Introduction The RTL-SDR receiver is a simple but very useful device. It can receive signals from 25MHz to about 1700MHz. It can be used to scan the aircraft VHF AM voice band from 118 to 137MHz and then the Marine VHF FM band from 156 to 164MHz. VHF Air AM Voice Frequency Band The VHF […]
Introduction In a previous post, I discussed how to use the Friis equation to determine the free space loss and receive level between a transmitter and receiver (Ref.1). Let’s consider an example that I saw in a recent sailing forum. The discussion was around the range of a typical marine VHF transmitter using a quality […]
Introduction In a previous post (Ref.1), I simulated an MSK144 modulator with Scicos. In this post, I will simulate the demodulator. Recalling the design parameters: -SSB Transceiver_USB interface (300,2700)Hz = 2400Hz-Baud Rate = 2000bdps, Tbaud = 0.500msec -MSK = Minimum Shift Keying, Frequency Shift = 0.5*BdRate = 1000Hz-Centre Freq = 1500Hz, Lower Freq = 1000Hz, […]
Introduction EPIRB or Emergency Position Indicating Radio Beacon Station is an emergency transmitting device that blue water sailors or explorers can use in case of distress. They have proven their worth over the years and are absolutely essential for anyone wanting to wander off the grid (Ref.1). At least 2000 people have been saved every […]
Introduction In a recent YouTube video I saw a demonstration of a commercial HF radio communicating over a distance of 90Km using NVIS and digital voice. Using SSB the received signal was barely above noise level, and hardly decipherable. However, when the digital voice modem was switched on, the signal was very clear. I decided […]