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QST 9/04 Xtal Osc Phase Noise ?
There's a cosntruction article by K2AOP on page 67 for a xtal osc that
sounds appealing to me. ARRL says it couldn't measure the phase noise because its lower than their equipment. I wish they would have stated how low their eqpt goes as I was lead to believe they had some of the best. Anyone have any ideas? tnx -- 73 Hank WD5JFR |
There's a cosntruction article by K2AOP on page 67 for a xtal osc that sounds appealing to me. ARRL says it couldn't measure the phase noise because its lower than their equipment. I wish they would have stated how low their eqpt goes as I was lead to believe they had some of the best. Anyone have any ideas? tnx They can usually get down to -160, -165 dBc/Hz depending on which cheek they hold their tongue in. I now wish, they'd get me my copy here. Don't often see a construction article in the rag. Do they take the output from the crystal using it as the "final" filter? W4ZCB |
I always thought I was last on the QST delivery line. It says its a Pierce
with a gate follower buffer for output. Quite stable and constant output! It uses 2 2N5460s. I need to find a half dozen 2N5460s so I can build at least a couple to test receivers.. If someone finds a source please let me know. Also it someone builds and measures the phase noise please let us know. tnx -- 73 Hank WD5JFR "Harold E. Johnson" wrote in message news:DjxSc.288203$Oq2.69146@attbi_s52... There's a cosntruction article by K2AOP on page 67 for a xtal osc that sounds appealing to me. ARRL says it couldn't measure the phase noise because its lower than their equipment. I wish they would have stated how low their eqpt goes as I was lead to believe they had some of the best. Anyone have any ideas? tnx They can usually get down to -160, -165 dBc/Hz depending on which cheek they hold their tongue in. I now wish, they'd get me my copy here. Don't often see a construction article in the rag. Do they take the output from the crystal using it as the "final" filter? W4ZCB |
"Henry Kolesnik" wrote in message m... I always thought I was last on the QST delivery line. It says its a Pierce with a gate follower buffer for output. Quite stable and constant output! It uses 2 2N5460s. I need to find a half dozen 2N5460s so I can build at least a couple to test receivers.. If someone finds a source please let me know. Also it someone builds and measures the phase noise please let us know. tnx Mousser has them, although they seem to be a very ordinary P channel FET. W4ZCB |
Harold E. Johnson wrote:
"Henry Kolesnik" wrote in message m... I always thought I was last on the QST delivery line. It says its a Pierce with a gate follower buffer for output. Quite stable and constant output! It uses 2 2N5460s. I need to find a half dozen 2N5460s so I can build at least a couple to test receivers.. If someone finds a source please let me know. Also it someone builds and measures the phase noise please let us know. tnx Mousser has them, although they seem to be a very ordinary P channel FET. W4ZCB Would 2n5461's work. IIRC they are basicly the same fet, different IDSS maybe. |
Mousser has them, although they seem to be a very ordinary P channel FET. W4ZCB Would 2n5461's work. IIRC they are basicly the same fet, different IDSS maybe Digi has them as well, and I have some on order. Doubt there are any surprises, but hope springs eternal. Suspect that the "Tech Correspondence" dept didn't have the clout to get the attention of the lab. Will let you know in about a week. W4ZCB |
Mousser has them, although they seem to be a very ordinary P channel FET. I have built it with MPF102s (invert the circuit for correct polarities). Works as specified. I realize it will oscillate, what's the phase noise? W4ZCB |
I didn't look closely at this circuit, but the Pierce seems to have the crystal from plate to grid, or drain to gate. This seems as though it is easy to slam the crystal pretty hard (depends on the drain resistor). I'd worry about crystal dissipation as this causes drift and ageing issues. In VCOs, the more tightly you couple the tuned circuit to the device, the poorer the phase noise. We always had to get the things to just barely oscillate under worst case conditions to get the lowest phase noise. There are other ways, but memory fails... I like the good old standby common collector colpitts used in just about all Motorola channel elements & oscillators. Hard to make one which won't oscillate. -- Steve N, Agreed, and the statement about starting with ~2 volts indicates way too much feedback at 12 volts. Certainly none of the above leads one to think it's a low noise circuit, just going to build one to measure. Suspect that the "no free lunch" still applies and that to get really low noise operation you still need current limiting, AGC 'd or otherwise and tricks like feeding the output thru the crystal to clean it up. Also believe there's probably a contribution by the draftsman again and the 22 meg gate resistor is really a second 2.2 Megohm . W4ZCB |
From Google on k2aop: www2.arrl.org/qst/feedback/2004/10/Feedback1004.pdf
Feedback A couple of errors crept into the K2AOP oscillator schematic in Technical Correspondence [Figure 1, "A Simple, Well-Behaved Crystal Oscillator," Sep 2004, p 67]. R1, shown as 22 M?, should be 2.2 M?. R5, shown as 100 ?, should be 1000 ?. The variable trimmer capacitor (shown as C4) should be C3 (18 pF). C4 should be a fixed capacitor. -- 73 Hank WD5JFR "Harold E. Johnson" wrote in message news:rDaUc.25808$TI1.9855@attbi_s52... I didn't look closely at this circuit, but the Pierce seems to have the crystal from plate to grid, or drain to gate. This seems as though it is easy to slam the crystal pretty hard (depends on the drain resistor). I'd worry about crystal dissipation as this causes drift and ageing issues. In VCOs, the more tightly you couple the tuned circuit to the device, the poorer the phase noise. We always had to get the things to just barely oscillate under worst case conditions to get the lowest phase noise. There are other ways, but memory fails... I like the good old standby common collector colpitts used in just about all Motorola channel elements & oscillators. Hard to make one which won't oscillate. -- Steve N, Agreed, and the statement about starting with ~2 volts indicates way too much feedback at 12 volts. Certainly none of the above leads one to think it's a low noise circuit, just going to build one to measure. Suspect that the "no free lunch" still applies and that to get really low noise operation you still need current limiting, AGC 'd or otherwise and tricks like feeding the output thru the crystal to clean it up. Also believe there's probably a contribution by the draftsman again and the 22 meg gate resistor is really a second 2.2 Megohm . W4ZCB |
"Henry Kolesnik" wrote in message . .. From Google on k2aop: www2.arrl.org/qst/feedback/2004/10/Feedback1004.pdf Feedback A couple of errors crept into the K2AOP oscillator schematic in Technical Correspondence [Figure 1, "A Simple, Well-Behaved Crystal Oscillator," Sep 2004, p 67]. R1, shown as 22 M?, should be 2.2 M?. R5, shown as 100 ?, should be 1000 ?. The variable trimmer capacitor (shown as C4) should be C3 (18 pF). C4 should be a fixed capacitor. That draftsman has to know where every skeleton is buried within 100 miles of Newington to hold down that job. W4ZCB |
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