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Rf engineer Interview Questions

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Qualcomm
RF Hardware Engineer was asked...1 December 2011

What are the effects of a mismatched circuit?

5 Answers

IIP2 & DC Offsets

IN the digital domain, zero crossings and ISI , as well as DC offset can be compromised.Loss of received signal strength with distortion, Overheating and damage to TX drivers Less

Worse is not working.

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Motorola Mobility

Why 50 ohm, not 75 ohm?

4 Answers

30 ohms gives better power handling, 75 ohms gives low insertion loss, so 50 ohms is the trade off between the power handling and low insertion loss. It is globally accepted to use connector, cables and equipment for 50 ohms. Less

50 ohms performs better (lower loss than 75 ohms), one advantage of 75 ohms is size (cable and connectors are smaller than 50 ohms) Less

Please disregard prior answer, best insertion loss case is at 75 ohms, 50 ohms provides the best compromise between low loss and power handling as mentioned above. Less

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Nokia

Describe basic Call Flow of GSM/UMTS ?

2 Answers

1.) First of all mobile+SIM should be detected by mobile station. 2.) Then it passes the signal to BTS of the area, (which is occured in BSS). 3.) Then it passes to the neareast MSC by this it is connected to HLR,VLR,AUC & OMC, (which is occur in NSS). 4.) from this it is connected to PSTN,ISDN,DATA NETWORK(this all is occur in public network) Less

Kindly refer notes from any book, call flow cant be explained in this block.

Qualcomm

Reverse a linked list Array and string manipulation

3 Answers

How soon did they get back to you about the result of onsite?

for me it was about a month because there was christmas holiday break. otherwise it should be max 2 weeks. Less

Okay Thank you

Qualcomm

During lunch, I was given a problem on how I would optimizing the traffic at the access point used at the cafeteria, we discussed about it during the entire time allotted for lunch

3 Answers

Think out loud, it was more of a general discussion than a question-answer session. The interviewer was very helpful too. Less

Hi, DId they inform about you being rejected? When did you interview happened? It will be of great help if you can answer these!! :) Less

Hello sir, can you tell me how many days it took for a onsite interview after your phone process, I already had a interview with software team and waiting for results. Less

Apple

2. if VSWR is 2, what is the reflection coefficient?

3 Answers

The magnitude of gamma=1/3, but you can't tell the phase. can be any point on the circle with a gamma=1/3 radius. Less

Gamma=(VSWR-1)/VSWR+1, so 0.333 is the reflection coefficient for VSWR=2

.3333333

SpaceX

Say we are receiving a signal (on Earth, from Space) at the level -174dBm, what is the next step we will do with this signal?

3 Answers

Assuming this is a "front end" of a receiver, the signal would be filtered and then pass through a LNA (Low Noise Amplifier). Less

This might have been your "trick" question. This signal wouldnt be detectable. Even if you reciever is completely ideal with a NF of 0 and your signal of interest is in a 1Hz bandwidth, and your recieved signal is noiseless, your signal to noise ratio will be zero. SNR = P - 10logKTB SNR = -174dbm - (-174dbm/hz + 10log(1hz)) SNR = 0 Less

Go to a really cold place to bring the surrounding noise down (near 0Kelvin ideally). Noise would only come from sky noise which is usually like 35Kelvin. Less

Nokia
RF Engineer was asked...28 February 2012

what would you do if you're a manager/team leader, and you face the following problem..........

2 Answers

I & my team member try to find the solution of every problem........and give the solution which is appropriate ans of solution Less

I'm not a manager, I couldn't answer that positively, I had to improvise

Apple

the use of pointers

3 Answers

used to point a particular address in the memory

- use to point a memory address - use to pass by reference- - in C used to initialize a character string Less

Just wondering if you still remember?

Ericsson-Worldwide

Reducing Pilot pollution

2 Answers

Avoiding overshooting

We can give mechanical tilt at sector which overshot and also power reducec at BTS. Less

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