Quantcast Beat-Frequency Oscillator

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Custom Search
 
  
 
2-23 be received, the setting should be high (no agc until the signal level is high). However, you should set it as low as possible to prevent overloading of the last IF amplifier by stronger signals. Finally, you must have two diodes to obtain delayed agc. If only one diode were used, the agc would be developed from the detector diode, and there would be no delayed action. Or, if a signal diode were biased to provide the delaying action desired, no signal would pass to the audio amplifier until the bias was exceeded by the input signal. Beat-Frequency Oscillator The beat-frequency oscillator (bfo) is necessary when you want to receive cw signals. Cw signals are not modulated with an audio component, you remember, so we must provide one. The action of the rf amplifier, mixer, local oscillator, and IF amplifier is the same for both cw and AM; but the cw signal reaches the detector as a single frequency signal with no sideband components. To produce an af output, you must heterodyne (beat) any cw signal with an rf signal of the proper frequency. This separate signal is obtained from an oscillator known as a beat-frequency oscillator. Figure 2-20 is a block diagram of a superheterodyne receiver capable of receiving and demodulating a cw signal. The bfo heterodynes at the detector and produces an af output. The detector (second detector) is used primarily because the mixer (first detector) is normally used as the source of agc. Figure 2-20.—Placement of the beat frequency oscillator. If the intermediate frequency is 455 kilohertz and the bfo is tuned to 456 kilohertz or 454 kilohertz, the difference frequency of 1 kilohertz is heard in the output. Generally, you will tune the bfo from the front panel of a receiver. When you vary the bfo control, you are varying the output frequency of the bfo and will hear changes in the tone of the output audio signal. Squelch The sensitivity of a receiver is maximum when no signal is being received. This condition occurs, for example, when a receiver is being tuned between stations. At this time background noise is picked up by the antenna, and you will hear noise greatly amplified. This noise is highly annoying and occurs because receiver gain is maximum without a signal. You can often overcome this problem by using a circuit called a SQUELCH, NOISE SILENCER, NOISE SUPPRESSOR, or NOISE LIMITER. All of these noise type circuits just clip the peaks of the noise spikes. Squelch will actually eliminate noise. Figure 2-21 is a


Electrical News
Could India's Analog Wafer Fab be Moving South?
Cricket Semiconductor, a company set up with the purpose of...
eetimes.com
Apple Watch Tear Down Reveals European Chips
The Apple Watch, is the trailblazer of a wearables equipment...
eetimes.com
Ethernet Standards Ramp Up For Faster IT
The Ethernet Alliance and UNH-IOL hosted a plugfest to test...
eetimes.com
3-D Fingerprint Scanner Beats Apple's
The University of California at Davis, in cooperation with the...
eetimes.com
No Respect!
Every now and then, you see someone doing something, and...
eetimes.com
Friday Quiz: Name That 1994 Test Instrument
If you can remember back to 1994, then take a...
eetimes.com
It's a Bird. It's a Plane! It's a Drone!!
EE Times has gathered a panel of drone experts, including...
eetimes.com
Firework display as seen through the eyes of a drone
Have been thinking about purchasing a drone? If so, watching...
eetimes.com
FinFETs + FD-SOI Proposition: May Save Power
Ron Martino, vice president of application processors and advanced technology...
eetimes.com
Biodegradable Electronics Debut
Single crystal silicon transistors operating in the same microwave frequency...
eetimes.com
DesignCon 2016 Abstract Deadline Extended
You now have until Wednesday, July 8 so get your...
eetimes.com
IBM Makes Lake George World's Smartest Lake
Over 60 researchers, including ones from IBM and Rensselaer Polytechnic,...
eetimes.com
Developing Safety Certified Code for Industrial Systems
The right design framework and RTOS can help simplify and...
eetimes.com
Intel President, Execs Step Down
Intel President Renee James is among several top executives who...
eetimes.com
High-Speed Converters Aid Record Terabit Field Trial
Ultra high-speed digital-to-analog and analog-to-digital converters from Socionext Inc. (Yokohama,...
eetimes.com
Speech Recognizer / Synthesizer Shield for Arduino & Other MCUs
A Kickstarter project the just launched promises a rather interesting...
eetimes.com
Want a Free GPAK4 Mixed-Signal FPGA Development Kit From Silego?
25 GPAK4 mixed-signal FPGA development kits will be given by...
eetimes.com
IMB-GlobalFoundaries Deal Finalized
Following final approval by U.S. regulators, IBM closed the sale...
eetimes.com
20% Discount for ESC Silicon Valley 2015 Using Secret Code
Max's top-secret-squirrel code for the forthcoming ESC Silicon Valley 2015...
eetimes.com
UWAS: Playing Hide and Seek with Drones
The Paris Air Show (June 15-21) was rich in drone...
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 +