Reversible path in the transceiver. Encyclopedia of radio electronics and electrical engineering

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

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It is very tempting to build a transceiver that would have a minimum number of switchings in high-frequency circuits. This can be done by using reversible converters on diodes or varicaps in the transceiver. The selective-converting path of the transceiver in this case will work for reception and transmission without any switching in the signal and output circuits of the local oscillators, and all switching will be carried out only in the cascades preceding the conversion path (HF amplifier, preamplifier) ​​or in the following them cascades (IF amplifiers).

Although reversible diode converters have already been used in amateur radio designs [1-3], they have not yet become widespread. The reason here, apparently, is purely psychological: everyone knows that the maximum sensitivity of the receiving channel in this case is limited due to losses in passive converters. However, today, when working on overloaded amateur HF bands, the determining parameter of the receiver is not sensitivity, but real selectivity. It, first of all, depends on such characteristics, conversion (and input) cascades as. dynamic range, lack of blocking by powerful interference, etc. For ring converters based on modern silicon diodes, these characteristics are on average 20 ... 25 dB higher than for simple converters based on lamps or transistors [4].

Losses arising due to the lower transmission coefficient of the passive diode converter. compared to the active one, can be compensated by increasing the gain in subsequent linear stages (IF amplifier, detector, low-frequency amplifier). We emphasize that in the case of using active converters (on lamps, transistors), the loss in real selectivity cannot be compensated by any filters in the IF and LF circuits [5].

Despite the fact that the total losses in the passive selective conversion path of the transceiver with double frequency conversion (two diode mixers, FSS and EMF) are 35 ... 40 dB in voltage, on all KB bands it is possible to achieve a sensitivity of the receiving channel no worse than 2. ..3 µV. True, at frequencies above 10 MHz in such a device, an RF amplifier must be used. In order for it not to worsen the real selectivity of the receiver too much, it is desirable to perform it according to a push-pull circuit on powerful transistors.

As an example, in fig. 1 shows a schematic diagram of a passive selective conversion path used by the author in a tri-band (14, 21, 28 MHz) semiconductor transceiver.

(click to enlarge)

The signal circuit L1C1, tunable within three ranges by the capacitor C1, is connected to the converter. made on diodes V1 - V4. The diode converter, in turn, is connected to a tunable FSS (elements L2 - L5, C2 - C6, C29.1, C29.2), having an overlap of 6 ... 6,8 MHz and a bandwidth of about 30 kHz. The second converter on diodes V5-V8, similar to the first one, is loaded on the electromechanical filter Z1. A smooth local oscillator on transistors V11-V13 covers the 5,5 ... 6,3 MHz section. In the range quartz local oscillator, made on the transistor V10, switchable quartz resonators V1 - VZ are used.

As can be seen from the figure, from point A to point B, the path is a single whole, without switching in cascades and in signal processing circuits both. when working at the reception, so. and for transmission.

The remaining stages of the transceiver, not shown in the figure, are typical, with minimal noise levels. They must have the following voltage transfer coefficients: RF amplifier - about 20 dB, IF - at least 80 dB. LF - at least 60 dB, detector - about 20 dB, DSB amplifier - at least 40 dB (with a margin for ALC). For the sake of simplicity, the figure does not show some auxiliary circuits (smooth local oscillator detuning, telegraph filter, linear stage switching).

Transformers T1-T4 are made on M600NN ferrite cores (size K7X4X2). Winding - in three wires. Windings T1 and T2 contain 27 turns each, and T3 and T4 - 30 turns of PEV-2 0,18 wire each (wound in three wires). Coils L3 and L4 have 6 turns of PEV-2 0,6 wire each, and communication coils L2 to L5 have one turn of the same wire. These coils are wound on a ZOVCH2 ferrite core (size K32X16X8). Coil L1 contains 9 turns of PEV-2 0,8 wire with a tap from the first turn and is made on a 30VCh2 ferrite core (size K12X6XZ). The T5 transformer contains 2X17 turns of PEV-2 0,2 wire on a M600NN ferrite core (size K7X4X2). The number of turns of the coupling coil L7 is 1/5...1/8 of the number of turns of the coil L6. Inductance L6 - 1,5 μH.

It is wound on a frame with a diameter of 8 mm (rigger - SCR-1) with PEV-1 0,42 wire. The number of turns is 12, the winding length is b mm. Coil L8 is made on a fluoroplastic frame with a diameter of 20 and a length of 35 mm. It contains 17 turns of silver-plated copper wire with a diameter of 0,5 mm, branch, from the 4th turn. Winding length - 17 mm. This coil is placed in a brass shield (screen diameter and height 36 mm). Its inductance without a shield is 4,7 μH, and with a shield - 3,6 μH.

Resistor R1 - non-inductive, SPO or SP3-1b. Capacitor of variable capacitance - from the radio receiver "Ocean" (only part of the range of capacitance change is used). KSO-G capacitors are used in the smooth local oscillator circuit and the FSS circuits. Capacitors C1 and C20 - with an air dielectric, the rest - K50-6, KLS, KM, KD, KT.

It is convenient to pre-configure the path cascading in the following order. The local oscillator outputs are disconnected from the converters and loaded with 50 ... 70 Ohm resistors. Selection of modes of transistors V10, V12. V13, as well as capacitor C 27 and the number of turns in the coil L7, set the necessary high-frequency voltages on the load resistors (see figure). The voltage waveform must be sinusoidal, without restrictions, which is important for obtaining good noise parameters of the converters. At the same stage, GPA frequency overlaps are set and the FSS is pre-tuned and its contours are paired. In this case, the coupling coils L2 and L5 must be disconnected from the windings, the coupling of transformers T2 and T3 and loaded with resistors with a resistance of 50 ... .70 Ohm.

Then, the connections of the GPA output with the midpoint of the winding of the transformer TK, as well as the coil L5 with the communication winding of the TK, are restored. A resistor with a resistance of 2 ... 50 Ohms is connected to coil L70 and a signal with a voltage of 5 ... 7 V with a frequency of 501 ... 502 kHz is applied to point B (if the EMF has an upper sideband). Engine. resistor R1 is set to the middle position. Selecting capacitors C7-C9, match the resistances of the filter Z1 and the converter.

After that, a measuring device is connected to the resistor on which the L2 coil is loaded, the pairing of the settings of the FSS and GPA circuits is corrected, and the GPA voltage is finally set at the midpoint of the TK winding.

Having restored the connection of the output of the quartz oscillator with the midpoint of the winding of the transformer T1, the coupling winding T1 is disconnected from the coil L1, loaded onto a resistor with a resistance of 50 ... 70 Ohm and the heterodyne voltage is finally set at the midpoint of the winding T1. Then the connection of the communication winding T1 with L1 is restored and the L1C1 circuit is adjusted.

The voltage at point A is, depending on the quality of the filter Z1, 25 ... 40 mV eff., with a signal voltage at point B of about 3 V eff. When operating the device, do not exceed the specified voltage value at point B, so. how this will cause the converter to malfunction.

In conclusion, the path settings are checked as part of the entire transceiver channel in the "Transmission" mode. Resistor R1 balances the converter in the "Receive" mode, achieving minimal noise at the output of the bass amplifier.

The transceiver operated by the author has the following main parameters of the receiving channel in SSB mode: blocking (with respect to the level of 10 μV at detuning by 300 kHz) - 28 mV, selectivity over the image channel (on the 55 MHz band) - 10 dB, sensitivity with signal / output noise. path 2 dB - not worse than 28 μV (in the range of XNUMX MHz).

Literature

1. Goroshchenya A. Minitransceiver. - "Radio". 1975. No. 5. p. 44-47; No. 6. p. 23-24.
2. Stepanov B., Shulgin G. Transceiver "Radio-76". - "Radio", 1976, No. 6. p. 17-19. 26; No. 7, p. 19-22.
3. Stepanov B., Shulgin G. Transceiver "Radio-77". - "Radio", 1977. No. 11, p. 21-24. No. 12. p. 19-23; 1978. No. 1. p. 17-20; No. 2, p. 20-21.
4. Movshovich M. Semiconductor frequency converters. L., "Energy", 1974.
5. Reinfelder V. Development of low-noise input circuits on transistors. M., "Energy", 1967.

Author: V. Vasiliev (UA4HAN); Publication: N. Bolshakov, rf.atnn.ru

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