Transceiver YES-97. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The "YES-97" transceiver is an improved model of the "YES-3" transceiver previously published in "KV-journal" No. 5 ... 1994, 93. The purpose of the subsequent modernization was to improve its main parameters and operational capabilities. During the operation and according to the reviews of the radio amateurs who built this Transceiver, there was no reason to doubt its merits and advantageous differences from other home-made and industrial models, of course, in this case we are not talking about its design and service capabilities.

It is appropriate to cite the eloquent confession of one radio amateur from the 3rd district - "... having a FT-990 transceiver, I work on the YES-97 transceiver on low-frequency bands, and especially during competitions ...".

Based on the obtained parameters and the used circuitry of the previous model, the task was to develop a more modern Transceiver with the minimum necessary service.

The result is a 9-band transceiver with the following main characteristics:

• sensitivity at s / w 10 dB - not worse than 0,1 μV;
• clogging dynamic range - more than 140 dB;
• real selectivity at detuning +/- 10 kHz - not less than 110 dB;
• AGC adjustment range when the output signal changes by 1 dB - at least 100 dB;
• departure of the GPA frequency after warming up no more than 5 Hz / hour;
• output power of the transmitter at the level of intermodulation products less than 40 d5 - 35 ... 50 W.

The measurements were carried out using the following instruments:

• improved universal device "Dynamics",
• noise generator on a 2D3B lamp,
• industrial GSS, modified to eliminate the penetration of the output signal, bypassing the attenuator.

When carrying out multiple measurements, special attention was paid to obtaining accurate and reliable results. For example, when measuring the sensitivity, the same results were obtained both with the Dynamics device, and with the signal generator, and with the noise generator. The indicated sensitivity is confirmed by the following fact - connecting a non-inductive, precision and shielded 50 Ohm resistor to the receiver antenna input increases the noise at the receiver output by only 1 - 2 dB. Reliable results were also obtained when measuring intermodulation according to the method of V. Drozdov. By the way, it should be noted that the intermodulation dynamic range of 110 dB is the limiting value that can be measured by the Dynamics device. This is due to the influence of lateral phase noise of the applied generators. The principle of operation and interaction of the transceiver nodes is clear from the block diagram in fig. I. The features of some of the main nodes will be discussed below.

Fig 1 Block diagram of the "YES-97" transceiver (click to enlarge)

In the bandpass filters (DFT), the connection between the input circuit and the antenna has been changed, which makes it possible to increase the transmission coefficient, especially in the TX mode. The first mixer (1-SM), Fig. 2 is made balanced. It has the ability to supply a pulsed voltage of the local oscillator frequency - a meander (instead of a sinusoidal voltage), which, in turn, leads to an increase in the mixer transfer coefficient and dynamic range. Also, the penetration through the mixer of signals with a frequency of the first IF - 8867 kHz in the receive mode has decreased. The circuit in the transmission mode was simplified, which additionally led to an increase in the output voltage after the DFT to 0,2 - 0,3 V in the TX mode. It should be especially noted that all the listed parameters of the transceiver are achieved solely due to the use of these mixers, including the receiver's SSB / CW detector.

Fig.2. First mixer RX-TX (click to enlarge)

A ten-crystal ladder quartz filter, made of inexpensive and common resonators, provides the necessary quality indicators in the receive-transmit mode. Loop matching the input and output of a crystal filter significantly reduces attenuation and improves passband ripple.

The second mixer, Fig. 3, has low noise and a high transmission coefficient. Due to the antiphase signal supply to the notch filter Ql, Q2, C1, it was possible to achieve a sufficiently deep rejection of interfering tones - (55 ... 60) dB.

Fig.3. Second mixer and notch filter (click to enlarge)

The signal from the EMF is fed to the cascode circuit of the intermediate frequency amplifier, which provides the main amplification of the receiving path, fig. 3. Next, the signal is fed to the 3rd mixer, converted to the frequency of the 3rd IF (IF-3) - 8867 kHz.

After the mixer, an additional 2-crystal quartz filter is installed and the filtered signal passes to the SSB detector, AGC amplifier and VLF. The AGC incorporates an S-meter anti-logarithmic amplifier stage, which makes it possible to uniformly calibrate its scale from one point to S9 + 60 dB. The mixers II-CM and III-CM will receive a reference frequency signal from a quartz oscillator tuned by the varicap. The varicap is affected by two signals. In the first case, the VCO frequency is changed from the "BAND" control by +/- 1 kHz, which narrows the bandwidth of the receiving path from above or below by 1 kHz.

A compromise solution has been chosen here in order to simplify the circuit, although it is not always convenient to use one knob when changing the IF bandwidth while simultaneously controlling the notch frequency (when the notch filter is turned on). The operation of this node is based on the following assumption - with interfering signals below 500 Hz and above 2 kHz in the passband of the IF, it is possible to use bandwidth narrowing, respectively, from below and from above. When a tonal interference enters the passband of 500 - 2000 Hz, the "REJECTION" mode should be used. Using these adjustments, it is possible to effectively suppress interfering signals without degrading the quality of the useful signal.

Fig.4. Amplifier IF-2, third mixer and "clean-up filter" (click to enlarge)

The second signal that affects the VCO varicap comes from the impulse noise suppression unit (PID). The PIP consists of a 500 kHz amplifier and a rectangular pulse signal shaper, which coincides in time with the arrival of the interference pulse and is equal in duration to it. As a result, for the duration of the control pulse, the VCO frequency jumps 5 kHz below the frequency of 8367 kHz, which leads to a “break” in the receiving path and attenuation of the interference signal by more than 80 dB. When exposed to impulse noise with a level of S9 +, the inclusion of the PIP allows you to confidently hear the signals of weak radio stations.

At the time of publication of this article, the panoramic indicator assembly (PI) on the 6L01I oscilloscope tube with a span of +/- 10 kHz has not yet been completed. A digital memory block will be installed in it, which will improve the information content of the signal under study.

The transceiver's transmission path has a switchable reverb combined with a microphone amplifier. This node is characterized by low power consumption and simple circuitry. It is housed in a small volume, comparable to a pack of cigarettes. The transmitter driver is more powerful. It is assembled according to a push-pull circuit, which allows you to "rock" one KP904A transistor to a telegraph power of about 40 W (option 1) or a push-pull amplifier on a KT930 (option 2) to a telegraph power of 60 W. Upon completion of the work related to the complete tuning of the transceiver, it is planned to equip it with a simple synthesizer with a frequency tuning step of 50 Hz.

Author: G. Bragin, RZ4HK Chapaevsk; Publication: N. Bolshakov, rf.atnn.ru

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