Qua. Jun 12th, 2024



The RF amplifier comprises one stage of amplification (VT1) followed by three emitter follower stages, (VT2-4). It is preceded and followed by variable attenuators in the forro of shunt diodes which are selected far high storage to prevent diode non-linearity effects. The front end diodes are controlled by a local a.g.c. loop (VT9 and VT10). The voltage which operates the control transistor is produced by VT10, which operates as a detector, with the signal from VT3 emitter applied to its base via C10, R16/C15. Under no-signal, or very low signal conditions, VT9 is held nonconducting since its base (via R36) and emitter is returned to the -15V line. Thus D1 and D2 cannot conduct and offer no attenuation to the input signal. As the signal level increases to 20mV the detector action of VT10 dri ves VT9 base less negati ve with the result t.hat VT9 conducts, drawing current via D1 and D2, decreasing its impedance, thus applying some attenuation to the input signal. With further increases in signal strength VT9 draws more current via D1 and D2, increasing the attenuation. The control circuit is prevented from responding to transient changes in signal level by capacitar C24. The output from VT4 is applied via R19 to the second variable attenuator circuit and via C13 to the first mixer. The a.g.c. line from module 8 is applied to a control amplifier VT5 and VT6. This operates in a similar way to VT9 and VT10. As VT6 draws more current via D4 so the output signal is attenuated to maintain an output of approximately 30mV to prevent overloading of the first mixer. Threshold variation is by adjustment of RV1, the voltage across which is held constant by zener diode D5 and·D6-D7.

Com um TinySA decidi verificar o que saia do amplificador 1 (antes dele nao ha sinal suficiente para ler no tinySA), liguei a antena na entrada do radio, e fui buscar o sinal depois do modulo 1

FL 3
Fl 6
FL 7

O fl 8 nbao apresentava sinal suficiente para ler algo de jeito.


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