[time-nuts] A new take on the all-hardware GPSDO concept
bpl521 at outlook.com
Mon Sep 12 18:37:11 EDT 2016
>From the Jupiter-T TU60-D120 datasheet
Figure 1-3 (next page) shows the typical 1PPS performance of the Jupiter-T GPS receiver. The 10 kHz output is also available from the receiver and is phase coherent with the 1PPS signal. This output is made available for functions such as phase locking of crystal oscillators, frequency synthesisers, and similar applications.
> Date: Mon, 12 Sep 2016 21:00:51 +0000
> From: bob at evoria.net
> To: nsayer at kfu.com; time-nuts at febo.com
> Subject: Re: [time-nuts] A new take on the all-hardware GPSDO concept
> Nick said:
> "Jim Miller's 10 kHz GPSDO that’s been referenced here has either solved this problem, or the 10 kHz output of the Jupiter is substantially better than the Venus’ 10 MHz output, or the design doesn’t give the results time-nuts expect from a GPSDO. Which of those applies?"
> Hi Nick,
> You have to be very careful about the receiver you select. I think it's the case that the Jupiter's internal oscillator is phase locked to the GPS signal. In that case, you can use the output from the receiver to directly drive a PLL giving a high quality 10MHz or whatever you like. But, the low cost receivers on the market now, including those from Ublox, do not phase lock their oscillators to the GPS signal. In the case of Ublox, they specifically say that the quantization value is only available for the 1PPS output. So, yes, you can get a 10KHz pulse train from a Ublox or any other modern inexpensive GPS receiver, but it will suffer from whatever quantization error the manufacturer specifies.
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