WA7NBF Wideband LV Offset Attenuator
Other active offset attenuators use a 9 volt battery for power. The WA7NBF approach is to use a 1.5 volt AA size cell. This is made possible by the use of the ALD110900 E-pad dual MOSFET which is designed for zero threshold. Data sheet for the ALD110900 is here. The WA7NBF design also uses a standard 2 pin crystal. The crystal can be socketed so that 1MHz, 2MHz, or 4 MHz crystals can be selected.
A Wideband Low Voltage Offset Attenuator
by Neil Robin, WA7NBF Revised: April 7, 2010
Schematic for WA7NBF Low Voltage Offset Attenuator
All the circuitry below R2 potentiometer is for the oscillator and power. R2 is available from Radio Shack and inexpensive. D1 is the mixer diode with the LO injected via R1. The return path is through R3. As the wiper of R2 travels more negative a small DC bias is placed on the diode to help its conductivity. When the wiper is in its low sensitivity position, the bias is removed but a strong RF signal coming in will bias the diode with C1 holding the offset voltage. Generally, its prefered to keep the oscillator circuit ground separate from the chassis but you can try it either way to minimize leakage of the LO.