Cardboard AM Radio Resonant Loop Passive Booster Antenna -  An excellent use for copper wire, a trimmer capacitor and some lovely cardboard.   __ Designed by Henry 

Cascode 7 Experimental Receiver -  Many amateur experimenters stay in the familiar comfort zone of HF.  A small number venture into VHF, and even fewer devote time designing, building and operating for the UHF & microwave spectrums.  __ 

Cheap Crystal filter -  Ladder filter using six 4.43MHz Crystals.  Building cheap side band filter for your bome brew SSB Rig__ 

Cheap Log Periodic Dipole Array -  This is a Radio Astronomy Project __ Designed by Radio-Sky Publishing

Cheap-N-Easy 433MHz Sniffer -  Here's a simple - and cheap - little 433MHz receiver that has many uses.  it is ideal for checking that a suspect 433MHz "wireless" device (and there are scads of them) is actually working.  it's great for finding out where interference is coming from.  But most importantly (we believe!) it makes a great tracker for "fox hunts" and the like.__ SiliconChip

Cigar box receiver -  in a  recent  issue of  Practical  Wireless the  writer described the "Cigar  Box  Transmitter, "  an  extremely  small  1  watt transmitter suitable for the amateur  without mains electrical supplies or who is so restricted for space that anything in the nature of a normal sized shack and transmitter is entirely out of the question.  in the present article it  is proposed to  describe the receiver counterpart __ Designed by Harry Lythall-SM0VPO

Circuit Detects Current Pulse -  01/06/94 EDN Design Ideas:  The pulse detector provide as a visible indication of positive and negative current pulses.  The pulses amplitudes can vary from20 to150 mA.  The pulses durations can range from10 to40 msec, and their repetition rate can span40 to180 pulses/minute Design by Richard McGillivray, Grey Bruce Regional Health Centre, Owen Sound, Ontario, Canada

Circuit keeps wandering children & pets nearby -  12/02/10  EDN Design Ideas:  The receiver circuit in Figure 1 sounds an audio alarm when the transmitter (Figure 2) moves beyond a designated perimeter.  The transmitter, a voltage-controlled oscillator, operates at approximately 915 MHz in the unlicensed iSM (industrial/scientific/me Design by Tom Au-Yeung and Craig Sakamoto, Maxim Integrated Products, Sunnyvale, CA

Class B Series Modulator -  Schematic only__ Amfone.net

Classic Detector Enables Low-Cost Receive -  01/06/94 EDN Design Ideas:  Using modern discrete JFETs and IC s, you can build a low-cost super-regenerative receiver that has �V-level sensitivity at VHF and above.  Such receivers also boast very low parts counts and low power consumption.  Super-regenerative detectors are practical for wideband FM reception Design by Charles Kitchen, Analog Devices Inc, Wilmington, MA

CMOS Inverter VCO tunes octave to UHF -  11/19/98 EDN Design Ideas:  NOTE:  File contain several designs.  Scroll to find this one.  A robust and versatile vco provide as a stable output to 300 MHz (Figure 1).  The circuit's simplicity, unconditional stability, and consistent high-drive capability over an octave make the oscillator ideal for many applications, such as synthesized sources, local oscillators, and transmitters.  The AHC logic family (Texas instruments, www. Ti.com) makes the circuit's performance possible.  AHC is a relatively new line of CMOS logic whose high speeds and good noise performance allow oscillator operation into regions in which bipolar-junction-transistor and FET designs prevail. Design by Shawn Stafford, AM Communications Inc, Quakertown, PA  

CMOS RF PLL sythesizer -  Synthesizer based on available CD4059.  CD4046 and CD4060 IC s.   __ Designed by Harry Lythall-SM0VPO

Collection of Crystal Radios -  Collection of Crystal Radio Circuits __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Collection of Reflex Receivers -  The reflex receiver uses the same transistors to amplify the RF and the audio independently, effectively doubling the transistor count! Reflex designs were born in an era when transistors cost several dollars each and pressing them into "double duty" was worth some effort __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Compact L Match ATU for Portable use -  amateur radio construction projects.   __ Designed by Peter Parker

Computer Speaker Radio -  Here is a version built into a surplus computer speaker using an LM386 audio amplifier IC .  The circuit is built onto a little piece of phenolic perfboard that is secured by wedging the edges of the perfboard into a couple of bifurcated standoffs.  The on-off switch is part of the volume control which is mounted next to the tuning capacitor. __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Constant-Impedance IF bandpass filters improve performance -  Application Note__ MiniCircuits.com

Convert 2m VHF FM PMR transceiver Motorola Radius M110 into an AM ateur radio -  Turn a professional 2m VHF FM PMR transceiver Motorola Radius M110 into an amateur radio __ Designed by Aleksander Stare

Converter to Hear AM ateurs on your FM Radio -  if you're the sort who'd like to have an HF receiver in every room, but can't afford it, this idea is for you.  it will also appeal to the beginner wishing to build the simplest possible direct conversion receiver.  Using a readily-available FM wireless microphone kit, it is possible to broadcast the audio output of a homebrew direct conversion receiver around your property and beyond. __ Designed by Peter Parker VK3YE

Converting a PCS Power Amplifier to 13cm Ham Radio Band -  Schematic only, no circuit description __ Designed by © 2001 - YO5OFH, Csaba Gajdos

COR Carrier Delay timer / Hang Timer -  Did you ever want a simple controller to key a transmitter from a receiver's cos?    Well here is a simple circuit that does just that.  The input impedance is fairly high, about 1 Meg, and will interface to most any receiver.  VR 1 is a sensitivity control that is adjusted to trigger the circuit with just about any available positive going signal.  A setable hang time is adjusted with VR 2.   __ Designed by Kevin Custer  W3KKC

Cross Band VHF-UHF repeater -  My Radio amateur callsign is OZ2CPU.  I like to use Atmel AVR Atmega PIC 16 PIC 16F876 PIC 16F84.  Most electronics easy made for the novice and something is for the more experienced.   __ Designed by Thomas Scherrer OZ2CPU

Crystal heater / temperature stablization (TXCO) -  OK, here is the circuit I used - See image below.   The original National Semiconductor circuit had a 30 K resistor in series with a 400 µF cap., both in parallel with the 100 K resistor on the input of the 1st LM324 section.   I found that combo to actually destabilize the operation of the controller for this particular application, so I removed them & changed the 2 µF cap in series with the 10 megohm resistor to 5 µF. __ Designed by Bob Dengler NO6B

Crystal Pulling -    NOTE: Must register on this site __ Designed by Published in Elecktor July/Aug, 2010

Crystal Radio -  RF Receivers & Receiver Circuits Crystal Radio __ Designed by Aaron Cake

Crystal Radio -  i have been listening stories from dad that he made a radio when he was little younger than me.  it was hard to digest that his radio worked without power!  I thought, its nothing more than those interesting old stories that we have been told at bed time! !  __ Designed by Nina Gajjar

Crystal Radio -  The crystal radio gets its name from the galena crystal (lead sulfide) used to rectify the signals.  A "cat's whisker" wire contact was moved about the surface of the crystal until a diode junction was formed.  The 1N34A germanium diode.   __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Crystal Radio -  This is a generic circuit, the first true radio receiver in history.  Description: Crystal radio requires no power supply to operate because it uses energy from the signals it receives.  Performance is like one should expect poor.  Nevertheless, __ tomzi.geo page

Crystal Radio RF Amplifier -  One of the best places to add a transistor to a simple crystal radio is at the front end in the form of an RF amplifier.  The circuit below is a simple but effective amplifier which will give surprising performance improvement.  This amplifier __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Crystal Radio Set Version 2 -  This uses a more standard ceramic / crystal earpiece and LT44 transformer that you can buy easily.  Look out though, this is a draft version.   __ Designed by Henry 

Crystal radio with Amplifier -  An improved crystal radio with a two-stage audio amplifier.  The 2N3904 (or any other general-purpose NPN) acts as a preamplifier while the LM386 boosts the signal high enough to drive low impedance Walkman headphones or perhaps even a small speaker.  __ tomzi.geo page

Crystal Radio--make your own -  Circuit Only __ Designed by Charles Wenzel

Crystal Set that Requires No Antenna -  amateur radio construction projects.   __ Designed by Peter Parker

CW Beacon Keyer -  This circuit stores a morse code message as bits in an EPROM chip, the message controls a relay that keys a CW (morse code) transmitter.  An Arduino processor can also be used in place of this circuit, that eliminates the need to build the circuit and program an EPROM. __ Designed by G. Forrest Cook

       >>>