[time-nuts] To improve a Tbolt?

[Richard W. Solomon]

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 <tvb at LeapSecond.com>
>Sent: Nov 21, 2008 2:33 PM
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>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
>
>
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