[time-nuts] Trimble Resolution SMT GG weirdness

[Azelio Boriani]

Have you any reference? A TBolt, Z3801 or similar?


On Mon, Apr 22, 2013 at 9:53 PM, Daniel Ginsburg <dginsburg at gmail.com>wrote:

> Hi all,
>
> I have bought a Resolution SMT GG for me to play with, and build a very
> simple breakout board.
>
> The receiver appears to be working (in a sense). That is, it powers up, it
> emits valid TSIP, it was able to survey it's position - a sane one. Trimble
> GPS Studio is able to recognize it, and extract validly looking data from
> it. In other words, I don't believe I have botched the module while
> hand-soldering it.
>
> Now I have hooked it up to a stm32f4discovery board to sync with PPS.
> That's were the weirdness begins.
>
> First, the frequency offset of the microcontroller. I use a built-in
> counting timer in the uC which runs at 84MHz to measure the duration
> between 2 PPS. What I get is ~84008000 timer ticks between two pulses,
> which corresponds to about 95ppm offset. While the crystal on the board is
> of the cheapest variety, I think 95ppm is just too much. Is that correct,
> and 95ppm offset even for a the most crappy oscillator is not a reasonable
> value?
>
> Second, the GPS sawtooth. The PPS does exhibit sawtooth, which is
> expected. But the sawtooth is HUGE. While the spec claims +-15ns, I see
> more that +-400ns with period about 30 seconds. This is not sane. I must
> have done something totally wrong.
>
> Something has to be terribly wrong with my measurements. I'd really
> appreciate any hints on how to find out the cause of the described
> weirdness.
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