rf interview question

RF Interview questions and answers

1. What’s a PCB? multilayer, calculation of impedance, skin effect, loss, grounding technique, isolation technique

2. Name some band definitions. L-Band – 1-2 GHz, S-Band – 2-4 GHz, C-Band – 4-8 GHz, X-Band – 8-12 GHz, Ku-Band – 12-18 GHz.

3. What’s the definition of gain? The signal going into the device is smaller than the signal going out.

4. What’s a definition of an amplifier? It’s a device that exhibits gain.

5. Insertion loss? The signal going in is greater than the signal that’s coming out.

6. Thermal impedance? A measure of how hot the device gets with varying electrical input.

7. What’s the relation between dB and change of signal? +3 dB is 2 times bigger, +10 dB is 10 times bigger.

8. What’s an octave? The bandwidth characterized by higher band being twice as much as lower band (100-200 MHz).

9. What’s a decade? A bandwidth, where the higher band is 10x the lower band (100 MHz – 1 GHz).

10. Skin effect? The signal is reported on the surface of the object, but not inside, e.g. a solid brick wall.

11. VSWR? Voltage Standing Wave Ratio. The numeric representation of the device leak, written like X:1 where X is greater when the leak is greater and 1:1 is the absolute no-leakage VSWR.

12. Describe an impedance matching circuit. A circuit capable of changing the impedance with different values for incoming and outgoing impedance.

13. Describe circular polarization. The signal travels both vertically and horizontally.

14. What’s the job of the amplifier? To increase the incoming signal.

15. What is noise figure? The level of noise that a low-noise amplifier (LNA) is capable of discriminating.

16. What’s a transfer curve? It is a graph of the output power versus the input power of an amplifier.

17. What’s the 911 point? The point where the input power results in flames on the other end.

18. What’s saturation point? The point where the amplifier loses its linearity of the transfer curve.

19. What does balanced amplifier consist of? Two amplifiers stuck together.

20. What is the filters function? To filter out all the unwanted radio signals.

21. What filter types are there? Low-pass (all frequencies below are allowed to pass in), high-pass, bandpass (all frequencies of a given bandwidth are allowed) and band-reject.

22. What are saw filters used for? Very low frequency filtering.

23. What are mixers used for? To change the frequency of the signal.

24. What’s a superheterodyne receiver? It’s a receiver that uses two mixers in a row.

25. Describe VCO. Voltage-controlled oscillators change the frequency of the produced sine wave depending on the voltage they receive.

26. Describe more on the function of PLL ?