Re: [Flexradio] Frequency calibration, measurement of unknowns with SDR1000Re: Question regarding commercial AM broadcasters' carrieraccuracy
Mike, Thanks! I figured there must be at least one station engineer on the list! Mark -Original Message- From: Mike Naruta [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 07, 2006 1:42 PM To: Jim Lux Cc: Eric Wachsmann; 'Mark Amos'; flexradio@flex-radio.biz Subject: Re: [Flexradio] Frequency calibration, measurement of unknowns with SDR1000Re: Question regarding commercial AM broadcasters' carrieraccuracy When I was chiefing, I think the AM tolerance was 20 Hertz. To tweak it, I would have to shut down a transmitter, open the door, and adjust the trimmer. They did not like me taking the station down, or switching to the auxiliary transmitter, so I just checked frequency occasionally. We also had quarterly, third party measurements, just to be sure that we complied. Let's see, 20 Hertz off at 1000 KHz is 200 Hertz off at 10 MHz. You're better off using WWV. They're fastidious about frequency. Mike - AA8K Jim Lux wrote: At 01:30 PM 11/6/2006, Eric Wachsmann wrote: For AM broadcast stations, something like a 10 MHz oscillator divided down to make a 25 kHz marker generator might work well. You'd be able to capture the BC station of interest, as well as more than one marker, in the same recording bandwidth. ___ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
[Flexradio] Frequency calibration, measurement of unknowns with SDR1000Re: Question regarding commercial AM broadcasters' carrieraccuracy
At 01:30 PM 11/6/2006, Eric Wachsmann wrote: That procedure makes more sense to me. It is probably going to come down to what tools you are using to make the final measurement. Our display is only accurate to 11Hz per bin at best (more likely more Hz / pixel on the display). Single point cals may not be adequate since there's two factors that affect the scale position of a signal on the display: the sample rate of the sound card and the DDS frequency. The preferred approach would be to feed in two signals separated by, say, 5-6 kHz, all derived from some reference. For instance, if you had a calibrator at 15 MHz, and modulated that with a sine (or square wave) at 3 kHz, where the 3 kHz is from dividing the 15 MHz down by 5000 (obviously, a divisor like 4096 might be more convenient), you'd get a set of well controlled sidebands. Then, by measuring the spacing of the sidebands you can calibrate the sample rate of the sound card, and by measuring the displacement of the center frequency you can calibrate the DDS reference oscillator. For AM broadcast stations, something like a 10 MHz oscillator divided down to make a 25 kHz marker generator might work well. You'd be able to capture the BC station of interest, as well as more than one marker, in the same recording bandwidth. James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875 ___ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
