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Active Antenna

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Published in issue 356, July 2006

Short-wave listeners often are not able to, or allowed to, install a long-wire antenna or other large dimension antenna in or around the home. In such cases, the present active antenna, intended for the frequency range 3–30 MHz, may be found useful. The author used a 1-metre long rod or brass tube with a diameter of 2–6 mm.

Components

Resistors

R1 = 470k

R2 = 220k

R3 = 1k

R4 = 100

R5 = 150

R6 = 39

R7 = 1M

P1= 470 logarithmic

Capacitors

C1 = 1nF

C2,C3,C8,C9 = 100nF

C4,C10 = 47µF 25V radial

C5,C7 = 47pF

C6 = 500pF tuning capacitor

Inductors

L1,L2,L6 = 10 turns 0.7mm ECW, 4mm diameter (wind on 3.5mm drill bit)

L3 = 1 turn 0.7mm ECW, around L4

L4 = 8 turns 0.7mm ECW, 12mm diameter (wind on 10 mm drill bit)

L5 = 22 turns 0.7mm ECW, 12mm diameter (wind on 10mm drill bit)

L7,L8 = 1mH miniature choke

Semiconductors

T1 = BF247B

T2 = BF245A

T3 = 2N5109

Miscellaneous

PCB, ref. 040383-1 from The PCBShop