Many integrated FM quadrature demodulation circuits, such as the MC3361 or MC3362, have a defined LC tank circuit that creates a specific phase shift of 90 degrees at the center frequency of the demodulator. Let’s take a closer in depth look at how they work. A quadrature demodulator for FM signals consists out of two … [Read more…]
A phase detector generates a voltage proportional to the difference in phase between two signals. They are used in Phase-Locked-Loop (PLL) designs and PM / FM demodulator circuits. But how do they work? I promised in a previous blog article titled ‘No Tune NE602 / NE612 FM Demodulator’ that I would explain how a quadrature … [Read more…]
The overall performance of any RF circuit in regards of it’s phase noise and spectral purity depends significantly on the frequency generating circuitry, commonly an oscillator. Low noise oscillators with high spectral purity are neither witchcraft nor black magic. Many people think the design of oscillators is black magic as such circuits usually either work … [Read more…]
FM demodulators have and always will be desired circuits. Many circuit designs use old and obsolete parts or appear to be too complicated for beginners. This design shows a very simple FM demodulator, a quadrature demodulator to be precise, for a 455 KHz IF using only a handful of parts and an NE602. The NE602 … [Read more…]
The core of any spread spectrum (and other cryptographic) system is a pseudo random number generator (PRNG). Pseudo random numbers play a big role in the world of electronics and cryptology. The quality of a spread spectrum link and its properties strongly depend on this device. For my Direct Sequence Spread Spectrum Experiments I needed … [Read more…]
In our digital communication age heavy cryptology becomes more and more necessary everyday to protect our data from eavesdroppers. Direct Sequence Spread Spectrum is one way of covertly transporting data over radio waves. Without the knowledge of the correct code sequence it is nearly impossible for an attacker to decrypt the original message. 47 CFR … [Read more…]
Crystals with higher frequencies than about 30 MHz are almost exclusively overtone crystals. Such a crystal is intended to be used on an odd multiple of it’s fundamental frequency. Unfortunately, the crystal doesn’t want to resonate on it’s overtone frequency voluntarily, the oscillator circuit needs to force the correct overtone. For a little 2m band … [Read more…]
Every now and then eBay offers electronic parts that could be of great interest for amateur radio operators and other rf interested electronic geeks. Some of the parts are proprietary components out of professional applications that come with absolutely no documentation. I recently got my hands on a few Voltage Controlled Oscillators (VCOs) for the … [Read more…]