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Ferry van Eeuwen
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Digital Modes De laatste zeg 10 jaren heeft zich door de krachtige combinatie van zenders/ontvangers en computers een kleine revolutie voltrokken. Een aantal modes kan bedreven worden door veelal freeware software programma's die de kwalitatief uitstekende analoog-digitaal omzetters in een geluidskaart toepassen. Vele nieuwe digitale technieken werden ontwikkeld en het eind ervan is nog lang niet in zicht. Hiernaast zijn een aantal digitale modes aangegeven die ik zelf gebruik. Een uitzondering in dit rijtje is de Pactor-mode. Zover mij bekend is hiervoor nog geen software-matige oplossing gevonden. Een uitstekend Pactor I en II modem is commercieel beschikbaar, maar vrij prijzig. Dit modem kan behalve de genoemde Pactor modes, ook diverse andere digital modes aan.During the last, let's say, 10 years the powerful combination of transmitters/receivers and computers has caused a small revolution. A number of modes are made available with the help of, often freeware, programs. These programs use the high tech analogue-digital converters available in the modern soundcards. Many new digital techniques have been developed and the end is not yet in sight. Some knobs to the left represent of number of digital modes used by radio amateurs these days and used by myself. An exception is the Pactor mode. As far as I know no software solution through the soundcard is available yet. An excellent Pactor I en II modem is available on a commercial basis, but rather high priced. This modem, apart from the Pactor modes, can also handle a number of other digital modes. A number of digital modes used by radio amateurs are mentioned below. Only a few are discussed in more detail via the 'buttons' on the left of this page. All (digital) modes mentioned on this Web Site are or have all been used by myself. Amtor Amateur Teletype Over Radio, the first popular digital communication protocol which included direct linking between two stations with data acknowledgement and error checking. It is the same mode as commercial Sitor, and has largely been replaced by Pactor on the ham bands. APLinkAn acronym for Amtor/Packet Link, a DOS-based mailbox program by Vic Poor W5SMM and the predecessor to WinLink. AX25 A version of the X25 protocol (AX25A -> the 'A' stands for Amateur adapted by hams from the landline X25 protocol for VHF Packet radio, which allows multiple stations to share the same radio frequency. Data is broken up into blocks, or packets, which are transmitted and acknowledged independently. AX.25 packet is sometimes used at 300 baud on the HF bands but not with any particular success. A disadvantage is the big 'overhead' on each packet which reduces the 'payload' and thereby reducing speed of communication. Clover A higher-speed HF protocol developed by HAL communications, utilizing multiple-tone phase-shift encoding. Effective throughputs are similar to Pactor-II, and it will be long debated which is the better protocol although Pactor-II has clearly won the popularity contest. DMB (See MBO) Digital Mailbox - An HF mailbox station for storing and forwarding messages, generally running WinLink software. DSP Digital Signal Processor, a specialized microprocessor for processing analogue signals. Signals are converted to digital form and processed using various mathematical transformations before being converted back to analogy form if required for output. FSK Frequency Shift Keying. A simple method of sending digital information over radio, where a binary "1" is assigned one tone and a "0" a second tone. These tones are called "Mark" and "Space" after RTTY practice, and are typically separated by 200 hertz on the HF ham bands. MBO Mailbox station - same as DMB - An HF mailbox station for storing and forwarding messages, generally running WinLink software. NetLink A program written by Jim Jennings W5EUT that provides a gateway between a WinLink MBO and Internet email. Packet (See AX25) The protocol used by digital VHF/UHF stations. A few HF stations operate Packet at 300 baud, but it is not considered reliable (at least by Pactor enthusiasts) and is not supported by WinLink. Pactor-I Pactor A digital radio protocol developed by a group of German hams in the early 80's, allowing faster and more reliable communications than Amtor. The name comes from Latin for the "Mediator". Pactor operates at 100 or 200 baud depending on conditions, with net throughput of up to 18 characters per second. Pactor-II An improved version of the original Pactor protocol, also designed by SCS, the same group that did the original Pactor protocol. Pactor-II is a two-tone phase-shift system rather than FSK, and operates at basic rates from 100-800 baud depending on conditions. Net throughput is up to 140 characters per second depending on conditions. PSK Phase-shift keying, the encoding method used by Pactor-II and Clover. Multiple frequencies (tones) can be used to transmit more information, and the phase of each tone is shifted to encode a binary "1" or "0". PTC-IIThe Pactor-II controller from SCS, a powerful DSP-based controller that also supports all of the basic digital modes (including grey-scale weather fax). RTTYRadio Teletype. Originally designed for electro-mechanical teleprinters, RTTY generally uses a 5-bit Baudot code and operates around 45 baud. There is no acknowledgement (except from the operator at the other end) and no error checking. WinLink A Windows program for MBO's which allows simultaneous operation on VHF packet and HF Amtor, Pactor and Clover (with suitable controllers), and provides store-and-forward message handling. WinLink was originally written by Vic Poor W5SMM as a development of his APLink (Amtor/Packet Link) program, and has been extensively rewritten and developed by Hans Kessler N8PGR. For reference and sounds of the following digital modes: FSK-systems (Frequency Shift Keying) MFSK-systems (Multi Frequency Shift Keying) MCVFT-systems (Multi Channel VFT) PSK(Phase Shift Keying) and QAM-systems (Quadrature Amplitude Modulation) ALE- and SELCALL-systems, tone calls, ionosondes and chirp sounders Voice encryption systems, VOCODERS please go to: http://people.wiesbaden.netsurf.de/~signals/DIG_intro.htm Further references: |
