[time-nuts] advice sought on basic gpsdo

[Robert Melville]

Fellow time nutters:

Any input or advice on the following project would be appreciated.

I want to make a small, portable, batter-operated clock that will
spend most of its time docked into a charging bay with access
to a signal from a GPS receiver -- either 1 PPs or 10.00000000 MHz.
The device will have a voltage-controlled TXCO that will be disciplined
by the GPS input unless the unit is traveling.

I have seen several designs for disciplined oscillators using a uP,
such as an Arduino or a PIC. The main decision seems to be between
1 PPs or 10 MHz as the input. 1 PPs might be preferable because
not all cheap GPS receivers seem to provide 10.000000 MHz out.
Mostly, I want accurate time but a frequency reference with
decent phase noise would be useful.

1. I am tending towards a published design from Lars Walenius, in part
because
it uses a familiar uP (an Arduino) but am open to other designs.

2. What advice to people have on glitch-free switching when
docking/undocking the unit from the GPS???
This seems to be something like the de-bouncing problem for a
push-button.

3. Has anyone used the Arduino time library withOUT the Dallas RTC chip --
i.e., some other source of time such as the from the locked oscillator?

4. Can anyone share experience with conditioning the power going into the
TXCO -- to what extent can digital noise from the uP or counters
contaminate the phase noise of the TCXO? Does a separate isolating buffer
help for the "osc out" port? I have had good success in the past with
so-called "active bypassing" to deliver very clean power to an oscillator.

Thanks to all for your attention to this message -- I am glad to look at any
and all possible designs.
Happy time-keeping!