I have a 10811 floating around here somewhere. What about marrying up one of your reject TAPR's to it ?
73, Dick, W1KSZ -----Original Message----- >From: Tom Van Baak <[EMAIL PROTECTED]> >Sent: Nov 21, 2008 2:33 PM >To: Discussion of precise time and frequency measurement <[email protected]> >Subject: Re: [time-nuts] To improve a Tbolt? > >> I've upgraded the graph on the http://www.ke5fx.com/tbolt.htm page to show >> the performance of my Thunderbolt from the TAPR group buy (in orange) next >> to the traces for my older unit before and after the 10811 upgrade. >> >> There is no upside to tinkering with the OCXO on the TAPR units, unless you >> have something that can beat a 10811. You could replace it with a rubidium >> source and get better short-term stability, but I don't think swapping one >> quartz OCXO for another would be a useful thing to do. >> >> -- john, KE5FX > >Hi John, > >Very nice work and I mostly agree with your conclusions. The >OCXO inside the TAPR TBolts is really quite good. And those >that aren't that good are not sent to TAPR for sale (my pile of >TBolt rejects is growing; more on that later). > >So, yes, the typical TBolt OCXO is in the same ballpark as many >10811, which is why replacing one with the other may be futile. > >A problem here is that 10811 are all over the map. There are >variants of 10811; and even those with the same part number or >part number suffix will vary. Some 10811 get way down in the >-13's and are thus much better than any TBolt I've seen (which >is also one reason that some HP 58503* or Z38* series GPSDO >command such a price). Also, some 10811 have much better >phase noise specs than other. Some people are after better PN >rather than better ADEV. > >So if you have the ability to measure each 10811, or measure >an assortment of good OCXO, clearly you can pick a superior >one and thus improve your TBolt performance. > >On your rubidium comment, one needs to be a little careful about >expectations. For short tau (say 0.1 to 10 seconds) your average >cheap eBay surplus telecom Rb will have far less performance >than a good OCXO. Yet mid-term (say 10 to 10^4 seconds), a >Rb-GPSDO will win. However, long-term the LO makes much less >difference since GPS always wins. And GPS aside, clearly the >holdover performance of Rb will blow away OCXO. > >So it all depends on ones need. I guess my main point is that a >typical rubidium-based TBolt is not necessarily, just because it's >"atomic", automatically better than a stock TBolt at every point. > >If you'd like to test an FRS or LPRO version of a TBolt for me let >me know. I'd rather see your plots than my words. > >Thanks, >/tvb > > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
