[time-nuts] Changes in commercial GPS clocks over the decades

[The Fiber Guru]

During my telco career I was responsible for Network Synchronization and
witnessed several generations of clock designs.  Post-telco I now
manufacture and sell Network synchronization systems.  Here are a few
observations from legacy and modern topologies:

 

1. BITS clocks used to consume an entire 8 ft rack in a large central office

2. Legacy clocks easily cost $35k to $50k

3. The most critical part of clock installation is the antenna......this has
never changed.  If you get this wrong the clock will flop around like a fish
out of water

4. Most critical part of antenna installation is to have unobstructed view
of the sky, but not be the highest electrical element (for lightning
protection....come of protection).  Of equal importance is selecting the
proper size antenna cable for the required distance (RG58 up to 100 ft,
RG213 up to 300 ft, LMR400 up to 600 ft)

5. Always, always, always install a lightning arrester.  Get away from me
with, "But we don't get lightning strikes."  Arresters are WAY less
expensive than GPS receiver modules in commercial clocks

6. The latest "smart ocxo's meet the performance of legacy Rb oscillators at
a fraction of the cost, and last much longer with very low heat dissipation

7. Since they don't use Composite Clock signals in Europe (64kbps with an
8kHz error rate), almost none of the Network Synchronization systems outside
the USA provide these TDM outputs, but thousands of small carriers and
government sites still require it

8. IEEE 1588 has been really slow to catch on.  Our first PTP product was
available for a decade with extremely low sales

9. We started with grandmasters, but now also have boundary and transparent
clocks to cut down on segments

10.  I've sold clocks for $50k, then we got them down to $30k, then $15k, to
$7k and we now sell $millions of clocks sub-$5k.  That's all in a 15-year
span.

When I present material on Network Synchronization, I always point out the
irony that multi-gigabit transmissions systems are synchronized by clocks
that rely entirely on a 

1 PPS signal (derived from GPS to discipline an oscillator).  So our fastest
networks are dependent on our slowest (but highly accurate) signal!

 

I enjoy reading your comments and learning about your projects.

 

Daniel B. Burch (The Fiber Guru)

 <http://www.fiber.guru/> www.fiber.guru