40 Meter Popcorn Superhet Receiver:
This schematic is a relatively low-cost CW superhet
receiver with a 4.00 MHz Intermediate frequency.
There is no AGC or RF gain control, however this
receiver has good large signal handling capability.
This receiver uses just 6 bipolar transistors and an
op amp for reasonable volume into headphones. Much
of the ideas/design of the various stages must be
credited to Wes Hayward as I borrowed heavily from
his previous work and through ideas obtained by
discussion. If one were to homebrew the diode ring
mixers, indeed this would be a very low cost
receiver giving reasonable performance which
outperforms any NE602 based superhet receivers that
I have built or listened to ...
The I.F. transformer primary has 18 turns, the
secondary winding has 4 turns. The capacitors across
the IFT primaries are 82pF. The input/output
transformer has 12 turns, tapped at 3 turns from
ground. This transformer is wound on a ferrite core.
The mosfets are 3SK45's. The diodes in the product
detector are 1N34's. I use a six pole SSB filter
from a scrap CB. The centre frequency is 7.8MHz. The
-6db bandwidth is about 2.5KHz.
IF Amplifier Circuit:
Three of these amplifiers are used in series to
build the 455 kHz IF amplifier. AGC voltage comes
from the AGC Circuit. The diagram above shows the
circuit for the second IF amplifier.
Tunable IF with TDA7000:
The main motive of the mods was not that the circuit
didn't work right, but were several tries to add
some kind of frequency indicator to the receiver.
The left RCA plug and associated components are
witnesses to the last version, adding a FET buffer
amplifiera and taking signal from the oscillator