Documenting an SDR RF Chain with a Block Diagram

[Pavel]

Short answer: Draw every RF and signal-processing stage from antenna or source to final decoder, label direction, frequency, gain or loss, sample rate and DC path. The diagram should reveal overload, power and bandwidth constraints at a glance.

Before you start​

• Define the project's purpose and one measurable success criterion before listing hardware.
• Document the complete RF and data path, including antenna, feedline, filters, gain, SDR, sample rate, software and processing output.

Step-by-step method​

1. Step 1: Place blocks in physical order: antenna, filter, LNA, feedline, attenuator, SDR, USB/network host and software stages.
2. Step 2: Label each RF component with band, gain/loss, connector and DC behavior. Mark bias-tee source and where DC is blocked or consumed.
3. Step 3: After the ADC, label complex sample rate, decimation, channel bandwidth and data format at each major processing step.
4. Step 4: Add expected signal levels or link-budget ranges and identify measurement points. Update the diagram when hardware or settings change.

Concrete example​

A chain labelled antenna → LNA → SDR hides why an LNA overloads. Adding FM notch before LNA, LNA +20 dB, 5 m coax -3 dB at target, SDR gain 25 dB and 5 V bias direction makes diagnosis possible.

How to judge the result​

The diagram is complete when every connector and rate transition is accounted for and no active block lacks power, gain or safe-level information.

What to record​

• Use equal observation windows and unchanged receiver settings for before-and-after comparisons.
• Include raw counts, signal-to-noise ratio or error rate alongside screenshots so the improvement is measurable.
• Record failed approaches and constraints; they often make a build log more useful than a polished final photograph.

Common mistakes​

• Changing several parts between baseline and result, then crediting one component without evidence.
• Publishing a polished result without the versions, settings, failures and measurement needed to reproduce it.
• Drawing software blocks without sample rates can hide an impossible decimation or bandwidth mismatch.

Final check​

Repeat the baseline or rebuild from the written log. Publish the result only when another member can follow the RF chain, settings and measurement without relying on private files or unstated changes.