[time-nuts] GPS ceramic patch in what plastic housing?

Robert Atkinson robert8rpi at yahoo.co.uk
Mon Sep 6 16:10:02 UTC 2010


That lit a light bulb (pun intended),
How about the cover of one of the encased low energy compact fluorescent. lamps? I've seen them in both glass and plastic (possibly PET).
 
Robert g8rpi. 

--- On Mon, 6/9/10, Chuck Harris <cfharris at erols.com> wrote:


From: Chuck Harris <cfharris at erols.com>
Subject: Re: [time-nuts] GPS ceramic patch in what plastic housing?
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Date: Monday, 6 September, 2010, 16:38


I know, cut the top off of a 150W incandescent light bulb and use it
to make a radome.

-Chuck Harris

jimlux wrote:
> Predrag Dukic wrote:
>>
>> Bill,
>>
>> Pyrex ( and any other glass) could reflect too much. It is true that
>> glass,
>>
>> depending on composition, is not absorbing microwaves, and does not
>> heat itself in the owen,
>>
>> but how much it is transparent at 2.4 ghz should be checked somehow...
>>
>> P. Dukic
>>
>>
>>
>
> I wouldn't use a glass jar/mixing bowl, what-have-you.
>
> A) glass is a bit lossy (even at 100-200kHz), but probably not enough to
> be an issue.. (Now, if you were building kW scale capacitors for a tesla
> coil, that's a different thing)
>
> B) A bigger problem: Glass has a (unevenly controlled) dielectric
> constant of around 2.5..
>
> So, you'll get reflections at both interfaces as well as some refraction
> as the signal passes through the "radome"
>
> The whole radome design thing is much trickier than one might think for
> a something where angle of incidence is important. There's a reason that
> you see lots of hemispheres, and one tries to control the thickness of
> the radome (in fact, sometimes, you make the shell from a honeycomb core
> with 2 face sheets, although at L band, this would be tricky).
>
> So, either you use something simple, and accept whatever defects it
> creates in your antenna pattern, or get fancy.
>
> Glass babyfood or canning jars will probably work, and will literally
> last your life time. White painted plastic would also work.
>
> Watch out for things like appropriately venting it (so moisture doesn't
> collect inside) and making sure it doesn't make a little solar oven
> (gotta paint that clear glass, I suspect)
>
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