antenna in PVC question

Wireless & IoT
1

I have a project using the RLP/TLP. It’s working pretty well in the breadboard stage and now I’m trying to understand the best way to package it.

It’s going to sit outside in weather so I want to encapsulate it as weather proof as possible. I was thinking of laying out the PCB so it could fit in a 2" PVC pipe with a cap. Ideally, I would seal the unit, including the antenna inside so it would be 100% weather tight… Before I go and buy some PVC pipe to test, anyone know any reasons not to do this? does PVC attenuate RF (433.9 mhz) too much? any other negatives? I’ve also found several cases made for outdoor use and they appear to all be PVC.

I suppose I could cut a hole in the cap and fit the antenna through but then I’d have to seal it. one more thing to worry about.

2

PVC can be rather lossy to RF, there are other plastics that are better.

Leon

3

Is it only the black PVC? I was wondering if the back pigment is carbon, which would presumably be more lossy. White or clear PVC might be less lossy.

4

I think the grey variety is worst.

Leon

5

Why don’t you try using fiberglass pipe like they use for communications antennas. A google on “fiberglass pipe antenna” returned this [resource among others.](Fiberglass Tube and Rod - Max-Gain Systems, Inc.)

6

thanks guys. fiberglass makes a lot of sense but I was hoping to make this pretty cheap and simple. Plus, my fiberglass skills, well, suck. oh well.

leon, other than fiberglass, any specific suggestions of other plastics that I should look at?

edit: ABS seems to be used for outdoor wifi cases. I assume that is better and is available at local HW stores. Polycarbonate is also mentioned in a couple of places. any thoughts on those materials?

7

The hard plastic used for hot water pipes should be OK, it’s more rigid as well.

Plastics can be tested in a microwave oven - put a piece in the oven with a glass of water as a load. If the plastic gets warm it isn’t much use.

Leon

8

Polystyrene is really easy to work with. Perhaps the best adhesive (really it forms a weld) to use is model airplane glue, but you could also use acetone. Polystyrene comes in sheets, which can be vacuum formed, and I have also seen it in both round and rectangular tubes.

ABS can be glued, and both it and polycarbonate are probably a lot more durable than styrene. I think the styrene is broken down by uv over time, so you may want to look into that.

9

thanks guys!

I think I’ll chase down ABS - it’s often used in the US for drains and such. Polycarbonate is readily available, easily worked and tough as nails but it too is a bit pricey.

10

I’m not sure the microwave oven test would work so well since he’s using it at 433MHz, not 2.4GHz.

11

wiml:
I’m not sure the microwave oven test would work so well since he’s using it at 433MHz, not 2.4GHz.

It’s relevant at any frequency. The technique is often used by radio amateurs for plastics used at much lower frequencies like HF.

Leon