Re: Using PU foam in feedhorns?

Richard <richard@...>
 

I'd be inclined to use your local rain water for the second part.
Tap water is pretty pure , unlike what falls out of the sky , salt ,bits of carbon etc, which could contaminate the surface.
It would avoid any misleading results
Unless of course if you are in the London area where they reckon the water has been through many kidneys before it come out of the tap.

On Thu, 2018-11-22 at 18:56 +0000, Richard GD8EXI wrote:
Can I suggest an experiment with B and Q polyurethane foam. Put a freshly made lump of it in a microwave oven along with a dummy load (cup of water) and see how hot it gets after say 3 minutes at full power. Then take the same the lump of foam, soak it in water for 24 hours or more, dry its surface and repeat the experiment in the microwave.

PU foam is used for microwave application as you already know for example.

https://www.generalplastics.com/wp-content/uploads/2016/12/White-Paper-PU-Foam-Dielectric-Materials-for-Use-in-Radomes-and-Other_Applications.pdf

However some of the additives in B and Q foam may make it less suitable. It only takes 1% or less of something with a high dielectric loss or something in there that make it hydroscopic to ruin the performance in a horn.


Richard
GD8EXI



On 22/11/2018, 17:16, "Barry Chambers" <b.chambers@...> wrote:

> Neil
>
> I suspect the Er will be around 1.05 at worst but you will need to think
> about whether the pores in the foam are open or closed. I'm thinking
> about water getting into the foam.
>
> 73
>
> Barry, G8AGN
>
>
>
>
-- 
 Best wishes /73 
 Richard Bown
 
 Email : richard@...

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