DIY Disguise home antenna project. "The Flowerpot" for Airband

[uplink]

Here's an excellent performing, low cost antenna you can build, paint, and hide in a tree or planter, or anywhere else a piece of PVC pipe might go unoticed.

  The Center-Fed half wave offers a shorter overall length (about 50 inches total) than the end-fed half wave designs, and it's incredibly easy and cheap to build.

 I used 3/4 PVC pipe from Lowe's and some RG/58U coax from my junk box.  You can cut it so the elements are 20-1/4 inches for airband, and do 10 turns for the coil.  Just be sure the entry and exit holes for the coil are either on the same side of the PVC or 180 opposite each other.  Not 90 degrees out.  I used some epoxy to seal the holes for the coil. Instead of fishing line, I sprayed the inside of mine with some of that expanding foam that comes in a can, to hold the center conductor in place.  You can use a PVC T or barrel connector depending on where you want the coax to exit the pipe.  You can cut an old pop-up sprinkler body, an old caulking canister, or anything similar to protect the coil from the elements.  
 Another option for more stealthines, go without the upper portion of PVC,  use a short piece of PVC just for the coil, protect if from the elements, and just hang it up!
 I am getting outstanding performance from airborne signals, and solid (ground) ATC signals from 25 miles away, and intelligible ATC signals 40 miles away.  

Here is the website for the Half Wave Flowerpot, with excellent instructions.  

http://vk2zoi.com/articles/half-wave-flower-pot/

[falstro]

Very cool!

Now we just need to camouflage it well, and we might get a feed in UK or Germany

[propwash]

Nice job!  I just built one using 1-inch OD pvc instead of the 3/4" inch.  I only used about 8 turns because of the larger diameter.  The choke really works, and is a lot more practical and cheaper than trying to hang a whole bunch of ferrites at the end.

I compared it to a standard center-fed coax-fed vertical with the coax coming out sideways for a few feet, and the directional pattern is the same.  I was kind of worried that this thing would have a funky pattern, but it seems to be behaving.  I can say that this is MUCH better than the old trick of just folding the upper braid back down onto the coax as there is insufficient decoupling and a strange pattern that way.  This choke is a much better performer.

When I first tried it, I merely taped the coax to the outside of the pipe, and this close coupling to the pvc required that I shorten the element lengths slightly to about 19 inches.  Inside the pipe where the coax isn't always touching, 20 inches seemed to be right on center freq of 128mhz or so - at least measured on a Comet swr analyzer.

I'm very happy with it.  I'm thinking about sealing the coil from the elements with some fine coats of the pipe-glue, but will research that to see if it will destroy the coax.

Thanks again...

[propwash]

Oops - my 1" pvc pipe is really 1.25" outside-diameter - no major difference.  7-8 turns seems to be the sweet spot for this diameter pipe.

Due to the tight bend radius of the choke coil, it is best to use solid rather than a foam core coax.  This helps prevent the center conductor from migrating over time internally due to the tight bend.  A 20 foot solid-core Radio Shack RG-58 jumper was convenient, allowing me to make two of these.  For one of my longer runs, I'll just cut the coax about a foot below the choke coil, put a connector on it, and run some higher quality foam coax for the remaining run to the shack.

[propwash]

Final touches:

Because exposed coax braid wicks moisture, I wrapped a small amount of black coax connector protectant goo-tape around the center where the cover and braid was cut away.  For temporary protection from the elements, I wiped an automotive interior protecant like ArmorAll around the coil, and pvc pipe.  Pulled the interior elements out, wiped them down lightly too and replaced back inside.  The Comet CAA-500 swr analyzer didn't show any detuning from this detailing.  Shiny!