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#1
June 17th 04, 12:41 AM
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Need a low noise VXO for narrow sweep
Hi
need a low-noise xtal oscillator using 14.7 or 15.7MHz rubber xtals in series mode circuit to sweep xtal filters with good as possible noise distance. The available xtals are believed to pull +/-10kHz or more. Any suggestions. 73 Jan-Martin, LA8AK http://home.online.no/~la8ak/c.htm --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
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#2
June 17th 04, 03:37 AM
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In article ,
says... Hi need a low-noise xtal oscillator using 14.7 or 15.7MHz rubber xtals in series mode circuit to sweep xtal filters with good as possible noise distance. The available xtals are believed to pull +/-10kHz or more. Any suggestions. Use a DDS hooked up to your PC's parallel port? -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
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#3
June 17th 04, 06:20 AM
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John Miles wrote:
In article , says... Hi need a low-noise xtal oscillator using 14.7 or 15.7MHz rubber xtals in series mode circuit to sweep xtal filters with good as possible noise distance. The available xtals are believed to pull +/-10kHz or more. Any suggestions. Use a DDS hooked up to your PC's parallel port? -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ A DDS isn't going to have good enough phase noise. The OP is correct in using a pullable crystal oscillator. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
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#4
June 17th 04, 05:08 PM
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In article ,
says... A DDS isn't going to have good enough phase noise. The OP is correct in using a pullable crystal oscillator. Eh? He wants to sweep a filter. You don't particularly care about phase noise when you do that. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
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#5
June 17th 04, 07:03 PM
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John Miles wrote:
In article , says... A DDS isn't going to have good enough phase noise. The OP is correct in using a pullable crystal oscillator. Eh? He wants to sweep a filter. You don't particularly care about phase noise when you do that. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ That depends on your filter. If you're trying to design a high pole count filter with really steep skirts and you want to verify it's final rejection then yes, you need a low phase noise oscillator. This is probably why he has "low noise" in his title. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
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#6
June 17th 04, 08:33 PM
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On Thu, 17 Jun 2004 11:03:44 -0700, Tim Wescott
wrote: ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ That depends on your filter. If you're trying to design a high pole count filter with really steep skirts and you want to verify it's final rejection then yes, you need a low phase noise oscillator. This is probably why he has "low noise" in his title. can't really see I've got any replies in the wanted direction; If I wish to measure a receivers ultimate performance I am not interested in seing something like 60dB selectivity when I am expecting 90dB or more. Had a discussion with LA8OJ, and he suggested that 6MHz ceramic resonator might be easier to use than a 15.7MHz xtal, 100kHz tuning range could be achieved instead of 20kHz. But I suppose it was a trick to limit the amplitude to improve phase noise of an xtal oscillator 73 Jan-Martin, LA8AK http://home.online.no/~la8ak/c.htm --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
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#8
June 17th 04, 10:49 PM
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In article , Tim Wescott
writes: John Miles wrote: In article , says... A DDS isn't going to have good enough phase noise. The OP is correct in using a pullable crystal oscillator. Eh? He wants to sweep a filter. You don't particularly care about phase noise when you do that. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ That depends on your filter. If you're trying to design a high pole count filter with really steep skirts and you want to verify it's final rejection then yes, you need a low phase noise oscillator. This is probably why he has "low noise" in his title. The "need" for low-noise RF sources was prompted by the electronics industry going hot and heavy on cellular telephony which uses partly phase demodulation and clock recovery circuits in digital electronics. Because of those particular markets, "low noise" has become a Big Buzzword. Whether you have one pole or twelve or whatever, you will NOT need a specific "low noise oscillator!" The very ordinary sweep oscillators of ten, twenty, or thirty years ago are quite fine. retired (from regular hours) electronic engineer person |
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#9
June 17th 04, 08:33 PM
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On Thu, 17 Jun 2004 11:03:44 -0700, Tim Wescott
wrote: ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ That depends on your filter. If you're trying to design a high pole count filter with really steep skirts and you want to verify it's final rejection then yes, you need a low phase noise oscillator. This is probably why he has "low noise" in his title. can't really see I've got any replies in the wanted direction; If I wish to measure a receivers ultimate performance I am not interested in seing something like 60dB selectivity when I am expecting 90dB or more. Had a discussion with LA8OJ, and he suggested that 6MHz ceramic resonator might be easier to use than a 15.7MHz xtal, 100kHz tuning range could be achieved instead of 20kHz. But I suppose it was a trick to limit the amplitude to improve phase noise of an xtal oscillator 73 Jan-Martin, LA8AK http://home.online.no/~la8ak/c.htm --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
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#10
June 17th 04, 10:29 PM
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In article ,
says... That depends on your filter. If you're trying to design a high pole count filter with really steep skirts and you want to verify it's final rejection then yes, you need a low phase noise oscillator. This is probably why he has "low noise" in his title. Perhaps, but if you want to verify final rejection, you want much wider tuning range than you're going to get from a pulled crystal. A 100 Hz- wide filter might be -100 dB down at 5 kHz but -50 dB down at 50 kHz, and if you care about that, you need to be able to look farther away from the carrier. His desire for a narrow-range source made me think he was more interested in shape-factor and ripple alignment than ultimate rejection. Maybe he can use two different oscillators to get the best of both worlds. A high-quality LC oscillator is actually pretty darned quiet at large offsets from the carrier. I think it was Tom Bruhns, or one of the other HP guys at least, who once pointed out that the old HP 608- series boatanchors were quieter at 100 kHz offsets than the flashy, high-dollar synthesizers that followed them. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
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