40-Metre Direct Conversion Receiver
 
 Using the circuit of 40-metre band direct-conversion receiver descr- ibed here, one can listen to amateur radio
 QSO signals in CW as well as in SSB mode in the 40-metre band. The circuit makes use of three n-channel
 FETs (BFW10). The first FET (T1) performs the function of ant./RF amplifier-cum-product detector, while the
 second and third FETs (T2 and T3) together form a VFO (variable frequency oscillator) whose output is
 injected into the gate of first FET (T1) through 10pF capacitor C16. The VFO is tuned to a frequency which
 differs from the incoming CW signal frequency by about 1 kHz to produce a beat frequency in the audio range
 at the output of transformer X1, which is an audio driver transformer of the type used in transistor radios. The
 audio output from transformer X1 is connected to the input of audio amplifier built around IC1 (TBA820M) via
 volume control VR1. An audio output from the AF amplifier is connected to an 8-ohm, 1-watt speaker. The
 receiver can be powered by a 12-volt power-supply, capable of sourcing around 250mA current. Audio-output
 stage can be substituted with a readymade L-plate audio output circuit used in transistor amplifiers, if desired.
 The necessary data regarding the coils used in the circuit is given in the circuit diagram itself. 