only by removing power from the cascade on the VT1 transistor, but also by breaking the C7C9 circuit. After these modifications, a resistor R22 should be selected. By monitoring the signal at output 5 of the K1209 board with an oscilloscope (at high signal levels - more than 1 mV at the input of the PRPU), achieve a minimum of non-linear distortion. We hope this publication will not close the discussion on improving the performance of professional RPUs. In the next publication, we plan to review modern domestic PRPU and advanced technology.

Authors: Y. Ivanko, UXOLW, A. Delimarsky; Publication: N. Bolshakov, rf.atnn.ru

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