LowPassFilter

SDR-Learning-Project

Repository of stuff to learn about and build an SDR

Learning Projects

• Mixer Board TS3A5017 (Direct Reciever)
• Op Amp
• Front End Amp
• Frequency Synthesizer
• Bandpass Filter

SDR Radio Research

Chips

• Mixer: TS3A5017
• Mixer: FST3253
• VFO: Si5351A
• DSP: F-V1
• DSP/Micro: https://docs.ai-thinker.com/en/esp32-a1s
• OpAmp: LMP7715
• OpAmp: LM4562
• OpAmp: THS4304 / LT1818
  • https://www.ti.com/lit/gpn/ths4304

Basics

Quadrature Signals

• https://www.ieee.li/pdf/essay/quadrature_signals.pdf

Phase Locked Loop (PLL):

Create stable signal reference. Use a stable low freq reference (Crystal) to stabilize a high freq unstable ref (VCO).

• https://www.youtube.com/watch?v=A9qt0JYdvFU
• https://www.youtube.com/watch?v=P8agoshy3H4
• https://www.youtube.com/watch?v=CM8n3wzNOvc

Voltage Controlled Oscillator (VCO)

• Usually unstable, and require something like a PLL to stabilize

Operational Amplifiers

• https://www.youtube.com/watch?v=7FYHt5XviKc
• Gain is huge
• In open loop configuration, they are just comparators; Add negative feedback to become amplifiers rather than comparators
• If non-inverting input is higher than inverting input, output will be V+
• If non-inverting input is lower than inverting input, output will be V-
• Called "Operational" cause they were designed to perform mathematical "operations."
• Can be used as a buffer in buffer configuration
• Input impedance is high, so won’t draw current or effect anything on the input side
• Output impedance is low, so you can drive a bit of current through it. Tens of milliamps
• Non-Inverting Amp Configuration (Single Ended Amp)
  • Gain = Rf/R1 + 1
• Inverting Amp configuration
  • Gain = Rf/R1
  • Input * Gain * -1
  • With DC supply, it can never go negative. So need to off set and can do that by supply 1/2 Vcc to non-inverting pin

Radio Designs

• https://circuitsalad.com/wp-content/uploads/2020/05/si5351_sdr3.jpg
• NA5Y - https://www.youtube.com/watch?v=prCrbD4T6I4
• NA5Y - https://www.youtube.com/watch?v=redvZ7LcXT0&t=171s
• https://www.zachtek.com/

Filters

Receive

• https://qrp-labs.com/images/bpfkit/bpf3.pdf

Transmit

Mixing and Switching

• VFO (SI5351A): https://www.youtube.com/watch?v=9Dz9BO6VJIk
• Mixers Part I: https://www.youtube.com/watch?v=uiTrCUNRUIA
• Mixers Part II: https://www.youtube.com/watch?v=nGOxNGZQ0EM
• Mixer: https://www.youtube.com/watch?v=JuuKF1RFvBM

https://www.allaboutcircuits.com/technical-articles/how-to-multiply-RF-signals-without-a-multiplier-the-switching-mixer/

Tayloe Detector/Mixer:

• https://norcalqrp.org/files/Tayloe_mixer_x3a.pdf
• https://www.youtube.com/watch?v=EarY64Lf3ls&t=327s
• https://github.com/thaaraak/Tayloe-Mixer-v3

RF Board Design

Research needed

• Impedance and traces - Use either JLC PCB impedance calculator or one built into KiCad
• Stackups and Ground planes - Use four layers or more. Put RF traces on top or bottom layers. Always a Ground plane above or bellow the RF layer for return currents
• Stripline: Internal Trace
• Microstrip: Outer layer trace