Lab 10.4 — KiCad Schematic Mini-Project

Goal

Prepare a small reproducible electronics mini-project for the SDR bench: an RF-safe attenuator/filter interface documented as a schematic, BOM and safety checklist.

Engineering question

Can another engineer reproduce the front-end helper circuit and understand its limits before connecting it to SDR hardware?

Mini-project concept

flowchart LR
    IN[Signal input] --> ATT[Attenuator / divider]
    ATT --> FILT[Optional RC filter]
    FILT --> OUT[SDR input / measurement node]
    OUT --> LOAD[Load / receiver impedance]

Required schematic blocks

Block	Purpose
Input connector	defines signal entry point
Attenuator	reduces level before receiver
Optional RC filter	limits low-frequency or high-frequency components
Output connector	connects to SDR or measurement input
Ground reference	avoids ambiguous return path
Notes	documents impedance and safety limits

BOM template

Ref	Value	Package	Purpose	Notes
R1	9 kOhm	THT/SMD	divider upper resistor	educational example
R2	1 kOhm	THT/SMD	divider lower resistor	gives about -20 dB unloaded
C1	100 nF	THT/SMD	optional RC capacitor	choose by target cutoff
J1	connector	SMA/BNC/header	input	depends on bench
J2	connector	SMA/BNC/header	output	depends on receiver

KiCad deliverables

A complete mini-project should include:

kicad/
  sdr_frontend_helper.kicad_pro
  sdr_frontend_helper.kicad_sch
  bom.csv
  README.md

If KiCad is not available, document the schematic in Markdown first and convert it to KiCad later.

Safety checklist

• Maximum input level is stated.
• Expected attenuation is calculated.
• Load impedance assumption is written.
• DC coupling/AC coupling is documented.
• SDR input protection is considered.
• Circuit is tested at low level first.
• Measurement metadata mention the interface circuit.

Report checklist

• Include schematic or clear diagram.
• Include BOM.
• Include attenuation calculation.
• Include RC cutoff calculation if filter is used.
• Explain limitations of the circuit.
• State whether it is safe for the intended SDR experiment.

Engineering conclusion template

The KiCad mini-project implements ______ with expected attenuation ____ dB and optional cutoff ____ Hz.
It is suitable / not suitable for the SDR bench because ______. The key limitation is ______.