attic J-Pole or external?

[Kart29]

I'm wanting to set up a dual band J-Pole antennae (VHF/UHF). My preference would be to keep the antennae up in the attic rafters rather than mount the antennae outdoors. The indoor installation has a lot of advantages to me. I would use the antennae with a 50W mobile radio fixed to a 110AC/113.8VDC power supply. Maybe sometimes I would connect it to an HT.

However, I have one major concern with the effectiveness of this plan. My workshop where I intend to install the antennae is constructed of refrigerated warehouse panels. The panels are two sheets of steel with about 3'' of Styrofoam between them. These panels go around all 4 side of the shop and all the way up to the peak of the two gable ends. The roof is standard plywood deck covered by shingles.

Do you think the metal skins on the barn walls will serious impede the signal getting out of the building? Do you have any ideas on how to test to what degree the walls deter the transmissions? I don't have any test equipment - just a couple of radios.

Any ideas, thoughts, or suggestions?

 

[Ed_Seedhouse]

You won't be able to get much of a signal out - what you describe amounts to a Faraday cage. Stick it outside is my advice. Or try the attic but be prepared to move it.

 

[Weaksignal]

This may work for you... Untitled

 

[popnokick]

Do you have or can borrow a handheld scanner or HT? Set it up to receive several NOAA weather broadcast channels. Take it up into the attic and make note of what you receive. All the better if there is some signal strength indicator on the HT. Now go out onto the roof and repeat the test. That will give you some idea of the attenuation you'll experience through your steel Faraday cage at VHF frequencies. And it will likely be even greater difference at UHF and 700 / 800 mHz.

 

[Kart29]

I have a couple of HT's and am able to receive with them inside the building with no noticeable reduction in signal quality. I never thought about tuning to a steady signal like NOAA and reading the signal strength meter both inside and outside.

I guess I could also try to get someone in a QSO on the handheld and ask them to report my signal when I move locations from inside to outside.

That might give me a general idea of how much the building is effecting RF signals on both RX and TX.

The idea behind the indoor J-pole is extreme economy, ease of installation, and that it would be somewhat portable. I don't know why I'd ever want my radio to be portable but it's cool to dream that I could use it as a base station on my imaginary hunting trip in the wilderness someday.

 

[N8IAA]

Being that the roof is plywood and shingles, an antenna up there would greatly increase TX and RX. Why put one outside, when you want to have it indoors?
Larry

 

[WA8ZTZ]

Having had a J-pole on my plywood/shingle roof for over 30 yrs, IMHO, put the antenna outdoors because, based on my experience, you will be pleased with the results.

The installation is fairly simple, all that is required is a tripod and a mast. Of course, it needs to be properly grounded per NEC Article 810.

Also, since you plan on operating UHF, use a good grade of coax, otherwise your effort will be for naught.

 

[Kart29]

This weekend I tuned an old Alinco HT to NOAA and checked the six bar signal strength meter inside the shop vs. outside and also inside but up in the rafters.

I was getting 5 to 5.5 bars outside and only 3 to 3.5 bars inside. Disappointing, for sure.

But when I took the HT up a ladder and held it above the rafters, the signal was 4.5 to 5 bars. Noticeably not as good as outside but significantly better than down below.

I think I'm going to start with the antennae up on the attic rafters and give that a try. My budget is $30 to $50 for antennae, cable, connectors... everything. Putting the antennae outside will require bodging together more hardware and cable length. It's just not worth the money to me - not to mention the loss of transportability.

Thanks for the tip on the coax. But how do I know what is a good grade of coax and what is not?