LTC Design Note: High input IP3 mixer enables robust VHF receivers
08/29/14 EDN-Design Ideas LTC Design Notes 515: An increasing number of applications occupy the 30MHz to 300MHz very high frequency (VHF) band. Television and radio broadcasting, navigation controls and amateur radios are a few examples. Modern RF component development is aimed at much higher frequency bands used for voice and data communications systems__ Circuit Design by Andy Mo
Mixer & Preamplifier for String Instruments
Most of the small musical bands have up to four string instruments like guitars and violins. The signal from the transducers of these instruments should be buffered and sometimes amplified before...___ Electronics Projects for You
Mix-It: an Easy-To Build 4-Channel Mixer
Anyone can build this high performance four-channel audio mixer...___ SiliconChip
Odd-order Diode Multiplier
The purpose of the circuit is to take advantage of the superior noise and switching characteristics of Schottky barrier diodes to make a high performance odd-order frequency multiplier. Modern quartz oscillators have reached a level of performance where it has become difficult to multiply the fundamental frequency without degrading the phase noise by more than the unavoidable 20 dB per decade of multiplication. Thanks to the Schottky barrier diode's extremely low flicker noise, this circuit adds little excess noise __ Reprint courtesy of RF Design Magazine
An amplifier may be added to boost the audio level as shown below. The current consumption of this amplifier is quite low and a power switch is not included. Disconnect the battery when the receiver is stored for long periods. __ Contact: Charles Wenzel of Wenzel Associates, Inc.
Post Mixer Amp
SSB Transceiver-Receiver Section: The post mixer amplifier, makes up for the losses in the passive mixer and I.F. port attenuator. The transistor is a 2N4427, if you don't have one, try a 2N3866, 2N5109, on any similar, medium power VHF transistor. The output transformer is 10 turns with a tap at 4 turns. The core is the same, high permeability ferrite ring, used in other parts of this project. The output supplies DC current for the RX/TX switching diodes at the SSB filter input __ Designed by EI9GQ homebrew radio
A few weeks ago I posted to QRP@WW the modifications to convert a cheap radio to the HF amateur bands. I have dug-out one of my radio's that was modified for 7MHz and found yet another circuit was built into it. This is the circuit for a Q-multiplier to reduce the IF bandwidth. I do not have any idea where this circuit came from, but other than scribbled on the back of a cigarette packet some 20 years ago. __ Designed by Harry Lythall-SM0VPO
This is the circuit for a Q-multiplier to reduce the IF bandwidth. I do not have any idea where this circuit came from, but it is NOT originally mine, so I claim NO credit. The circuit is basically an oscillator that does not quite oscillate, so when it is connectd to the IF HOT end of the first IF transformer it will increase the Q-factor, thereby reducing the IF bandwidth considerably. It does this by cancelling the losses in the 1st IF transformer using gain from an additional transistor circuit. __ Designed by Harry Lythall-SM0VPO
Simple Circuit 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.
Simple Circuit Two-transistor Radio
Here is a simple radio that was designed to minimize unusual parts; there isn't even a detector diode! The sensitivity isn't as high as the one-transistor reflex but the simplicity is attractive. Strong stations will provide plenty of volume __ Contact: Charles Wenzel of Wenzel Associates, Inc.
Simple Circuit Variable Voltage Source
The high current regulator below uses an additional winding or a separate transformer to supply power for the LM317 regulator so that the pass transistors can operate closer to saturation and improve efficiency. For good efficiency the voltage at the collectors of the two parallel 2N3055 pass transistors should be close to the output voltage. The LM317 requires a couple extra volts on the input side, plus the emitter/base drop of the 3055s, plus whatever is lost across the (0.1ohm) equalizing resistors (1volt at 10 amps) , so a separate transformer and rectifier/filter circuit is used that is a few volts higher than the output voltage __ Designed by Bill Bowden
TL431 Crystal Radio Amplifier
Here is a simple audio amplifier using a TL431 shunt regulator. The amplifier will provide room-filling volume from an ordinary crystal radio outfitted with a long-wire antenna and good ground. The circuitry is similar in complexity to a simple one-transistor radio but the performance is far superior. The TL431. __ Contact: Charles Wenzel of Wenzel Associates, Inc.
Two Diode Odd-Order Multiplier
It is often necessary to multiply the frequency of low noise oscillators without significantly degrading the phase noise beyond the theoretical 20 log (N). Low noise frequency doublers constructed with Schottky signal diodes are readily available but higher-order multipliers often __ Contact: Charles Wenzel of Wenzel Associates, Inc.
Variable Frequency Oscillator
This is a very simple circuit utilising a 555 timer IC to generate square wave of frequency that can be adjusted by a potentiometer. With values given the frequency can be adjusted from a few Hz to several Khz. To get very low frequencies replace the 0.01uF capacitor with a higher value __
Very High Gain Crystal Earphone Amplifier
This simple, one-transistor amplifier provides a voltage gain over 1000 (60 dB) for driving a high impedance ceramic (crystal) earphone. The high gain is achieved by replacing the traditional collector resistor. __ Contact: Charles Wenzel of Wenzel Associates, Inc.
VLF/LF Block Converter for the Shortwave Receiver
This converter shifts the VLF/LF bands, from below 20 kHz to over 350 kHz to the shortwave frequencies, determined by the selected crystal. In this prototype, the crystal frequency is 5 MHz, so the LF band comes out at 5.02 MHZ to 5.35 MHz, suitable for use with a shortwave receiver. Notice the lack of an expensive mixer or special IC! __ Contact: Charles Wenzel of Wenzel Associates, Inc.