Friday, 25 August 2017

Twin diode receiver

This radio uses two receiver chains; the supply voltage needed for the transistor amplifier is generated by a strong local broadcast station to which diode receiver number 1 (left side of the schematic) is fix-tuned. Tune with the aid of a meter and adjust for maximum detection. Low-level stations are detected with the diode receiver number two (right side of schematic). Use a germanium low signal AF type transistor (AC151, 2SB187) and Ge-diodes (AA119, AA112, AO85...). Design coil1 and 2 in such a way that Medium Wave broadcast stations are received.

A supply voltage as low as 450 mV produces audible signal amplification. Of course you have to use TWO antennas.
The designer of this radio uses for receiver number 2 (right) a loop (frame) antenna, for receiver number 1 (left) a a 20 meters outside antenna (wire). 

Receiver 1 generates a supply voltage of approx. 900 mV under load of receiver number 2.
Adjust the variable 250 kOhms resistor to approx 50 % of the voltage generated by receiver number 1 voltage (measured at + pole). Best value for 10 kOhms trim pot is 3 to 6 kOhms.

Do not use electrolytic capacitors for the 0.1 uF capacitors. Do not forget to install the 1 nF capacitor. Attention for the polarity of the diode (AA112, AO85, AA119...) in receiver nr 1.


Off topic:

Canal in Den Haag (Zuidwal / Dunne Bierkade), 7 Sep.  2017

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