HB3YAQLucerne
Understand the signal path.
From antenna to audio: explore loss, gain, filtering and volume in an explicitly simulated receive chain.
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Explicit simulation. All levels, noise values and limits are chosen learning assumptions. No live reception, measurement of your devices or actual sound.
Controls and exercises require JavaScript. The initial display, five explanations, model assumptions and further links remain readable.
Select a stage and change one value. Then read the feedback and compare the levels below.
STAGE 01
Your wanted signal starts here.
Change pickup of the wanted signal. In this example, environmental noise and a strong neighbouring transmitter stay fixed. A real antenna can change their levels too; this control does not describe a particular antenna model.
Understand antenna gain →The model signal path is complete: no overload, correct sideband and open audio output.
- Model SNR after filter
- 17.4 dB
- Signal bandwidth passed
- 100 %
- Audio output
- Open · display only
Where the level changes.
Wanted signal (blue) and noise (gold), on the same logarithmic scale from −140 to −40 dBm. Out-of-range values sit at the edge. Stages 1–3: noise in 2.4 kHz; stage 4: selected filter width.
1. Antenna
Wanted signal-100.0 dBm
Noise-126.2 dBm
2. Cable
Wanted signal-103.0 dBm
Noise-129.0 dBm
3. Receiver
Wanted signal-83.0 dBm
Noise-100.4 dBm
4. Filter & mode
Wanted signal-83.0 dBm
Noise-100.4 dBm
Your turn.
Each task sets the controls to an intentionally faulty starting state. Fix it and explain your decision.
Link to these settings ↗ · The link contains the settings. Saved items store only the tool, not its values.
Read about the five stages.
1. Antenna
Change pickup of the wanted signal. In this example, environmental noise and a strong neighbouring transmitter stay fixed. A real antenna can change their levels too; this control does not describe a particular antenna model.
Understand antenna gain →2. Cable
The cable attenuates the wanted signal, blocker and incoming noise. At 290 K it also contributes thermal noise. Later gain can raise the level but cannot simply restore the signal-to-noise ratio lost here.
Understand feed-line loss →3. Receiver
Gain raises signal and noise together and can reduce the impact of the following converter. Too much gain lets the strong neighbour exceed the model limit. A digital filter afterwards cannot undo this overload.
Understand gain and AGC →4. Filter & mode
Our USB signal spans +0.3 to +2.7 kHz relative to the suppressed carrier reference. The ideal filter starts at +0.3 kHz. Below 2.4 kHz width you cut away signal components; above it you admit more white noise. LSB selects the wrong side here.
Try it in the waterfall →5. Audio
Volume changes the output after demodulation. It repairs neither a cut sideband nor an overloaded receiver stage. The output indicator is schematic only: this lab plays no sound and requests no microphone access.
Troubleshoot real reception →Model assumptions, formulas and limits
This lab explains relationships using a simplified power budget. It calculates neither speech intelligibility nor actual IQ data, AGC, intermodulation, filter skirts or audio demodulation. During overload SNR is hidden; no distortion curve is invented.
- Wanted signal: −100 dBm at 0 dB antenna loss, uniform power density from +0.3 to +2.7 kHz. The antenna control changes only this signal. Blocker: −45 dBm at +8 kHz, outside every selectable digital filter but inside the 24 kHz input window.
- Incoming white noise: −160 dBm/Hz. Cable temperature 290 K. With L = 10^(attenuation/10), linear power units give N_cable = N_in/L + kT(1−1/L). Thermal reference level kT is about −174 dBm/Hz.
- Fixed receiver noise figure 6 dB, ideal variable gain and additional converter-input-referred noise of −135 dBm/Hz. The overload warning compares summed linear power in the 24 kHz window with a chosen −20 dBm limit. Not a universal clipping threshold.
- Levels in dBm are converted to linear power before addition. After filtering, N = N_density × bandwidth and SNR = S_dBm − N_dBm. Halving noise bandwidth means about 3 dB less noise power, but an overly narrow filter also loses wanted power here.
Connect it to your equipment interests.
These principles help when reading receiver manuals. The controls and limits above do not reproduce these devices. Open the documented dossiers for specific features and manufacturer sources.
Technical foundations reviewed on 15 October 2026. Sources explain gain, noise and dynamic range; the lab’s numbers are our own learning assumptions.