Re: [time-nuts] Best GPSDO
On 9/28/12 8:31 PM, Chris Albertson wrote: On Fri, Sep 28, 2012 at 5:29 PM, Bob Camp li...@rtty.us wrote: HI Sort of an open ended question, but there is a fairly simple couple answers: SInce it's close in phase noise and not far removed, things like PLL's are going to transfer it directly from the reference to the output. It will of course scale by 20 log N where N is the amount you multiplied or divided the reference frequency by. Double the frequency and the phase noise goes up by 6 db. So in my example case of scaling the 10Mhz t-bolt to 14.5Mhz Assuming a perfect DDS chip the T-Bolt's phase noise would be scaled up by 20 Log(1.45) I'm assuming this works, that I can go from 10MHz to 120Mhz and then to 14.5MHZ and the total effect is the same as going directly from 10 to 14.5, except for the noise the equipment introduces as added. You can guess the real question here: how good does the 10MHz reference need to be to test real-world receivers? It has to be quieter than the oscillator in the real world receiver. If your real-wold receiver is a cryogenic ruby maser with a downconveter driven by a hydrogen maser reference, then the answer is really, really good.. If the real world receiver uses a run of the mill TCXO, then not nearly as good. The 20log10(N) thing does work pretty well. In a PLL synthesizer, you'll pick up a little extra noise from the phase detector and other circuitry, but for back of the envelope to see if your idea is going to work, the 20log10(N) is just fine. This gets into a whole interesting area of microwave source design, because inside the loop the phase noise is the reference oscillator multiplied up (20log10(N) noise), and outside the loop, it's the microwave oscillator. So you have an interesting optimization problem, particularly if you want tuning over a wide range. Wide range VCOs implies that the MHz/volt gain is quite high, so noise on the tuning signal shows up on the output. The resonator is often lower Q, so that it can be moved around by the control signal (usually some sort of varactor scheme), and that means the medium distance away phase noise suffers. High performance DROs for instance, have a tough time tuning the entire 50 MHz deep space comm bands at 7 or 8 GHz ___ 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] Best GPSDO
Hi For close in noise, you can go from 10 to 120 to 14.5 and the net result will be the same as 10 to 14.5. In the case of 10 to 120, close in might be DC to 50 Hz or DC to 250 Hz. Past that a reasonable crystal oscillator could beat the multiplied 10 MHz. In most microwave chains, the low frequency reference only is responsible for a fairly small range of phase noise offsets. For most radio testing, you use wide spaced tones. What you care about is far removed phase noise rather than close in noise. If you have a tone that's 10 KHz to 100 KHz away from the passband, phase noise at 10 KHz is what you would worry about. If you are building a radio with 10 Hz selectivity for 40 Hz spaced channels, you would worry about close in noise. For what ever it's worth, I don't lock up the sources I use for most radio testing. I just use free running oscillators with good noise characteristics past 1 KHz. Bob On Sep 28, 2012, at 11:31 PM, Chris Albertson albertson.ch...@gmail.com wrote: On Fri, Sep 28, 2012 at 5:29 PM, Bob Camp li...@rtty.us wrote: HI Sort of an open ended question, but there is a fairly simple couple answers: SInce it's close in phase noise and not far removed, things like PLL's are going to transfer it directly from the reference to the output. It will of course scale by 20 log N where N is the amount you multiplied or divided the reference frequency by. Double the frequency and the phase noise goes up by 6 db. So in my example case of scaling the 10Mhz t-bolt to 14.5Mhz Assuming a perfect DDS chip the T-Bolt's phase noise would be scaled up by 20 Log(1.45) I'm assuming this works, that I can go from 10MHz to 120Mhz and then to 14.5MHZ and the total effect is the same as going directly from 10 to 14.5, except for the noise the equipment introduces as added. You can guess the real question here: how good does the 10MHz reference need to be to test real-world receivers? -- Chris Albertson Redondo Beach, California ___ 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] Best GPSDO
On 09/29/2012 06:19 PM, Tom Knox wrote: Best of course is such a vague question. Best For 5MHz today is a Cesium Fountain used periodicly to calibrate 6-12 Symmetricom 5071A option 004 disciplining 5-6 Symmetricom Hydrogen Masers disciplining 5-6 Oscilloquartz 8607 option 08 BVA's. I am a part owner in just such a system. Notice the system ends with quartz and I think therein lies the key. I am a big believer that for the best system find the best piece of quartz you budget can afford. On eBay I would currently I would argue that the Datum 1000B's for around 4-500USD is the way to go. From my experience how you steer it and set up your GPS or other timing source is important but only a major factor if you do something wrong. It's a little out of the hobby budget there. If you don't happen to have a caesium fountain, 5071As, masers and loads of 8607s, there is still a few things to pick up from this setup. An atomic clock such as a rubidium can provide holdover and be quieter than GPS, so you can allow your steering to have long time-constant. Next, you might not have best wide-band phase-noise, so using a quality oscillator to achieve that. Then again, I can give you an address for those extra 5071As, masers, 8607s and odd caesium-fountain. :) Cheers, Magnus ___ 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] Best GPSDO
Hi The address is pretty easy, the *real* question is when is the swap meet? Bob On Sep 29, 2012, at 1:21 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 09/29/2012 06:19 PM, Tom Knox wrote: Best of course is such a vague question. Best For 5MHz today is a Cesium Fountain used periodicly to calibrate 6-12 Symmetricom 5071A option 004 disciplining 5-6 Symmetricom Hydrogen Masers disciplining 5-6 Oscilloquartz 8607 option 08 BVA's. I am a part owner in just such a system. Notice the system ends with quartz and I think therein lies the key. I am a big believer that for the best system find the best piece of quartz you budget can afford. On eBay I would currently I would argue that the Datum 1000B's for around 4-500USD is the way to go. From my experience how you steer it and set up your GPS or other timing source is important but only a major factor if you do something wrong. It's a little out of the hobby budget there. If you don't happen to have a caesium fountain, 5071As, masers and loads of 8607s, there is still a few things to pick up from this setup. An atomic clock such as a rubidium can provide holdover and be quieter than GPS, so you can allow your steering to have long time-constant. Next, you might not have best wide-band phase-noise, so using a quality oscillator to achieve that. Then again, I can give you an address for those extra 5071As, masers, 8607s and odd caesium-fountain. :) Cheers, Magnus ___ 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] Best GPSDO
On 09/29/2012 07:52 PM, Bob Camp wrote: Hi The address is pretty easy, the *real* question is when is the swap meet? I just want him to send the stuff to me. ;-) Cheers, Magnus ___ 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] Best GPSDO
Ulrich, I think this is a bit like discussing one's favourite wine or favourite stereo! Especially since many of the participants here will not have the capability to compare GPSDO performance reliably. I have a few GPSDOs, and it's my impression that of them all the Agilent Z3815A with MTI260 DOCXO has the best phase noise. Of course these units were originally equipped with an E1938A, and the later MTI260 version is not as common. I also have an E1938A, which I operate standalone. It is very impressive, excellent AD, in fact my best source now that I've given away my HP 5065A. There is some phase noise well away from the carrier, but I've put that down to my own construction (switching power supply noise). Another of my favourites with low phase noise is the Trimble/Nortel NTGS50AA, which has a CMAC/Rakon CFPO-DO OCXO. I've had no opportunity to measure the AD apart from what Lady Heather reports. This unit is physically large but is not power hungry and talks to LH very well. I also own a Z3801A, a Samsung GCRU-D and a small homebrew GPSDO with a CFPO-DO. Sorry, no Timepod for comparisons. 73, Murray ZL1BPU ___ 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] Best GPSDO
how important is the close in phase noise of a 10MHz reference? I means after all, the oscillator you are measuring, say the local oscillator in a receivers or whatever, is likely not running at 10MHz so you have some step where you convert your t-bolt reference to the desired freq. using either DDS or a synthesizer and I'd bet that step introduces more noise and is the weak link. I did mean this as a question because I really don't know how to compute the effect. Say my DDS needs 120MHz clock and I PLL that 120Mhz clock to my t-bolt and then the DDS as asked to outout 14.5MHz. How do phase noise in the 10MHz t-bolt output effect the DDS' 14.5 output. Or does it even matter compared to all the noise from other sources. Is there a simple rule of thumb? OK, maybe we are not really doing any real-measurements, just comparing 10MHz standards to each other? But the above assumes the end goal is some real-world device who performance we want to determine. On Fri, Sep 28, 2012 at 11:50 AM, Murray Greenman denw...@orcon.net.nz wrote: Ulrich, I think this is a bit like discussing one's favourite wine or favourite stereo! Especially since many of the participants here will not have the capability to compare GPSDO performance reliably. I have a few GPSDOs, and it's my impression that of them all the Agilent Z3815A with MTI260 DOCXO has the best phase noise. Of course these units were originally equipped with an E1938A, and the later MTI260 version is not as common. I also have an E1938A, which I operate standalone. It is very impressive, excellent AD, in fact my best source now that I've given away my HP 5065A. There is some phase noise well away from the carrier, but I've put that down to my own construction (switching power supply noise). Another of my favourites with low phase noise is the Trimble/Nortel NTGS50AA, which has a CMAC/Rakon CFPO-DO OCXO. I've had no opportunity to measure the AD apart from what Lady Heather reports. This unit is physically large but is not power hungry and talks to LH very well. I also own a Z3801A, a Samsung GCRU-D and a small homebrew GPSDO with a CFPO-DO. Sorry, no Timepod for comparisons. 73, Murray ZL1BPU ___ 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. -- Chris Albertson Redondo Beach, California ___ 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] Best GPSDO
HI Sort of an open ended question, but there is a fairly simple couple answers: SInce it's close in phase noise and not far removed, things like PLL's are going to transfer it directly from the reference to the output. It will of course scale by 20 log N where N is the amount you multiplied or divided the reference frequency by. Double the frequency and the phase noise goes up by 6 db. If you look at jitter, measured in the time domain. It will stay constant as you scale frequency. That's provided it's dominated by phase noise in the frequency range that the 20 log N rule applies. If you strip off noise with a filter (or what ever) jitter will go down. If you are building a receiver, phase noise will limit the selectivity of the radio. If you are looking at very tight selectivity, then close in phase noise matters. Past that, we get out of the fairly simple stuff. Bob On Sep 28, 2012, at 4:44 PM, Chris Albertson albertson.ch...@gmail.com wrote: how important is the close in phase noise of a 10MHz reference? I means after all, the oscillator you are measuring, say the local oscillator in a receivers or whatever, is likely not running at 10MHz so you have some step where you convert your t-bolt reference to the desired freq. using either DDS or a synthesizer and I'd bet that step introduces more noise and is the weak link. I did mean this as a question because I really don't know how to compute the effect. Say my DDS needs 120MHz clock and I PLL that 120Mhz clock to my t-bolt and then the DDS as asked to outout 14.5MHz. How do phase noise in the 10MHz t-bolt output effect the DDS' 14.5 output. Or does it even matter compared to all the noise from other sources. Is there a simple rule of thumb? OK, maybe we are not really doing any real-measurements, just comparing 10MHz standards to each other? But the above assumes the end goal is some real-world device who performance we want to determine. On Fri, Sep 28, 2012 at 11:50 AM, Murray Greenman denw...@orcon.net.nz wrote: Ulrich, I think this is a bit like discussing one's favourite wine or favourite stereo! Especially since many of the participants here will not have the capability to compare GPSDO performance reliably. I have a few GPSDOs, and it's my impression that of them all the Agilent Z3815A with MTI260 DOCXO has the best phase noise. Of course these units were originally equipped with an E1938A, and the later MTI260 version is not as common. I also have an E1938A, which I operate standalone. It is very impressive, excellent AD, in fact my best source now that I've given away my HP 5065A. There is some phase noise well away from the carrier, but I've put that down to my own construction (switching power supply noise). Another of my favourites with low phase noise is the Trimble/Nortel NTGS50AA, which has a CMAC/Rakon CFPO-DO OCXO. I've had no opportunity to measure the AD apart from what Lady Heather reports. This unit is physically large but is not power hungry and talks to LH very well. I also own a Z3801A, a Samsung GCRU-D and a small homebrew GPSDO with a CFPO-DO. Sorry, no Timepod for comparisons. 73, Murray ZL1BPU ___ 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. -- Chris Albertson Redondo Beach, California ___ 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] Best GPSDO
Close in phase noise is of utter importance to radar applications that rely on Doppler frequency shift. Think trying to detect walking intruders at the border. Frequency synchronization is important if one tries to link up multiple radar units. Thus good to great Adev and phase noise is needed for those types of applications. Bye Said Sent From iPhone On Sep 28, 2012, at 17:29, Bob Camp li...@rtty.us wrote: HI Sort of an open ended question, but there is a fairly simple couple answers: SInce it's close in phase noise and not far removed, things like PLL's are going to transfer it directly from the reference to the output. It will of course scale by 20 log N where N is the amount you multiplied or divided the reference frequency by. Double the frequency and the phase noise goes up by 6 db. If you look at jitter, measured in the time domain. It will stay constant as you scale frequency. That's provided it's dominated by phase noise in the frequency range that the 20 log N rule applies. If you strip off noise with a filter (or what ever) jitter will go down. If you are building a receiver, phase noise will limit the selectivity of the radio. If you are looking at very tight selectivity, then close in phase noise matters. Past that, we get out of the fairly simple stuff. Bob On Sep 28, 2012, at 4:44 PM, Chris Albertson albertson.ch...@gmail.com wrote: how important is the close in phase noise of a 10MHz reference? I means after all, the oscillator you are measuring, say the local oscillator in a receivers or whatever, is likely not running at 10MHz so you have some step where you convert your t-bolt reference to the desired freq. using either DDS or a synthesizer and I'd bet that step introduces more noise and is the weak link. I did mean this as a question because I really don't know how to compute the effect. Say my DDS needs 120MHz clock and I PLL that 120Mhz clock to my t-bolt and then the DDS as asked to outout 14.5MHz. How do phase noise in the 10MHz t-bolt output effect the DDS' 14.5 output. Or does it even matter compared to all the noise from other sources. Is there a simple rule of thumb? OK, maybe we are not really doing any real-measurements, just comparing 10MHz standards to each other? But the above assumes the end goal is some real-world device who performance we want to determine. On Fri, Sep 28, 2012 at 11:50 AM, Murray Greenman denw...@orcon.net.nz wrote: Ulrich, I think this is a bit like discussing one's favourite wine or favourite stereo! Especially since many of the participants here will not have the capability to compare GPSDO performance reliably. I have a few GPSDOs, and it's my impression that of them all the Agilent Z3815A with MTI260 DOCXO has the best phase noise. Of course these units were originally equipped with an E1938A, and the later MTI260 version is not as common. I also have an E1938A, which I operate standalone. It is very impressive, excellent AD, in fact my best source now that I've given away my HP 5065A. There is some phase noise well away from the carrier, but I've put that down to my own construction (switching power supply noise). Another of my favourites with low phase noise is the Trimble/Nortel NTGS50AA, which has a CMAC/Rakon CFPO-DO OCXO. I've had no opportunity to measure the AD apart from what Lady Heather reports. This unit is physically large but is not power hungry and talks to LH very well. I also own a Z3801A, a Samsung GCRU-D and a small homebrew GPSDO with a CFPO-DO. Sorry, no Timepod for comparisons. 73, Murray ZL1BPU ___ 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. -- Chris Albertson Redondo Beach, California ___ 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] Best GPSDO
On Fri, Sep 28, 2012 at 5:29 PM, Bob Camp li...@rtty.us wrote: HI Sort of an open ended question, but there is a fairly simple couple answers: SInce it's close in phase noise and not far removed, things like PLL's are going to transfer it directly from the reference to the output. It will of course scale by 20 log N where N is the amount you multiplied or divided the reference frequency by. Double the frequency and the phase noise goes up by 6 db. So in my example case of scaling the 10Mhz t-bolt to 14.5Mhz Assuming a perfect DDS chip the T-Bolt's phase noise would be scaled up by 20 Log(1.45) I'm assuming this works, that I can go from 10MHz to 120Mhz and then to 14.5MHZ and the total effect is the same as going directly from 10 to 14.5, except for the noise the equipment introduces as added. You can guess the real question here: how good does the 10MHz reference need to be to test real-world receivers? -- Chris Albertson Redondo Beach, California ___ 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] Best GPSDO
On 9/28/2012 8:31 PM, Chris Albertson wrote: You can guess the real question here: how good does the 10MHz reference need to be to test real-world receivers? Pretty sure the answer is good enough, but... Depends on the receiver and what it is receiving. I got interested in time-nuttyness because I am a ham. My interests are mainly in the microwave bands, typically 10 GHz and higher. I got a couple GPSDOs primarily to make accurate measurements in the many-GHz range by feeding ref inputs to my test equipment. Mostly I wasn't interested in the nitty-gritty, just being good enough for good trustworty results. Before the GPSDOs, getting accuracy to 100's of Hz at 10 GHz was an act of faith. Now, to Hz is pretty easy. Recently I got involved in building some boards for an intermediate IF (is that redundant?) for a 24 GHz radio that have their LO at 3600 MHz and are locked to 10 MHz. (Details to be presented at Microwave Update 2012 in a couple weeks -- http://microwaveupdate.org/ . Feel free to sign up and attend if you are interested.) Around 2006, John Miles shared with us some measurements he did using microwave brick phase locked oscillators to get the phase noise from OCXOs multiplied up enough to see the differences on a decent spectrum analyzer. ( http://www.ke5fx.com/brick/brick.htm ) He used an 8566b SA and his own PN software ( http://www.ke5fx.com/gpib/pn.htm ) to drive it with GPIB to make the measurements. Many thanks to John for all he has shared with us. I hadn't made any measurements like this before, but this seemed like a good way to get a feel for the quality of the 3600 MHz boards (which turned out good.) I also have an 8566b SA, so that with John's PN software seemed like a good setup to try. The 3600 board has a loop filter about 10 KHz wide so in the audio range the output PN is related to the quality of the 10 MHz reference. My two main frequency references are two GPSDOs, an HP Z3816A and (few years ago added) a Z3805A Sumsung. Both have an MTI 260 OCXO as their internal locked source. Testing the 3600 MHz board using these two references, the best phase noise came with the 3805 at about -90 dBc. The 3816 was about 7 dB higher. Not sure why. The MTI 260 oscillators are 5 MHz so are doubled in the GPSDOs to 10 MHz. Maybe that is part of it, or maybe the two MTI 260s are that much different. I also measured with two small eBay oscillators from China -- all in equivalent small packages about 2 inch square by 1.5 inch high. A CIC STP2145A gave results similar to the 3816. A Morion MV89A was the worst so far, about 10 dB higher than the 3805. Clearly, the affects of the the oscillator PN are quite visible when multiplied by 360 to 3600 MHz. (20 log 360 = 51 dB.) I'm not sure about the exact accuracy of my measurements, but I am certain I am seeing the relative effects of the PN from the OCXOs. I have a bunch of 10 and 5 MHz OCXOs I have accumulated and now that I have this tool for evaluating, I need to take the time to fire them up and sort them by PN quality. I guess I need to build a trustworthy doubler too, for the 5 to 10 MHz like the ones on Bruce's pages at KO4BB. ___ 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.
