CEPD News 
September, 2012 - Vol 5, Issue 3


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In This Issue
Society News
CEPD is on the move
Bidirectional Transmission
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Society News

The IEEE Signal Processing Society Presents
Modeling Speech and Music Quality 
by James Kates
When: October 2, 2012  06:00PM-08:30PM

Location: Engineering Center ECEE 1B32,

2055 Regent Dr, Boulder, CO 


Note: 6:00 PM - 7:00 PM is reserved for snacks and networking.


Please see the SPS Events page to register for this meeting.

CEPD is Moving

We are moving back to the building we occupied at the turn of the century! 

We will be at 5485 Conestoga Ct. Suite 210 on November 1st.


Full Duplex Bidirectional Transmission

In applications where simultaneous full duplex communications is necessary, sometimes the transmission media is too expensive for separate transmit and receive lines or an antenna must be shared between transmit and receive signals. It is possible to use FDM, TDM, orthogonal coding or other methods to send information over the same link in two directions simultaneously.


However, there are also a few methods to send arbitrary analog and digital signals over the same link without special coding or modulation, and without the signals interfering significantly with each other. All these methods employ matched impedances and cancellation techniques to reject the transmit signal from being received locally. The principle of superposition is used to analyze these methods.

A circulator is a passive three or four port device, in which a radio or optical signal entering any port is transmitted only to the next port in rotation.

Figure 1 Circulator used to split transmit and receive from a bidirectional transmission line

A hybrid coil (or bridge transformer, or sometimes hybrid) is a transformer that is designed to have four ports in conjugate pairs.  


Figure 2 Unbalanced to balanced hybrid 


A signal arriving on one branch is divided between the two adjacent branches but does not appear at the opposite branch. 


Figure 3 Fully balanced hybrid 


An active hybrid employs a subtraction technique. The amount of transmit signal appearing at the receiver is predicted and subtracted. The subtracted portion can adjusted adaptively and incorporate delay as with an echo canceller.

Figure 4 Active 2 wire to 4 wire hybrid 


This article presented a few of the methods which are employed to solve the bidirectional signal transmission and separation problem.



If you would like help developing a new product or if you find your project understaffed, CEPD can help you meet your deadlines. Our staff draws on years of diverse product design experience to provide creative and timely solutions for your product needs. Some of our specialties include:
  • DSP
  • Embedded Systems Hardware and Software
  • Data Acquisition
  • Wireless Sensor and Telemetry Systems (Zigbee, Cellular, VHF, Bluetooth, ANT+, etc.)
  • Control Systems
  • Programmable Logic: FPGA / CPLD / EPLD
  • Analog Circuit Design
  • Switching Power Supply Design
  • Battery charging (all chemistries)
  • PCB Design and Layout
  • Analysis and Documentation
Our goal is to provide cost effective and expedient design options for our clients. Our services range from an hour of consultation to large turn-key product development projects. We provide detailed proposals, accurate estimates and time schedules to help you manage each phase of the project. We can offer fixed cost or time and materials proposals to suit your specific needs. There is no cost to you for the initial proposal we create and the initial discussion required! 

The Staff of CEPD, Inc.
2012, CEPD, Inc.             
 303 415-1112    Fax 720 306-4445