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This is a picture of the inside of the Drake 2B.  It shows the low frequency converter I built on 11/15/98.  The Drake is excellent for LF listening with this converter because of the extra sensitivity and selectivity when the Q multiplier is used.  The BNC connector on the right is the input (0 to 500 kHz) and the connector on the left is the output (14.000 to 14.500 MHz).  Since the Drake gets its signal through the jack on the bottom of the converter, the output BNC can be connected to another receiver so one frequency can be monitored while scanning other frequencies.  The small feed through on the side of the converter is a 12 volt input to the converter so it can be used outside of the Drake with other receivers.

This is the underside of the converter.  It shows the connector for the Drake 2B.  The pins are from an old octal plug relay.  The box fits in the slot that normally contains the calibrator.  It would be easy to build a 100 kHz calibrator into this box with the converter.  The pins are ground, B+, input signal (electrically the same as the antenna input), and filament voltage.  I use a 15 k ohm resistor and a 12 volt zener diode to reduce the B+ to 12 volts and then a 1 k ohm resistor and a 6 volt zener to drop the 12 volts to 6 for the NE612 mixer chip.

This is the inside of the converter.  It uses an NE612 mixer chip (similar to the NE602).  Above the two green disk capacitors is an MPF102 FET that is used as an RF amp and provides a balanced input to the NE612.  The crystal is 14.000 MHz.  Thus the conversion from LF to the 20 meter band.  Another frequency could be used but the Drake is fairly sensitive on 20 meters and the crystal was available.  The circuit is similar to the first stage of a direct conversion QRP receiver.