MFJ-8100
World Band Receiver
5
To put it very simply, a detector converts radio energy from
an antenna into audio energy, i.e., a sound which you can
hear. A detector can be as simple as a crystal diode, which
is the heart of the simple "crystal radio.'' If you've ever
heard unwanted radio signals on a stereo, telephone, PA
system or intercom, you can assume that some part of those
devices has acted as a detector to convert a nearby CB, taxi
or broadcast signal into intelligible sound. (This process
of detection is also referred to as demodulation.)
In the following explanation, the words regeneration,
feedback and oscillation all mean approximately the same
thing.
By itself, a detector can interpret or demodulate only very
strong signals such as a nearby AM radio station. However,
the process of regeneration can make a detector MUCH more
sensitive by turning the detector into an "oscillating
amplifier.'' The regeneration circuit repeatedly feeds the
detected signal back to the input which boosts its strength
many hundreds of times. This feedback process must be
carefully controlled, which is the function of the
regeneration control.
The frequency of oscillation is determined by the choice of
inductors (bandswitch) and the setting of the tuning
capacitor. If the oscillator is tuned to 10.1 MHz, for
example, any radio signal on that frequency will be boosted
and detected in the regeneration process. The resulting
output from transistor Q2 is a low-level audio signal which
is boosted to comfortable listening level by the LM386
integrated circuit amplifier.
The RF amplifier serves two purposes. It boosts the RF
signals from the antenna to the detector, and it minimizes
the amount of oscillator RF going back out to the antenna.
Again, we hope you'll also look at the somewhat more
technical explanation of how your 8100 Receiver circuit
works. If any terminology used in this book is unfamiliar to
you, please check the Glossary.
For Experienced Hams, Enthusiasts or Engineers