QRP Labs High Performance SDR Receiver

Features

• Three modules
  • QRP Labs High Performance Receiver Module
    • Direct Conversion Receiver
    • Uses a Quadrature Sampling Detector (QSD), also known as a Tayloe Detector
    • FST3253 Mixer is arranged as a double-balanced mixer for maximum performance
    • Circuit to mute receiver during transmit
    • Low noise LM4562 op-amps are used in instrumentation amplifier configuration to provide excellent common mode noise rejection
    • The audio output of the module is isolated using two 600:600-ohm transformers to reduce or eliminate the ground loop problems which can easily occur in SDR systems
    • The module is designed to directly drive a stereo input sound-card or with a polyphase filter card
    • Receiver board has a socket for the standard QRP Labs Band Pass Filter kit which can be routed to an external bandpass filter switch card
    • The receiver requires a local oscillator (LO) input at 4x the receive frequency
    • Receiver Build instructions
  • QRP Labs Band Pass Filter
    • 10/15/20/40/80M QRP Labs Band Pass Filter Kits
    • Band Pass Filter Build instructions
    • Can be used with a Switched Bandpass filter board for multiband operation
      • Look for "Using the Rev. 5 relay-switched LPF kit to switch Band Pass Filters" for jumpers and I/O connections
      • Relay Switched Kit Build Instructions
      • Relay driver for Relay Switched Kit
        • 6 Channel Relay Driver Card
      • Use bypass filter card on receiver when using Switched Bandpass filter, filters get installed in the switch card
  • QRP Labs Polyphase filter
    • Polyphase network plug-in module kit cancels the unwanted sideband and produces a single sideband (SSB) output
    • Polyphase Filter Build instructions
• Band Pass Filter and Polyphase filter mount on Receiver Module
• Current draw - measured total 70 mA (5V regulator
• The receiver module is sized 80 x 37mm

Build / Assembly

• Power supply + 12V in
  • Distribute 12V using TinyGrid85 card with caps
  • Needs 5V supply
    • Partly populated TinyGrid85 card with caps and 5V regulator (no ATTiny85 chip)
  • Opamps can be powered from 5V or 12-14V (for higher dynamic range)
• Audio Amplifier
• The receiver requires a local oscillator (LO) input at 4x the receive frequency
  • Using VFO-003 with 4x output option software
    • Si5351 Driver
  • CLK0 = VCO clock
    • 14MHz
    • 4x
  • CLK1 - RF test signal
    • 60 dB attenuator into RF input
    • 60+40 dB = 100 dB attenuator into RF input
  • CLK2 turned off
• SMA-HDRS board to feed LO into card
  • Mount 1x3 female flat to board
• Used right angle SMT for RF in connector - works well

Silkscreen / Pinout

Pins

• IQ pins
• I, GND, Q outputs
• Power pins
• GND, +5V, +5V or +12V to +14V
• Tx Mute Input
  • 5V mutes inputs
• LO input
  • 3.3V from Si5351A oscillators
• IF input
  • From external Bandpass Filter Switch

Receiver Module

Polyphase Module

• Important to observe part outlines
  • Adjacent resistors can be incorrectly installed "sideways"

• USB/LSB select jumpers
  • Set to USB in the above picture

Bandpass Module

• Bandpass Filter module
• 20M - 14 MHz Filter

• NanoVNA
  • 12-16 MHz

• Data

Build Issues

• Transformers don't fit well and crowd parts around them
  • 3.5mm jack crowded
  • C1/C2 footprints overlap
• QRP Labs polyphase module pics are for older revision card before 47 ohm resistors were added
• One of the two variable caps on the Bandpass filter was very hard to turn even after the first turn

Reference Documents

• Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier
• Understanding and Designing Sequence Asymmetric Polyphase Networks
• The double-tuned Circuit: An experimenter's tutorial
• 40/80m CW/SSB receiver
• Experimental Polyphase Receiver
• A Software Defined Radio for the Masses
• Very High Performance Image Rejecting Direct Conversion Receivers - NC2030 Radio