Re: [time-nuts] 74AC gates phase noise
Bruce Griffiths wrote: Only if the noise figure of the following amplifier is 4dB or so. With no extra amplification is used one only needs a signal level of +1dBm to achieve a phase noise floor of -178dBc/Hz if the output is extracted through the crystal in such a way that the thermal noise of the load dominates. Read US Patent 4283691, which explains how the 10811 works. The situation is far more complicated than the simple analysis above. If you play your cards right, you can get much better phase noise than what you have indicated. The thermal noise of the load does not enter into it. Unfortunately, the very low noise first stage in the 10811 is degraded by the emitter follower after it. As I previously stated, you can bypass these additional stages if you want a lower phase noise floor. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 74AC gates phase noise
Richard (Rick) Karlquist wrote: Bruce Griffiths wrote: Only if the noise figure of the following amplifier is 4dB or so. With no extra amplification is used one only needs a signal level of +1dBm to achieve a phase noise floor of -178dBc/Hz if the output is extracted through the crystal in such a way that the thermal noise of the load dominates. Read US Patent 4283691, which explains how the 10811 works. The situation is far more complicated than the simple analysis above. If you play your cards right, you can get much better phase noise than what you have indicated. The thermal noise of the load does not enter into it. Unfortunately, the very low noise first stage in the 10811 is degraded by the emitter follower after it. As I previously stated, you can bypass these additional stages if you want a lower phase noise floor. Rick Karlquist N6RK Eventually the buffer chain usually has to drive a resistive load such as a cable terminated in its characteristic impedance. Even with a noiseless source, the thermal noise of the load will affect the apparent phase noise floor (unless the source impedance is much lower than the load impedance). Neither the 10811A nor a set of cascaded common base buffers have near zero output impedance. Of course one can correct for this but in a real world application the thermal noise of the load is always present. I should have said that the signal level in the load (not the crystal dissipation or the input signal level at the input to the first common base buffer as Ulrich Rohde would have us believe) needs to be at least +1dBm when a high output impedance (eg a transistor collector) OCXO output is driving a resistive load. When a resistor is used to match the output impedance of the output stage to the 50 ohm load then the thermal noise is that of a 25 ohm load and the required signal level at the load for a -178dBc system noise floor due load thermal noise alone is -2dBm. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 74AC gates phase noise
Martyn Smith wrote: Garry, Are you also saying your 100 MHz OXCO is making -178 dBc/Hz? Unless your 100 MHz OXCO is some special $10k type, there's no way your OXCO has a -178 dBc/Hz floor noise? Regards Martyn Can you explain this further? It isn't clear to me that there is any fundamental reason why this noise floor is not possible, especially if other specs (like aging) can be relaxed. Also, the noise floor tends to be limited by issues having to do with physics, not economics. How would having $10,000 to spend get around the physics issues? I think I could approach this noise floor by taking a 10811 and bringing the signal directly out of the grounded base buffer, and then readjusting the ALC to double or triple the crystal current. The biggest unknown is at what point the crystal sustains damage. The 10811 is definitely not optimized for phase noise floor. The designers were well aware of this. But phase noise floor isn't everything. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 74AC gates phase noise
-178 is about the same broadband floor that you see from the higher-end Wenzel ULN parts. These can be custom-ordered in the $2000-$2500 range in single quantities. Pascall's product line seems relatively similar. Obviously the carrier needs to be over +4 dBm to get to -178 dBc/Hz at 25C, but it can certainly be done. :) What you get for $10,000 and up are the BVAs and similar ultrastable OCXOs. These have unremarkable phase noise but ungodly stability, around 10x better than the best 10811s and E1938As. The most economical way to get into the -170 dBc/Hz range with commercial oscillators seems to be the Valpey-Fisher parts. These are in the $100 neighborhood. -- john, KE5FX -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Rick Karlquist Sent: Thursday, February 25, 2010 1:34 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 74AC gates phase noise Martyn Smith wrote: Garry, Are you also saying your 100 MHz OXCO is making -178 dBc/Hz? Unless your 100 MHz OXCO is some special $10k type, there's no way your OXCO has a -178 dBc/Hz floor noise? Regards Martyn Can you explain this further? It isn't clear to me that there is any fundamental reason why this noise floor is not possible, especially if other specs (like aging) can be relaxed. Also, the noise floor tends to be limited by issues having to do with physics, not economics. How would having $10,000 to spend get around the physics issues? I think I could approach this noise floor by taking a 10811 and bringing the signal directly out of the grounded base buffer, and then readjusting the ALC to double or triple the crystal current. The biggest unknown is at what point the crystal sustains damage. The 10811 is definitely not optimized for phase noise floor. The designers were well aware of this. But phase noise floor isn't everything. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 74AC gates phase noise
John Miles wrote: -178 is about the same broadband floor that you see from the higher-end Wenzel ULN parts. These can be custom-ordered in the $2000-$2500 range in single quantities. Pascall's product line seems relatively similar. Obviously the carrier needs to be over +4 dBm to get to -178 dBc/Hz at 25C, but it can certainly be done. :) Only if the noise figure of the following amplifier is 4dB or so. With no extra amplification is used one only needs a signal level of +1dBm to achieve a phase noise floor of -178dBc/Hz if the output is extracted through the crystal in such a way that the thermal noise of the load dominates. Half of the -174dBm/Hz (at 300K) thermal noise contributes to the phase noise the other half contributes to amplitude noise. Thus the contribution of the load thermal noise to the phase noise floor ( dBc/Hz) is -177 + Pout (dBM). What you get for $10,000 and up are the BVAs and similar ultrastable OCXOs. These have unremarkable phase noise but ungodly stability, around 10x better than the best 10811s and E1938As. The most economical way to get into the -170 dBc/Hz range with commercial oscillators seems to be the Valpey-Fisher parts. These are in the $100 neighborhood. -- john, KE5FX Bruce -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Rick Karlquist Sent: Thursday, February 25, 2010 1:34 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 74AC gates phase noise Martyn Smith wrote: Garry, Are you also saying your 100 MHz OXCO is making -178 dBc/Hz? Unless your 100 MHz OXCO is some special $10k type, there's no way your OXCO has a -178 dBc/Hz floor noise? Regards Martyn Can you explain this further? It isn't clear to me that there is any fundamental reason why this noise floor is not possible, especially if other specs (like aging) can be relaxed. Also, the noise floor tends to be limited by issues having to do with physics, not economics. How would having $10,000 to spend get around the physics issues? I think I could approach this noise floor by taking a 10811 and bringing the signal directly out of the grounded base buffer, and then readjusting the ALC to double or triple the crystal current. The biggest unknown is at what point the crystal sustains damage. The 10811 is definitely not optimized for phase noise floor. The designers were well aware of this. But phase noise floor isn't everything. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 74AC gates phase noise
Rick Karlquist wrote: I think I could approach this noise floor by taking a 10811 and bringing the signal directly out of the grounded base buffer, and then readjusting the ALC to double or triple the crystal current. The biggest unknown is at what point the crystal sustains damage. The 10811 is definitely not optimized for phase noise floor. The designers were well aware of this. But phase noise floor isn't everything. And, if a crystal is rejected for phase noise at 10 or 100 Hz, that does not mean that it could not be used as a post filter for offsets 1KHz. It even could be somewhat damped so that its own phase noise does not kill the close-in phase noise performance. And we could hit it with more power. If it runs away by 100 Hz, so what? All we would expect from a second crystal is another 10 dB far-off. And I think there are a lot of leftover crystals; the really good ones, close-in, are few. Did I forget a show stopper b4 I try it? 73s, Gerhard P.S. Magnus, I havn't forgotten about you. I don't think that my locking scheme will work for your beacon application, but the VCXO might. Maybe I'll have to give up that no microcontroller, no FPGA, no CPLD, just programming resistors hybris. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
