Electronic Tuning Device (ETD) users: While looking around for a better way to calibrate TuneLab, I have revisited the use of NIST services and it seems to me that this can be a practical means of checking the calibration of not only TuneLab but SAT and RCT as well. The services I refer to are the 500 Hz and 600 Hz standard tones available on shortwave radio and by telephone at (303)499-7111 (Colorado). Leaving aside the shortwave option, since most techs do not have access to shortwave radios, I would like to consider the use of the telephone service. The number is not toll-free, so it is wise to plan your use of this service carefully. NIST says this is a very popular number. They get over 2,000,000 calls per year. When you call this number, you will hear the WWV broadcast. If you can get your computer or the SAT to pick up the sound from the telephone receiver, then you can check calibration. Try holding the telephone right up to the microphone. Before you call, try to get the dial tone to register on your ETD just to see if the phone is loud enough. You will want to figure out how to place the phone on the ETD's microphone so that it will stay put without your hanging on to it and causing noises that will interfere with the pickup of the tones. In order to be sure of hearing a 500 Hz or 600 Hz tone when you call, check the following broadcast schedule, which is repeated every hour. When a tone is present, it is present for the first 45 seconds of the minute and is silent for the last 15 seconds. As you can see, the best time to call is between 19 and 24 minutes after the hour, or between 30 and 39 minutes after the hour. Minute Contents 0 station ID 1 600 Hz tone 2 (440 Hz tone) 3 no tone 4 no tone 5 600 Hz tone 6 500 Hz tone 7 600 Hz tone 8 storm warnings 9 storm warnings 10 storm warnings 11 600 Hz tone 12 500 Hz tone 13 600 Hz tone 14 GPS reports 15 GPS reports 16 OMEGA reports 17 600 Hz tone 18 Geoalerts 19 600 Hz tone 20 500 Hz tone 21 600 Hz tone 22 500 Hz tone 23 600 Hz tone 24 500 Hz tone 25 600 Hz tone 26 500 Hz tone 27 600 Hz tone 28 500 Hz tone 29 no tone 30 500 Hz tone 31 600 Hz tone 32 500 Hz tone 33 600 Hz tone 34 500 Hz tone 35 600 Hz tone 36 500 Hz tone 37 600 Hz tone 38 500 Hz tone 39 600 Hz tone 40 500 Hz tone 41 600 Hz tone 42 500 Hz tone 43 no tone 44 no tone 45 no tone 46 no tone 47 no tone 48 no tone 49 no tone 50 no tone 51 no tone 52 500 Hz tone 53 600 Hz tone 54 500 Hz tone 55 600 Hz tone 56 500 Hz tone 57 600 Hz tone 58 500 Hz tone 59 no tone In order to use the 500 Hz and 600 Hz tones to check your pitch calibration, select a no-stretch tuning. If your ETD uses the fundamental to tune C5 and D5, then customize the stretch for those two notes so the C5 is stretched -78.69 cents and D5 is stretched +36.95 cents. Save these customizations in a tuning file or a page in the SAT memory. These stretches will make C5 exactly 500 Hz and D5 exactly 600 Hz. If you want to use the standard SAT partials, then use C3 and D3 instead. The SAT uses the 4th partial to tune these notes and so you will again get 500 Hz and 600 Hz if you use the stretch numbers shown above. Once you have the ETD all set up to look for 500 Hz and 600 Hz on C and D, then call the Colorado number at a time when you can be sure of hearing the desired tones. You will only have three minutes maximum because they automatically disconnect you after three minutes. With the tone sounding in the microphone of the ETD, select either the C or D depending on which tone is playing. Having the stretch numbers preset in memory makes it easy to switch between 500 Hz and 600 Hz quickly. Once you determine which tone is playing, note the rotation of the lights in the SAT or the spinner in the RCT or the movement of the squares in TuneLab. Any movement in these displays indicates the error in calibration. If you can adjust the offset to make the display stand still, then that offset tells you exactly how far off your ETD is. When checking the SAT, you will be limited to one decimal place in setting the stretch. How much will that affect the results? Well, if you set D5 (or the 4th partial of D3) to a stretch of +36.9 instead of +36.95, that difference of .05 cents will mean that a perfectly calibrated SAT listening to a perfect 600 Hz ought to indicate sharp by .017 beats per second, which means the lights in the SAT ought to rotate one light clockwise in 14 seconds. This is barely recognizeable in the 45 seconds during which you can observe the 600 Hz tone. And what about the C5 offset by -78.7 cents instead of -78.69 cents? This error of .01 cents when listening to 500 Hz means the SAT should indicate sharp by .0029 beats per second, which means the lights ought to rotate one light clockwise in 86 seconds - definitely not detectable during the 45 seconds of 500 Hz tone. When checking the RCT, I'm not sure whether you can actually refine your calibration or just check it with this method, since Dean supplies a calibrated 440 Hz source to perform the initial calibration. When checking TuneLab you can trim the offset until the phase display is absolutely stopped and then enter 500 or 600 in the New Calibration menu. Then you can say that your calibration is traceable to NIST, the most precise reference that there is. And if you do have a shortwave radio, try picking up WWV on 2.5, 5, 10, 15, or 20 MHz and save yourself the phone call. However, I have had great difficultly getting a reliable signal during the day in Michigan. It works better at night. -Rober Scott Ypsilanti, Michigan
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