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…]
Luckily the times when DIY projects in the GHz range have been the final frontier that’s rarely been crossed are over. Monolithic Microwave Integrated Circuits (short MMIC) are making the design of microwave (pre-)amplifiers a piece of cake. Mini-Circuits GVA-84+ is a perfect candidate for a simple 7 GHz preamplifier. The datasheet [1] of the … [Read more…]
The Sudden Storm receiver from QRPme is a simple direct conversion receiver. The circuit is nothing new: A NE602 mixer with crystal oscillator for downconversion and a LM386 as audio amplifier. What is new though is the enclosure. The parts for the sudden storm kit are being delivered in a tuna can. But the tuna … [Read more…]
Working low earth orbit (LEO) satellites is fairly easy and a great exercise for amateur radio operators of all classes. A simple HT for both 2m and 70cm (440 MHz) and a directional antenna is all that is needed for first experiments. There’s an 2m / 70 cm Antenna from Arrow that is highly recommended … [Read more…]
For homebrew crystal filters such as Cohn-Type or Ladder-Type filters it is often necessary to select crystals within 10 – 50 Hz of the target frequency. To make the selection process a little bit more pleasant, I designed this little test circuit. It is basically just a very simple oscillator utilizing a hand full of … [Read more…]