Schematics > RF circuit > 40 meter Direct Conversion Receiver
40 meter 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.
Title: 40 meter Direct Conversion Receiver
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-09
Reads: 532
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