1. Home
  2. Ece 320 spring 2004
  3. Project labs
  4. Communications
  5. Communications: using direct

Communications: using direct digital synthesis

<< Chapter < Page
  Ece 320 spring 2004     Page 2 / 3
Chapter >> Page >

Spectral copies

Spectral Copies: The digital-to-analog converter on the DDS is unfiltered, which means that there is no anti-imaging filterto remove the spectral replicas. To see this, plug the output of the DDS board directly into the vector signal analyzer(VSA), and observe the spectrum. Use 104.9 MHz as the center frequency, and set the span wide enough so that you can seethe spectra of the replicas to the left and right of the 104.9 MHz signal. Use the marker to find the peaks of the otherreplicas, and record their frequencies. Once you've done that, reattach the antenna to the DDS output, and tune thereceiver to the frequencies you just recorded. You should be able to hear your audio on each of the other frequencies.

The clock rate of the DDS is 60MHz, which corresponds to 2 in digital frequency.
Therefore, the 104.9 MHz signal you just listened to is roughly equivalent to 7 2 in digital frequency. What are the digital frequencies of the other copies you saw on the VSA?

How to use the dds

The DDS has several different modes of operation: single-tone, unramped Frequency Shift Keying ( FSK ), ramped FSK, chirp, and Binary Phase Shift Keying ( BPSK ). In this lab we will use the DDS in single-tone mode. Single-tone mode is easy touse, and is powerful enough to create many different kinds of waveforms, including FM and FSK.

Fm code

The FM code you just ran (also listed here ) is fairly straightforward. The program first calls the radioinit subroutine. This routine sets the DDS to single-tone mode and turns off an inverse-sinc filterto conserve power. Following radioinit , the setcarrier subroutine is called. This routinesets the frequency of the DDS output by writing to the two most significant 8-bit frequency registers of the 48-bitfrequency-tuning word on the DDS

Communication between the DSP and the DDS is done through a parallel bus.
. Although the frequency-tuning word on the DDS has 48 bits of resolution,the upper 16 bits provide us with enough resolution for the purposes of this lab, and so we will only be writing to thetwo most significant registers. See page 26 in the DDS data sheet for a layout of the frequency-tuningword.

To set the carrier frequency, we first need to determine what frequency word has to be written to the frequency registers onthe DDS. This can be done using :

Frequency word baseband frequency 60 MHz 2 48
where baseband frequency corresponds to the desired frequency that lies in the range of 0-30 MHz. Forexample, to get the DDS to transmit at 104.9 MHz, you would choose the baseband frequency to be 15.1 MHz since 104.9 MHzis one of the unfiltered spectral replicas of 15.1 MHz. Then, using , the frequency word for 15.1 MHz (and 104.9 MHz) would be equal to 406D 3A06 D3D4h . But since we only write to the two most significant registers of the frequency-tuning word, we onlyneed the first 4 hexadecimal numbers of this result, i.e. 406Dh . The first two of those, 40h , need to get written to the most significant 8-bit frequency register, while the second twohex numbers, 6Dh , need to get written to the second-most significant 8-bit frequency register. This iswhere the 40h and 6Dh in the setcarrier subroutine of the FM code come from.

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
what is titration
John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
hello friend how are you
Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
<< Chapter < Page Page > Chapter >>

Read also:

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Ece 320 spring 2004. OpenStax CNX. Aug 24, 2004 Download for free at http://cnx.org/content/col10225/1.12
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ece 320 spring 2004' conversation and receive update notifications?

Ask