PVC Pipe for mast?

[JoshuaHufford]

I'm planning on mounting an antenna to an un-used chimney on the back of my house. I was thinking of getting a piece of thick PVC pipe, maybe 2" or 3" to use as a mast. I have about 4' of Chimney to work with for mounting, was thinking I could use pipe straps? I'd like to get the antenna 10 Ft. above the top of the chimney, might have to glue 2 sections together. Any reason not to do this? Just thought it would be a light weight and cheap material for a mast.

Thanks!

 

[mmckenna]

Why PVC? Do you have a specific reason for using that over something more appropriate?

Issues with PVC…
Some of it can break down from extended UV (sunlight) exposure.
It'll flex is the wind. Constant flexing will likely cause stress fractures.
Even if you want with something like schedule 80, you'll have long term issues.

 

[jonwienke]

PVC gets brittle and degrades when exposed to sunlight, and isn't a particularly strong material to begin with. It's the wrong material for the job.

 

[JoshuaHufford]

I just figured it was light and cheap.

So what would you suggest for this situation then?

 

[mmckenna]

20 foot fence top rail is a popular choice.

If you don't need the full 10 feet above the chimney, use rigid galvanized conduit.

You just need to be sure the mounting is strong enough for it. Height is important, but so is stability.

 

[jonwienke]

2" galvanized steel electrical conduit isn't that expensive, and comes in 10' lengths.

 

[JoshuaHufford]

Nice, thanks.

 

[Golay]

A better choice

A couple of things:

1. Like others have said, forgo the PVC. It won't stay up long without breaking apart. Plus 2 to 3" PVC isn't going to be light anyway. A better choice would be aluminum pipe. Much stronger and 10' of that is going to be light. or the fence rail. I see someone suggested 20' pipe. Unless you really need the height, 20' on a chimney mount, well I don't know. I guess it depends on what antenna is going up.

2. Now let me say something about your chimney mount. Get some angle, and put it behind the straps on the corners. You don't want the bare straps cutting into the brick or mortar. Using angle behind the straps distributes the force on the chimney. You can use either a bedframe cut apart (an old bedframe is a CHEAP source of angle iron). Or buy some aluminum angle, which is easier to cut than iron.

 

[mmckenna]

Make sure of your antenna mounting bracket size before purchasing. Not all antennas will fit on a 2" diameter mast. 1 1/4 or 1 1/2 may be appropriate.

And since you are going to stick a big metal pole up in the air on top of your home, make sure you ground everything appropriately.

 

[DJ11DLN]

+1 on the galvanized steel conduit for that application. Also on proper grounding. Also check the wind load specs on the antenna. Chimneys aren't exactly designed to take a lot of lateral loading...if you put too much up there you could actually damage the chimney. Which will likely damage the roof as it comes apart. A small antenna without a lot of wind load just a few feet above the chimney will probably be fine, if the chimney is in good condition. A bigger antenna and/or a lot of distance above the mount is not a good idea.

And just to pick a nit, there is PVC electrical conduit that is UV-resistant...but you're better off with the metal kind.:wink:

 

[iMONITOR]

I think a lot of people started using PVC pipe when the Antennacraft ST2 was popular because a metal mast would cause directional disturbance.
Is the gray PCV also not good to use? I thought it was more immune to ultra-violet damage?

 

[mmckenna]

Is the gray PCV also not good to use? I thought it was more immune to ultra-violet damage?

The grey PVC used for electrical conduit will stand up to the UV exposure. I've got some schedule 80 running up the side of a parking garage with 7/8 heliax in it. Been up there for 12 years or so now, no issues. It's next to the stairs, so it had to stand up to some abuse.

But it's not supporting an antenna. It's anchored every few feet into the concrete. It goose-necks near the top and the coax runs out to the antenna.

 

[JoshuaHufford]

Thanks everyone, I really appreciate all the input.

The antenna is a copper pipe Slim Jim, this one to be exact except tuned to 160-164 Mhz so slightly shorter.

https://www.jpole-antenna.com/shop/vhf-public-safety-murs-marine-scanner-slim-jim-antenna/

So I'm going to use the metal pipe, probably fence post. Do I need to isolate the antenna from the metal post? I didn't know if being directly connected to a large metal pipe would affect the performance of the antenna.

If directly attaching to the pipe isn't a problem, can I connect my ground wire directly to pipe and have a properly grounded system?

 

[KC4RAF]

Grey schedule 80 will stand up against UV, but I would not use it for hanging an antenna on it. Just not the best for a mast.

Also, if you have some where else to mount your mast, I'd go for that. Chimneys aren't the best for mounting antennas. If the antenna is small with wind load, you could be ok, but the bigger the antenna, the more stress placed on the mortar, and over time it will break loose. You can buy metal pipe, any length you need/want and using stand-off mounts, anchor to you house.
As others commented, leave the PVC alone....

 

[JoshuaHufford]

I'll look around the house for other ideas but I really don't see anything else to get the height I need, and I don't want to mount anything on the roof.

I've tried a few locations and don't receive well because of the needed height.

 

[JoshuaHufford]

Forgot to add, my house has a hip roof, no gable ends so there is an overhang all around the house.