Railfan Technology > Weather protection for J-Pole Antenna

I have built a J-Pole antenna cut to 161.00 MHz from copper pipe. It is slightly flimsy and I am anxious about hanging it in a tree near my cabin. I am considering putting it in a piece of 5 or 6 inch PVC or ABS pipe for protection and to disguise it a little.
Can anyone comment on the relative merits of the two kinds of pipe. Which would affect reception the least?

BTW the web page that calculates J-Pole dimensions provides excellent information.

Jeff Pape

I probably wouldn't bother covering the antenna other then waterproofing your connections. I haven't tried it, but I have heard to see if a pipe is suitable for covering an antenna, test a piece of pipe in the microwave for a few seconds. If the pipe gets warm or hot it will not work well for your purposes. You might be able to find a supplier for "radome" pipe that is actually designed for shielding antennas, but it will be costly.

I would waterproof the connections first, then give the entire antenna a coat of paint.

If the copper is pretty clean, it should paint ok.

I tried making a ham antenna inside PVC pipe and conduit. It did change the tuning with both types. Commercial radomes are normally fiberglass. Honestly, unless your fighting ice, the radome wont be worth the effort.

Randy
KK4EJ

Jeff Wrote:
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> I have built a J-Pole antenna cut to 161.00 MHz
> from copper pipe. It is slightly flimsy and I am
> anxious about hanging it in a tree near my cabin.

Unless you were dealing with high winds, tree limbs hitting it, or ice, I wouldn't bother with protecting the antenna other than sealing the connections.

> I am considering putting it in a piece of 5 or 6
> inch PVC or ABS pipe for protection and to
> disguise it a little.

If you're trying to disguise it I would think the 5 or 6 inch pipe would be more noticable than a couple of 1/2 or 3/4 inch copper pipes. Also, if the wind is blowing the copper around, the larger pipes are going to catch alot more air.

If you want to make the antenna stronger you might be able to put some fiberglass or Plexiglass rods inside the pipes. Not sure how it would effect the antenna. Just a thought.

> Can anyone comment on the relative merits of the
> two kinds of pipe. Which would affect reception
> the least?
>
>

I got a message from the fellow that makes the Ventenna, which is a coil inside a piece of ABS pipe that slips over a plumbing vent on your roof. It is to defeat restrictive covenants and works very well. He said that PVC does warm in a microwave and thus affects the electronic properties of an antenna within. ABS either does not affect the electronic properties very much or not at all. It does not warm in a microwave. The Ventennas are in ABS. Shameless plug: go to WWW.Ventenna.com and see what he has on offer.

I need to disguise and hide the antenna as much as possible due to restrictive covenants. Wind and limbs are also an issue. The J-Pole when made from copper pipe is fairly flimsy. However it seems to be worth the hassle as it is a superior antenna for a base station. For example I hear at least one trackside scanner "farther" than before.

Jeff:

I have built a J-pole for myself a few years ago, and compared it to a ground plane ( 1/4 wave ) and found it had a bit over 3.5 db of gain. I carefully tuned it and found it very good, bandidth was around 2mhz at VHF. The size of the pipe will effect the bandwidth, I tested half inch and 3/4 inch, 3/4 was better. I would think 1 inch would be even broader and more sturdy.

Some hams bad mouth them, but they are a good antenna!

Good luck with the discuise......

Another issue about good RX is decent coax from antenna to radio. I personally like Belden 9913. Same size as RG8 but less loss, and uses same connectors.....

Randy
KK4EJ

There is also a J-Pole that is made out of Tv twin lead. You just hang that up with some fish line, Ham Radio Outlet has them tuned for the Ham bands or have seen calculators for them also.

Unless you're transmitting with it, just use any nonmetallic paint. Even the pvc won't significantly impair reception. The J-pole is a 3db gain single frequency antenna. The band spread (lower to upper frequency range) is proportional to the diameter of the elements.

KK5OL

Also... don't worry about the disguise. Copper pipe will oxidize quite rapidly over a period of months and will become a flat, dark brownish-red. You won't see it at all suspended form a tree.
I use one that I built six years ago from 1/2 inch copper tubing. Still works great and is solid as a rock.

Danny Harmon
Tampa