[time-nuts] EOL Motorola Oncore Remote Antenna

[ew]

Jim, I agree. As part of my OSA 8607A GPSDO project I planned to place the OCXO in an aluminium box to eliminate pressure change. Step one included buying a separate unit to make sure the rubber gasket did do the job. Attached first results. Temperature does change pressure more than ambient. The vertical steps are the result of gentle tightening the lid, did not know how much lid had to be tightened. Now I know and have a 10 day test running. With AC running, the AC control at the other end of the house lab temperature stays within ! C. Today a cold front hit, no AC and temperature will drop more than 1 C. Taking advantage of the forecast I am extending the test for a couple more days.                                                                                                       Doe to the low power dissipation of the 8607 fan cooling is not an option but I will use the box , seal it and characterize the 8607 for pressure and temperature and use external pressure and temperature sensors for compensation once combined with a new generation GPSDO.                                                                                



I'll bet pressure changes inside the "sealed" radome due to temperature 
changes are bigger than those due to local barometer changes.

But an interesting thing - water vapor will go through cracks, porosity, 
that liquid water will not. The commercial success of GoreTex is an 
example of this, but cracks, o-rings that aren't quite right, etc. are 
also ways it can happen.

Making a truly hermetic box is hard.

> 
> -----Original Message-----
> From: Poul-Henning Kamp <phk at phk.freebsd.dk>
> Sent: Sunday, November 29, 2020 11:19 PM
> To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>; Art Sepin <art at synergy-gps.com>
> Subject: Re: [time-nuts] EOL Motorola Oncore Remote Antenna
> 
> --------
> 
>> It's obvious from the photo that the O-Ring seal failed its purpose
>> over its many years of service. Has the unit totally failed or does the electronic portion still function?
> 
> No, the electronics is stone dead.
> 
> To me it looks more like water ingress through micro-cracks in the plastic-dome, and the O-ring did its job and kept that water in.
> 
> The microcracks are uniform and seem to follow the molding flow, and that is probably to be expected in our climate:  We have a lot of humid freeze-thaw cycles.
> 
> I wonder if buffing the radomes with car-wax would help ?
> 
>> I said lucky because I found some GSynQ parts here in an engineering
>> storage cabinet that we  can send to you at no charge to revive your unit.
> 
> Thanks for the offer, but dont bother: I had a spare on hand, and I may still have third one lying around somewhere.
> 


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