This page is about digital mode experiments. In addition to SSTV my station also operates true digital modes in order to decode signals heard on any part of the shortwave spectrum. Moreover, the station will attempt 11m DX, trasmitting beacons or CQ calls addressed to any listening station worldwide. Transmissions will occur on frequencies and modes listed on the left when the band is wide open; all contacts will be confirmed with an eQSL. I've been using ROS since its first release with good satisfaction and results; ROS today seems to be well appreciated by Hams and 11 meter enthusiasts and although this transmission method initially has undergone an unfair and undeserved level of criticism, ROS has ever done exactly what it promised to do, as it demonstrated to be capable of decoding signals well under the noise floor. It's creator, Josť Alberto Nieto Ros (EA5HVK) claims that ROS is theoretically capable of decoding signals at levels of -35 dB of SNR at the lowest symbol rate (1 baud speed). After some quick tests performed on 27.245MHz over long distances I realized that signals lower than -16dB may be very hard to decode because errors displayed on the screen are usually more than readable text. As early tests were conducted on just one frequency (mostly at 8/16baud over 2000Hz bandwidth) I needed to do more tests. One morning, in the middle of a nice QSO with 43DR01 David in Melbourne (Thanks a million, Dave!) in a comparative test between ROS mode and Olivia, while the ROS transmission was decoded almost perfectly (-15dB S/N over a 16319Km QRB) the Olivia TX instead was not received at all. Too less to say ROS is better than Olivia? Yes, of course, these tests can't be certainly the royal evidence and there are plenty of digital modes to work weak signals, but I'm still having fun with ROS and there's one thing I'm pretty sure of... ROS mode really *works*. Thank you Josť Alberto, good job!
Ros (M=144) is a digital mode for weak signals based on M-ary orthogonal modulation where multiple bits are transmitted simultaneously using M analog carrier waveforms (tones). In other words, it's about a multi-frequency signaling scheme over a certain bandwidth (MFSK). Ros can easily decode signals a human cannot even hear.
Unlike ROS, PSK31 is an extremely narrow band mode based on PHASE shifting modulation. In particular, we talk about BPSK31 when a single bit of information (0 or 1) is being transmitted every time a 180 degree shift occurs to an audio signal. Binary sequences representing the characters composing the text to be sent are determined by a so-called Varicode scheme where lowercase and the most used chars have the shortest encoding. As a BPSK31 transmission has a symbol rate of 31.25 baud and takes only 31Hz bandwidth several signals may coexist in a typical SSB channel. Unnecessary power usage exceeding the real needs of a QSO must be avoided not to create waveform distortion. Overdriven audio is not good for RF amplifiers to maintain a linear response and intermodulation products would cause splatters on adjacent QSOs in the waterfall. Remember, PSK31 works very, very good with 10-15W only; experienced dx'ers are not addicted to unnecessary QRO operations.
JS8 by Jordan Sharer, KN4CRD
JS8 is a very efficient weak signal digital mode based on the robustness of FT8 protocol. It's been thought for keyboard-to-keyboard communications between amateur radio stations under the most challenging working conditions. By means of a custom FT8 modulation Jordan Sharer developed a software called JS8Call (formerly known as FT8Call), which permits long messages to be transmitted over a narrow bandwidth (50Hz @16WPM), allowing real-time chats over the air, also offering message relay capabilities. Modulation uses 8-tone CPFSK (continuous-phase frequency shift keying) with forward error correction (FEC) and Gaussian pulse smoothing. It's a type of FSK modulation where a Gaussian filter is used to shape the pulses prior to being modulated (GFSK). This reduces spectral sidelobes, optimizing power and minimizing interference with adjacent channels. That's all you need to know if you're not an engineer or a scientist. Rock-solid theories, brilliant ideas, and lot of math lay behind all this and believe me, Jordan is absolutely right. JS8Call truly stands on the shoulder of giants... That said, give JS8 a try. Get yourself a beer and have loads of QSOs. - CHEERS!
BPSK31 reception on HRD Digital Master. DM can handle several digimodes.
Based on FT8, JS8 is extremely efficient at working weak signals buried deep in noise. In addition, it permits conversations as well as message relaying, rendering the QSO more "human". Software for JS8 is the well-known JS8Call.
To operate digimodes is very easy; if you are used to SSTV you are ready to go digital. The only thing you'll need is new software installed on your computer covering each mode of your interest.
Not ready yet?
Here's an EEZEE interfacing solution. All you have to do is build the two circuits as follows and have some fun.
Wanna try something different (and harder to build)? See my lastest CAT/AFSK interface (for kenwood radios) here.