[time-nuts] What's best an HP 58503A, Z3805A, or Z3801A upgraded to 58503A?

Magnus Danielson magnus at rubidium.dyndns.org
Sun Nov 30 17:11:58 EST 2014


> As far as I can see, there are really only two basic sets of hardware here.
> 1) The earlier 10811 / Motorola design
> 2) The later 260 / Furuno design.

Having dig deep into the Z3801 firmware, I can say that it has many 
features that doesn't even exist on the Z3801 hardware. Well, sort of.
The reason that Z3801 is so easy to convert to 58503 is because it is 
essentially the same design in different packaging. The Z3801 firmware 
even has the code for loading a second FPGA which isn't even on the 
Z3801 PCB, but there is an empty position for such an FPGA on the PCB, 
and it fits the FPGA the secondary image is for. Dropping in such an 
FPGA, mounting some more components on other location of the PCB and you 
have more functionality at your hands. I doesn't take much imagination 
to realize that this is part of the conversion process. I'd love to see 
the photos of a 58503 PCB as well as a converted Z3801.

It also makes good sense to anyone building these things to have a large 
common core.

There is the Z3815A which has the hockey-puck / Furuno combination.
I've seen that more Z38xx variants have been listed here, but I have not 
kept track of them all. Have someone complied a list?

> The rest is packaging and luck. ADEV performance wise, some of the 3801’s do quite well, some not quite as well. There was a lot of variation in the 10811 since it was not targeted at ADEV. Phase noise wise, the 10811 design will be better. Both will have spurs. The 10811 designs are older and may have more running hours on them. Either one may have been impacted negatively by the salvage process.

The Z3801 attempted to have good hold-over phase stability rather than 
phase-noise property. It does a drift calibration using least-square 
drift fitting, which indicates that focus was on hold-over properties, 
with active drift compensation. It's not bad, but it may or may not be 
what you are looking for.

None of the techniques is very difficult, it's just that it's a fully 
integrated package of several pieces.


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