# 0.2 Derivation of the equations for a basic fdm-tdm transmux  (Page 8/10)

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Shown across the top of [link] is a stylized version of that seen in the bottom portion of [link] . The uniform weight shown on the top right leads to the bandpass filter shapes shown on the left. Note that the filters are separated in frequency by $\frac{{f}_{s}}{N}$ Hz.

Now suppose we employ non-uniform weighting to improve the shape of the bandpass filters. As discussed in Appendix A , such non-uniform weighting can be used to attain the desired transfer function shape, but virtually always at the expense of the bandpass filter's bandwidth. In fact, to obtain the desired characteristic shown in [link] , with its flat passband, sharp skirts, and high-attenuation stopband, the minimum passband bandwidth is more than a factor of ten larger than the unweighted response. Thus the use of a non-uniform weighting, as shown on the right of [link] (b), results in the situation shown on the left side. There are still N bandpass filters, and their center frequencies are still separated by integer multiples $\frac{{f}_{s}}{N}$ Hz, but each filter has been widened considerably, leading to a high degree of overlap.

The first problem to deal with is not the overlap, but rather the fact that the individual bandpass filters are far wider than the original goal of about $\frac{{f}_{s}}{N}$ Hz. This is dealt with by returning to [link] and simply letting the delay line length, the number of weighting coefficients, and the DFT order grow until the filters are sufficiently narrowband to meet our objectives. Again using the example of the desired frequency response seen in [link] , the dimensions must grow by more than a factor of ten.

While the resulting dimensions can take on rather arbitrary values (above some minimum value) we'll assume here that the new size N' is an integer multiple of N . In particular, we assume that the delay line, and the weighting and DFT with it, are extended to the length N' where:

${N}^{\text{'}}=Q·N,$

where Q is a positive integer. We further assume that Q is chosen to be large enough that a weighting function of length N ' can be designed to produce not only the desired shape but also a bandwidth of about $\frac{{f}_{s}}{N}$ Hz. The resulting situation is shown in [link] (c). The weighting function is now longer than before (by a factor of Q ). On the left we see that there are now N ' filters in the filter bank. Each one of them now has the desired nominal bandwidth of $\frac{{f}_{s}}{N}$ Hz, but their center frequencies are now separated by $\delta f=\frac{{f}_{s}}{{N}^{\text{'}}}=\frac{{f}_{s}}{NQ}$ Hz instead of $\frac{{f}_{s}}{N}$ Hz. The overlap seen just above still exists but now there is a factor of Q more filters, a factor of Q narrower, and a factor of Q more closely spaced. Thus the positive effect of expanding the delay line dimension to $QN$ is that the resulting filter bank includes the desired bandpass filters, both in bandpass characteristics and center frequencies. The negative aspects include the fact that the amount of weighting and DFT computation have gone up by a factor of Q and that there are now $\left(Q-1\right)·N$ superfluous bandpass filters.

Suppose now that we choose to compute only every Q-th point of the DFT. The delay line is still $QN$ samples long, there are still $QN$ coefficients in the weighting function, and the DFT still has order $QN$ , but we'll choose to only compute those output bins ${X}_{m}\left(k\right)$ where m is an integer multiple of Q . This results in the situation shown in [link] (d). The same QN-point weighting function is used as immediately above. This case, with N filters of nominal bandwidth $\frac{{f}_{s}}{N}$ Hz and spaced $\frac{{f}_{s}}{N}$ Hz apart, was our objective. To achieve it, however, required expanding the dimensions of the preceding operations quite considerably.

are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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