There are different hardware variations of the Thunderbolt out there. There is the commercially available Thunderbolt which available from Trimble that everyone is familiar with, and then there are the industrial versions that are made for the telecoms. The Andrews E-911 version, unfortunately, looks to be regular commercial version from what I can see from the board layout and the form factor.
I'm lucky enough to own a couple of Thunderbolts as well as some of the different telecom versions and they DO NOT have the same performance. The commercially available Thunderbolt (the one comes in the little red box) has the least favorable performance when compared to the industrial versions. I've found that the industrial Thunderbolts, with their better hardware and much nicer oscillators, have a stability that is comparable to the Z3801A (if not exceeding it). My commercial Thunderbolts have more jitter and don't stabilize as quickly as the higher end boards. I don't have a cesium or hm to give hard Allan Variance numbers but I do use a counter that in it's nulling mode will show differences as small as 1.9e-9Hz ( 0.0000000019 Hz ). Using a 10sec gate I'll watch how often the lower differences are displayed. So if I see a number displayed >1.0e-3Hz show up a lot, I'll know that the oscillator has more jitter than an oscillator that consistently displays <1.0e-3Hz. But when I have an oscillator that is very stable I will see a lot of differences in the 1e-6Hz and 1e-9Hz range. I notice that commercial Thunderbolts display readings that have greater variance than the industrial boards when referenced against one of my favorite HP Z3801A's. The industrial boards have a much tighter variance will show a lot of differences in the 1e-6Hz and 1e-9Hz range much more often. Hardware wise: The industrial versions seem to have better power supplies with more filtering (since they are not limited by space I guess). They also have to seem more components that support the cpu (possibly for added functionallity or to support different algorithms). And of course, the oscillators. The single oven in the commercial Thunderbolt does seem to even come close to the industrial boards. The industrial boards I have are the Z3801A clone with a double oven oscillator and a couple of boards with high-end Vectrons. On Trimble's Thunderbolt web page, there is a link for a Thunderbolt Performance with a Double Oven Oscillator. I think people might be mislead to believe that is the performance of the commercial Thunderbolt that they are selling, but it's not. What the are showing is the performance of what I believe to be one of the industrial boards with an older high-end Vectron double-oven (the model 330Y4472) which was available in the Z3801A clone made for Nortel. The commercial version doesn't even come close to that. I think the "holy grail" of Thunderbolt boards is the Nortel boards. The are still in service and have their firmware updated by Trimble unlike (the commercial version which Trimble doesn't give any info about firmware upgrading). Unfortunately, the Thunderbolt everyone want to buy from this seller who has "hundreds" of them, is (and I say this with 99.94% certainty) a regular, commercial Thunderbolt in a different housing. I certainly won't pay $250 for one. And if this guy has 'hundreds', he will discover there is no market for them at $250. I'll pick one up when it dips below $100. The other Thunderbolt board on ebay now, with the 5 10mhz outputs is a steal at $225 if you can get one of the "last four". _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts