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Working the World with Ham Digital Modes

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Working the World with Ham Digital Modes Working the World with Ham Digital Modes By Larry Van Horn, N5FPW urn on your television set here in the output, and the sound card line input to the audio States and you won’t have to wait long output of the radio. You can use the transceiver T for a commercial promoting the lat- VOX to switch from receive to transmit and est text messaging plan for various cellular back. You can learn more about this method telephone services. In fact, texting is the “in” on the WM2U website (see our resource guide, thing to do these days. Walk around the office, Table 2). at school, in a restaurant and you will see that If you want to roll your own interface, Jack, everybody is texting. KE0VH, has an interesting website with infor- But texting isn’t limited to just a cellphone mation on building a computer to transceiver or Blackberry. You might be surprised to learn interface. If you can read a schematic, have a that in the ham radio world we have been texting few junk parts and can handle a soldering iron, Saratoga’s EZ PSK USB Interface long before it became popular among other por- then his ham brewed project may be just what tions of our populace. you need to get into the fun of digital ham radio to keep up with the rapid changes in the ham With the advent of more powerful comput- without breaking the bank. digital world. If you want the latest information ers and the sound card, hams have been texting If you have two thumbs, burn yourself I recommend subscribing to the Digital Radio using digital modes since the end of 1998. Peter frequently with a soldering iron, or just have newsgroup based on the Yahoo website (see Martinez, G3PLX, was the first amateur to ex- some cash to spare, you can purchase one of the resource guide). ploit the computer sound card by creating the commercial interface units that are available in On the other hand, there are some digital PSK31 mode, a keyboard to keyboard digital the ham radio marketplace. Manufacturers such modes that are the staple of the digital ham com- mode that lets amateurs text each other via radio. as MFJ, RigExperts, Saratoga, Tigertronics, and munity. CW and RTTY are still widely used. Since that milestone event, sound cards have West Mountain Radio all make inexpensive in- These modes are widely supported by quite a become more powerful and versatile, resulting terface units (see our link to the DX Zone Digital few of the software decoder packages in our in digital communications becoming one of the and Packet Radio Resource Guide). sampler in Table 2. fastest growing segments of the amateur radio When setting up to transmit or receive, Other modes that have been in common use hobby. sound card digital modes are used using upper by the amateur radio community over a number In this article we will explore some of the side band (USB). Do not use LSB. The older, of years include: AMTOR, APRS, Clover, G- newer digital modes currently being used by not more conventional digital modes such as Clover, TOR, Packet, PACTOR I (DOS freeware pack- only the amateur radio community, but some RTTY, PACKET, AMTOR and PACTOR typi- age that requires a PSA chip set sound card and other inhabitants of the HF spectrum as well. cally use LSB. will not do Airmail, Sailmail or WinLink2000), Before we move on, there is one important and Slow Scan Television (SSTV). What do I need to get point that needs to be mentioned. Most of the A lot of reference material is already avail- problems in setting up the computer, interface, able on the Internet and in printed form regarding started? and radio can be attributed to the proper setup of these modes, so I won’t cover them in-depth If all you want to do is to receive some the sound card and mixer panels on the computer. in this article. If you want more information digital communications or if you are a shortwave Del Schier, K1UHF, wrote an excellent article on radio listener, all you will need is a computer all of this in the October 2003 issue of QST. equipped with a sound card, an audio cable, a The good people at West Mountain Radio Key to Abbreviations/Acronyms shortwave receiver with SSB capability, and have made this article available in Adobe PDF BPSK Binary Phase-Shift Keying a soundcard software package (see Table 1) form on their website. I highly recommend you CW Continuous Wave (aka Morse code) that will decode the digital stream you want to download this file (link in our Resource Guide) DSP Digital Signal Processing receive. and study it thoroughly. It will save you a lot of FEC Forward Error Correction If you are a licensed amateur radio opera- time and grief when you start setting up your IFK Incremental Frequency Keying tor, replace the receiver with a transceiver, add MFSK Multi-Frequency Shift Keying station to work the various digital sound card PSK Phase Shift Keying a hardware interface between the computer and modes. QPSK Quadrature Phase-Shift Keying the transceiver, and you can get in on the fun of QRM Interference working the world via digital modes. QRP Low Power The simplest and quickest computer to ham Digital Modes RTTY Radio Teletype radio interface is to connect the line output from The rate of software and hardware develop- SSB Single Side Band the sound card to the transceiver audio input with ment has moved so fast that it is nearly impos- WARC World Administrative Radio Con- ference a 100:1 voltage divider to reduce the voltage sible for even an article with short turn-around May 2008 MONITORING TIMES 9 on these modes, an excellent reference is the MT63: MT63 500 Hz (5.0 baud) MT63 pseudo-122.5 baud (one “pixel” is 8.163 ARRL’s HF Digital Handbook by Steve Ford, 1000 Hz (10.0 baud) MT63 2000 Hz (20.0 ms long). WB8IMY (see the February MT What’s New baud) PSK Hell encodes the pixel’s brightness in Q15X25: Q15X25 (15 x 83.333 baud) the carrier phase instead of the amplitude. column, page 74). Strictly speaking, it’s encoded in the change of the phase (differential phase shift keying): The Sound Card Revolution You can expect to find PSK digital com- an unchanged phase in the beginning of a It was the mode that started the amateur munication in and around the following HF/ pixel means white, and a reversed phase radio sound card digital mode revolution and is VHF/UHF frequencies: means black. It operates at 105 or 245 still today the big daddy of them all: the PSK31 baud. It has the same traits as standard mode. HF – 1838 3580 7035 (ITU Region 1) 7070 PSK31 including its great sensitivity. Great Phase modulation communication modes 10140 14070 18100 21080 24925 for DX work in bad QRM. It is, however, have many more advantages than the CW 28120 kHz sensitive to drift. VHF/UHF – 50.290 144.144 222.070 FM Hell uses frequency modulation with a mode, which uses amplitude (On/Off) keying. 432.200 and 909 MHz careful control of phase, essentially mini- In a noisy or distorted propagation environ- mum-shift keying. ment, the amplitude of a signal will shift and Duplo Hell is a dual tone mode which sends vary much more than the phase of a signal. A CHIP off the old PSK block. two columns at a time at different frequen- When compared to CW, PSK31 is a much more One of the PSK modes mentioned above cies (980 Hz and 1225/1470 Hz). Wide reliable operating mode. that is heard occasionally in the ham bands shift, but better immunity to noise. LSB is the CHIP 64/128 mode. CHIP 64/128 is a recommended. PSK31 uses a varicode character coding C/MT Hell or concurrent multitone Hell sends that provides the operator with a top data rate of Direct Sequence Spread Sequence (DSSS) all rows at the same time using tones at around 50 wpm (31.25 baud). Instead of using mode using an original algorithm. CHIP 64/128 different frequencies. The transmission can FSK or on/off keying, PSK31 uses Binary or is a very robust mode, getting through when be read using an FFT display. It allows for Quadrature Phase-Shift Keying with a Viterbi conditions are poor. high resolutions. Not very sensitive, but it decoder. Based on a RTTY style of operation, In the United States, 7090.0 kHz USB has great noise immunity. appears to be the most active frequency CHIP S/MT Hell or sequential multitone Hell is like this mode is most useful for live keyboard C/MT but with a discrete number of tones to keyboard conversations at 31.25 baud (31 frequency, but 14077.0 and 14110.0 kHz have (characters are restricted to 5x7 pixels). Hz bandwidth). It is easy to use and monitor, also been reported. Slowfeld is a very slow mode (2 characters per highly immune to noise and QRM, and is suit- Be aware that on 7090.0 kHz there is also minute) intended for beacon use. able for low power (QRP) operations. Olivia (see section below) activity. Olivia has a chirpy sounding tone, a kind of combination of MFSK16 and SSTV sounding signals. Chip 64 is nothing like this: It is more a “whooshing” or “roaring” white noise type of signal, not as low in tone as MT63.
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