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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 |
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 |
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 |
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 ------------------------------------------------------ |
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 ------------------------------------------------------ |
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 |
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 |
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 |
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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