Display Devices and Digital Reception: CRT, LCD/LED Panels, DTH and Set-Top Boxes
What this domain tests
Display Devices and Digital Reception: CRT, LCD/LED Panels, DTH and Set-Top Boxes tests display technologies, resolution, interface, the DTH signal chain, LNB, set-top box tuning, demodulation, and decoding.
Core rules
- CRT: electron gun, deflection yoke, shadow mask or aperture grille, phosphor triads; EHT can exceed 25 kV and remains stored after switch-off.
- LCD: backlight (CCFL or LED), liquid-crystal shutter, TFT matrix, polarizers; LED TV usually means an LED backlight, not LED pixels.
- Resolution: 1280×720 (HD), 1920×1080 (Full HD), 3840×2160 (UHD); aspect ratio 16:9.
- DTH: the dish focuses Ku- or C-band to the LNB; the LNB downconverts to IF (for example, Ku 11.7 GHz with a 9750 MHz LO gives 1950 MHz); the STB tunes, demodulates DVB-S/S2, decodes MPEG, and outputs video and audio.
- Conditional access uses a smart card or CI; signal quality is measured by strength and bit error rate.
Worked example
A Ku-band transponder at 11.700 GHz with a universal LNB using a 9750 MHz LO gives 11,700−9,750=1,950 MHz at the STB input. If the STB shows no signal, check dish alignment, LNB power, cable, and the correct LO setting before replacing the box.
Traps
Treating LED backlight as emissive pixels is wrong. Touching a CRT anode is dangerous. Setting the wrong LNB LO gives no channels. Confusing signal strength with signal quality misleads alignment. Ignoring the HDMI/HDCP handshake can look like a dead STB.