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The SOP is a "universal" HF CW receiver:

- Low current drain; able to operate from 9V battery or 12V source;

- Small size enables use as custom rig or as standalone portable monitor receiver;

- Jumper selectable operation on 80m or 40m;

- Can be set up on any other HF band (30m-10m) with few component changes;

- No critical assembly or alignment required;

- Tailorable for advanced homebrewers - extra pcb space provided for experimentation;

- No odd-ball crystals, variable capacitors or other components;

- Plug and play design ideal for beginners or advanced homebrewers;

- Solid repeatable design;

- Open layout on PC board simplifies construction.

RF Amp:

- Provides front end gain and selectivity

- Very stable grounded gate FET design

- Provides adequate gain and enhances noise figure on higher HF bands

- Can be tailored to any HF band via parallel inductor or capacitor (pcb space provided)

Local Oscillator:

- Simple, trouble-free VXO design provides variable tuning control

- Uses ceramic resonator for 80m & 40m operation, easily placed anywhere on band with alternate resonator/crystal

- Tuning range is > 50 KHz on 80m, and > 100 KHz on 40m, ensuring coverage of the standard QRP operating frequencies on each band

- Tuning range can be limited simply by changing padding resistors

- Can use other crystal or resonator to cover any HF band on 80m to 10m

- Output tank is shielded inductor - eliminates fragile trimmer capacitors

- Output tank tailored to any HF band via parallel inductor or capacitor (pcb space provided)

- Varactor tuning via potentiometer eliminates need for big, expensive variable capacitor

LO buffer:

- Stable, repeatable design provides high-level drive to mixer stage for improved performance

- No adjustments

- Broadband performance


- Single-chip, passive double balanced mixer (dbm)

- No diode matching or toroid winding, yet all the benefits of discrete dbm performance

- Better performance in crowded HF bands than single IC mixers

- Simple wide-band termination on output helps reject interference

Audio Stage:

- Low noise bipolar amplifier provides amplification and filtering

- Integrated circuit audio filter helps with cw reception

- Low pass filter peaked for CW tones

- No adjustments

- No ringing or ear fatigue

- Filters out high frequency "monkey chatter"

Audio Muting and Amplifier:

- Proven muting design quiets receiver audio during transmit via keyline signal from transmitter

- Bypass resistor on muting switch allows operator to hear sidetone of the transmitted signal

- Allows verification of transmit frequency offset

- Proven LM386 amplifier features high frequency hiss rejection

- Anti motorboat components give clean audio output

- Sufficient output for low impedance headphones or small speaker

FreqMite - Audio Frequency Annunciation:

- Optional components fit onto base SOP pc board

- Provides an "audio dial" to announce operating frequency in Morse code

- Pressing SPOT pushbutton triggers audio readout

- PIC microcontroller used in Small Wonder Labs' "FreqMite" product

- Design and parts graciously provided at attractive discount by NN1G of SWL

Last Modified: June 26, 2000