Question 1

Cordless telephones typically operate within what approximate range?

Accepted Answer

Introduction / Context: Cordless telephones are designed for short-range indoor and household communication. Their range is limited by power, frequency, and regulatory restrictions. Given Data / Assumptions: Frequency band: typically 900 MHz, 1.9 GHz, or 2.4 GHz ISM bands. Power levels: low, consumer device limits. Concept / Approach: In practical usage, cordless telephones cover around 30–100 meters indoors, extended slightly outdoors depending on environment. Step-by-Step Solution: Indoor walls reduce signal range significantly.Standard specification: ~100 meters in open areas.Therefore, 100 m is the most appropriate option. Verification / Alternative check: Manufacturer datasheets for DECT cordless phones confirm 50–100 m indoor range. Why Other Options Are Wrong: 1000 m / 500 m: unrealistic for consumer cordless phones.10 m: too small; corresponds more to Bluetooth. Common Pitfalls: Confusing cordless phones with mobile phones (cellular). Final Answer: 100 m

Question 2

In television broadcasting, why is Vestigial Sideband (VSB) modulation preferred?

Accepted Answer

Introduction / Context: VSB modulation is a compromise between AM (double sideband) and SSB (single sideband). It is commonly used in TV broadcasting for video signals that have a wide baseband spectrum. Given Data / Assumptions: Full AM doubles bandwidth. SSB saves bandwidth but complicates filtering. Concept / Approach: VSB transmits one sideband fully and the other partially, ensuring that low-frequency components are preserved without distortion while reducing bandwidth. Step-by-Step Solution: TV video baseband ≈ 0–5 MHz.SSB filtering near 0 Hz is problematic → causes distortion.VSB retains a 'vestige' of the second sideband near DC, preventing distortion at low frequencies. Verification / Alternative check: TV standards (NTSC, PAL) explicitly specify VSB for this reason. Why Other Options Are Wrong: Half bandwidth reduction: not exact, VSB still > SSB.Better reception: a vague benefit, not the technical reason.Antenna design is unrelated. Common Pitfalls: Confusing bandwidth efficiency with distortion control. Final Answer: it avoids phase distortion at low frequencies

Communication Systems Questions