[Premium-Rx] Frequency Standards

[John Miles]

Agreed, Gary's observations don't make a whole lot of sense at first blush.
A GPS standard *is* a high-quality quartz standard, kept in constant
calibration against the GPS signal in a *very* low-bandwidth PLL.  The
effective loop time constant on the Thunderbolt is probably on the order of
a minute or two.

Trimble characterizes the phase noise of the Thunderbolt's output at about
15 dB worse than an HP 10811E at 10 kHz from the carrier (-145 dBc/Hz
versus -160 dBc/Hz), and in my experience, you can take that to the bank.

Sounds like the Datum receivers had faulty internal standards.  It's really
inconceivable that GPS disciplining, by itself, could increase a standard's
phase noise.

-- john KE5FX

  -----Original Message-----
  From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org]On Behalf Of Charles Hutton
  Sent: Monday, July 21, 2003 8:22 PM
  To: premium-rx at ml.skirrow.org
  Subject: RE: [Premium-Rx] Frequency Standards


  Oddly enough, my experience is the exact opposite. A previous project used
GPS as the timebase for an OFDM based Wireless Local Loop system. OFDM is
very phase noise sensitive; that is one of its significant drawbacks. GPS
timebases served us well, although we weren't buying $200 units - more like
$1200 Trimble boards.

  I would not give up on GPS at all, as long as you've climbed out of the
homeowner receiver level.
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