Re: [time-nuts] GPSDO project - 66.667MHz from 10MHz
Both for locking with a 10MHz or 1pps you have a single chip solution using one of my reflock designs. http://w3ref.cfn.ist.utl.pt/cupido/reflock.html For a 1pps lock of fractional 1/3 frequencies you have already a code. (check the list of files for reflock 1) For locking a 66.666(6) VCXO to 10MHz you can use the same reflock I design and the configuration is kind of trivial (but no one asked for it before) and I can make a file for you. Luis Cupido ct1dmk. From: Bruce Griffiths bruce.griffi...@xtra.co.nz To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, 28 June, 2009 11:04:49 PM Subject: Re: [time-nuts] GPSDO project Hal Murray wrote: You want 66. MHz from 10 MHz. I can think of several approaches. 1) Patch the radio stuff to work with 10 MHz. Since 10 MHz is common from things like GPSDOs or Telco surplus rubidium clocks, somebody may have done that already. 2) Build a PLL. The first step is probably to find a 66.666 MHz oscillator that has an external fine tuning pin. Then it's divide by 20 and 3, compare, filter... 3) Get to 66.666 MHz by dividing by 3 then multiplying by 2 and 5. I don't know much about this area, but there was a lot of discussion here a few months ago. Check the archives. Actually need to multiply 3.333.. MHz by 20 (5 x 2 x 2) No need to multiply by 2 or 4, if the output of the divide by 3 is a 1/3 duty cycle square wave, one can extract the 2nd (or 4th) harmonic of the square wave repetition rate with a filter. Amplify and multiply by 5 (can use the same approach as used in the 5370A/B frequency multiplier chain (1 transistor per multiplier) and filter. A high level injection locked divider can have lower close in phase noise than a digital one. 4) Use a DDS chip to synthesize 66.666 MHz. Analog Devices makes lots of nice ones. One problem with DDSes is that they normally make spurs. But they aren't a problem if the target frequency is a clean multiple of the source frequency. 20/3 doesn't sound clean, but I'd have to do a lot of work to check the details. There may be a clean frequency that is close enough to 66.666 MHz and/or one that has spurs that are far enough out so you can filter them. 5) Use a low cost 66.666 MHz oscillator and live with the error. You may be able to correct any errors. The key step would be to feed the 66.666 MHz to a counter running off the T-Bolt clock so you know the real frequency of your 66.666 MHz osc. Suppose your 66.666 MHz is 73 ppm fast and you want to listen to 12.123 MHz. You would set the radio to listen to 73 PPM below 12.123 MHz. 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. ___ 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] GPSDO project - 66.667MHz from 10MHz
Hi Luis, Are kits available again for your design? 73's Nic VK2KXN / VK5ZAT Subject: Re: [time-nuts] GPSDO project - 66.667MHz from 10MHz Both for locking with a 10MHz or 1pps you have a single chip solution using one of my reflock designs. http://w3ref.cfn.ist.utl.pt/cupido/reflock.html For a 1pps lock of fractional 1/3 frequencies you have already a code. (check the list of files for reflock 1) For locking a 66.666(6) VCXO to 10MHz you can use the same reflock I design and the configuration is kind of trivial (but no one asked for it before) and I can make a file for you. Luis Cupido ct1dmk. ___ 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] GPSDO project - 66.667MHz from 10MHz
Nic, I think yes but I'm not sure, please check Darrel's VE1ALQ and NTMS(Kent Britain) for reflock I pcb's and/or kits (as I've not heard from them recently). I believe TAPR is no longer offering the reflock II kit :-( Luis Cupido ct1dmk. Nic McLean wrote: Hi Luis, Are kits available again for your design? 73's Nic VK2KXN / VK5ZAT Subject: Re: [time-nuts] GPSDO project - 66.667MHz from 10MHz Both for locking with a 10MHz or 1pps you have a single chip solution using one of my reflock designs. http://w3ref.cfn.ist.utl.pt/cupido/reflock.html For a 1pps lock of fractional 1/3 frequencies you have already a code. (check the list of files for reflock 1) For locking a 66.666(6) VCXO to 10MHz you can use the same reflock I design and the configuration is kind of trivial (but no one asked for it before) and I can make a file for you. Luis Cupido ct1dmk. ___ 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] GPSDO project
Many thanks to all who responded to my request for help on this project. The SDR-IQ (http://www.rfspace.com/SDR-IQ.html) already has a built-in 66.6667 MHz osc, I just want to make it more stable and reasonably accurate, as I use it as a general coverage HF receiver with a one- Hertz read-out. There is a place for a surface-mount jack on the PC board -- so that an external osc can be used -- although this feature is not promoted by the manufacturer. This SDR does most of its own processing in hardware and doesn't rely on a computer sound card as much as some SDRs do. There was one response, offering a kit to do what I need, but it requires more test equipment for tuning and calibration than what I have available. I am still looking for a simple, completed oscillator that will accept 10 MHz from a Thunderbolt GPS receiver and supply 66.6 MHz for my SDR as described here: http://www.braddye.com/gps_do.html My background is in radio paging where we use GPS receivers to keep our 900 MHz transmitters on frequency for simulcast operation. I really appreciate the time everyone took to offer suggestions. 73s Brad Dye, K9IQY Springfield, Illinois ___ 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] GPSDO project
Consider a 2nd hand low phase noise source like a PTS-160. Best regards, Xtof. Brad Dye wrote: Many thanks to all who responded to my request for help on this project. The SDR-IQ (http://www.rfspace.com/SDR-IQ.html) already has a built-in 66.6667 MHz osc, I just want to make it more stable and reasonably accurate, as I use it as a general coverage HF receiver with a one-Hertz read-out. There is a place for a surface-mount jack on the PC board -- so that an external osc can be used -- although this feature is not promoted by the manufacturer. This SDR does most of its own processing in hardware and doesn't rely on a computer sound card as much as some SDRs do. There was one response, offering a kit to do what I need, but it requires more test equipment for tuning and calibration than what I have available. I am still looking for a simple, completed oscillator that will accept 10 MHz from a Thunderbolt GPS receiver and supply 66.6 MHz for my SDR as described here: http://www.braddye.com/gps_do.html My background is in radio paging where we use GPS receivers to keep our 900 MHz transmitters on frequency for simulcast operation. I really appreciate the time everyone took to offer suggestions. 73s Brad Dye, K9IQY Springfield, Illinois ___ 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. begin:vcard fn:Christophe Huygens n:Huygens;Christophe org:DistriNet;Dept. Computerwetenschappen - K.U.Leuven adr:;;Celestijnenlaan 200A;Leuven;;3001;Belgium email;internet:christophe.huyg...@cs.kuleuven.be title:Gastdocent tel;work:+32 16 32 7561 x-mozilla-html:FALSE url:http://www.cs.kuleuven.be/~xtof version:2.1 end:vcard ___ 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] GPSDO project (SDR)
Hi Brad. Just catching up with this, after a hot weekend, and doing White Van Man impressions on (an even hotter) M1 this morning... Personally, I wouldn't bother with any high accuracy clock/oscillator for the SDR, unless you can also synch the AD sampling clock in the soundcard. As that will have much more of an effect on carrier frequency generation/indication etc than even an undisciplined oscillator in the SDR mixer itself. Then there is the issue of just how accurate is the software in it's DSP routines in interpreting the (sampled) data from the soundcard. Much SDR software has a frequency calibration function, as it is well known that most consumer soundcards are not that accurate in their timing, not just that the RFI/Q mixer clock is often off a bit. Even some of the 96k sampling 24 bit golden ears types can be somewhat wayward. Have you also ascertained that Power SDR run's OK on Vista? Only ask, as I know that others have found Big trouble with much SDR software, and the way it tries to use the PC's sound system, and how that interacts with Vista's way of doing things. I've not run Power SDR myself on anything other than demo files on XP/2000 by the way. Vista's background timekeeping is crap too I'm told, quite how that will impact SDR software though, I do not know. Check out the SDR lists on Yahoo, their maybe people there who have done what you describe, but I also monitor those lists too, and can't recall anyone doing that (GPSDO) thing with the mixer osc'. Though there has been much discussion about soundcard sampling clocks! http://groups.yahoo.com/group/softrock40/join Also the KGKSDR list, the address of escapes me at the moment. There are probably others. Wonder if anyone has integrated ClickLock into any SDR software yet... 73. Dave G0WBX. -Original Message- In a message dated 28/06/2009 20:34:25 GMT Daylight Time, b...@braddye.com writes: I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). Building such an oscillator is a little over my head so I thought I would ask the group if anyone knows where I could buy the missing link of this project. I have put a drawing of my project on the web showing the specs of what I need. The oscillator is shown in the blue box. Any help or suggestions would be greatly appreciated. http://www.braddye.com/gps_do.html ___ 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] GPSDO project
Does anyone have a Reflock that they would sell me? Best regards, Brad Dye K9IQYom ___ 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] GPSDO project (SDR)
Dave Baxter wrote: Personally, I wouldn't bother with any high accuracy clock/oscillator for the SDR, unless you can also synch the AD sampling clock in the soundcard. The SDR-IQ, SDR-14, Qs1r, Perseus and the HPSDR project do not rely on a sound card ADC to sample any signals. The RF signal is directly sampled at RF, with sampling rates up to 122.88 MHz (depending on the model), then it is frequency-shifted, then downsampled by the firmware in the accompanying FPGA. Then the downsampled stream is sent to the PC via the USB 2.0 port. The software on the PC receives directly digital data, no pesky sound card is needed to digitize it. So the _only_ factor affecting the frequency calibration is the clock of the RF ADC. 73 Alberto I2PHD ___ 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] GPSDO project
Hello Brad, VE1ALQ has them. He will also make VCXO's. Do a google search for his webpages. He sells the kits as well as the assembled units. By far easier to get a PTS or Fluke sysnthesizer. Stan, W1LE Brad Dye wrote: Does anyone have a Reflock that they would sell me? Best regards, Brad Dye K9IQYom ___ 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] GPSDO project
I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). Building such an oscillator is a little over my head so I thought I would ask the group if anyone knows where I could buy the missing link of this project. I have put a drawing of my project on the web showing the specs of what I need. The oscillator is shown in the blue box. Any help or suggestions would be greatly appreciated. http://www.braddye.com/gps_do.html 73s Brad Dye K9IQY ex KN9IQY, KN4BK, KM5NK, WB4JCF, ZP5TQ, WA4VXU, WA9RVL, /TI2, /9Y4, / 6Y5, /KP4 52 years as a FCC licensed amateur radio operator 36 years as a FCC licensed first class commercial radio operator ___ 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] GPSDO project
In a message dated 28/06/2009 20:34:25 GMT Daylight Time, b...@braddye.com writes: I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). Building such an oscillator is a little over my head so I thought I would ask the group if anyone knows where I could buy the missing link of this project. I have put a drawing of my project on the web showing the specs of what I need. The oscillator is shown in the blue box. Any help or suggestions would be greatly appreciated. http://www.braddye.com/gps_do.html --- One option, although perhaps a bit bulky as it's a 3U 19inch rackmount unit, would be to use something like a PTS160 synthesiser, or Wavetek 5120A which is similar, which can be driven by an external 10MHz reference and can provide outputs between 100KHz and 160MHz with resolution as fine as 0.1Hz depending on number of incremental modules fitted. regards Nigel GM8PZR ___ 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] GPSDO project
Additional suggestions, for short term realization, and cost effective: PTS synthesizer that will cover the desired freq, Programmed Test Sources are common on Ebay. Can use an external 10 MHz reference. Get one with front panel knobs (setability). Possibly a FLUKE model 6061B synthesizer, tunable in 1 Hz steps. Can use a 5 MHz reference Useable to 160 MHz. Other synthesizers from commercial test equipment manufacturers. Stan, W1LE Brad Dye wrote: I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). ___ 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] GPSDO project
You want 66. MHz from 10 MHz. I can think of several approaches. 1) Patch the radio stuff to work with 10 MHz. Since 10 MHz is common from things like GPSDOs or Telco surplus rubidium clocks, somebody may have done that already. 2) Build a PLL. The first step is probably to find a 66.666 MHz oscillator that has an external fine tuning pin. Then it's divide by 20 and 3, compare, filter... 3) Get to 66.666 MHz by dividing by 3 then multiplying by 2 and 5. I don't know much about this area, but there was a lot of discussion here a few months ago. Check the archives. 4) Use a DDS chip to synthesize 66.666 MHz. Analog Devices makes lots of nice ones. One problem with DDSes is that they normally make spurs. But they aren't a problem if the target frequency is a clean multiple of the source frequency. 20/3 doesn't sound clean, but I'd have to do a lot of work to check the details. There may be a clean frequency that is close enough to 66.666 MHz and/or one that has spurs that are far enough out so you can filter them. 5) Use a low cost 66.666 MHz oscillator and live with the error. You may be able to correct any errors. The key step would be to feed the 66.666 MHz to a counter running off the T-Bolt clock so you know the real frequency of your 66.666 MHz osc. Suppose your 66.666 MHz is 73 ppm fast and you want to listen to 12.123 MHz. You would set the radio to listen to 73 PPM below 12.123 MHz. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] GPSDO project
Hal Murray wrote: You want 66. MHz from 10 MHz. I can think of several approaches. 1) Patch the radio stuff to work with 10 MHz. Since 10 MHz is common from things like GPSDOs or Telco surplus rubidium clocks, somebody may have done that already. 2) Build a PLL. The first step is probably to find a 66.666 MHz oscillator that has an external fine tuning pin. Then it's divide by 20 and 3, compare, filter... 3) Get to 66.666 MHz by dividing by 3 then multiplying by 2 and 5. I don't know much about this area, but there was a lot of discussion here a few months ago. Check the archives. Actually need to multiply 3.333.. MHz by 20 (5 x 2 x 2) No need to multiply by 2 or 4, if the output of the divide by 3 is a 1/3 duty cycle square wave, one can extract the 2nd (or 4th) harmonic of the square wave repetition rate with a filter. Amplify and multiply by 5 (can use the same approach as used in the 5370A/B frequency multiplier chain (1 transistor per multiplier) and filter. A high level injection locked divider can have lower close in phase noise than a digital one. 4) Use a DDS chip to synthesize 66.666 MHz. Analog Devices makes lots of nice ones. One problem with DDSes is that they normally make spurs. But they aren't a problem if the target frequency is a clean multiple of the source frequency. 20/3 doesn't sound clean, but I'd have to do a lot of work to check the details. There may be a clean frequency that is close enough to 66.666 MHz and/or one that has spurs that are far enough out so you can filter them. 5) Use a low cost 66.666 MHz oscillator and live with the error. You may be able to correct any errors. The key step would be to feed the 66.666 MHz to a counter running off the T-Bolt clock so you know the real frequency of your 66.666 MHz osc. Suppose your 66.666 MHz is 73 ppm fast and you want to listen to 12.123 MHz. You would set the radio to listen to 73 PPM below 12.123 MHz. 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] GPSDO project - 66.667MHz from 10MHz
You can also use a DFS (Direct Frequency Synthesiser) to produce 66.667MHz in two ways - either 50 + 16.667MHz, or 70 - 3.33MHz. Information on the 50+16.667 is on my web site (http://g4hup.com), and has been implemented as a reference source for an SDR-IQ receiver. Another customer of mine has also implemented the 70-3.33MHz version for the same application - I don't have the filter component values or detail design posted, but could provide them on request.. My personal preference is for the slightly more complex 50+16.667Mhz option, since the filtering is a little easier at VHF - but both solutions work, and give a good clean, stable low-noise output (depending on the quality of your 10MHz reference input, of course!) Kits are available. Hope this helps 73, Dave, G4HUP From: Bruce Griffiths bruce.griffi...@xtra.co.nz To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, 28 June, 2009 11:04:49 PM Subject: Re: [time-nuts] GPSDO project Hal Murray wrote: You want 66. MHz from 10 MHz. I can think of several approaches. 1) Patch the radio stuff to work with 10 MHz. Since 10 MHz is common from things like GPSDOs or Telco surplus rubidium clocks, somebody may have done that already. 2) Build a PLL. The first step is probably to find a 66.666 MHz oscillator that has an external fine tuning pin. Then it's divide by 20 and 3, compare, filter... 3) Get to 66.666 MHz by dividing by 3 then multiplying by 2 and 5. I don't know much about this area, but there was a lot of discussion here a few months ago. Check the archives. Actually need to multiply 3.333.. MHz by 20 (5 x 2 x 2) No need to multiply by 2 or 4, if the output of the divide by 3 is a 1/3 duty cycle square wave, one can extract the 2nd (or 4th) harmonic of the square wave repetition rate with a filter. Amplify and multiply by 5 (can use the same approach as used in the 5370A/B frequency multiplier chain (1 transistor per multiplier) and filter. A high level injection locked divider can have lower close in phase noise than a digital one. 4) Use a DDS chip to synthesize 66.666 MHz. Analog Devices makes lots of nice ones. One problem with DDSes is that they normally make spurs. But they aren't a problem if the target frequency is a clean multiple of the source frequency. 20/3 doesn't sound clean, but I'd have to do a lot of work to check the details. There may be a clean frequency that is close enough to 66.666 MHz and/or one that has spurs that are far enough out so you can filter them. 5) Use a low cost 66.666 MHz oscillator and live with the error. You may be able to correct any errors. The key step would be to feed the 66.666 MHz to a counter running off the T-Bolt clock so you know the real frequency of your 66.666 MHz osc. Suppose your 66.666 MHz is 73 ppm fast and you want to listen to 12.123 MHz. You would set the radio to listen to 73 PPM below 12.123 MHz. 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. ___ 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] GPSDO project
Hi Brad, I am a little confused about your intentions. There is no mention on the RFspace web site about a provision of being able to feed in an external reference signal to the SDR-IQ or the SDR-14 for that matter. If you study the Analog devices AD6620 component, you will see that it is a 3.3 volt * * * ONLY * * * process, which only adds to the problem. Additionally there are constraints on the rise and fall times of the timing signal. This is a horrifically complex component with intricate dependencies tied to the specific A/D used. This is not your daddy's VFO from yester-year. The fact that the internal DDS is a digital function means you will never, ever, get to a perfect cardinal point, except under very special conditions. In this case it will have an offset of 16 pico-seconds because that is the smallest resolution the DDS can do. While small it would require very special hardware for you to keep it locked to the GPS. As the internal clocking system runs more then just the DDS, other considerations come into play. The clocks built to run these chips are not designed for external control and studying the physical layout of the SDR-IQ, it does not appear that they provided any means to have external clocking ability. Besides the computer's sound card DSP is heavily involved with regards to the frequency calibration. So there are two independent clocks to keep synchronized that are not related to the listening time, particularly if you record the digital bits for later listening or analysis. Fortunately, the software will allow for you to calibrate, to some degree, but it is not and you will not be able to approach what you expect to do with the Thunderbolt. Keep in mind that the best you could do with a Thunderbolt on a 1 second per second comparison basis is only 1 part in 10 to the minus ninth (1x10^-9). It gets worse if you consider shorter times like a continuous analog aspect that you would have for active listening. The noise of the GPS system would mask the 16 pico-second resolution of the SDR-IQ DDS. The real problem is temperature. You could improve that by providing a chamber for the SDR-IQ and raising, carefully, the temperature to just above your highest ambient level. After all that, I am not saying you couldn't/wouldn't/shouldn't consider it. Keep in mind that the SDR-IQ, or for that matter, the SDR-14 DDS only sets the center of the 190 KHz bandwidth swath that you are viewing at any one time. The real fine aspect is done in the computer and the clocks in those are all over the map, so to speak. In order to have a really tight calibration, with Timenuts quality, would involve some serious effort to build a clocking system for both the SDR-IQ and the computer. The final result is you would still be offset due to the digital processes in both the SDR-IQ and the computer, plus, perhaps, some latency in the software. As I get to the point of sending this email I see that Dave Powis, G4HUP, has gone to the trouble to lock the SDR-IQ internal oscillator to an external 10 MHz. If you look at all the information on his web site, you will see that it is not a trivial project. As I pointed out, this only stabilizes the window of the SDR-IQ still leaving the computer to tend with. My experience with the Thunderbolt shows that it has some temperature dependencies and the expected nominal noise of the GPS system in the short term regard. What most people do is have a high quality house standard and do long term comparisons to the GPS. A high quality house standard would, in effect, filter the short term noise of the GPS system. At any rate, this is my fantasy and I am sticking to it ! BillWB6BNQ Brad Dye wrote: I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). Building such an oscillator is a little over my head so I thought I would ask the group if anyone knows where I could buy the missing link of this project. I have put a drawing of my project on the web showing the specs of what I need. The oscillator is shown in the blue box. Any help or suggestions would be greatly appreciated. http://www.braddye.com/gps_do.html 73s Brad Dye K9IQY ex KN9IQY, KN4BK, KM5NK, WB4JCF, ZP5TQ, WA4VXU, WA9RVL, /TI2, /9Y4, / 6Y5, /KP4 52 years as a FCC licensed amateur radio operator 36 years as a FCC licensed first class commercial radio operator ___ 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] GPSDO project
GPSDO project Brad Dye brad at braddye.com Sun Jun 28 19:33:14 UTC 2009 I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). Building such an oscillator is a little over my head so I thought I would ask the group if anyone knows where I could buy the missing link of this project. I have put a drawing of my project on the web showing the specs of what I need. The oscillator is shown in the blue box. Any help or suggestions would be greatly appreciated. http://www.braddye.com/gps_do.html 73s Brad Dye K9IQY ex KN9IQY, KN4BK, KM5NK, WB4JCF, ZP5TQ, WA4VXU, WA9RVL, /TI2, /9Y4, / 6Y5, /KP4 As already mentioned, a DDS produces unwanted spurs. You can elminate them by using it backwards. 1. get a 66.MHz VCXO with good phase noise 2. drive the SDR as normally done 3. also drive a suitable DDS chip 4. set the DDS to produce 10MHz output with 66.MHz reference 5. feed the TBolt and DDS outputs to a 10MHz pfd 6. use loop filter to correct 66.MHz VCXO 7. you are now locked to GPS without the spurs from the DDS Simplified Diagram (view in fixed font) TBolt 10MHz --- PLL Ref Loop Filt ---+ 66.MHz - DDS - 10MHz -- PLL Clk | | OCXO I/P --+ Trim the frequency by adjusting the DDS as desired, perhaps to give a slight offset to the receive frequency. Mike ___ 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] GPSDO project
TI, AMD National all make synthesizer chips which would work nicely. The problem is that they all charge $$$ for the evaluation kits, which would kake a very handy way to use them. Maybe you can sweet talk your local salesman into a freebie? Pete Rawson ___ 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] GPSDO project
TI, AMD National all make synthesizer chips which would work nicely. What sort of phase noise and/or spurs do they have? (relative to a good/OK crystal) Do the data sheets have good info? -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] GPSDO project - connecting external 66.667MHz into the SDR-IQ
See the pages on my web-site (http://g4hup.com) - instructions for connecting external LO signal to SDR-IQ are given there - these came from RFSpace. WW2R has implemented this with a small switch on the back panel of the SDR so he can use internal or external LO when available. Would be very interested to hear whether these same instructions apply to an SDR-14 - anyone prepared to open theirs up and have a look? 73, Dave, G4HUP From: WB6BNQ wb6...@cox.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, 28 June, 2009 11:55:46 PM Subject: Re: [time-nuts] GPSDO project Hi Brad, I am a little confused about your intentions. There is no mention on the RFspace web site about a provision of being able to feed in an external reference signal to the SDR-IQ or the SDR-14 for that matter. If you study the Analog devices AD6620 component, you will see that it is a 3.3 volt * * * ONLY * * * process, which only adds to the problem. Additionally there are constraints on the rise and fall times of the timing signal. This is a horrifically complex component with intricate dependencies tied to the specific A/D used. This is not your daddy's VFO from yester-year. The fact that the internal DDS is a digital function means you will never, ever, get to a perfect cardinal point, except under very special conditions. In this case it will have an offset of 16 pico-seconds because that is the smallest resolution the DDS can do. While small it would require very special hardware for you to keep it locked to the GPS. As the internal clocking system runs more then just the DDS, other considerations come into play. The clocks built to run these chips are not designed for external control and studying the physical layout of the SDR-IQ, it does not appear that they provided any means to have external clocking ability. Besides the computer's sound card DSP is heavily involved with regards to the frequency calibration. So there are two independent clocks to keep synchronized that are not related to the listening time, particularly if you record the digital bits for later listening or analysis. Fortunately, the software will allow for you to calibrate, to some degree, but it is not and you will not be able to approach what you expect to do with the Thunderbolt. Keep in mind that the best you could do with a Thunderbolt on a 1 second per second comparison basis is only 1 part in 10 to the minus ninth (1x10^-9). It gets worse if you consider shorter times like a continuous analog aspect that you would have for active listening. The noise of the GPS system would mask the 16 pico-second resolution of the SDR-IQ DDS. The real problem is temperature. You could improve that by providing a chamber for the SDR-IQ and raising, carefully, the temperature to just above your highest ambient level. After all that, I am not saying you couldn't/wouldn't/shouldn't consider it. Keep in mind that the SDR-IQ, or for that matter, the SDR-14 DDS only sets the center of the 190 KHz bandwidth swath that you are viewing at any one time. The real fine aspect is done in the computer and the clocks in those are all over the map, so to speak. In order to have a really tight calibration, with Timenuts quality, would involve some serious effort to build a clocking system for both the SDR-IQ and the computer. The final result is you would still be offset due to the digital processes in both the SDR-IQ and the computer, plus, perhaps, some latency in the software. As I get to the point of sending this email I see that Dave Powis, G4HUP, has gone to the trouble to lock the SDR-IQ internal oscillator to an external 10 MHz. If you look at all the information on his web site, you will see that it is not a trivial project. As I pointed out, this only stabilizes the window of the SDR-IQ still leaving the computer to tend with. My experience with the Thunderbolt shows that it has some temperature dependencies and the expected nominal noise of the GPS system in the short term regard. What most people do is have a high quality house standard and do long term comparisons to the GPS. A high quality house standard would, in effect, filter the short term noise of the GPS system. At any rate, this is my fantasy and I am sticking to it ! BillWB6BNQ Brad Dye wrote: I have just purchased a Thunderbolt GPS receiver. I hope to use this to discipline an oscillator on 66.6 MHz so I can use it as a LO on my Software Defined Receiver (SDR-IQ). Building such an oscillator is a little over my head so I thought I would ask the group if anyone knows where I could buy the missing link of this project. I have put a drawing of my project on the web showing the specs of what I need. The oscillator is shown in the blue box. Any help or suggestions would be greatly appreciated. http://www.braddye.com/gps_do.html 73s Brad Dye K9IQY ex KN9IQY, KN4BK, KM5NK
