[time-nuts] GPSDO Alternatives

Bob Camp lists at rtty.us
Thu Dec 6 21:56:03 UTC 2012


The single best thing about a TBolt is Lady Heather.

Consider how many years it's taken to get it to where it is today. Consider
how many people have worked extensively on it. It's a wonderful thing to
have available. 

Could you make a homebrew gizmo look "just like a TBolt"? Sure you could. It
might well take you forever to do all the reverse engineering, validation,
and testing, but it can be done. I'd guess it would take less time to
re-write a version of LH from scratch....


Another thing to consider:

Z3801's got scrapped out, flooded the market, and the price went to "real
good". The supply dried up and prices climbed. This took years.

TBolts went through the same cycle. Again over a time period of many years.

In both cases you had a long time to look at them and make a decision about
weather you wanted one or not. It was never a "buy it this week or they are
gone" thing. 

These aren't the only things that will ever get scrapped. There's something
somewhere in the world that's going to get junked. Some sort of GPSDO will
flood the market in the future. It will be around for many years at low

What ever you do as a project needs to be pretty good to survive the
competition. Otherwise it'll die before anybody ever sees one. 


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Charles P. Steinmetz
Sent: Thursday, December 06, 2012 4:36 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPSDO Alternatives

Don wrote:

>you guys are reinforcing that just because its' cheap won't mean it 
>won't work.

Of course it doesn't.  But keep in mind that "working" spans several 
orders of magnitude in this area, and what one needs to design and 
build depends on what degree of "working" one needs to support the 
uses to which the finished standard will be put.  First, there is 
performance during normal operation (good, continuous satellite 
tracking) -- ADEV at all taus of interest, PN at all offsets of 
interest, distortion and spurs, residual AM, stability over 
temperature, PPS jitter, etc.  Then, there is performance with poor 
satellite visibility, and finally performance in holdover (no 
satellite visibility) for however long one needs it (if one needs it 
at all, which many amateurs may not).  For some, there will be power 
consumption issues.  There may also be issues of interfacing to 
monitoring devices, both simple (e.g., LCD status displays) and 
sophisticated (e.g., computer running Lady Heather or Z38xx).  Does 
it need to work with existing programs, or is writing a new 
monitoring program part of the project?  Then there are the 
construction issues.  Does it need to be assembled entirely from 
connectorized modules, no soldering required?  Or capable of being 
thrown together on a scrap of perfboard?  Or will a PC card be 
designed?  If so, can it use SMT parts?  How adaptable must it be, 
particularly in accommodating different oscillators?  Does it need to 
support rubidium oscillators as well as quartz?  Etc., etc., etc.

Thunderbolt and Z38xx commercial GPSDOs are plentiful and relatively 
affordable, so they are natural benchmarks for any DIY project.

 From my perspective, the most interesting development would be an 
offer by someone with a very well equipped lab to test any DIY GPSDO 
with a consistent protocol and publish the results.  That way, we 
could all see how the various approaches compare with respect to the 
characteristics that are most important to each of us.

Best regards,


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