Radio Lab

Explore how radio works with this Beta tool. Follow a transceiver, build circuits, inspect components, use formulas and explore Australian amateur radio references.

Mode i
Architecture i
Simple view: follow the major functional blocks without extra detail.
Superheterodyne example. This is one common architecture, not the only way to build a radio.
📥 RECEIVEProcessing toward audio →
📤 TRANSMITProcessing toward the antenna →
🎙️
Selected block i

Microphone

Converts sound pressure into a small electrical audio signal.

Try: select any block above.

Audio frequencyInput transducer
Signal view · illustrative · auto-scaled iSSB RF
~8.0 visible cycles / screen 100% relative tuned-circuit level Fixed 8-division reference grid
Relative wavelength
21.13 m
Mixer → IF filter iRF 14.200 + LO 4.200 MHz
Wanted IF · filter keeps Unwanted product · filter rejects LO input reference
0 5 10 15 20 Frequency (MHz)
LO input4.200 MHz
Wanted IF10.000 MHz
Rejected18.400 MHz
🧠 Learning model: this deliberately simplifies a modern transceiver so the major functions are visible. Real radios may combine these stages in DSPs, ICs and multiple conversion paths.

⚡ Circuit Lab

Series & parallel builder

Change the part type, connection and values. The diagram and equivalent value update together.

Build it
Component
Connection
Number
Equivalent2.00 kΩ
RuleSeries adds
ConnectionSeries
Rₜ = R₁ + R₂

🧲 Transformer turns ratio

Set the windings, primary voltage and primary current. The ideal transformer then calculates the secondary voltage and current.

Faraday
12 V → 6.0 V · 2:1 step-down
Secondary voltage
Secondary current
Calculated voltage12.0 V → 6.0 V ↓
Calculated currentPrimary 2.00 A · Secondary 4.00 A
Ideal transformer power24.0 W ≈ 24.0 W

Sliders above are inputs. Secondary voltage and both currents below are calculated outputs, so they deliberately do not have sliders.

➡️ Diode direction

Switch the polarity to see the basic one-way behaviour used in rectifiers, detectors and protection circuits.

Diode direction
➜—|>|—Forward bias · conducting
Forward bias → diode conducts

Typical silicon diode: forward voltage is often about 0.6–0.7 V. Actual forward voltage varies with diode type, current and temperature.

〰️ Reactance vs frequency

Raise frequency from the audio/RF region through HF, VHF and into UHF, and compare the opposite behaviour of an inductor and capacitor.

AC behaviour
Inductor XL↗increases with frequency
Capacitor XC↘decreases with frequency
L: 62.8 Ω ↑ · C: 159.2 Ω ↓

Example values: L = 10 µH, C = 1 nF. Where XL and XC become equal is the basis of LC resonance.

Fast rule: resistors and inductors add in series; capacitors add in parallel. For the opposite connection, use the reciprocal rule.

🧩 Component Explorer

Choose a physical component, then use the interactive panel to see the electrical behaviour that makes it useful in a radio.

/\/\/
Passive

Resistor

Opposes current flow and develops a voltage drop.

Where you see it in radio

Biasing · current limiting · gain setting · loading.

Key idea

Series resistance adds. Parallel resistance is lower than the smallest branch.

V = I × RVoltage · current · resistance
P = V × IElectrical power
λ = c ÷ fFrequency ↔ wavelength
+3 dB ≈ 2×Power ratio anchor

⚡ Ohm's law & power i

Choose the quantity to calculate, then adjust the other two values.
0 V125 V250 V
1 mA500 mA1 A
1 Ω5 kΩ10 kΩ
Result500 Ω · 0.20 W

📏 Frequency ↔ wavelength

1.8 MHz450 MHz
Relationship145.800 MHz ≈ 2.056 m

📊 dB ↔ power ratio

−20 dB0+20 dB
Power ratio6 dB ≈ 3.98× power

Power ratio = 10dB/10. Useful anchors: +3 dB ≈ 2×, +6 dB ≈ 4×, +10 dB = 10×.

🔢 Engineering prefixes

Converted value0.001 k

🧾 Core formulas

V = I × ROhm's law
P = V × IElectrical power
P = I²RPower from current + resistance
λ = c ÷ fWavelength
f₀ = 1 / 2π√LCLC resonance
dB = 10 log₁₀(P₂/P₁)Power ratio

🧭 High-level overview

A compact reference for Australian amateur band access, licence power levels, common emission modes and basic operating concepts.

Licence levelFoundation, Standard and Advanced each have different permitted bands and power limits.
Band segmentThe legal band edge is not enough. Use the band plan to choose voice, CW, data, repeater or satellite segments.
Mode & powerJ3E/SSB-style voice often has a different power category to FM, CW and data modes.

📡 Band access by minimum qualification i

Choose a licence level to show what that level can generally access. The coloured buttons show the cumulative licence path: Standard includes Foundation bands; Advanced includes Foundation and Standard bands.

BandFrequency rangeMinimumOperating notes
2200 m
135.7–137.8 kHzAdvanced
〰️ LF; special limits
630 m
472–479 kHzAdvanced
〰️ MF; special limits
160 m
1.800–1.875 MHzAdvanced
🌏 Advanced HF band
80 m
3.500–3.700 MHzFoundation
🌏 All classes; HF bandwidth limits
80 m DX window
3.776–3.800 MHzAdvanced
🌏 Advanced-only segment
40 m
7.000–7.300 MHzFoundation
🌏 All classes; split conditions
30 m
10.100–10.150 MHzAdvanced
⌁ Advanced; ≤8 kHz bandwidth
20 m
14.000–14.350 MHzStandard
🌏 Standard+; HF bandwidth limits
17 m
18.068–18.168 MHzAdvanced
🌏 Advanced; HF bandwidth limits
15 m
21.000–21.450 MHzFoundation
🌏 All classes; HF bandwidth limits
12 m
24.890–24.990 MHzAdvanced
🌏 Advanced; HF bandwidth limits
10 m
28.000–29.700 MHzFoundation
📡 All classes; wider HF/VHF-style use
6 m
50.000–54.000 MHzStandard
📡 Standard+; mixed conditions
2 m
144.000–148.000 MHzFoundation
📡 All classes; no specific mode limit
70 cm
430.000–450.000 MHzFoundation
📡 All classes; secondary
23 cm
1.240–1.300 GHzStandard
📶 Standard+; secondary
13 cm
2.300–2.302 GHzAdvanced
🌏 Advanced narrow segment
13 cm
2.400–2.450 GHzStandard
📶 Standard+; secondary
9 cm
3.300–3.600 GHzAdvanced
📶 Advanced; location restrictions
6 cm
5.650–5.850 GHzStandard
📶 Standard+; secondary
3 cm
10.000–10.500 GHzAdvanced
📶 Advanced microwave
1.2 cm
24.000–24.250 GHzAdvanced
📶 Advanced microwave
6 mm
47.000–47.200 GHzAdvanced
📶 Advanced microwave
4 mm
76.000–81.000 GHzAdvanced
📶 Advanced microwave
2.4 mm
122.250–123.000 GHzAdvanced
📶 Advanced mm-wave
2 mm
134.000–141.000 GHzAdvanced
📶 Advanced mm-wave
1.2 mm
241.000–250.000 GHzAdvanced
📶 Advanced mm-wave
⚖️ ACMA vs WIA:ACMA is the legal source for access, power and emission limits. WIA band-plan segments are practical guidance for where CW, data, voice, satellite, repeater and beacon activity normally belongs. Use the chevron in Operating notes for band-specific notes, including J3E/SSB voice context where useful.

🔊 Common emission codes i

The code describes the type of transmitted signal. The most useful practical shortcut: J3E is normal SSB voice.

Reading codes like J3E
ITU emission codes are shorthand: 1st character = modulation type · 2nd character = signal type · 3rd character = information type.
JSSB, suppressed carrier
3One analogue channel
ETelephony / voice
Example: J3E = normal USB/LSB SSB voice. R3E is SSB voice with a reduced/vestigial carrier; F3E is FM voice; A1A is CW Morse.
🗣️ A3E · AM voiceCarrier plus two sidebands.Amplitude changes with voice.
🎙️ J3E · SSB voiceSuppressed carrier; one sideband.Normal HF USB/LSB voice.
🎙️ R3E · SSB voiceReduced or vestigial carrier.Less common than J3E.
📻 F3E · FM voiceAmplitude mostly steady.Frequency shifts with audio.
•– A1A · CW MorseOn/off keyed carrier.Used for Morse code.
🖼️ C3F · Image/videoAnalogue television-style emission.Not normal voice operation.

📶 Signal reports i

A signal report is a short way to tell another station how readable and strong they are.

5/9“Five and nine” — perfectly readable and very strong.
5/5Perfectly readable, but only medium strength.
3/3Readable with difficulty and weak.
🎙️ What you might say: “VK4ABC, you are five and seven.” That means readability 5, signal strength 7.

For normal voice contacts you usually give two numbers: Readability and Strength. For CW/Morse, RST adds a third number for Tone, for example 599.

🧰 Handy operating basics

↔️ SimplexStation-to-station on one frequency.
🔁 RepeaterTransmit on the repeater input and listen on its output.
🎚️ CTCSS toneA sub-audible repeater access tone. Not privacy or encryption.
📣 Calling frequencyA recognised place to make initial contact, then move if the contact continues.
🗺️ Band planA voluntary operating map for voice, CW, data, repeaters, satellites and beacons.
⚖️ Primary / secondary iSecondary amateur operation must not cause harmful interference to primary users.

🗣️ Common things you may hear on air

CQGeneral call: “I am calling any station.”
QTHLocation. Example: “My QTH is Brisbane.”
QSYChange frequency.
73Friendly sign-off meaning best regards.
Signal reportA short report of readability and signal strength. “Five and nine” means readability 5 and strength 9.
NetA scheduled or organised on-air group contact.

🔗 Official references

ACMA Amateur Class Licence page
ACMA amateur class licence conditions and Schedule 2 guidance
ACMA operating procedures and emission examples
WIA Australian Amateur Radio Band Plan 2026