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#1
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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#2
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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#3
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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#4
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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#5
June 17th 04, 06:23 AM
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J M Noeding wrote:
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 This is a fairly standard circuit -- why not just look in an ARRL manual or one of the many QRP transmitter designs for an oscillator? You can check for phase noise by mixing it with a good (fixed) crystal oscillator, or you can just trust it. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
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#6
June 17th 04, 01:52 PM
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On Wed, 16 Jun 2004 22:23:01 -0700, Tim Wescott
wrote: 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. This is a fairly standard circuit -- why not just look in an ARRL manual or one of the many QRP transmitter designs for an oscillator? You can check for phase noise by mixing it with a good (fixed) crystal oscillator, or you can just trust it. many of those amateur constructions are not very good, just put together, and if they generate a sort of signal the constructors are happy without worrying what they sound like. Some of the constructor have of course well reputation, but ARRL handbook usually don't tell who have designed it. and in this case I want a definite low noise construction. Remember when I built my first of many VHF/UHF beacons made after an amateur concept I listened to the carrier with R-4C and converter, the sound was awful, so I decided to built a new 12MHz xtal oscillator using some practice described by Ulrich Rohde, DJ2LR. The improvement on 144MHz was increadible, and I later learned that the sound was very good compared with all sorts of rubbish somebody else used, even on 2320MHz Jan-Martin, LA8AK --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
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#7
June 17th 04, 05:03 PM
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J M Noeding wrote:
On Wed, 16 Jun 2004 22:23:01 -0700, Tim Wescott wrote: 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. This is a fairly standard circuit -- why not just look in an ARRL manual or one of the many QRP transmitter designs for an oscillator? You can check for phase noise by mixing it with a good (fixed) crystal oscillator, or you can just trust it. many of those amateur constructions are not very good, just put together, and if they generate a sort of signal the constructors are happy without worrying what they sound like. Some of the constructor have of course well reputation, but ARRL handbook usually don't tell who have designed it. and in this case I want a definite low noise construction. Remember when I built my first of many VHF/UHF beacons made after an amateur concept I listened to the carrier with R-4C and converter, the sound was awful, so I decided to built a new 12MHz xtal oscillator using some practice described by Ulrich Rohde, DJ2LR. The improvement on 144MHz was increadible, and I later learned that the sound was very good compared with all sorts of rubbish somebody else used, even on 2320MHz Jan-Martin, LA8AK --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm Well, that's why I suggested verifying it's phase noise with a good fixed crystal oscillator. I certainly wouldn't proceed without doing this check -- the nice thing is that unless the oscillators lock together too tightly you get an upper bound to your phase noise, so you know when you're doing well enough. "Solid State Design for the Radio Amateur" has some good (older) circuits. It's been superseded by "Experimental Radio Design" which should also have some good ones. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
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#8
June 17th 04, 05:03 PM
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J M Noeding wrote:
On Wed, 16 Jun 2004 22:23:01 -0700, Tim Wescott wrote: 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. This is a fairly standard circuit -- why not just look in an ARRL manual or one of the many QRP transmitter designs for an oscillator? You can check for phase noise by mixing it with a good (fixed) crystal oscillator, or you can just trust it. many of those amateur constructions are not very good, just put together, and if they generate a sort of signal the constructors are happy without worrying what they sound like. Some of the constructor have of course well reputation, but ARRL handbook usually don't tell who have designed it. and in this case I want a definite low noise construction. Remember when I built my first of many VHF/UHF beacons made after an amateur concept I listened to the carrier with R-4C and converter, the sound was awful, so I decided to built a new 12MHz xtal oscillator using some practice described by Ulrich Rohde, DJ2LR. The improvement on 144MHz was increadible, and I later learned that the sound was very good compared with all sorts of rubbish somebody else used, even on 2320MHz Jan-Martin, LA8AK --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm Well, that's why I suggested verifying it's phase noise with a good fixed crystal oscillator. I certainly wouldn't proceed without doing this check -- the nice thing is that unless the oscillators lock together too tightly you get an upper bound to your phase noise, so you know when you're doing well enough. "Solid State Design for the Radio Amateur" has some good (older) circuits. It's been superseded by "Experimental Radio Design" which should also have some good ones. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
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#9
June 17th 04, 01:52 PM
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On Wed, 16 Jun 2004 22:23:01 -0700, Tim Wescott
wrote: 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. This is a fairly standard circuit -- why not just look in an ARRL manual or one of the many QRP transmitter designs for an oscillator? You can check for phase noise by mixing it with a good (fixed) crystal oscillator, or you can just trust it. many of those amateur constructions are not very good, just put together, and if they generate a sort of signal the constructors are happy without worrying what they sound like. Some of the constructor have of course well reputation, but ARRL handbook usually don't tell who have designed it. and in this case I want a definite low noise construction. Remember when I built my first of many VHF/UHF beacons made after an amateur concept I listened to the carrier with R-4C and converter, the sound was awful, so I decided to built a new 12MHz xtal oscillator using some practice described by Ulrich Rohde, DJ2LR. The improvement on 144MHz was increadible, and I later learned that the sound was very good compared with all sorts of rubbish somebody else used, even on 2320MHz Jan-Martin, LA8AK --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
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#10
June 17th 04, 12:35 PM
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Why do you need such such good phase noise?
An average oscillator will be good enough to measure to -70 dBc or so. You could use a DDS with a crystal clock - this will have good close in phase noise (neasrly as good as the clock), though coherent spurs might be a problem. Richard J M Noeding wrote: 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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