At work I have access to an industrial one that (I am told) uses lasers to 
harden a liquid... something. I'm not a plastic expert. We use that stuff for 
outdoor enclosures and it is UHF transparent, at least to some degree (it would 
have to be given our use case). I used it once to make a couple of wall mount 
J1772 fake inlets to hold our car charging plugs. Those have survived outdoors 
without any issues. At some point in need to repaint them, as the native color 
is battleship grey, and the white paint is starting to wear off.

If Tupperware made something conical, I'd chose that in a hurry. It may not 
have a great deal of UV staying power, but "microwave safe" implies good RF 
performance. I've used that solution to quickly weatherproof home brew stuff 
before. 

Even if whatever the cap is made of isn't perfectly RF clear, I've certainly 
got S/N margin for some attenuation, even if it isn't uniform. I would posit 
that as long as it's performance doesn't alter over time scales shorter than a 
few minutes that the impact would be immeasurable - certainly compared to the 
ionosphere's.

I probably won't bother, though, as we don't seem to have bird trouble and it 
doesn't snow here in Silicon Valley. If it were an unattended installation, 
that might change things. 


Sent from my iPhone

> On Nov 23, 2016, at 5:07 AM, Bob Camp <kb...@n1k.org> wrote:
> 
> Hi
> 
> Ummm …. errrr …. radio transparent plastic. You want to avoid making a 
> lens that distorts the paths over the antenna so it’s not just an issue of 
> transparent. 
> You also want it to be “clear” (non distorting). You need it to be stable in 
> terms of UV,
> humidity and temperature. The guys who made the antenna didn’t have it quite 
> so tough, 
> they could design the cover as part of what determined the pattern of the 
> antenna.  
> 
> The short list of what your low cost printer will handle:
> 
> PLA
> ABS
> PETG
> 
> If it is really low cost, it will only handle the first one. All are a bit of 
> a 
> disaster at 1.5 GHz. PLA likely will not hold up outdoors, let alone do well 
> at RF.
> The other two are poor at RF. 
> 
> The longer list on a higher priced printer:
> 
> Nylon
> Polycarbonate
> HIPS
> Flexable’s 
> 
> The last two are out right from the start. One dissolves in water, the other 
> has no structural integrity. Nylon is hydroscopic 
> and not all that great at 1.5 GHz. For what ever reason the polycarbonate 
> that they sell also is a bit hydroscopic. It also is 
> quite challenging to print unless you have a very fancy printer. 
> 
> Certainly not an easy thing to do.
> 
> Bob
> 
>> On Nov 23, 2016, at 1:05 AM, Nick Sayer via time-nuts <time-nuts@febo.com> 
>> wrote:
>> 
>> 
>>> On Nov 22, 2016, at 9:39 PM, Dennis Lloyd <dll...@musi-tronics.com> wrote:
>>> 
>>> Your problem will be Birds and Debris, it is flat and you will have 
>>> interruptions and phase shifts.
>>> 
>>> Did you not understand why we use pointed antennas for timing and fixed 
>>> installations.
>> 
>> No, I guess I didn’t.
>> 
>> That said, our cats seem to be doing a good job discouraging any birds, and 
>> I can see the antenna mornings when I go out to the car and there’s been no 
>> debris problem I’ve been able to detect.
>> 
>> If it were required, I’d suspect it would be fairly easy to 3D print a 
>> pointy hat from radio-transparent plastic.
>> 
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