AM Modulation on GNU Radio

Introduction In AM modulation, the amplitude of the carrier wave is varied in accordance with the modulation wave. This can be described by the modulation equation: AM = Ac*[1+m*cos(wm*t)]*cos(wc*t)]Modulation Waveform = Am*cos(wm*t)Carrier Wave = Ac*cos(wc*t)m = modulation index = Am/Ac <=1 When m = 1 (100%), the amplitude of the mod waveform is equal to… Continue reading AM Modulation on GNU Radio

RTL-SDR for HF Beacons Propagation Prediction

Introduction In a previous post, I looked at how the RTL-SDR can be used to receive HF stations in the NCDX/IARU HF Beacon network (Ref.1). These stations transmit on a schedule and can be used for HF propagation analysis. Various programs can also be used for HF propagation prediction (Ref.2), such as VOACAP (Ref.3) and… Continue reading RTL-SDR for HF Beacons Propagation Prediction

VHF Marine Antenna Testing with NanoVNA

Introduction Recently I discovered the NanoVNA vector network analyzer. I had seen articles in QST magazine over the last several years and was intrigued (Ref.1/2). My first experiment was with my HF vertical antenna. I calibrated the unit for the HF band from 1MHz – 30MHz and tested the SWR (Ref.3). The results were exactly… Continue reading VHF Marine Antenna Testing with NanoVNA

HRF1 as a Signal Generator for Amateur Radio

Introduction About 20 years ago I was building various SDR receivers and I needed a signal generator to test their performance. I decided like most hams to build my own using the latest Analog Devices 8 bit DDS chip AD9850. The unit was controlled by a simple Atmel ucontroller, was battery powered/portable and worked up… Continue reading HRF1 as a Signal Generator for Amateur Radio