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Preselector for Elektor SDR

Here’s the automatic tuning upgrade!

Preselector for Elektor SDR
The performance of a receiver depends to a large extent on its input filters. A selective input circuit improves antenna matching and immunity to interference from other strong signals. The preselector described here allows the use of up to four filters, tuned under software control using varicap diodes. A tuned loop antenna is also described that lets you use the Elektor SDR receiver without an outdoor antenna.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info, Update

Features

  • Four tuneable front-end circuits
  • Controlled by free SDR tuning software
  • I²C bus control
  • Long-, medium- and short wave reception
  • 500 pF varicap diodes
  • Suitable for use with a wire antenna, a loop antenna or a ferrite rod
Resistors
R1,R2,R3 = 100kOhm
Capacitors
C1,C2,C3,C4,C5,C6,C7,C8,C9 = 100nF ceramic
Semiconductors
IC1 = 78L05
IC2 = LM358N
IC3 = PCF8591P
D1 = 1N4001
D2–D5 = 1SV149 (www.ak-modul-bus.de)
Miscellaneous
4 inductors on former type T1.4 (www.ak-modul-bus.de)
DC power adaptor type NEB 21 R (Lumberg)
PCB, ref. 090615-1
Alternatively, kit of parts # 090615-71, contains partly populated board, coil formers, ferrite rod with coils
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