Main Receiver
RF Preamp
Log Amp
Slow Background Remover designed by Kenneth Kuhn
Above — Slow background Noise Remover. The receiver had no AGC system. This circuit is basically a coupling capacitor and resistor to a baseline voltage. The effective time constant can be set to many tens or even hundreds of seconds. This circuit removes large slowly varying background and enables viewing of only the relatively short time changes. I explored this circuit plus variants in my "sky" receivers. DC + Analog solutions from my analog life.
ADC
Older, discrete BJT preamp for ~6 mA IC
Above — 1 of the initial preamp circuits built for an electrically short dipole Jovian antenna. We love using PNP transistors -- and learned to bias them (including with negative feedback) in both single + split DC supply situations to enhance our knowledge and nimbleness making BJT circuits. The MPSH81 [PNP, 20V, 50mA, 600MHz, 350mW, through-hole, TO-92] gave a surprisingly hot ~24 dB gain even when configured as a common base amp with very careful input/output impedance matching (we calculated 19.7 dB gain). The input bandpass filter has a 3 dB BW of 264 KHz and proved a good design. This preamp seems a little too hot for 20 MHz, but shows the potential of this simple circuit with only ~ 6 mA collector current. Really old school, super-fun building.
MISC
Yes, the main receiver can go on any HF band. What follows is a 7 MHz version of the 3 dB hybrid. You'll also need a 7 MHz quadrature splitter for the VFO.
