Classical QRP Circuits: An SSB generator with the MC1496N mixer IC

Introduction

The MC1496 has been well known in the amateur community for several decades. It is still available today, either in the 14-pin DIL package as well as in the smaller SMD equivalent. The mixer uses a Gilbert-cell, offers high carrier suppression (around 50dB) and is ideal as an active Mixer either in SBB generators or transmit mixers. Here is the circuit of a compact module using this IC plus a microphone amplifier and an SSB ladder filter. The filter is switsched by a relay so that it can also be used in the receiver of a complete QRP radio.

Classical QRP Circuits - An SSB generator with an MC1496N
Classical QRP Circuits – An SSB generator with an MC1496N

The Schematic

The circuit of this SSB generator consists of 3 parts:

  • Microphone amplifier (ua741)
  • DSB generator
  • Ladderfilter for SSB filtering
Classical QRP Circuits - An SSB generator with an MC1496N
Classical QRP Circuits – An SSB generator with an MC1496N

The circuit is designed for a dynamic microphone (impedance about 500Ω). A 741 operational amplifier has been applied here. It is equipped with an adjustable negative feedback circuit that in the same time is used as a volume control for the input signal. Next is the MC1496N (in contrast to the “G” type (not more available) it uses 14 pin DIL package). A ladderfilter made of 4 crystals in the frequency range between  8 and 12 MHz completes the module. The relay that has been used with this prototype is a high quality type made by Teledyne(R). On request PCBs for other relay types are available. Please ask peter(at)dk7ih.de!

The mixer IC’s output is lead out using a transformer to make use of the symmetric output configuration of the Gilbert cell. The winding data is to be found in the schematic.

The parts on the PCB are placed as follows. Please note that this version varies slightly concerning the arrangement shown in the photo above.

Classical QRP Circuits - An SSB generator with an MC1496N - PCB layout
Classical QRP Circuits – An SSB generator with an MC1496N – PCB layout

Results

When driven by a dual tone signal of about 100mVpp. the generator produces an SSB signal voltage of about 300mmVpp. Carrier suppression is the range of 50 dB (as expected).