Appendix: Notes For Instructors, Etc - Ten-Tec 1253 Assembly And Instruction Manual

APPENDIX:
Notes for Hams,
Club Leaders, Teachers, Engineers, etc.
A regeneratve circuit for a 1990's SWL receiver? This is a fair concern which we
ourselves have debated, but the T-KIT 1253 is not like any regeneratve receiver
you've ever bought or used before! We wanted these features:
✔
GOOD recepton of BOTH shortwave AM and CW-SSB
✔
Ease of kit-constructon for newcomers
✔
An atractve price
✔
A quality look and feel
✔
No critcal alignment requirements
✔
Serious atenton to AUDIO circuit
✔
Low parts count, yet not dependent on specialty IC's
✔
Purposeful choice of tuning ranges for SWL-ing anytme.
Satsfactory AM-CW-SSB listening and circuit simplicity were our primary goals.
Despite the popularity of the "direct conversion" circuits re-pioneered among hams
by TEN-TEC in our frst years, direct conversion is NOT satsfactory for enjoyable
listening to AM shortwave broadcasts. Merely nulling the carrier does not result in
true listenability. Similarly, a mult-band superhet with BFO cannot ft our goals of
economy and simplicity.
To meet our goals, we adapted a more contemporary design approach to
regeneraton plus sophistcated yet simple bandswitching and maximized audio
output. Our main goal was to help even beginners enjoy and understand the use of
Regeneraton while also experiencing audio strength and quality taken for granted in
today's consumer electronics. The result is an HF SWL receiver with beter
performance than some low-end superhets of yesteryear – but stll at yesteryear's kit
prices!
This manual is addressed to electronics beginners of all ages, but it is writen in the
hope that a knowledgeable radio amateur ("Elmer"!) may be looking over the kit-
builder's shoulder!
Supplementary Circuit Discussion
(see also page 6-7 and schematc on pages 32-33):
In brief, the circuit uses RF regeneraton and high levels of DC feedback. Notce that
the antenna is coupled directly to the drain of RF amplifer FET Q1 rather than
through the L-C tuning network. Direct coupling of the drains of Q2 and Q3 isolates
the L-C circuit from the antenna input, enhancing stability and greatly minimizing RF
oscillator output to the antenna. Such RFI was a signifcant problem in traditonal
regeneratve circuit which permited the oscillatng detector to behave as an
unstable but potent QRP transmiter. Adjustment of trimmer pot R6 provides for
smooth regeneraton over all tuning ranges, compensatng for individual FET
characteristcs.
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