<< Chapter < Page Chapter >> Page >

By inspection it would appear that the proper value of l o g 2 ( f s Δ f ) = l o g 2 N is 8, 9, or 10. Assuming a nominal value of 9, we can use [link] to accurately estimate the optimum value of f s . Performing this calculation yields 437 kHz. In the actual design, this value was rounded up to 512 kHz, the next-higher power-of-two integer multiple of 4 kHz. The choice of f s = 512 kHz in turn means that the tuner decimation M t must equal 4 and the tuner's pulse response duration L t must equal at least 20.

The resulting tuner/transmultiplexer, shown in [link] and described in [link] , was built on a single circuit card. The 12-bit A/D module was mounted separately in the chassis. One multiplier chip operating at 4.096 megamultiplies/sec performed the tuner's quadrature downconversion. Two multiplier-accumulators (MACs) filtered and decimated the downconverted signal, preserving the center 248 kHz. Two more MACs perform the window-and-fold preprocessing for the transmultiplexer while a single MAC is used to compute the radix-2 FFT. Seven stages are used to compute the 128-point FFT and an additional one is used to perform sideband inversion on those voice channels designated by the user. This transmultiplexer also happens to use the so-called offset-bin DFT instead of the usual DFT. The motivation for this and the method for implementing it are discussed in Offset Bin Operation from "An Introduction to the FDM-TDM Digital Transmultiplexer: Appendix B" .

Design of the fsk vft telegraphy demodulator

The section "Example: Using an FDM-TDM Transmux to Demodulate R.35 Telgraphy Signals" discussed the use of an FDM-to-TDM transmultiplexer as an integral part of a demodulator capable of handling all 24 FSK signals present in an FDM voice frequency telegraphy (VFT) system. The analysis developed in that section showed that, in absence of other system-level factors, the best input sampling rate to the transmux-based filter bank was 3840 Hz, 64 times the 60 Hz fundamental tone spacing in the R.35 standard. In this section, we re-examine that choice in terms of the tuner required to provide the VFT signal to the transmultiplexer.

To pass all 24 FSK components of an R.35 VFT signal, the tuner must have a passband B t of slightly more than 2880 Hz. The system must be able to accept real-valued digital samples from a commercial PCM link. These are provided at a rate of 8000 samples/sec This demodulator was also capable of digitizing real-valued analog inputs at a rate of 16 kHz. . From the section "Example: Using an FDM-TDM Transmux to Demodulate R.35 Telegraphy Signals" we recall that the other key parameters in the filter bank's design are: Q = 3 , M = 12 (assuming the input rate is 3840 Hz), K = 16 3 , and N = 64 . Using the values in [link] , and assuming a nominal value of 2.5 for α t , yields 3920 Hz as the optimal value of fs . This is very close to the best choice without taking the tuner into account. We therefore fix on 3840 Hz as the overall best choice.

Figure four is a photograph of a supergroup tuner and transmultiplexer.
Photograph of a Supergroup Tuner and Transmultiplexer [link] , circa 1985- M = 32 , Q = 16 , N = 128 , Δ f = 4 kHz

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, An introduction to the fdm-tdm digital transmultiplexer. OpenStax CNX. Nov 16, 2010 Download for free at http://cnx.org/content/col11165/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'An introduction to the fdm-tdm digital transmultiplexer' conversation and receive update notifications?