EMRFD Message Archive 4256

Message Date From Subject
4256 2010-02-11 14:33:36 Chris Trask CA3046 Superflexodyne Receiver
Since we're deeply into applications of the CA3046, I went and uploaded
the partial schematic I have for a superheterodyne reflex receiver using the
CA3046 and one diode. The schematic is missing a few parts associated with
the base voltage bias string, and there are no parts values. I set this
aside a couple of years ago and never followed up on the documentation as it
was one of those weekend fun projects.

Basically, the CA3046 differential pair (Q1 and Q2) is used as a
mixer/oscillator. The blocking capacitor from the tank inductor to the
emitters can be replaced with a crystal for single-frequency operation, such
as a WWV receiver. The ceramic filter can easily be replaced with a
two-crystal narrow-band filter to improve CW operation.

The IF amplifier also serves as the audio preamplifier, making that a
reflex section that uses the transistor twice.

The BFO is fairly straight forward, coupling the BFO and IF signals to
the product detector diode. A centre-tapped secondary on the second IF
transformer would allow a full-wave product detector, which would improve
the demodulated signal voltage some.

The audio output amplifier should use device Q5 as it will have the
lowest emitter voltage. The audio output transformer is one of those Xicor
miniature types from Mouser.