<html><head></head><body style="zoom: 0%;"><div dir="auto">Yes on all counts, I think. Cheaper, simpler, and better performance. All we lose is frequency agility -- which I still very much want, but as an option.</div>
<div class="gmail_quote" >On Sep 29, 2019, at 9:41 PM, Scotty Cowling via TangerineSDR <<a href="mailto:tangerinesdr@lists.tapr.org" target="_blank">tangerinesdr@lists.tapr.org</a>> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="blue">Hi John,<br><br>So does it look like the Crystek oscillator with a 4-way output buffer <br>is the best solution for the stand-alone (no CKM) version of the DE?<br><br>The oscillator is about $15 in quantity, with the 4-way buffer (Si Labs <br>SI53341-B-GM) at $1.17 in quantity. This seems to be the cheapest way to <br>get the best non-GPSDO performance, and if we can get the Hermes method <br>to work we could use it as the basis of the GPSDO CKM, couldn't we?<br><br>73,<br>Scotty WA2DFI<br><br>On 2019-09-29 16:27, John Ackermann N8UR via TangerineSDR wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> Thanks for that Lyle. The 570 is a neat device, but as you said is<br> stand-alone.<br><br> We were looking at the SiLabs 543x series clock generator/cleanup/driver<br> chips which are basically complex synthesizers with virtually arbitrary<br> input frequency and multiple independent outputs settable to anything<br> from 1 Hz to over 1 GHz. The niftiest versions use a 48 MHz crystal<br> oscillator as a phase noise cleanup and can get to a pretty impressive<br> noise floor (something around -150 at 144 MHz) but not as good as the<br> Crystek 122.88 MHz VCXO.<br><br> But they're in the $13-18 price range (depending on type), have some<br> fiddly layout requirements (want a six layer board), and require<br> ultra-low-noise regulators at significant current, so as much as I love<br> the idea, I'm not sure it's the right choice, at least for a first-out<br> version.<br><br> For just a 122.88 output, the Crystek with a four-way output buffer is<br> cheaper and cleaner. And we've learned what caused the PLL performance<br> problem in the Hermes-derived boards, so hopefully can avoid that this<br> time around.<br><br> 73,<br> John<br> ----<br><br> On 9/29/19 6:27 PM, Lyle Johnson wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #ad7fa8; padding-left: 1ex;"> We used the Si570 in the K3S and KX3 synthesizers. Excellent noise characteristics but can’t be slaved to an external reference. We use a SiLabs synth in the KX2 that can use an external reference but noise performance is much worse.<br><br> FWIW, Lyle KK7P<br><br> Sent from my iPhone<br><br><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #8ae234; padding-left: 1ex;"> On Sep 29, 2019, at 2:39 PM, John Ackermann N8UR via TangerineSDR <tangerinesdr@lists.tapr.org> wrote:<br><br> To the TangerineSDR list --<br><br> I've spent the week since DCC thinking about GPSDO questions and getting<br> things in place to do some experiments. I was going to put together a<br> starting-point paper and send it to you and a few time/gps-nuts but<br> thought it was better to get some data first.<br><br> In quick summary:<br><br> A GPSDO is nothing more than a crystal oscillator ("XO") with an EFC<br> input that is steered to frequency by reference to the precise time<br> available from a GPS receiver, usually in the form of a pulse-per-second<br> signal. The crystal oscillator can have excellent short-term stability,<br> but will drift (age) over time and is subject to environmental<br> variables, particularly temperature. The GPS system has excellent long<br> term stability and accuracy, ultimately tracking USNO(UTC) but short<br> term usually requires long averaging times to reach that performance.<br><br> The task of the GPS designer, given the known performance of the XO and<br> the GPS constellation, is to optimize the control loop to extract the<br> best of both.<br><br> A better XO allows the time constant of the control loop to be longer.<br> A quieter GPS implementation allows the time constant of the control<br> loop to be shorter. What's of interest to me is that a shorter control<br> loop implies lower performance requirements on the XO, and that might<br> result in a way to lower overall GPSDO cost.<br><br> This wouldn't be very interesting except that there are now some low<br> cost GPS receiver modules available that might -- maybe, perhaps,<br> possibly -- provide a lower-noise GPS time reference. u-Blox<br> (<a href="https://www.u-Blox.com">https://www.u-Blox.com</a>) has released a bewildering variety of<br> navigation and timing modules with varying capabilities. I've attached<br> a table that I put together by extracting data from the u-Blox web site.<br><br> I'll soon have my hands on five of these modules with different<br> capabilities (and price points). Once I've had a chance to take some<br> initial measurements, and verify some specs that aren't clear from the<br> documentation, I'll provide an updated report that might serve as the<br> basis for some design discussions.<br><br> I'm also reaching out to a few friends in the time-nuts world to get<br> some recommendations for readily available 10 MHz XOs at a couple of<br> different price/performance points that we can at least use to provide<br> cost information.<br><br> Finally, I'm thinking about whether the SiLabs frequency synthesizer<br> chip is the most cost-effective way to get the low-phase-noise 122.88<br> MHz performance we need. It might be cheaper, and better, to use the<br> Hermes scheme, where a very low jitter 122.88 VCXO is locked to the 10<br> MHz reference -- provided we fix the known problem with the Hermes<br> implementation. The synthesizer offers flexibility, but I think its<br> cost (with required supporting components) will be greater than the<br> Crystek 122.88 oscillator module, and its phase noise performance not<br> quite as good.<br><br> Anyway, more to come.<br><br> 73,<br> John<br><br><br><br> <uBlox_GPS_Comparison_v2.pdf><br> -- <br> TangerineSDR mailing list<br> TangerineSDR@lists.tapr.org<br> <a href="http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org">http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org</a><br></blockquote></blockquote><br></blockquote><br><br><br></pre></blockquote></div></body></html>