DT3: RF On/Off Remote Control Technology

Rodney Singleton Joe Larsen Luis Garcia Rafael Ocampo Mike Moulton Eric Hatch

Agenda

 Radio Frequency Overview  Frequency Selection  Signals Methods  Modulation Methods

Radio Frequency

Spans from 3kHz to 300GHz  Advantage:  Long Distance  No stress on line-of-sight  Disadvantage:  Needs to be operated in accordance with the FCC  Interference occurs between RF devices

Remote Control using RF

 Remote Control:  Wireless device used to operate audio, video and/or other electronic equipment using transmission.

 Car opener  Garage Door  Specifically for our project:  Using RF as a remote control to power on/off a system.

Selecting a frequency

 Spectrum Characteristics  How “rich” is your signal  Distance and environment  Legal Considerations  Licensed or unlicensed  Allowed power output  International regulations

Generalizing the RF Spectrum

Frequency

3 Hz – 30 kHz 30 kHz – 300 kHz 300 kHz – 3 MHz

Examples

Submarine Communications RFID, Navigation Signals AM Broadcasts 3 MHz – 30 MHz 30 MHz – 300 MHz FM Radio, Line of sight aircraft communication, Maritime Radio 300 MHz – 3 GHz Broadcast TV, Cell phones, WLAN, Bluetooth, GPS 3 GHz – 30 GHz Amateur radio, RFID WLAN, Backhaul Communications • Lower frequencies will go further and more easily penetrate obstacles • Higher frequencies have greater bandwidth

Licensed Frequencies

 If a RF signal is considered “Mission Critical” a license should be considered  Allows for sole use of that frequency  Significant cost  $19 Billion raised in 700 MHz auction  Large Telecommunication providers  Other options do exist in the unlicensed spectrum

ISM Band

   Industrial, Scientific, and Medical bands A shared and unlicensed set of frequencies    Must accept all interference received Transmission power regulations Usage regulations Regulations vary by country   Max power output for 2.4 GHz:   US: 30 dBm, before antenna. 36 dBm, with antenna.

Europe: 20 dBm 900 MHz is unlicensed only in North and South America

Frequency range

6.765

–6.795 MHz 13.553

–13.567 MHz 26.957

–27.283 MHz 40.66

–40.70 MHz 433.05

–434.79 MHz 902 –928 MHz 2.400

–2.500 GHz 5.725

–5.875 GHz 24 –24.25 GHz 61 –61.5 GHz 122 –123 GHz 244 –246 GHz

ISM Congestion

 900 MHz and 2.4 GHz ranges are extremely congested  Urban areas will have higher congestion

RF Detection

 RF detector monitors the output of an RF circuit and develops a dc output voltage.

 RF detectors are used primarily to measure and control RF power in wireless systems.

   In a receiver: Signal strength is a key factor in maintaining reliable communications.

 In a transmitter: The amount of power transmitted is critical because of regulatory guidelines.

Main Applications of RF Detectors

 Transmitter output power measurement is the primary application.

 It is essential to know the RF output power.  In many cases, the transmitter power is controlled automatically.  As a result, the output power is measured and compared to a set point level in a feedback control circuit so power can be adjusted as required.

Types of RF Detectors

There are two basic types: 1.

2.

Logarithmic type RMS type.  The log type converts the input RF power into a dc voltage proportional to the log of the input, making the output directly related to decibels.  The RMS detector creates a dc output proportional to the RMS value of the signal.

General Criteria for Selecting RF Detectors

 The type of RF signal to be measured is the most important determining factor in the type of detector to use.  Log type is best for:   general power measurement and control applications pulsed RF signals  RMS type is best for:  those applications where then signal has a high crest factor or a widely varying crest factor *The crest factor is the ratio of the peak to RMS value of the signal.

Binary Coding

The process of coding pieces of information and are assigned the values of “0” or “1”.

Examples of binary coding for: • Unique codes for different devices • Character strings to bit strings • Security

Amplitude Shift Key Modulation (ASK)

 Most basic of shift key modulations.

 Binary form of AM  Type of ASK  On/Off Key

Advantages v. Disadvantages of ASK

 WOO HOO’s:  Cheaper  Conserves power with the case of OOK  BOO’s:  Susceptible to interference

What is FSK ???

 A frequency modulation scheme where digital information is transmitted through discrete frequency changes of a carrier wave.

 Two types are Minimum-shift keying (MSK) Audio frequency-shift keying (AFSK) .

and

Common Applications of FSK

   Remote Metering  Automatic Meter Reading (AMR) Car door openers/remote car starters.

Garage door openers

Advantages of FSK

 Rejects unwanted noise  Better signal-to-noise ratio  Automatic volume control

Disadvantages of FSK

 Expensive  High power consumption  Slow data transmission

Phase Shift Keying (PSK)

 A digital implementation of Phase Modulation (PM)  Most forms of digital data transmission used a form of Phase Modulation  Very high bitrate capabilities  Unnecessarily complicated for most remote control applications

Analog Signaling (Tone Signals)

 Information sent using analog tones within the voice band (20 Hz – 20 kHz)   Tones detected or not detected, corresponding to binary ‘1’ or ‘0’ Tones of frequency ‘a’ corresponds to ‘1’, frequency ‘b’ corresponds to ‘0’ (AFSK)  Can use any analog modulation technique and existing equipment  Commonly used by amateur radio and emergency services

Conclusion

 Frequency Selection  RF Detection  Types of Encoding  Types of Modulation  Questions?