Instrument - signal processor

Question 1

main function of the signal processor (4)

Answer 1

• filter
• detection
• compression
• rejection

Question 2

filters do what (2)

Answer 2

• gets rid of unnecessary frequencies (rejecting those above/below bandwidth)
• harmonics

Question 3

benefits of harmonic imaging (4)

Answer 3

1. narrow beam (lateral res)
2. narrow z plane (elevational res)
3. eliminate side/grating lobes
4. decrease anterior reverberation/main bang

Question 4

solution to bandpass filter

Answer 4

pulse inversion

Question 5

detection AKA

Answer 5

demodulation

Question 6

purpose of detection/demodulation

Answer 6

converts echo voltages from radio frequency to video/amplitude

Question 7

two parts to detection

Answer 7

1. rectification

2. smoothing

Question 8

what does rectification do

Answer 8

turns negative voltages into positive voltages

Question 9

what does smoothing do

Answer 9

levels out differences in amplitude, makes it less bumpy

Question 10

what is compression? how does it work?

Answer 10

the process of decreasing differences between smallest and largest echo amplitudes to a usable ratio

weaker signals are amplified MORE than stronger ones

Question 11

dynamic range is done by

Answer 11

compression

Question 12

what is dynamic range

Answer 12

power ratio of the largest to smallest amplitude that the system can handle

Question 13

what does 60 dB DR mean

Answer 13

the strongest echo is 10^6 times stronger than the weakest echo

Question 14

the smallest voltage is 1 mV and the largest voltage is 1000 mV. what is the dynamic range?

Answer 14

voltage ratio = 1000/1 = 10^3
power ratio is (10^3)^2 = 10^6
10^6 in dB is 10+10+10+10+10+10 = 60dB

Question 15

human vision can only handle ___ dB. what does this mean?

Answer 15

20 dB

for us to view the highest brightness, can only be 100x the lowest

Question 16

there is more contrast when you ___ DR

Answer 16

decrease DR (fewer shades of gray)

Question 17

a more smooth image is seen when you ____ DR

Answer 17

increase DR (more shades of gray)

Question 18

Rejection AKA

Answer 18

signal to noise ratio (SNR)/suppression/threshold

Question 19

what does rejection do

Answer 19

gets rid of low amplitude echoes/signals - improves SNR (signal to noise ratio)

Question 20

the signal processor detects doppler shifted echoes using ____ in the _____. what does this determine?

Answer 20

autocorrelation in the quadrature phase detector

autocorrelation determines mean and variance of the the doppler shifted angle at each location along the scan line allowing detection of bidirectional doppler shifts.