Low Frequency Receiver Circuit John Kielkopfand Charles Cow an November 29,2000 1 Design and … Very LowFrequency Radio Stations Site ID Frequency Radiated Power KHz KW Cutler, ME NAA 24.0 … The receiver usesacommercial ampliedloop antenna manufactured by\Palomar”with its\Omega”loop. The loop is approximate 25 cmindiameterand can be oriented in any direction. In a concrete and wood building away fromsignicant structural iron the plane of the loop is vertical and its normal is approximately along a line directed from Louisville, KY, to …

The receiver for the solar are monitor is a simple circuit designed to detect the 24KHzsignal from the station in Cutler, Maine, and reject signals at nearby frequencies from other directions. The receiver usesacommercial ampliedloop antenna manufactured by\Palomar”with its\Omega”loop. The loop is approximate 25 cmindiameterand can be oriented in any direction. In a concrete and wood building away fromsignicant structural iron the plane of the loop is vertical and its normal is approximately along a line directed from Louisville, KY, to Cutler, ME. This antenna has an internal FET preampwhichmaybe battery operated. In our system the battery is not connected, and the internal circuit has been mo died to accept power delivered on the coax from the antenna to the receiver. The amplied RF from the antenna is capacitively coupled toa LC resonator tuned to 24 KHz. Thisrststageof the receiver is shown in Fig. 1. The output from the LC resonator connects to an RF 2-stageamplier shown in Fig. 2. The amplierusesa commonly available LF353 dual JFET opampwiththerst stage as a voltage follow er of unity gain, and the second stage with gain (R 1 +R 2 ) =R 1 101 inthisexample. The output of this ampliermaybefed directly to an oscilloscope to monitor tuning of the LC circuit and the antenna. The RFamplieris capacitively coupled to a detector circuit thatrecties the 24KHzsignal and provides some additional gain. This section also uses anLF353 asshownin Fig. 3. Additional gain, lo w-passltering, andbueringis provided byathird dual JFETopampin the section shown in Fig. 4. The gain is adjusted by the resistor R9, which is omitted for 1 or decreased to 10Kfor 100. L1 L2 C1 A B LC Circuit Figure1: The LC resonator. A preamplied signal from the antenna enters at A. This section is enclosed in a grounded box inside the receiver chassis. The station is selected by varying L2 while monitoring the output of the next stage. B D C C2 R1 R2 1 2 3 6 5 7 U1A U1B 4 8 +V -V RF Amplifier Figure2: The signal Bfromthe LC circuit enters a voltage follow er (U1A) and is then capacitively coupled to anamplier (U1B). The output goes to an oscilloscope (C) fortuning, and to a detection circuit (D)….

Download Low Frequency Receiver Circuit.pdf