Quantcast FREQUENCY DIVISION

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Custom Search
 
  
 
3-33 Common methods of time-division multiplexing include PULSE AMPLITUDE MODULATION (pam), PULSE WIDTH or PULSE DURATION MODULATION (pwm or pdm), PULSE POSITION MODULATION (ppm), and PULSE CODE MODULATION (pcm). We have been studying an example of pulse amplitude modulation. (These methods of tdm were discussed in NEETS, Module 12, Modulation Principles.) FREQUENCY DIVISION.—Frequency division multiplexing (fdm), unlike tdm, transmits and receives for the full 360 degrees of a sine wave. Fdm used presently by the Navy may be divided into two categories. One category is used for voice communications and the other for tty communications. The normal voice speaking range is from 100 to 3,500 hertz. During single channel AM voice communications, the audio frequency amplitude modulates a single rf (carrier frequency). However, in voice fdm, each voice frequency modulates a separate frequency lower than the carrier frequency (subcarrier frequency). If these subcarrier frequencies are separated by 3,500 hertz or more, they may be combined in a composite signal. This signal modulates the carrier frequency without causing excessive interference. In figure 3-30, the output of channel one is the voice frequency range of 100 to 3,500 hertz. The output of channel two is the combination of a different voice frequency with a subcarrier frequency of 4,000 hertz. The output of channel three is another voice frequency. This voice frequency combined with a subcarrier frequency of 8,000 hertz gives you an output frequency range of 8,100 to 11,500 hertz. The overall bw for the composite modulation package shown is 100 to 15,500 hertz. Each separate channel occupies its own band of frequencies. The composite signal is used to modulate the carrier frequency of the transmitter. Figure 3-30.—Block diagram of a frequency-division multiplexing system. Multichannel broadcast and ship/shore terminations use tty fdm. With this system, each channel of the composite tone package of the broadcast is assigned an audio frequency. By multiplexing tty circuits, up to 16 circuits may be carried in any one of the 3,000 hertz multiplexed channels described above. Don't confuse the two types of multiplexing. In the first case, 3,000 hertz audio channels have been combined. In the second case, a number of dc tty circuits are converted to tone keying and combined in a single 3,000-hertz audio channel. Figure 3-31 illustrates a 16-channel, tty-multiplexing system. The output of the dc pulsed circuits is converted to audio keying. Each channel has a separate audio center frequency. Channel frequencies range from 425 hertz for the lowest channel to 2,975 hertz for the highest


Electrical News
Creating an 8x8x8 3D LED Cube: The Base PCB
Creating an 8x8x8 3D tri-color LED cube from the ground...
eetimes.com
Allocating MCU Resources Accurately
When you need a new MCU and new I/O for...
eetimes.com
Experts Call for Secure Sensors
Sensor nodes are the most vulnerable point of attack in...
eetimes.com
AMD Integrates X86, GPU & I/O
Early next year, AMD will ship Carrizo, its most integrated...
eetimes.com
Test Your Way to a Better IoT
Better design and test procedures will lead to much lower...
eetimes.com
12 Startups I Saw at Demo
The consumer Internet of Things sector is getting crowded and...
eetimes.com
Megachips: Japan's Best Kept Secret
In a recent interview with EE Times, Megachips' president and...
eetimes.com
Intel Expects 2015 Mobile Speedup
Intel is back on track with mobile, company officials said...
eetimes.com
Culture Is King in Job Search
Programmers, web developers, and software engineers often assume that technical...
eetimes.com
LEDs Go Color-Temperature & Tunable
The LED manufacturer Everlight introduced what it calls the world's...
eetimes.com
Drag An Oscilloscope Through 6km of Mud?
Sponsor Dave in the 2014 Sydney Mud Run, proceeds go...
eevblog.com
Friday Quiz: More Radar
An EE Times reader submitted our second Friday quiz about...
eetimes.com
Dick Smith – Amateur Radio & Adventure
Dick Smith talks about how he got started, the early...
eevblog.com
Want to Present a Paper at ESC Boston 2015?
If you are interested in presenting a paper on the...
eetimes.com
Transparent Car Shows Automotive's Future
TE Connectivity's clear-plastic, full-size model car shows the latest advances...
eetimes.com
Why No One Leaves Linear Technology
Why culture makes Linear Tech a winner....
eetimes.com
The Messe U-Bahn Crush Business Indicator
Electronica's healthy glow means good things for Europe's electronics sector....
eetimes.com
Automotive Industry Drives Chip Demand
Among all major end use-applications for integrated circuits, the automotive...
eetimes.com
Power Week: Duracell Buyout Tied to Wireless Power, EVs?
The acquisition of the Duracell battery brand by Warren Buffett's...
eetimes.com
What Are You Wearing?
The wearables market is at $6B this year and is...
eetimes.com
 


Privacy Statement - Copyright Information. - Contact Us

comments powered by Disqus

Integrated Publishing, Inc.
9438 US Hwy 19N #311 Port Richey, FL 34668

Phone For Parts Inquiries: (727) 755-3260
Google +