Re: [time-nuts] HP 3586 entirely referenced to 10MHz: A solution II
I am thinking the answer is not the interesting thread. Its yes, that approach was considered. I can't speak for Bert but the issue has been understood for a long time actually. At least 10 years since my first purchase. When I consider a problem I tend to look at the trade offs trade offs. The ability to actually be reproduced, simple, parts availability, low cost, stable, and a lot of other factors. Kind of would anyone else ever build something like X. So when FPGAs get introduced into the thread it starts to change the complexity of the project and the likelihood of very few actually having the ability to design or enhance and then burn the chip. The is a heck of answer to a tough problem at a cost of $ 8 total for both chips. Can be improved, gets more difficult as you improve it. Like everything else. Regards Paul WB8TSL On Mon, Apr 4, 2011 at 5:33 PM, David I. Emery d...@dieconsulting.comwrote: On Mon, Apr 04, 2011 at 07:19:38AM -0400, Chuck Harris wrote: Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. No question about that, indeed. But I am talking about a very low bandwidth loop (presumably well under 1 HZ should work) which means the phase noise contribution from the dividers and reference should be only inside that 1 Hz bandpass. Outside of that the original crystal oscillator phase noise should control, and while this won't improve that it also won't make it any worse. You can think of it this way: Both the reference, and the oscillator being controlled, need to be divided down to some common frequency that you feed to the phase detector. The entire time the counter is counting up the cycles to get you a cycle of that common frequency, the oscillator is not being disciplined. It is only after the count gets done that the phase detector can compare the two signals and create a correction correct for the error in the oscillator. True, but I am pretty sure the original crystal oscillator (even modified with a varactor for tuning) was not phase-noisier than the rest of the instruments LOs. It is, after all, a LF crystal oscillator running at 13 or 17 KHz with presumably a high Q crystal which shouldn't to the first order have unreasonable phase noise in the band around it. The original problem was that this oscillator was not locked to a reference and could drift a few tenths of a HZ (and maybe even Hz) randomly with temp - not that it had too much phase noise. The DDS is essentially a hardware solution to finding a suitable divider ratio to convert one frequency into another. I do understand DDSes. -Chuck Harris -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote: Unlike simply stabilizing the BFO crystal as you propose. Has anyone given any thought to an alternative - phase locking the original BFO Xtals with a very narrow bandwidth loop to something derived from the 10 Mhz standard in such a way that the final frequency of the BFO comes out exact ? Looks to me (superficially without looking at the schematic carefully) like this might be possible too... -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
On Mon, Apr 04, 2011 at 02:00:14AM -0400, David I. Emery wrote: On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote: Unlike simply stabilizing the BFO crystal as you propose. Has anyone given any thought to an alternative - phase locking the original BFO Xtals with a very narrow bandwidth loop to something derived from the 10 Mhz standard in such a way that the final frequency of the BFO comes out exact ? Looks to me (superficially without looking at the schematic carefully) like this might be possible too... To elaborate a tiny bit, if you divide 10 MHz to 25 HZ you could use that as the reference for a classic PLL loop that stabilized the crystals with a varactor... provided of course suitable low pass filtering was used. There are also approaches involving doing early late sampling of the BFOs on selected edges of the 10 MHz clock which could be done more digitally in a FPGA. I presume one can pull the existing crystals enough with some hacking of the oscillator to add a varactor... This would avoid a non integer frequency setting where the DDS approach does not (unless you multiply by 3 to 30 MHz first I think). -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. You can think of it this way: Both the reference, and the oscillator being controlled, need to be divided down to some common frequency that you feed to the phase detector. The entire time the counter is counting up the cycles to get you a cycle of that common frequency, the oscillator is not being disciplined. It is only after the count gets done that the phase detector can compare the two signals and create a correction correct for the error in the oscillator. The DDS is essentially a hardware solution to finding a suitable divider ratio to convert one frequency into another. -Chuck Harris David I. Emery wrote: On Mon, Apr 04, 2011 at 02:00:14AM -0400, David I. Emery wrote: On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote: Unlike simply stabilizing the BFO crystal as you propose. Has anyone given any thought to an alternative - phase locking the original BFO Xtals with a very narrow bandwidth loop to something derived from the 10 Mhz standard in such a way that the final frequency of the BFO comes out exact ? Looks to me (superficially without looking at the schematic carefully) like this might be possible too... To elaborate a tiny bit, if you divide 10 MHz to 25 HZ you could use that as the reference for a classic PLL loop that stabilized the crystals with a varactor... provided of course suitable low pass filtering was used. There are also approaches involving doing early late sampling of the BFOs on selected edges of the 10 MHz clock which could be done more digitally in a FPGA. I presume one can pull the existing crystals enough with some hacking of the oscillator to add a varactor... This would avoid a non integer frequency setting where the DDS approach does not (unless you multiply by 3 to 30 MHz first I think). ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. In that case, that may not be a problem. Since the oscillator is a crystal, phase noise should be low enough. One other issue is that most crystals only want to move in one direction (with the varactor pulling trick), so if it is on the wrong side of where you want it, that won't work. Otherwise, I have been thinking about that myself. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Chuck Harris cfhar...@erols.com Sender: time-nuts-boun...@febo.com Date: Mon, 04 Apr 2011 07:19:38 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] HP 3586 entirely referenced to 10MHz: A solution II Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. You can think of it this way: Both the reference, and the oscillator being controlled, need to be divided down to some common frequency that you feed to the phase detector. The entire time the counter is counting up the cycles to get you a cycle of that common frequency, the oscillator is not being disciplined. It is only after the count gets done that the phase detector can compare the two signals and create a correction correct for the error in the oscillator. The DDS is essentially a hardware solution to finding a suitable divider ratio to convert one frequency into another. -Chuck Harris David I. Emery wrote: On Mon, Apr 04, 2011 at 02:00:14AM -0400, David I. Emery wrote: On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote: Unlike simply stabilizing the BFO crystal as you propose. Has anyone given any thought to an alternative - phase locking the original BFO Xtals with a very narrow bandwidth loop to something derived from the 10 Mhz standard in such a way that the final frequency of the BFO comes out exact ? Looks to me (superficially without looking at the schematic carefully) like this might be possible too... To elaborate a tiny bit, if you divide 10 MHz to 25 HZ you could use that as the reference for a classic PLL loop that stabilized the crystals with a varactor... provided of course suitable low pass filtering was used. There are also approaches involving doing early late sampling of the BFOs on selected edges of the 10 MHz clock which could be done more digitally in a FPGA. I presume one can pull the existing crystals enough with some hacking of the oscillator to add a varactor... This would avoid a non integer frequency setting where the DDS approach does not (unless you multiply by 3 to 30 MHz first I think). ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
Hi Didier, If you want to convert the Xtal to a VCO, you will have to adjust the parallel capacitance so that the crystal can get above the desired frequency, and then design the varactor circuit so that it can pull from there to below the desired frequency...which should be possible if the crystal was capable of being tuned on frequency. The crystal might be high enough Q to run in a PLL with a very high division ratio, but I would still expect it to hiccup around about the period of the divider but as you say, it might not matter. The DDS works out to be such a simple solution, I think the minuscule offset is hardly worth getting worked up over. -Chuck shali...@gmail.com wrote: Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. In that case, that may not be a problem. Since the oscillator is a crystal, phase noise should be low enough. One other issue is that most crystals only want to move in one direction (with the varactor pulling trick), so if it is on the wrong side of where you want it, that won't work. Otherwise, I have been thinking about that myself. Didier 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.
Re: [time-nuts] HP 3586 entirely referenced to 10MHz: A solution II
Hello Didier; I don't have a copy of the schematic however I was wondering if there are trim caps installed for these crystals?? If so, then a varactor can tune above and below in place of the mechanical cap if you remove it. Undoubtedly there is some loading cap in the circuit that could be tweaked a tad. Crystals drift over time though, this could have an effect on this concept. It may be that they have already drifted too far to tweak with the VCO concept. Also, there are many ways that a PLL ideas interact with phase noise. If the PLL reference source is quieter than the intrinsic noise of the VCO then the loop band width does govern the close in noise spectrum. However, there are many systems wherein the reference bandwidth is very small and the VCO noise governsl. Take for instance the PPS control of the GPSDO OXCO. The PPS frequency reference is unable to reduce the noise of the OXCO above about one half Hz, so the ultimate phase noise above that frequency is that of the oscillator itself. This can be a creative brain buster when working on designs for these ideas. My vote is to do a DDS synthesizer, this is a fine evolution low in cost and easy to implement, to displace approximate oscillators. What frequencies are you generating? Regards; Greg On 4/4/2011 7:29 AM, Chuck Harris wrote: Hi Didier, If you want to convert the Xtal to a VCO, you will have to adjust the parallel capacitance so that the crystal can get above the desired frequency, and then design the varactor circuit so that it can pull from there to below the desired frequency...which should be possible if the crystal was capable of being tuned on frequency. The crystal might be high enough Q to run in a PLL with a very high division ratio, but I would still expect it to hiccup around about the period of the divider but as you say, it might not matter. The DDS works out to be such a simple solution, I think the minuscule offset is hardly worth getting worked up over. -Chuck shali...@gmail.com wrote: Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. In that case, that may not be a problem. Since the oscillator is a crystal, phase noise should be low enough. One other issue is that most crystals only want to move in one direction (with the varactor pulling trick), so if it is on the wrong side of where you want it, that won't work. Otherwise, I have been thinking about that myself. Didier 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. ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
On Mon, Apr 04, 2011 at 07:19:38AM -0400, Chuck Harris wrote: Basically, the higher the division ratio in a PLL synthesizer, which is what you are describing, the greater the phase noise. No question about that, indeed. But I am talking about a very low bandwidth loop (presumably well under 1 HZ should work) which means the phase noise contribution from the dividers and reference should be only inside that 1 Hz bandpass. Outside of that the original crystal oscillator phase noise should control, and while this won't improve that it also won't make it any worse. You can think of it this way: Both the reference, and the oscillator being controlled, need to be divided down to some common frequency that you feed to the phase detector. The entire time the counter is counting up the cycles to get you a cycle of that common frequency, the oscillator is not being disciplined. It is only after the count gets done that the phase detector can compare the two signals and create a correction correct for the error in the oscillator. True, but I am pretty sure the original crystal oscillator (even modified with a varactor for tuning) was not phase-noisier than the rest of the instruments LOs. It is, after all, a LF crystal oscillator running at 13 or 17 KHz with presumably a high Q crystal which shouldn't to the first order have unreasonable phase noise in the band around it. The original problem was that this oscillator was not locked to a reference and could drift a few tenths of a HZ (and maybe even Hz) randomly with temp - not that it had too much phase noise. The DDS is essentially a hardware solution to finding a suitable divider ratio to convert one frequency into another. I do understand DDSes. -Chuck Harris -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] HP 3586 entirely referenced to 10MHz: A solution II
Perry, The bad part of your solution, that you seem to be missing is the BFO will not be locked or referenced to any standard but itself. If that is acceptable to you, then there is no need to reference your 3586 to anything but itself rendering the entire subject void to you. The DDS solution makes the BFO frequency, which is very important in using audio solutions to frequency measurement with 3586 referenced to the same standard as the rest of the unit. The small offset (not error) is easily removed by simply subtracting, or adding it when figuring the result. It is constant, and will never change. Unlike simply stabilizing the BFO crystal as you propose. -Chuck Harris Perry Sandeen wrote: List, Wrote: Your simple idea is a non-workable concept. Now how do you actually know that? It’s an opinion that would have to be proved or disproved by actually doing it. I based my opinion on the graph that showed the HP crystal frequency change verses temperature which was IIRC, quite small. Wrote: Instead of whining about the complexitysnip Well, I’m sorry if a different viewpoint, in the way I expressed mine, causes you to give me a personal derogatory label instead of the usual gracious responses others on the list have provided me. Wrote: why not contact Bert or Paul Swed and see if one of them would do you a favor and build the item for you. Well that never occurred to me. If that thought had occurred to me, I wouldn’t have pursued it for two reasons. 1. It almost works. It it is a great improvement over the stock HP crystal oscillator but it still has some small errors do to the DDS scheme. 2. I have five working 3586B units and as I understand the article, I might need to have five different programs as each unit may have different nuances. And as I noted in my post, I have no programming ability or any source to one. And I also said in my post that if one can do it to go for it. Wrote: I do not believe the hookup part is that hard to do and if you follow instructions well it should be quite doable. I completely agree. I’ve worked on the innards of mine changing out a WECO connector for a BNC. The 3586 at 58 pounds it is heavy as heck because of all of its shielding but is surprisingly modular and easy to open and dis-assemble. (One should seriously consider replacing the power supply electrolytics is one is going to open the beast up.) For the present I plan on using the measurement technique that Burt Weiner K6OQK so graciously shared on the net and to us on the list. Locking my 3586 and 3336 to my GPSDO should allow me to get good results. I also can compare my first GPSDO to a second redundant GPDSO. This I can understand and do. Regards, Perrier ___ 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.
