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This was the Low Frequency Transmitter that I used until 9/17/2000.  The box in the upper right is the transmitter.  It contains the oscillator and power amp boards for the transmitter.  A 7400 chip oscillator with a 2187 kHz crystal has its output divided by 12 with a 7492 chip making 182.25 kHz. This is amplified by the 2N2222A/2N2907A push pull amp.  The main idea for this simple LF transmitter design came from the web site of Lyle Koehler, K0LR.  One of the 7400's nand gates is used for keying the RF to the PA.  A 0 to 100 milliamp meter on the front of this box measures PA current.  An LM317 adjustable voltage regulator sets the PA voltage (about 18 volts with a PA current of 55ma = 1 watt).  Also in the box is a PIC chip CW keyer that can send different messages according to the positions of the switches on the front of the box.  The circuits on the breadboards are an EEPROM keyer (Bill de Carle) and a timer circuit that switches the keyer from BPSK to CW every half hour.  I have replaced this transmiter with one of Lyle's All-in-1 BPSK/CW Transmitters.  Breadboarding is handy but not too permanent.

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