Active DCF77 antenna
Last updated: November 7, 2010
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Under Construction
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Enclosure |
Straightforward active antenna for DCF77. The amplifier is designed for a
power supply of 5V and a remote DC resistance of 120 ohm (Hopf 6021 board).
It consists of a FET buffer, a 10x amplifier and an output buffer.
Choose the base resistor of the first BC548 for approx. 2.5V at the collector.
The ferrite coil came, as usual, from the junkbox. Measure it's inductance
and add capacitors to get resonance at 77.5 KHz.
Tuning
The input has to be tuned to 77.5 KHz. Wind a few (8-10) turns of wire around
a piece of PVC tube (32 mm on the photo). Couple this coil to
the ferrite antenna and drive it through a large resistor (100Kohm) from a
signal generator. Power the amplifier with 5V through a 120 ohm resistor and
measure the output with a millivoltmeter or scope. Now tune for maximum
output.
Archive containing the Xcircuit file
(encapsulated postscript).
