[time-nuts] EOL Motorola Oncore Remote Antenna

[Bob kb8tq]

Hi


> On Nov 30, 2020, at 6:08 PM, jimlux <jimlux at earthlink.net> wrote:
> 
> On 11/30/20 1:22 PM, Art Sepin wrote:
>>> 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.
>> Interesting. That's the first we've heard about micro-cracks in the Radome but that's certainly a likely possibility with such a long exposure to U/V. The more common failure mode reported was moisture ingress due to "breathing;" the uptake of moisture laden air past the O-Ring, due to a small pressure differential. But, once the moisture was inside, it was also trapped internally by the O-Ring. This condition was reported more often in geographic areas that experienced a wide variation in barometric pressures.
>> Art
> 
> 
> 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.

About the only way to do it is to weld the beast shut with a “compression” welder.
Resistance weld is pretty good. Cold weld is better. Both impact your choice of 
materials and the shape / size of the part. Both are very much a one way street. 

Yes, there’s more to it if you want to get connections in and out. Forget about 
“hermetic” connectors, they aren’t up to the task. You need glass to metal seals 
embedded in the structure. Now you have even more constraints on the package.

There are a few other ways (glass bottles …. ), but they are even more complex /
harder to seal properly. All of them are a one time process.

(Yes this *is* how / why you seal up a crystal …..)

Bob


> 
>> -----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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