TECHNICAL OVERVIEW
BLOCK DIAGRAM:
QUICK SPECS:
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
Mixer:
- 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
