Fullscreen HTML5Med Res (??MB)HTML4

Plots weather decodes Fig.1: a typical weather map as transmitted by the Bureau of Meteorology in Canberra on 5100kHz. It was decoded using the following switch settings on the Radfax Decoder: S1 1.7-2.0; S2 ± 600Hz; and S3 600 baud. Note that this particular map is leaning slightly to the left. This is corrected by altering a value in the software. 18 SILICON CHIP maps on your computer1 radioteletype and Morse code. a ax Got a computer and a shortwave receiver? Why not link the two together with this Radfax Decoder and plug into the world of FSK transmissions? You can get up to the minute weather charts, read overseas radioteletype messages as they are transmitted and eavesdrop on Morse transmissions, without even knowing Morse code. Circuit design by JOHN CLARKE If you have an IBM PC or PCcompatible computer and a shortwave radio you can plug into the intriguing world of non-voice transmissions on the shortwave bands. These include radioteletype (RTTY), Morse code and perhaps the most interesting of the lot, facsimile (fax). Of the fax transmissions, weather maps are the most interesting and useful, particularly if you are in a remote rural area or at sea. Weather faxes can take quite a lot of different forms . We have plotted out maps giving the conventional isobars with lows and highs, just as shown on TV every night. As well, we have received cloud maps (nephanalysis), also as seen on TV weather reports. We also have charts of wind wave and swell height which are not shown on TV and these could be very useful if you were at sea in a sm"l.ll boat! Regardless of whether maps are shown on TV or not, the attraction of being able to decode your own is that you get them as soon as they are transmitted. And of course, you can decode RTTY and Morse as well. FSK transmissions Both fax and RTTY transmissions use the FSK principle. FSK stands for "frequency shift keyed" and refers to a system whereby the modulation on a radio transmission is ·continually switched or "keyed" between two frequencies such as 2400Hz and 1200Hz. The rate of switching sets the "Baud" rate which is an old telegraphic term which means bits/second. Typical nominal rates for RTTY are around 75 baud (bits/sec) while typical transmission rates for fax transmissions are 1200, 600 or 300 baud. As for Morse - well Morse is pretty slow. Decoding FSK tranmissions does not take a lot of circuitry but it does require some software to allow the computer to turn the decoded digital data into something intelligible which can be displayed on the screen or printed out on a dot matrix printer. We have designed the circuit of the Radfax Decoder while the soft- ware, called " Radfax 2" , was written by Michael Delahunty. The software is only available directly from Michael Delahunty, as detailed in a panel in this article. The hardware OK, let's be specific about the hardware you need if you want to get into the world of fax and RTTY. First, as already stated, you need an IBM PC XT or compatible computer with a CGA or EGA monitor. The software requires the CGA or EGA monitor so if your machine presently only has a monochrome monitor and MDA card, you will need to do something about it. There is a version of the software available to suit a Hercules Graphics card or, alternatively, you could install a new Combo card from Electronic Solutions which lets a monochrome monitor work with software which needs a CGA card. You simply install it in place of the existing MDA card and change the DIP switch settings on the computer motherboard to suit. The program requires at least 2 56K of RAM in the computer and it will not work if you attempt to use it in conjunction with memory resident programs such as Sidekick. This is easily fixed by booting up the computer just with Radfax 2. If you want to print out weather maps and other info received via fax or RTTY transmissions, you will need an IBM or Epson compatible printer. The Radfax 2 software is rather clever in that it allows you to print out faxes sideways on your printer. This not only gives larger NOVEMBER 1989 19 This photo shows how a fax transmission appears on screen. Once the transmission has been completed, the picture can be saved to disc and printed out. This map is of wave swell height and is from the Bureau of Meteorology in Canberra. \i . ,, I printouts but gives much more detail than is available from the smaller printouts or from the screen. The shortwave receiver ___..... ·j } Fig.2: a printout has much better resolution than the corresponding on-screen picture. This printout was made in the conventional fashion but the software also allows you to print out faxes sideways for even better detail. The map shows wind wave height for 23rd September, 1989 (Bureau of Meteorology, Canberra on 5100kHz). 20 SILICON CHIP The FSK tones for fax and RTTY can only properly be received on a radio that has a facility for picking up SSB (single sideband) transmissions. This means you need a shortwave radio which either has a BFO (beat frequency oscillator), which is normally used for picking up Morse, or an SSB switch for selecting USB (upper sideband) or LSB (lower sideband). You will also need a decent outdoor antenna for your shortwave radio although we have successfully picked up some transmissions using just a whip antenna. For best results though, you need an outdoor antenna - the bigger, the better. The Radfax Decoder Next, there is the Radfax Decoder which connects to the audio out- put of your shortwave receiver. The output of the decoder then connects to the RS-232 (serial) or to the parallel printer port on your computer. If your computer has an RS-232 port, we suggest that you use it for the Radfax Decoder input, leaving the parallel port for the printer. That way, you can print out faxes at will, without having to disconnect the Radfax Decoder. The decoder is housed in a standard plastic utility box which has three rotary switches and one fine tuning control. The only other front panel feature is a LED to tell you that the decoder is working. Now let's have a look at the circuit. There is not a lot to it, just two integrated circuits and a 3-terminal regulator. +5v---..------------~ LOCK LE01 .01 0--I AUDIO INPUT 220k ¼ .016 Bandwidth and baud rate S2 sets the operating bandwidth of ICl, for which it will generate high and low error signals. In general, use a wide bandwidth 2 .>o-1"" ---OMORSE (CW) .022 OUTPUT 2 3;:r S1 : 1 2 3 4 2525/2D57Hz 2066/1663Hz 1663/1371 Hz 1377/1122Hz 430k 220k CENTRE FREQUENCY S1 IC1 XR2211 S2 : 1 : ±6DOHz 2 : ±400Hz 3 : ±3DOHz 4 : ±2QOHz 5 : ±100Hz 6: ±50Hz S2 6ANOWIOTH 470k 11 .0056I Phase lock loop The heart of the unit is ICl which is an XR2211 FSK demodulator/ tone decoder. As its name suggests, it is designed especially for decoding FSK signals. It is basically a phase lock loop which generates a high or a low error signal depending on whether the tone at its input is high, say 2400Hz or low, say 1200Hz. The error signal, at pin 7, is buffered by inverter IC2a and then fed to the computer input which may be the RS-232 port or the parallel printer port. Switch Sl and the associated four capacitors provide for four separate free-running frequencies for the phase lock loop. The 5k0 potentiometer (VRl} allows these frequencies to be adjusted within the limits shown for Sl on the front panel. For example, for setting 2 on S1, VR 1 allows the centre frequency of ICl to be set anywhere between 1683Hz and 2066Hz. This is the setting that we used most of the time, by the way, but depending on the nature of the transmission, you will need the facility provided by Sl. For example, when receiving Morse or RTTY, you may want to use setting 4. .,. .,. 100k ..-------+5V 36k 4.7k 12 IC2a 16,1 1-'---+--.:!!5 4 FSK/FAX OUTPUT 22k .,. FREQUENCY FINE ADJUST VR1 5k LIN 560k S3 : 1 : 1200 2 600 3 300 4 . 150 5 75 6 45 01-04 4x1N4002 12VAC 100 16VW GNO .,. RADFAX DECODER Fig.3: the circuit is based on an XR2211 FSK demodulator/tone decoder IC (IC1). This IC is basically a phase lock loop and generates a high or low error signal, depending on the incoming tone frequency. when receivmg fax (ie, ± 600Hz) and a narrow bandwidth for Morse and RTTY. Using a low bandwidth reduces data errors due to noise but if the bandwidth selected is greater than the difference between the two FSK tones, the circuit will not work. S3 gives the optimum filtering to suit the various data rates. In general, a smaller filter capacitor is used for the higher data rates. For example, at the 1200 baud setting, the filter capacitor is .0022µF . Morse output Since Morse is transmitted by switching on and off the carrier frequency, ICl will respond to a Morse transmission by switching its lock indicafion output, pin 6, on and off. To provide a visual indication of this, inverter IC2d drives LED 1. IC2b and IC2c provide buffering of the lock indication output before it is fed to the computer port. LED 1 will light continually when the Radfax Decoder is correctly NOVEMBER 1989 21 Fig.4: the PCB parts layout. Be sure to adjust each switch for the correct number of positions before installing it on the board (see text). The 3-terminal regulator is mounted flat on the board and secured using a screw and nut. picking up a fax or RTTY signal and will flicker on and off in time with a Morse signal. Power The Radfax Decoder is powered from an external DC or AC plugpack which can be 9-12 volts (nominal). D1 to D4 are connected in a bridge so that a DC or AC source can be used (and also without regard to polarity in a DC source). The diodes feed a 220µF 16VW capacitor and then the 3-terminal 5V regulator. Further filtering of the 5V output is provided by a lOOµF capacitor. The total current drain is quite modest and should be around 20 milliamps. Construction We housed our prototype Radfax Decoder in a standard plastic box measuring 159 x 95 x 52mm. All the components, including the switches and pot, are mounted on a printed circuit board measuring 125 x 88mm (code SC 03111891). Since the rotary switches are soldered directly to the printed board, it does not attach to the case but hangs off the front panel via the switch bushes. Assembling the decoder board is a fairly straightforward matter although it's best to install the PC pins, links, resistors and other small components before mounting the three rotary switches. The board pattern is designed specifically to suit rotary switches with PC pins. Before installing the switches, they should be adjusted to give the required number of switch positions. For example, S1 is adjusted to four positions and S2 and S3 to six positions. This is done by removing the nut from the switch bush and lifting out the lock washer to reveal the stop ring. You then reposition the stop ring tab in the hole marked '4' for a 4-position switch and in '6' for a 6-position switch. Check that each switch will give the required number of positions before installing it on the board. The 3-terminal regulator is laid flat onto the board and its tab anchored with a screw and nut. The red LED is installed with leads about 10mm long so that it protrudes through the front panel (when it is fitted). The potentiometer is installed by soldering its three connections to the three PC pins on the board. Note that the 220µF power supply filter capacitor is a pigtail type. A PC-mounting type will be too high to fit between the lid and PC board. RESISTORS □ □ □ □ □ □ □ □ □ □ □ 22 No Value 1 1 1 560k0 470k0 430k0 220k0 100k0 75k0 56k0 36k0 22k0 4.7k0 2200 2 2 1 1 1 1 2 1 SILICON CHIP 4-Band Code green blue yellow gold yellow purple yellow gold not applicable red red yellow gold brown black yellow gold not applicable green blue orange gold not applicable red red orange gold yellow purple red gold red red brown gold 5-Band Code green blue black orange brown yellow purple black orange brown yellow orange black orange brown red red black orange brown brown black black orange brown purple green black red brown green blue black red brown orange blue black red brown red red black red brown yellow purple black brown brown red red black black brown When all components are on the board, check all your assembly and soldering carefully. Now connect power and check that the + 5V rail is present at the output of the 3-terminal regulator, at pin 1 of IC1 and at pins 1 & 16 of IC2. If that's OK, put the board aside and start work on the case and lid. The case itself requires two 4mm The 5k0 frequency adjust potentiometer (VR1) is mounted on the board by soldering its terminals to three PC stakes. Note that the 220µF capacitor must be a pigtail type (if you install a PC-mounting type, it will foul the lid of the case). Take care when installing the two ICs as they face in opposite directions to each other (see Fig.4). diameter holes for the power supply and output leads and another hole to suit the RCA panel socket. Use the front panel artwork as a template to mark the lid for drilling, then drill a 5mm hole to suit the LED and the holes for the switches. Hint: drill these Qoles to 10mm diameter then open them up slightly with a tapered. reamer, · if necessary. You can now attach the front POLYESTER AND CERAMIC CAPACITORS □ □ □ □ □ □ □ □ □ □ □ □ No Value IEC EIA 1 2 1 1 1 1 2 1 2 1 1 1 0.15µF 0 .1µF .068µF .039µF .033µF .027µF .022µF .018µF .01µF .0056µF .0047µF .0022µF 150n 100n 68n 39n 33n 27n 22n 18n 10n 5n6 4n7 2n2 154K 104K 683K 393K 333K 273K 223K 183K 103K 562K 472K 222K When installing the LED, leave its leads about 10mm long so that it will protrude through the front panel. NOVEMBER 1989 23 panel label to the lid. This done, attach the various input, output and supply leads to the printed board, then fit the lid over the switch and pot shafts and install the locking nuts. Attach knobs to the switches and pot, screw the lid to the case and you are almost in business. The final wiring task involves connecting the Radfax Decoder output wires to a DB-25 male or female plug to suit the RS-232 or parallel printer port on your computer. As noted above, if you have an RS-232 port we suggest you use that for the Radfax Decoder output. That way you don't have to bother with connecting and disconnecting the printer each time you want to print out a fax or RTTY page. If you are using the RS-232 port, the connections are as follows: ,a, c:o ,,- ,M 0 (.) en RS-232 Connections Radfax Decoder RS-232 Port RTTY /Fax output pin 5 pin 6 pin 7 Morse output GND If you are using the parallel port, the connections are follows: Parallel Port Connections Radfax Decoder RTTY /Fax output Figs.5 & 6: here are actual size artworks for the PC board and the front panel. Inspect the PCB pattern carefully after etching and correct any defects before mounting any of the parts. Morse output GND • Parallel Port pin 13 pin 12 pins 18-25 • • ±50 • • • • ±100 • 2-2.5 • e 1.7-2.0 1-1 .3 1.3-1.7 ±200 • • kHz CENTRE FREQUENCY • • ±400 ±300 • ±600 45• 75. •1200 •soo • • 150 300 Hz b/S BANDWIDTH BAUD RATE • LOCKe • • 24 SILICON CHIP e • • • FINE ADJUST fi'McooER • PARTS LIST 1 PCB,codeSC03111891, 125 x 88mm 1 front panel label, 1 53 x 90mm 1 plastic case, 159 x 95 x 52mm 4 knobs 3 single pole 12-position PCmounting rotary switches (Jaycar Cat. SR-1 21 0, Altronics S-3021 ) 1 5k0 linear potentiometer 1 RCA panel socket 1 DB-25 plug to suit IBM serial or parallel port 10 PC stakes Semiconductors The audio input to the Radfax Decoder is fed in via an RCA panel socket mounted on one side of the case. The LED lights continuously when you are picking up a fax or RTTY signal and flickers on and off in time with a Morse signal. Now connect your shortwave receiver to the Radfax Decoder and the Decoder output cable to the computer. Boot up your Radfax 2 software disc; ie, type in "Radfax 2" and hit return. The main menu should come on and then you can enter a sample fax chart from the files directory. Having displayed a fax on the screen, you will know that the software is working OK. You now have to check that the software knows which port you are using for the Radfax Decoder input. To do this, you call up the Settings Menu by typing S (when the main menu is displayed). If you are using a serial port, the address is 02FE Hex (Com2) or 03FE Hex (Coml). If you are using a parallel port, the address is 279 Hex (LPT2) or 379 Hex [LPTl ). You call up the correct port address by using the juggle command until the right value is displayed (type J). What to look for It is now simply a matter of tuning in a good fax signal. On the east cost of Australia, the most reliable signal is 5100kHz which is the Bureau of Meteorology in Canberra. They also broadcast on 11,030kHz. If you are in the north of Australia, try the Bureau's Dar- win transmitters on 7535kHz, 10,555kHz and 13,920kHz. The New Zealand weather station on 13,550kHz is also worth a try. Other international fax stations worth trying are 13,510kHz, 14,826kHz, 14,685kHz, 16,320kHz, 17,068kHz and 18,130kHz. For RTTY stations, try 7542kHz and 10,730kHz [France), 9968kHz and 10,552kHz [Germany), 7695kHz and 13,563kHz (Taiwan), 13,780 kHz [Korea), 6845kHz, 9120kHz, 10,960kHz and 14,514kHz [Reuters), and 9985kHz, 16,232kHz and 19,520kHz [UPI). Many other fax and RTTY stations are listed in the book "Shortwave Radio Listening With the Experts", by Gerry L. Dexter. This was reviewed in our June 1989 issue and is available from Jaycar Electronics stores at $25.95. ~ 1 XR2211 FSK demodulator (IC1) 1 4049 or 4009 inverter (IC2) 1 7805 5V 3-terminal regulator 1 5mm LED (LED 1) . 4 1 N4002 1 A diodes (D1-D4) Capacitors 1 220µ.F 16VW pigtail electrolytic 1 100µ.F 16VW PC electrolytic 1 0 .15µ.F metallised polyester 2 0 . 1µF monolithic ceramic 1 .068µ.F metallised polyester 1 .039µ.F metallised polyester 1 .033µ.F metallised polyester 1 .027 µF metallised polyester 2 .022µ.F metallised polyester 1 .018µF metallised polyester 2 .01 µF metallised polyester 1 .0056µ.F metallised polyester 1 .004 7 µ.F metallised polyester 1 .0022µ.F metallised polyester Resistors (0.25W, 5%) 1 1 1 2 2 1 560k0 470k0 430k0 220k0 100k0 75k0 1 1 1 2 1 56k0 36k0 22k0 4. 7k0 2200 Where to buy the software The Radfax 2 software is only available directiy from the author, Michael Delahunty, who has kindly given us permission to use the name "Radfax Decoder" for this project. The software is priced at $35 plus $3 for postage and packing. It comes on a 5 ¼-inch 360K floppy disc and with a 1 3-page instruction manual. You need to specify whether you have a CGA, EGA or Hercules Graphics card. Write to Michael Delahunty, 42 Villiers Street, New Farm, Qld 4005 . Phone (07) 358 2785 . NOVEMBER 1989 25