[time-nuts] [qs1r] Looking for good, cheap, external reference

[Mark Spencer]

Would a newer unit with the 3.00 firmware, the trimble branded OCXO and the 
older temperature sensor be one of the better (or perhaps best ?) TBOLT 
combinations ?



----- Original Message ----
From: John Miles <jmiles at pop.net>
To: lester at veenstras.com; Discussion of precise time and frequency measurement 
<time-nuts at febo.com>; David <n7aig at yahoo.com>
Sent: Wed, September 22, 2010 12:42:06 PM
Subject: Re: [time-nuts] [qs1r] Looking for good, cheap, external reference


>      John, unless I am going mad, the ADEV plots for both auctions you
> mentioned look the same - maybe the bad one has been replaced since
> you posted your message?

The black-and-white plot that everybody uses is from the original
Thunderbolt data sheet, which was way conservative even for the older units.
Towards the bottom of the 290308733659 auction, though, the seller has
appended a half-dozen or so photographs of a TSC 5120A screen showing what
are (for a Thunderbolt) some weak results.  The ADEV plot shows poor
long-term disciplining and the PN plot doesn't look good either.  Possibly
he's using a noisy reference, or the unit was tested during a 2-day-long
earthquake.

I've never seen one do ~-88 dBc/Hz at 10 Hz.  Even my original one with the
lower-quality OCXO was good for -105 dBc/Hz, while the ones with the
Trimble-labelled OCXO can do -130 or better.  Likewise the 'good' ones will
do several dB better than the -150 dBc/Hz broadband floor he shows.

I've also never seen one in a black anodized(?) housing like that (has
anyone else?)  Mark is right in that the 3.00 firmware doesn't necessarily
do much for you, but the newer units also had the good OCXOs, which IMO is
more important than the temp sensor.

-- john, KE5FX


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