Refinement of TRX RA3AO. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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In this article, I offer some comments with a kind attitude towards the author of the transceiver and the authors of the improvements. First of all, I advise remake the coils of the DPF circuits, because in the first, author's design, it is almost impossible to set up their optimal connection. It is more difficult, but more reliable, to use the proposal presented in [1]. The winding data remains the same. but the input and output resistances of the DFT (50 or 75 ohms) will have to be "adjusted" again with capacitors C1, C3, C8, C7, since the manufactured filter gave a spread (mismatch) of the input from 30 to 250 ohms on different ranges. Using the simplest "antennoscope" (K. Rothammel's HF bridge) and the HF-18 generator, this parameter was significantly improved.

It seems to me that the author has unsuccessfully applied mixer input matching circuit A2 (T1), since such a transformer circuit is not balancing. A suitable transformer could be suggested according to scheme 1.14 (p. 17 from the same book). A more complex, but high-quality, one matching-balancing transformer according to fig. 1.18, (p. 19 ibid.). It has been experimentally established that it is best to use ferrite rings of the same diameter with a permeability of 100 ... 200 units. The scheme proposed by UZ1ZWD [3] provides neither symmetry (for the reason described above) nor matching, since transformers Т1, Т2 are shunted by low-resistance input impedance 10...12 Ohm of mixer А2.

In the mixer, you need to install transistors VT1 ... VT4 with a low gain (< 15 ... 30), then turn the DPKD board "upside down" (connector up), the RF cable through the cut in the wall of the GPA in the shortest way to solder directly to pin 9 microchips DD1. This measure improves the SWR in the cable and, accordingly, increases the RF signal level at the DPCD input. An effective measure to eliminate failures in the DPKD is the UA3AIC recommendation [4] to install radiators on DD2, DD4, which finally made it possible to get rid of these defects. Having not achieved the nominal level of the GPA supply voltage +3,5 V ... 2V located on the DPKD board, I used the circuit published in [5], which is still working properly, but, unfortunately, is afraid of a short circuit. I placed the board of this stabilizer under the vernier drive cable on the GPA housing.

In the MOU board, due to the apparent lack of gain DA2.1 (A 17), limitation (compression) occurs only at frequencies of 300 ... 500 Hz, the rest of the low-frequency spectrum decreases in level and is distorted in shape. The low-frequency signal at the output of the limiter has the shape of a "carrot". The symmetry of the limited signal was restored by shifting the operating point of the DA2.1 microcircuit by applying a negative bias to pin 6 through a megohm resistor. Additional asymmetry of the low-frequency signal is introduced by the DA1.2 microcircuit due to the constant component of the diode limiters VD3 ... VD10, which is fed to the open input K.3 of the DA1.2 microcircuit. It is also eliminated by selecting a compensation bias resistor.

circuit lack of balanced modulator - inclusion of the EMF on the low-resistance load of the output DD1, which does not allow to realize the resonant properties of the input circuit of the EMF. The solution was found by YL2GL [6]. .

To achieve the rated power RA, the transformer Tr1 is made according to the scheme of fig. 1.14 [2] to ensure signal symmetry on transistors VT 1, VT2. To provide the necessary power "buildup" transistors VT3, VT4 in addition to the transistors VT1, VT2 added one more in parallel. The excitation was eliminated by replacing VT3, VT4 with transistors with V<30. Significant. a decrease in the output power of the RA causes a "drawdown" of the supply voltages +9V and +18V.

Literature

1. Radio amateur. - 1992. - No. 2.
2. Red E. High-frequency circuitry. - M.: Mir, 1990. - P.16, fig.1,13.
3. Radio amateur.-1991. - No. 1.
4. Radio amateur. - 1992. - No. 10.
5. Radio amateur.-1991. - No. 4.
6. Radio amateur. - 1992. - No. 9.

Author: A. Buzherya (UA9NM), Omsk; Publication: N. Bolshakov, rf.atnn.ru

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