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

Bob Camp lists at rtty.us
Wed Sep 22 23:08:35 UTC 2010


Hi

That's my feeling. The firmware isn't the issue. The OCXO and the temp sensor are the important points. The firmware is just an easy way to get the right OCXO.

Bob



On Sep 22, 2010, at 7:00 PM, Mark Spencer <mspencer12345 at yahoo.ca> wrote:

> 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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