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.On the whole USsuppliers seem better than those in the UK or Japan-- products areadvertised in the US magazines QST and 73.Setting Up Particular attention should be paid to linking all theequipment together; there are special problems about using sensitiveradio receiving equipment in close proximity to computers and VDUs.Computer logic blocks, power supplies and the synchronising pulses onVDUs are all excellent sources of radio interference (rfi).RFIappears not only as individual signals at specific points on theradio dial, but also as a generalised hash which can blank out allbut the strongest signals.Interference can escape from poorly packaged hardware, but alsofrom unshielded cables which act as aerials.The remedy is simple todescribe: encase and shield everything, connecting all shields to agood earth, preferably one separate from the mains earth.Inpractice, much attention must be paid to the detail of theinterconnections and the relative placing of items of equipment.Inparticular, the radio's aerial should use coaxial feeder with aproperly earthed outer braid, so that the actual wires that pluck thesignals from the ether are well clear of computer-created rfi.It isalways a good idea to provide a communications receiver with a properearth, though it will work without one: if used with a computer, itis essential.Do not let these paragraphs put you off; with care excellentresults can be obtained.And bear in mind my own first experience:ever eager to try out same new kit, I banged everything together withgreat speed--ribbon cable, poor solder joints, an antenna tapedfile:///E|/Books/Hackers Handbook.htm (97 of 133) [11/28/2000 5:58:50 AM] Hacker's Handbookquickly to a window in a metal frame less than two meters from thecommunications receiver--and all I could hear from 500 kHz to 30MHz, wherever I tuned, was a great howl-whine of protest.Where to listenScanning through the bands on a good communications receiver, yourealise just how crowded the radio spectrum is.The table in AppendixVI gives you an outline of the sandwich-like fashion in which thebands are organised.The 'fixed' bands are the ones of interest; more particularly, thefollowing ones are where you could expect to locate news agencytransmissions (in kHz):** Page 1033155 -- 3400 14350 -- 149903500 -- 3900 15600 -- 163603950 -- 4063 17410 -- 175504438 -- 4650 18030 -- 180684750 -- 4995 18168 -- 187805005 -- 5480 18900 -- 196805730 -- 5950 19800 -- 199906765 -- 7000 20010 -- 210007300 -- 8195 21850 -- 218709040 -- 9500 22855 -- 23200ggoo -- 9995 23350 -- 2489010100 -- 11175 25010 -- 2507011400 -- 11650 25210 -- 2555012050 -- 12330 26175 -- 2800013360 -- 13600 29700 -- 3000513800 -- 14000In addition, amateurs tend to congregate around certain spots on thefrequency map: 3590, 14090, 21090, 28090, and at VHF/UHF: 144.600,145.300, MHz 432.600, 433.300.Tuning InRadio Teletype signals have a characteristic two-tone warble soundwhich you will hear properly only if your receiver is operating inSSB (single-side-band) mode.There are other digital tone-basedsignals to be heard: FAX (facsimile), Helschcrieber (which uses atechnique similar to dot-matrix printers and is used for Chinese andrelated pictogram-style alphabets), SSTV (slow scan television, whichcan take up to 8 seconds to send a low-definition picture), andothers.But with practice, the particular sound of RTTY can easily berecognised.More experienced listeners can also identify shifts andspeeds by ear.file:///E|/Books/Hackers Handbook.htm (98 of 133) [11/28/2000 5:58:50 AM] Hacker's HandbookYou should tune into the signal watching the indicators on yourterminal unit to see that the tones are being properly captured--typically, this involves getting two LEDs to flicker simultaneously.The software will now try to decode the signal, and it will be upto you to set the speed and 'sense'.The first speed to try is 66/7words per minute, which corresponds to 50 baud, as this is the mostcommon.On the amateur bands, the usual speed is 60 words per minute(45 baud); thereafter, if the rate sounds unusually fast, you try 100words per minute (approximately 75 baud).** Page 104By 'sense' or 'phase' is meant whether the higher tone correspondsto logical 1 or logical 0
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