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z PADDLE OR COMPUTER IN CCW KEVER PULSE PHASE TRANSMITTER PULSE LENGTH REFERENCE FREQUENCY MASTER FREQUENCY STANDARD CCW FILTER RECEIVER REFERENCE FREQUENCY MASTER FREQUENCY STANDARD PULSE PHASE AUDIO OUT PULSE LENGTH FILTER DRIVER Fig.2: the basic CCW system. The receiving and transmitting stations are synchronised by signals received from a time and frequency station (eg, WWVB in the USA or VNG in Australia). Normally, CW dots, dashes and spaces begin at random times depending upon the operator, and thus the frame length varies to an unpredictable degree. By sending CCW so that all dots, dashes and spaces are multiples of the basic time unit, the signal will be received within predictable time frames. Now although this may sound difficult, users report that this technique is usually mastered within a short time. Naturally, the use of a keyer or computer to generate characters makes the job even easier. Fig.2 shows the basic CCW system. In order for CCW stations to communicate, it is necessary for both stations to agree in advance on the operating frequency and the frame length (normally 0.1 second) for an operating speed of 12 words per minute. Since a dot and a space each require 0.1 seconds, a string of dots at 12 WPM is a square wave having a basic frequency of 5Hz. To establish communications, a CCW station sends a sequence of dots , allowing the receiving station to acquire the signal and synchronise the IF " filter" . Once locked, the filter should remain stable for hours. There is great deal more to CCW than this short article indicates but it is clear that the technique shows a lot of potential for amateur experimentation, particularly for long distance transmissions and EME (Earth-Moon-Earth) work. Further reading on CCW (1). "Coherent CW" ; QST magazine, May & June 1981. (2). "What Is Coherent CW? "; Japanese Ham Radio Journal , January 1976. (3). "Coherent CW : Amateur Radio's New State of the Art" ; QST magazine, September 1975 (Ray Petit). (4). "Universal Frequency Standard"; Ham Radio magazine , February 1974. (5). The 1989 ARRL Handbook for Radio Amateurs (page 21-16). Sangean ATS-803A shortwave receiver There are a number of receivers available to the shortwave listener today but most are useless if you want to listen to CW or SSB transmissions on the HF bands. This receiver offers continuous coverage from 150kHz to 30MHz and as a bonus will pick up the FM broadcast band. The ATS803A is made in Taiwan and looks similar to the Sony ICF-2001 (which is now superseded) but with a number of refinements including FM stereo reception via headphones, variable RF gain control, a tuning knob and a much larger battery compartment. The cabinet is well finished in black plastic, with gold trim on the tuning knob and brushed aluminium around the LCD readout. The LCD readout has 12mm digits and is very easy to read. Below the readout is a list of the frequency ranges for the various shortwave bands. Below that again is the control panel which has 22 buttons. Five of these select the band: FM (88 to 108MHz), AM, LW (beginning at 150kHz), MW (beginning at 520kHz) and SW (beginning at 2300kHz). Tuning can be done in several ways: (1) you can punch the station frequency in directly via the pushbuttons and then hit the "execute" button; (2) you can use the Start/Stop buttons for scanning upwards from .any frequency; (3) you can use the up/down buttons or the tuning knob for manual tuning; or (4) you can call up one of 14 stored station frequencies. RF gain control For dedicated HF enthusiasts, the unit has an adjustable RF gain control, which allows the user to adjust the receiver sensitivity in cases where signal overload is a problem. The provision of a BFO (beat frequency oscillator) allows reception of single sideband (SSB) and CW signals. This feature is of particular importance for those interested in amateur, aircraft or marine HF transmissions. There is also provision for the connection of a number of accessories, including external antenna, external DC supply (9V at up to 400mA), headphones (stereo for stereo FM reception, mono for JU NE 1989 67 AMATEUR RADIO - CTD The Sangean ATS-803A receiver features fully synthesised digital tuning and provides continuous coverage from 150kHz to 30MHz in both AM and SSB modes. As a bonus, it will also pick up the FM broadcast band. shortwave reception), and a high impedance output for connection to a tape recorder. Other features include a built in digital clock with alarm (which allows the receiver to be turned on at a particular time), and a sleep timer, which turns the receiver off after a period settable between 10 and 90 minutes. The battery compartment takes 6 D-size cells and 2 AA cells for backing up the computer, so that station settings can be stored. The latter two cells are not essential to the radio's operation, which is handy if you use mains power most of the time. What we found Using the telescopic antenna on the unit, we had no problem in receiving the long wave weather beacons at Sydney, Richmond and Camden airports. These weather beacons are particularly useful for providing accurate weather information. Using the scan-UP control we scanned through the AM broadcast band to the 2MHz marine band, where most broadcasts are USB. Specifications Receiver type: dual conversion superheterodyne (LW, MW, and SW). Intermediate frequencies: AM, 55.845MHz and 450kHz; FM , 10.7MHz. IF suppression: AM, 50dB; FM, 60dB. Shortwave bands Shortwave 1: 2.30-2.50MHz Shortwave 2: 3 .20-3.40MHz Shortwave 3:. 3.90-4.00MHz Shortwave 4: 4 .75-5.06MHz Shortwave 5: 5.80-6 .20MHz 68 SILICON CHIP Shortwave 6: 7. 1 0- 7. 50M Hz Shortwave 7: 9.50-9 .90MHz Shortwave 8: 11 .65-12.05MHz Shortwave 9: 15.10-15.60MHz Shortwave 10: 17.55-17.90MHz Shortwave 11: 21 .45-21 .85MHz Shortwave 12: 25 .60-26.10MHz Note: these SW bands are selectable in sequence by repeatedly pressing the SW button. Long wave band: 1 S0kHz-281 kHz . FM band: 87.5MHz-108MHz. AM band: 150kHz-29,999kHz continuous (SSB reception using BFO) . The BFO allowed good reception of Sydney Radio on 2182kHz. Working up through the HF bands we covered shortwave 1 and 2, then the 80-metre amateur band, using the BFO for SSB and CW reception. At 5.0MHz we were able to monitor the revamped, privately operated VNG time signal, although at greatly reduced signal level compared with the original Lyndhurst site. 6677kHz provided interesting listening as many international airports broadcast current meterological conditions on this frequency. The 40, 20 and 10-metre amateur bands are also covered, although we did not hear any 10-metre activity. Towards the upper end of the receiver coverage we noticed a lack of signals, although this seemed to be due to inactivity rather than a problem with the receiver as we were able to hear an increase in background noise when we connected an external long wire antenna. FM reception was good, which is to be expected in any capital city where signal levels are high, and stereo separation was quite respectable (quoted specification is 25dB). Incidentally, stereo FM is only available via the headphones with the sound being heard in mono via the loudspeaker. Sound quality is acceptable for a communications receiver and the tone controls can give an improvement in intelligibility in difficult reception conditions. In summary, this receiver is keenly priced, a good performer, and offers features that should suit the enthusiast and dedicated shortwave listener alike. Recommended retail price is $299.00. In addition to the instruction manual, a 60-page service manual is available which contains all circuit diagrams, voltage charts, parts lists, PCB foil patterns, alignment procedures and troubleshooting flow charts. This we consider a vital factor for users not located in capital cities or close to service facilities. Our review unit was supplied by the Australian distributors, Access Communications Pty Ltd, 33 Alleyne Road, Chatswood, NSW 2067. Phone (02} 406 5311. ~