lrj@UUNET.UU.NET> (02/01/90)
In article <35299@mips.mips.COM> crisp@mips.COM (Richard Crisp) writes: >In article <15809@haddock.ima.isc.com> trb@haddock.ima.isc.com (Andrew Tannenbaum) writes: >>My tools: >>a Sony 2010 receiver >>Passport to World Band Radio >>World Radio and TV Handbook >> >>(All three in concert are important). >> >>Passport is important because its primary section has schedules sorted >>by frequency. WRTH is important because its primary section has >>stations sorted by country. The 2010 is important because it has >>pushbutton digital tuning. Actually, you can get by without Passport by using the frequency list at the back of the WRTH, and checking against the schedule section. (A lot of listings for frequency can be ruled out without looking at the schedule, based on propagation, program content, etc.) So if you get stuck with only one book, make sure it's a WRTH :-). In addition, a radio with two or more VFO's (i.e., frequency memories) can also be used, even if there are no push buttons. The ICOM R-70 is an example. It uses a dial to tune, and displays its frequency digitally. It can remember two frequencies, with whichever is selected being the one controlled by the dial. Once the two frequencies are entered, they can be switched by the push of a single button. >>Oh, I almost forgot to mention, whether you like the sound provided by >>2010's sync tuning or not (it sometimes whistles), it's great for >>helping you find the center of a frequency - since the 2010's display >>seems accurate to 100 Hz, this is also convenient for DX ID's. >> > Ditto again, short of having an oscilloscope for tuning, I've found >the synch tuning lights really helpful for finding the center of the >tuning of the station (AM) that I'm listening to. I will say that >for SSB and FAX/RTTY this technique doesn't seem to be the best. The standard technique for tuning exactly onto an AM stations carrier is to "zero-beat" it with the receivers BFO (if it has one). In practice, you select an SSB setting, and tune the AM signal. You should get a pure, steady, load whistle that varies as you tune around the signal. You tune until the pitch becomes too low to hear. If the filters in your receiver are good, it may be hard to hear the tone as it gets lower. In either case, the point where the tone is lowest is also the point where the AM audio is undistorted: this is what you are aiming for. Now you can read off the frequency of the station. If you use this technique on stations of known accurate frequency (WWV, CHU, and most big international broadcasters), you can find out how much to add or subtract from your reading to get the true frequency. This is sometimes useful to find stations that are slightly off frequency, since they tend to be small, and hence more interesting, to listen to (e.g., Tahiti on ~15070.6 kHz). P.S. For those who don't have a 2010: if you tune a weak AM station in SSB mode, and adjust as described to eliminate the audio distortion, don't be surprised if the signal sound better than in standard AM mode, particularly if you select the sideband (LSB or USB) with less interference. This is also a standard technique, and works best for receivers that can tune in small steps (<=10 Hz, or with RIT). For those with a 2010, this is exactly what sync does for you automatically. The whistle that you sometimes hear is the same as the whistle described above. P.P.S. The whistle produced by an AM carrier received in SSB mode can be used to gage the presense and relative strength of a carrier. For example, if you tune across the medium-wave broadcast band at night, listening for each whistle, you can tell which frequencies have stations. This makes it easy to find stations that are not on the standard frequencies (e.g., every 10 kHz in the U.S. and Canada), though only the strongest may be audible on a particularly night. BTW, this will also spot all the internally generated spurious signals in a receiver, so try disconnecting the antenna before spending all night trying to ID a "birdie." 73, Larry, WB1FOF -- Larry Johnson INTERNET: lrj@fibercom.com FiberCom, Inc. UUCP: uunet!fibercom!lrj P.O. Box 11966 PHONE: +1 703-342-6700, 800-423-1183, X317 Roanoke, VA 24022-1966 FAX: +1 703-342-5961