Signals Around Us — Reaz Romen

A research series about the signals around us: radio, telephony, embedded electronics, networks, sound, light, living systems, Earth observation, and space. Each full article aims for about 3,000 words, with worked examples, references, and diagrams where they explain the mechanism.

Available now:

Progress: 14 full articles; 286 planned investigations. This page is the editorial roadmap, not a claim that all 300 articles are already written. Planned titles may change as research develops.

The style is conversational and paragraph-led. An observation leads to a question, then to mechanisms, competing explanations, evidence, and limits. Constructed examples are labeled. Personal experiences, quotations, and field measurements are never invented. Similarities between engineering and biology are tested rather than assumed.

Signal foundations

001. Signals Are Everywhere. Why Do We Notice So Few of Them? — available
1. Signals, Messages, and Meaning Are Different Problems — planned
1. When Noise Becomes the Evidence — planned
1. Where Does a Signal Begin and End? — planned
005. Time and Frequency: Two Views of One Observation — available
1. Why Larger Amplitude Does Not Mean More Information — planned
1. Phase: How Waves Reinforce and Cancel — planned
1. Measuring an Analog World Digitally — planned
1. What Sampling Leaves Out — planned
010. Aliasing and the Apparently Backward Wheel — available
011. What Bandwidth Actually Limits — available
1. Shannon Information and Human Meaning — planned
1. What Signal-to-Noise Ratio Can Tell Us — planned
014. Why Decibels Add While Power Ratios Multiply — available
1. Correlation Is Where an Investigation Starts — planned
1. Convolution and a System's Memory — planned
1. Filtering: What We Keep and What We Lose — planned
1. Detection Thresholds, False Alarms, and Misses — planned
1. How an Attractive Graph Can Mislead — planned
1. Building an Evidence Trail for a Signal Investigation — planned

Electrical and embedded signals

1. The Message Behind a Voltage Trace — planned
1. How Analog Are Digital Ones and Zeros? — planned
1. When Two Devices Disagree About Ground — planned
1. One Button Press, Ten Firmware Events — planned
1. UART and the Wrong Baud Rate — planned
1. The Conversation Between I2C ACK and NACK — planned
1. SPI Clocks, Data, and Chip Select — planned
1. PWM and the Meaning of Pulse Width — planned
029. ADC Resolution Is Not Measurement Accuracy — available
1. From a DAC to a Speaker — planned
1. Interrupts Versus Polling for News — planned
1. How a Clock Coordinates a Board — planned
1. Jitter: The Right Event at the Wrong Time — planned
1. Ringing and Reflections on Long Wires — planned
1. Why Differential Signaling Uses Two Conductors — planned
1. Reaching Remote Sensors with RS-485 — planned
1. Who Speaks First on a CAN Bus? — planned
1. What USB Negotiates Besides Data — planned
1. How I2S Moves Audio Between Chips — planned
1. What Oscilloscopes and Logic Analyzers Prove — planned

Radio and antennas

1. How Messages Ride on Radio Waves — planned
1. Why an Antenna Is More Than a Piece of Wire — planned
1. Wavelength and Antenna Dimensions — planned
1. Where Power Goes During an Impedance Mismatch — planned
1. Can Good SWR Coexist with a Bad Link? — planned
1. Polarization and the Effect of Turning an Antenna — planned
1. Antenna Gain Does Not Create Energy — planned
1. Near Fields and Far Fields — planned
1. Distance and the Link Budget — planned
1. The Invisible Obstacle in a Fresnel Zone — planned
051. One Message Arriving Along Several Paths — available
1. Why a Stationary Radio Signal Can Fade — planned
1. AM and FM Change Different Things — planned
1. I/Q Samples and a Two-Dimensional Radio View — planned
1. The Consequences of Carrier Frequency Offset — planned
1. Reading a Spectrum with Software-Defined Radio — planned
1. Harmonics Versus Spurious Emissions — planned
1. When a Low-Noise Amplifier Helps—and When It Does Not — planned
1. A Weak Signal Beside a Strong Neighbor — planned
1. Investigating a Complete RF Link Budget — planned

Wi-Fi and local wireless

1. Full Wi-Fi Bars, Slow Internet — planned
1. RSSI and SNR Tell Different Stories — planned
1. Overlapping Channels in a Crowded Neighborhood — planned
1. Co-Channel Contention Versus Interference — planned
1. The Hidden-Node Problem — planned
1. What an Access Point Says in a Beacon — planned
1. Probe, Authenticate, Associate — planned
1. OFDM and Its Many Subcarriers — planned
1. Sharing Time and Frequency with OFDMA — planned
1. What Multiple Antennas Contribute to MIMO — planned
1. What Beamforming Actually Shapes — planned
1. Reading a Room Through Channel State Information — planned
1. Wi-Fi Presence Sensing: Person or Moving Curtain? — planned
1. Why Wireless Sensing Calibration Changes — planned
1. The Small Messages in Bluetooth Advertising — planned
1. The Logic of Bluetooth Frequency Hopping — planned
1. The Paths Inside Zigbee and Thread Meshes — planned
1. What LoRa Trades for Range — planned
1. Reticulum over LoRa and Resilient Low-Rate Messages — planned
1. A Measurement Plan for an Urban Wireless Link — planned

Mobile, satellite, and navigation

1. The Phone's First Conversation After a SIM Is Inserted — planned
1. Changing Cells Without Losing a Call — planned
1. Who Gets Radio Resources and When? — planned
1. LTE Control and User Planes — planned
1. How 5G Numerology Divides Time — planned
1. Why Uplink and Downlink Differ — planned
1. How a Phone Chooses Transmit Power — planned
1. Diameter Signaling and Its Boundaries — planned
1. Why SS7 Still Matters — planned
1. IMS and the Mobile Voice Session — planned
1. Distance and Delay in Satellite Links — planned
1. Keeping a Link to a Fast-Moving LEO Satellite — planned
1. Doppler Shift as Evidence of Motion — planned
1. How GPS Broadcasts Time — planned
1. Four Satellites and the Positioning Problem — planned
1. Urban Multipath and GNSS Position Errors — planned
1. The Ionosphere's Effect on Signal Delay — planned
1. Rain Fade in Satellite Links — planned
1. Satellite Phones and Terrestrial Phones — planned
1. Before Trusting a Navigation Reading — planned

Telephony and real-time media

101. A Connected Call with Silence at Both Ends — available
1. The Session Conversation Inside SIP — planned
1. SDP and the Address Where Audio Should Go — planned
1. RTP Packets and Media Time — planned
1. How RTCP Reports on Media Delivery — planned
1. Does Ringback Mean the Other Phone Is Ringing? — planned
1. Early Media Before a Call Is Answered — planned
1. Three Ways to Send a DTMF Digit — planned
1. Investigating One-Way Audio Behind NAT — planned
1. When Codec Negotiation Does Not Produce Useful Audio — planned
1. What Packet Loss Sounds Like — planned
1. The Jitter Buffer's Delay Trade-Off — planned
1. How Echo Cancellation Identifies Returning Audio — planned
1. Voice Activity Detection and the Treatment of Silence — planned
1. ICE, STUN, and TURN in WebRTC — planned
1. PBX Registration Does Not Prove Calling Works — planned
1. An OpenSIPS Proxy and a Media Server Have Different Jobs — planned
1. Tracing Call State Through FreeSWITCH and Asterisk — planned
1. The Complete Path Through an ESP32 Voice Device — planned
1. Investigating Latency in an AI Voice Receptionist — planned

Network and distributed signaling

1. Packets and Application Messages Are Different Units — planned
1. Finding a Neighbor with ARP — planned
1. The DHCP Address Conversation — planned
1. From a DNS Name to an Address — planned
1. Does a TCP Handshake Prove an Application Is Ready? — planned
1. What an Acknowledgment Actually Confirms — planned
1. Timeouts: Decisions Made from Silence — planned
1. How Retries Turn a Small Failure into a Storm — planned
1. A Service with a Heartbeat That Still Cannot Work — planned
1. How Gossip Protocols Spread News — planned
1. Trust and Messages in Consensus — planned
1. The Timing of Leader Election — planned
1. Why Distributed Clocks Disagree — planned
1. Lamport Clocks and Event Ordering — planned
1. Message Delivery Versus Message Processing — planned
1. Idempotency and Repeated Instructions — planned
1. Backpressure as a Request to Slow Down — planned
1. Identity and Encryption in a TLS Handshake — planned
1. Desired State and Observed State in an OTA Control Plane — planned
1. Combining Logs, Metrics, and Traces During an Incident — planned

Sound, audio, and vibration

1. What Changes When Sound Travels Through Air? — planned
1. A Microphone Turns Pressure into an Electrical Signal — planned
1. The Reverse Journey Through a Speaker — planned
1. Pitch and Timbre Explain Different Experiences — planned
1. Harmonics and the Identity of an Instrument — planned
1. Room Reverberation as a Record of Reflections — planned
1. Phase Cancellation Between Two Microphones — planned
1. What Noise-Canceling Headphones Remove — planned
1. Reading Sound on a Spectrogram — planned
1. What Audio Compression Discards — planned
1. Loudness Is Not Peak Level — planned
1. Sensing with Ultrasound — planned
153. Sonar and the Time of a Returning Echo — available
1. The Strategies and Limits of Bat Echolocation — planned
1. Why Underwater Audio Links Behave Differently — planned
1. A Machine's Condition in Bearing Vibration — planned
157. Seismic Waves as Evidence of Earthquakes — available
1. Distant Events Recorded in Infrasound — planned
1. When Musical Silence Carries Information — planned
1. Investigating the Origin of an Audio Recording — planned

Light, optics, and imaging

1. Light as a Signal and the Eye as a Receiver — planned
1. A Message Traveling Through Optical Fiber — planned
163. Attenuation and Dispersion: Two Ways an Optical Signal Can Fail — available
1. From Light to Current in a Photodiode — planned
1. What a Camera Pixel Measures — planned
1. When More Exposure Loses Information — planned
1. Rolling Shutters and Distorted Time — planned
1. The Invisible Instructions in an Infrared Remote — planned
1. Lidar and the Return Time of Light — planned
1. Depth from Time-of-Flight Cameras — planned
1. What a Thermal Camera Observes — planned
1. Spectroscopy and Material Identification — planned
1. Following Cellular Events with Fluorescence — planned
1. Structures Revealed by Polarized Light — planned
1. Small Distances Measured with Optical Interference — planned
1. Human Color and Sensor Data — planned
1. How Atmospheric Scattering Changes What We See — planned
1. Communication Through Rapid LED Modulation — planned
1. Image Processing and the Creation of Artifacts — planned
1. When an Image Counts as Scientific Evidence — planned

Cells and chemical signaling

1. What Does It Mean for Cells to Communicate? — planned
1. Ligands and Receptor Selectivity — planned
1. Endocrine, Paracrine, and Autocrine Distances — planned
1. An External Event and an Internal Cellular Response — planned
1. G Proteins as Molecular Switches — planned
1. Amplification Through Kinase Cascades — planned
1. The Timing of Calcium Pulses — planned
1. Why Cyclic AMP Is Called a Second Messenger — planned
1. Do More Receptors Always Mean a Stronger Response? — planned
1. How Feedback Regulates Cellular Signaling — planned
1. Bacterial Chemotaxis and Directional Behavior — planned
1. Quorum Sensing and Local Population Information — planned
1. Communication in a Biofilm Environment — planned
1. What Evidence Supports Chemical Signaling in Plants? — planned
1. Recognition and Alerts in Immune Cells — planned
1. One Cytokine and Several Possible Effects — planned
1. What the DNA-as-Source-Code Analogy Misses — planned
1. Timing and Dose in Gene-Expression Responses — planned
1. Disrupted Signaling in Cancer Research — planned
1. A Cell Diagram Is Not a Living Cell — planned

Nerves, senses, and the body

201. How a Neuronal Signal Begins — available
1. Where the Binary Analogy Fails for Action Potentials — planned
1. Electrical and Chemical Events at a Synapse — planned
1. What a Neuron's Firing Rate Can Tell Us — planned
1. The Information Question in Spike Timing — planned
1. From Retinal Light to Visual Interpretation — planned
1. From Air Pressure to Hearing — planned
1. Odor Molecules and Receptor Patterns — planned
1. Different Pathways for Pressure, Vibration, and Temperature — planned
1. Is Pain Adequately Described as an Alarm? — planned
1. What an ECG Measures—and What It Does Not — planned
1. The Combined Activity Recorded by EEG — planned
1. Observing Muscle Activity with EMG — planned
1. Light, Models, and Pulse Oximetry — planned
1. Motion Artifacts in Wearable Measurements — planned
1. Several Sources Behind a Breathing Trace — planned
1. Control in the Autonomic Nervous System — planned
1. Feedback and Homeostasis — planned
1. The Limits of Decoding in Brain–Computer Interfaces — planned
1. Uncertainty Between a Body Measurement and a Decision — planned

Animals, environments, and social signals

1. What Evidence Reveals the Message in a Bird Call? — planned
1. Chemical Communication Through Pheromones — planned
1. Direction and Distance in the Honeybee Dance — planned
1. Patterns in Firefly Light — planned
1. The Multiple Functions of Octopus Color Changes — planned
1. The Cost of a False Alarm Call — planned
1. Mimicry and Borrowed Signals — planned
1. Testing Claims About Costly Signaling — planned
1. An Evolved Signal Versus an Incidental Cue — planned
1. Animal Communication in a Changing Soundscape — planned
1. Why Facial Expressions Need Context — planned
232. Traffic Lights and the Shared Rules Behind a Signal — available
1. Words, Tone, and Conflicting Messages — planned
1. Signals of Trustworthiness and Their Imitation — planned
1. The Limits of Treating Prices as Signals — planned
1. Popularity Is Not Evidence on Social Media — planned
1. Feedback in a Rumor Network — planned
1. What Ranking Systems Treat as Signals — planned
1. Can Signaling Theory Explain Every Behavior? — planned
1. Testing a Social Claim with Data and Context — planned

Weather, rivers, and Earth observation

1. A Sensor's Temperature Is Not a City's Temperature — planned
1. Rain a Gauge Does Not Capture — planned
1. What Weather-Radar Reflectivity Means — planned
1. Radial Wind Motion in Doppler Radar — planned
1. Seeing Clouds Versus Estimating Rainfall — planned
1. Cloud-Top Temperature in Infrared Images — planned
1. Reading a Sequence of Himawari Frames — planned
1. The Electrical and Radio Traces of Lightning — planned
1. River Level Is Not River Discharge — planned
1. GloFAS Model Output Versus a Field Gauge — planned
1. Tidal Timing, Phase, and River Flow — planned
1. Wave Spectra from Ocean Buoys — planned
1. Separating Storm Surge from the Tide — planned
1. Water Elevation from Satellite Altimetry — planned
1. What NDVI Reveals About Vegetation — planned
1. Does a Fire Hotspot Establish an Actual Fire? — planned
1. Humidity and Low-Cost Air-Quality Measurements — planned
1. Timing in Coastal Salinity Observations — planned
1. Models, Sensors, and Forecasts on a District Dashboard — planned
1. Thresholds and Human Decisions in Disaster Alerts — planned

Space and fundamental physics

1. Why Starlight Is Information from the Past — planned
1. Chemical Evidence in Stellar Spectra — planned
1. The Different Causes of Redshift — planned
1. The Regular Signals of Pulsars — planned
1. What We Know—and Do Not Know—About Fast Radio Bursts — planned
1. Evidence in the Cosmic Microwave Background — planned
1. Removing Terrestrial Interference from Radio Astronomy — planned
1. Combining Distant Antennas with Interferometry — planned
1. How a Gravitational Wave Becomes an Observation — planned
1. An Astrophysical Event Versus Detector Noise at LIGO — planned
1. Searching for Rare Events in Neutrino Detectors — planned
272. The Small Dip Produced by a Planetary Transit — available
1. Searching an Exoplanet Atmosphere for Biosignatures — planned
1. Why a Biosignature Is Not Automatically Proof of Life — planned
1. What SETI Means by a Technosignature — planned
1. The Wow! Signal and the Limits of a Single Event — planned
1. Recovering Voyager's Faint Transmission — planned
1. How Solar Activity Changes Radio Propagation — planned
1. Measurement Rules in Quantum Communication — planned
1. When Calling the Universe a Message Becomes a Metaphor — planned

Investigation, design, and interpretation

1. No Data, or a Receiver That Is Not Working? — planned
1. An Alarm's Postmortem — planned
1. Wrong Timestamps and a Misleading Incident Story — planned
1. The Consequences of Incorrect Units — planned
1. Measuring Change Without a Baseline — planned
1. Mistaking Sensor Drift for a New Event — planned
1. Using Synthetic Data to Test a Model's Limits — planned
1. What a Control Condition Contributes — planned
1. Blind Analysis and the Influence of Expectations — planned
1. Multiple Tests and Coincidental Findings — planned
1. How Filter Choices Change the Result — planned
1. Does an AI Detector Learn the Signal or a Shortcut? — planned
1. Prediction, Explanation, and Causation — planned
1. Auditing an Open-Source Signal Pipeline — planned
1. More Observability Data Versus Better Evidence — planned
1. The Meaning of Silence in Fail-Safe Communication — planned
1. Different Interpretations of the Same Signal — planned
1. The Boundary Between Information Theory and Meaning — planned
1. Measurement, Consent, and Surveillance — planned
1. What Three Hundred Investigations Should Teach Us — planned