# Communications: using direct digital synthesis  (Page 2/3)

 Page 2 / 3

## 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 $2\pi$ in digital frequency.
Therefore, the 104.9 MHz signal you just listened to is roughly equivalent to $\frac{7\pi }{2}$ 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 :

$\mathrm{Frequency word}=\frac{\mathrm{baseband frequency}}{60\mathrm{MHz}}2^{48}$
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.

where we get a research paper on Nano chemistry....?
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
Got questions? Join the online conversation and get instant answers!