[time-nuts] Thunderbolt reception problems

bg at lysator.liu.se bg at lysator.liu.se
Sat Nov 21 22:17:12 UTC 2009


Hi Said,

As we talked about some weeks ago... your test is unfair to the Tbolt, but
that is perhaps intentional. The Tbolt will need more gain to work. You
are giving it a signal that is out of spec.

--

   Björn

> Hi guys,
>
> some weeks ago we talked about reception problems on Trimble Thunderbolt
> units. I finally took the time to download the Trimble monitor again, and
> get
> my  unit locked again. Here is what I found:
>
> The unit was running continuously for the last months, but wasn't  locked.
> Using the Trimble monitor, I restarted the unit, now connected  directly
> to
> my antenna, then after the survey was done let it run from my  antenna
> splitter.
>
> This works, but just barely. I use an Agilent 58512A amp, followed by a
> Mini Circuits ZB4PD1-152-75+ 1-to-4 passive splitter.
>
> In the attached plot a JLT FireFly-IIA and the Thunderbolt are both
> running
>  from the same Mini Circuits splitter. The Antenna sense circuit in the
> Thunderbolt is happy, but the signal strength is just at the threshold of
> working. The Sats kick in and out. Please see the attached screen  shot.
>
> At the same time the FireFly-IIA receiver is tracking 11 Sats with perfect
> signal strengths (up to 45dB+ C/No), from the same feed.
>
> The difference in receiver performance is quite clear. Unfortunately I
> have only a single antenna, so need to run the Thunderbolt from a
> splitter.
>
> One can also see two more interesting tid-bits in the screen shot: the
> FireFly-IIA is tracking and using WAAS Sat PRN 48 (PRN 51 goes in and out
> of  lo
> ck due to a chimney being in the way), and it is showing true MSL rather
> than  just GPS Height.
>
> Thanks for the help,
> bye,
> Said
>
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