[time-nuts] Which First GPSDO to buy?

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Sat Dec 13 08:02:20 EST 2014

On 13 December 2014 at 06:55, David J Taylor
<david-taylor at blueyonder.co.uk> wrote:
> Or get a more modern using such as the LTE-Lite evaluation kit.  I see a
> 19.2 MHz version as item 171504588307, but 10 MHz and 20 MHz versions have
> also been made available.  It's a lot smaller and lighter than last
> century's kit, and might even come with a guarantee!

I'm sure you said that in a joking way David, as I am sure you know as
well as I do the guarantee status. But just to be clear, the LTE Lite
does come with a 6 month guarantee.


The above is the 19.2 MHz one, but 10 and 20 MHz are available too.
The choice between those is not exactly too obvious either - I think
if I were to buy one, (and I am certainly not discounting that
possibility), I would get the 20 MHz one and use a divide by 2 on the

Finding the most suitable GPSDO does seem to be a difficult task. I
went for what I believed was an original, unmodified HP 58503A. A part
of the reason for that choice was because the 58503A available runs on
mains electricity, so does not need any sort of power supply. (There
are DC versions too).

But with hindsight, choosing a mains powered one was a pretty dumb
decision. Since it is desirable to keep the OCXO powered 24/7 for
maximum performance, being able to power them in the event of a power
failure is desirable. That is *much* easier if something wants a few
tens of volts of DC, rather than an AC supply. An uninterruptible
power supply (UPS) typically lasts only 30 minutes or so, which is not
that good. It is long enough to shut a computer down, but not a whole
lot more. Their efficiency at full load is quite high, but at 10 or so
Watts, which is all a GPSDO is likely to want, the efficiency of the
UPS is very low. So even if one had a big high power UPS with huge
batteries, it is unlikely to last more than a couple of hours, as the
efficiency will be so low. The only solution would appear to be a very
small UPS, with a much larger battery mounted externally, which is a
whole lot more messy/expensive/large/inefficient than what one could
achieve if the GPSDO needs just a single DC supply.

So if I were the original poster, I would go for one which takes DC,
rather than AC. Fortunately that is most of the GPSDOs - especially
the cheaper ones.

The LTE Lite, with a power consumption of < 0.16 W @ 3.3 V, which is a
current of less than 50 mA, could be powered for several days from
fairly small non-chargeable cells. I personally would not  bother
using rechargeable batteries for that, as I don't think it would
warrant the extra cost of the charger, but others might feel

I assume it is worth powering the TCXO based LTE-Lite 24/7, but
perhaps it is not as important as with a higher performance OCXO. I
don't know.


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