MFJ MFJ-8100, Инструкция по эксплуатации, Страница: 6 / 27

MFJ-8100
World Band Receiver
6
Why use a REGENERATIVE circuit for a kit new for the 1990's?
A fair question, but the MFJ-8100 is not like any
regenerative HF receiver you've ever used before!
Our GOAL determined the design and circuitry of this
receiver. We wanted the following features:
GOOD reception of BOTH shortwave AM and CW-SSB
Ease of kit-construction for newcomers
Reasonable price
A quality look and feel
Relatively simple circuit
No critical alignment requirements
Low parts count, yet not dependent on specialty IC's
Purposeful choice of tuning ranges for SWLing anytime.
Satisfactory AM-CW-SSB listening and circuit simplicity were
our primary goals. Despite the popularity of NE602-type
"direct conversion'' circuits among today's experimenters and
some kit vendors, direct conversion is NOT satisfactory for
ENJOYABLE listening to AM shortwave broadcasts. Merely
nulling the carrier does not result in true listenability.
Similarly, a multi-band superhet with BFO could not fit our
goals of simplicity and economy.
To meet our goals, we chose to refine the regenerative
concept as much as possible, using contemporary design
concepts and component characteristics. Our first goal was
to "tame'' the regeneration process itself to minimize the
instability and unwanted oscillations so typical of
traditional regenerative circuits -- and so that even a
beginner can enjoy and understand the use of the Regeneration
Control. The result of our re-design is an HF SWL receiver
with better performance than many low-end factory-built
superhets of yesteryear.
Some highlights of our design efforts:
__ Significantly reduced RFI back through antenna, a chronic
regen receiver shortcoming, through use of carefully
designed RF amplifier stage.
__ Effective RF filtering between detector and audio sections
of the receiver.
__ Simplified L-C tuning: notice that there are 5 band switch
positions but no coil taps or second windings!
__ Elimination of antenna trimmer so critical in most
regenerative designs. We replaced the traditional trimmer