Shortwave transceiver Ural D-4. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Shortwave transceiver Ural D-4. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Recently, I often had to work on a rotational basis. In this regard, there was a need for a compact transceiver - a monoblock. The desire to work on the air during the shift made me sit down "for a soldering iron and a file." The transceiver appeared quickly enough, and I named it "URAL D-04". Structurally, it repeats my previous design "URAL-84M", but with significant changes in the concept. Some shortcomings of the earlier model, RX9JK, are also taken into account.

Some differences from "URAL-84M"

a simpler circuit implementation of the main nodes, it has become less difficult to configure the transceiver as a whole;
more attention is paid to the preselector, as a result, the dynamic range has increased, noise has decreased, and sensitivity has increased;
more advanced design (outwardly resembles a TS-140 transceiver), quasi-touch control is used;
the tuning knob is located on the side, it has become more convenient to tune in, especially in rotational conditions;
reduced size and, consequently, weight.

Main Specifications

Receiver

Operating frequencies - all amateur bands from 1.8 to 29 MHz + WARC;
Mode of operation - CW / SSB.
Antenna input impedance - 50 Ohm;
Dynamic range (measured by a two-signal method on a range of 14 MHz, frequency spacing 15 kHz) - not less than 94 dB;
Selectivity on the mirror channel is not worse than 80 dB;
IF bandwidth in SSB mode 2,4 kHz, in CW mode 0,8 kHz;
Sensitivity (s / w + w 10 B) - not worse than 0,3 μV;
AGC control range - 95 dB;
The output power of the ULF is 2 watts.

Transmitter

Output power - adjustable up to 60 W;
The level of out-of-band emissions - not worse than 35 dB;
Carrier and unused side suppression - not less than 60 dB;
Dimensions - 250 x 120 x 270 mm. Weight - about 6 kg.

Structural diagram of the transceiver

The block diagram of the transceiver is shown in fig. 1. The received signal from the antenna input through the relay contacts (RPV-2/7) and the step attenuator minus 6,12,18 dB (assembled according to the T-shaped circuit, switching to the RES-60 relay) passes through the band filters (3 loop on cores SB-12, SB-9 and relay RES-49) and comes to the main board of the transceiver - block A2 This block is the "heart" of the transceiver. It contains RX-TX mixers, crystal filters and an intermediate frequency amplifier.

Fig.1 Structural diagram of the transceiver "URAL D-04" (click to enlarge)

The first mixer is reversible, assembled on KD922 Schottky diodes. Quartz filter - self-made (ladder) with a center frequency of 9100 kHz, assembled on resonators from the Granit museum radio stations (it is possible to use more modern filters for frequencies of 8-9 MHz, with appropriate input-output matching). The main intermediate frequency gain is provided in the third stage by the K174XA2 microcircuit. It also contains a balanced CW / SBB detector, and it also provides basic AGC control. In front of the microcircuit there is a low-noise cascade with a common gate on a KP903 field-effect transistor, so the intrinsic noise of this microcircuit is almost imperceptible. To further reduce the noise level at the output of the low-frequency signal, a ready-made low-pass filter from the r / st "Granit" - D3,4 is used. The main low-frequency gain is provided by the K174UN14 microcircuit. It also allows you to connect an external speaker.

Node A2 also contains part of the transmission path of the transceiver. The balanced modulator is assembled on varicaps. The DSB signal passes through the main filter KF1, and then the filtered SSB signal through the matching stage SK comes to the reversible mixer RX-TX. After passing through the band filters, the contacts of the "reception-transmission" relay, it enters the power amplifier - block A4. The broadband power amplifier is assembled according to the classical scheme on transistors KT610, KT921 and 2 transistors KT956A. The maximum power of this amplifier is about 60 watts.

Actually, the entire transceiver consists of 8 blocks (boards) A1 ... A8, on which the main components are located - the GPA, the reference generator of the OCG, the microphone amplifier, the low-pass filter, etc. In this issue of the collection, I will talk in more detail about the base board of the transceiver - block A2.

Shortwave transceiver Ural D-4
Schematic diagram of block A2

The received signal, having passed the DFT, is fed to the receiver mixer, assembled on diodes VD1 ... VD8. It is a high-level broadband mixer using matching transformers T1, T2 with a volume short-circuited turn. Their design has been described many times in amateur radio literature. I (out of poverty) used metal cups from old P605 transistors and ferrite rings 1000 ... 2000NN, with a diameter of 10 mm. The winding of each coil is ordinary, strictly symmetrical, made with one wire PUZH1Yu (PEV) -0,21 (and not two. as usual) evenly over three quarters of the ring.

Schematic diagram of block A2 (part 1, 29 Kb)
Schematic diagram of block A2 (part 2, 39 Kb)
Schematic diagram of block A2 (part 3, 42 Kb)

Losses in such a mixer, as a rule, are 4-6 dB. Better performance in terms of "dynamics" is obtained if 2 Schottky diodes are installed in series in each arm of the mixer. Naturally, this will require two hundred local oscillator signal amplitudes up to 3 Veff. Pay special attention to the shape of the local oscillator signal. The closer it is to a pure sinusoid, the less noise and the higher the sensitivity of the receiver. Even higher performance is obtained by applying a voltage of a rectangular-shaped local oscillator (meander) with good fronts.

A diplexer R11, C5 L1 and C6, L2 is installed at the mixer outlet (its load). Through a matching transformer TZ, wound with a double twisted wire on a ferrite ring 600 ... 1000 NN, the signal comes to the input of the matching stage (SC), assembled on a KP903A field-effect transistor. It is connected according to a common base circuit and at a current of 40 ... 50 mA it has high dynamic characteristics, low noise and the necessary gain. There is no need to surround it with an AGC signal. Transformer T4 provides good matching with a quartz filter having an impedance of about 300 ohms. With careful tuning of RC chains (R14, C9 and R15, C15), it is possible to obtain unevenness in the passband of the filter 1 .. 2 dB. The output of the quartz filter is loaded on a broadband transformer T5 with a transformation ratio of 1:9. It is wound in three twisted wires on a ferrite ring 600 ... 1000HN and contains 9 turns. The termination is provided by a 26 kΩ resistor R2,7 and is brought to a filter impedance of 1 Ω via a 9:300 transformation ratio. The use of such an inclusion allows you to get good matching when reversing along the transmission path. The next stage, also assembled on a KP903A field-effect transistor, has the same goal - low noise, high dynamics and the ability to do without AGC. And this, in turn, does not change the characteristics of the next switchable KF2 filter. The main intermediate frequency gain, as noted above, is provided by the DA1 K174XA2 microcircuit. It is possible to note some features in its work. The control voltage of the AGC is supplied to it through the diodes VD15 and VD16. The VD15 diode is germanium, unlike the silicon VD16, so the AGC voltage enters the output stage of the microcircuit earlier than the previous ones, since it is subject to large overloads.

The microcircuit contains a detector, which is used as a balanced one for receiving CW and SSB signals. The low frequency signal is fed to two low frequency amplifiers. Through the volume control to the power amplifier and to a separate AGC amplifier. By selecting resistor R49, you can set the AGC threshold, for example, from 4 to 5 points. By selecting and switching capacitors, you can change the time constant. C49 - slow and C50 - fast AGC. Switching is provided by relay contacts K4 separately when working on search, CW or SSB.

The remaining nuances of the circuit are insignificant and, in order to finish with the IF receiving path, I can advise you to replace the C37 capacitor, if desired, with a simple, at least two-crystal quartz filter. A well-known "wiping" filter will be obtained, which reduces the noise of the entire IF amplifier.

Shortwave transceiver Ural D-4

The IF amplifier was repeated several times and showed the constancy of parameters and sufficient stability. A slight tendency to self-excitation can be eliminated by shunting the circuit L9, C36 with a 5 ... 20 kΩ resistor.

In the transmission mode, the IF receiver path from the transistor VT5 and further is closed. To ensure self-listening during CW operation, the DA1 chip is slightly opened by selecting the resistor R38.

The balanced modulator is assembled according to a well-known scheme on varicaps VD12, VD13. Coils L5, L6 are wound in SB-12(9) pot-shaped cores. The gate of the transistor VT4 is supplied with a control voltage from 0 to +6 V, which regulates the output power of the transmitter or ALC.

Again, a T5 transformer with a ratio of 1:9 is used as a load, and then a quartz filter, etc., is used along the path. Transistor VT2 now becomes a source follower, the output of which is connected to the RX-TX mixer. Here, one should also take into account the ratio of the signal amplitudes to the local oscillator signal, approximately 1:10. Further, from the output of the mixer, the transmitted signal, having passed through the band filters and the buffer stage, is fed to the power amplifier.

Shortwave transceiver Ural D-4

Note

Anatoly, RX9JK reports that this transceiver exists and has been in operation for about 2 years. In addition to the usual work, it was tested in full-time competitions in the city of Zarechny near Yekaterinburg at the same table with the FT-990 and surpassed its neighbor in dynamics. "In terms of its characteristics, measured, however, in amateur conditions, it is not inferior to its prototype" URAL-84m ". Printed circuit boards exist in a single draft version in the transceiver itself. They are not in the drawings. Those who are interested in repeating block A2 can be advised to refer to the main board of the URAL-84m transceiver.

The design of the board itself and the arrangement of elements are approximately the same, but the linear dimensions are somewhat smaller. To simplify the "printing" of the power bus, you can not do it, bring the MGTF wire to the places where you need it. In order to reduce the dimensions, the D3,4 filter was opened, disassembled and reassembled on the printed circuit board of the A2 block.

I would like to thank Alexander, RN3DK from Mytishchi for his help in preparing this article, RW3AY.

Author: A Pershin, RX9JK (ex UA9CKV) Surgut; Publication: N. Bolshakov, rf.atnn.ru

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