K0GKJ – Just Another Ham
The New QTH – A Floating Shack

Homebrew Microwave Antennas That Perform!

I had a problem.

My apartment is surrounded and divided by twelve+ inch thick steel-reinforced concrete walls, and sandwiched between steel pan and prestressed/reinforced concrete floors and ceilings (we’re on the middle of three floors). In effect, I live in an efficient Farraday Cage! Great for preventing RFI on the neighbor’s toaster oven and resisting storms here in hurricane country, but lousy for RF signal propagation. Might also have an interesting effect on lightening strikes as we’re near the lightening capitol of the U.S., but not sure about that…

Two reasons why I care.

First, indoor HF antennas don’t work – the topic for another story.

Second, and germain to this post, my wireless router doesn’t penetrate those walls well enough for my 2.4 GHZ router to shroud my 75 foot long apartment with an adequate wireless “bubble”. My neighbor, closest to the router, gets a better wireless signal than I do in some of my rooms!

I spotted a clever but simple design that costs virtually nothing to try (the best kind) that appealed to my homebrew antenna DNA. The principle: slide a homebrewed parabolic reflector over each of the two antennas on a Linksys router to direct its RF energy, thereby ostensibly creating about 9dbi of gain!
Check it out:
The design and template can be found at www.freeantennas.com. Just print it out to cut the wood scraps into the proper parabolic shape, and apply a little creativity and elbow grease! 
Lookin’ down:
These crude 2.4 gig parabolic reflectors increased the range of my old wireless router by at least 60%, maybe more. Not bad for less than a buck worth of materials, ALL of which came from various junk shelves ‘n drawers.
I now have a strong WiFi signal down the entire 75 foot length of my apartment/fortress! The only weaker spot is right at the opposite end of a forty-something foot load-bearing (steel-reinforced concrete) wall at least 15 inches thick from the router’s location, but even then, the signal is adequately bouncing around to get a medium-strength signal there too !
I wouldn’t be surprised, though, if my neighbor “behind” those reflectors (and down one floor) now finds he’ll have to buy into his own WiFi signal instead of pirating mine (I really don’t mind, but he’s on his own!). That gain obviously came from the backside of these antennas 🙂
Amazing! And yes, I do enjoy homebrewing antennas (antennae?), as I’m sure do many of you, but this was so easy, it was almost disappointing in its lack of challenge. I didn’t even need my MFJ269 antenna analyzer – there’s really nothing to analyze and tune as all the modeling and design was a simple “cut ‘n paste”…
I did also increase the ‘altitude’ of the router itself by about three feet (top shelf instead of middle shelf) and ‘aimed’ the reflectors down the length of my condo. I’m thinking that helped a bit too. My signal now easily penetrates at least three non-load-bearing (steel studs and sheet rock) walls and one set of sliding glass doors out to our lanai (that’s ‘4 season porch’ to you northerners!) almost twice as far away as its previous effefctive range!
  • A couple of pieces of scrap wood (sawed out with a skill saw after marking the parabolic shape on each with Mr. Erskine’s template and a piece of old-fashioned carbon paper (yup, lo-tech all the way!). I then took a belt sander, inverted it and clamped to a workbench, and moved the wood over the sander to quickly shape the pieces of wood more precisely to the lines transferred to the wood.
  • Two 8 inch plastic squares cut out of a storage bin lid (a box cutter did the job nicely). This stuff is stiff enough to keep a curve, but soft enough to bend by hand (others have reported used old cookie sheets or other pieces of metal – too ambitious for this lazy sod!)
  • About a yard of heavy-duty aluminum foil
  • Six small brass screws to screw the foil-lined plastic square (dimensions included on Mr. Erskine’s template).
  • Some spray adhesive (optional) to ensure the foil adhered well to the plastic backing as it was bent to its parabolic curve.

That’s about it. Cool, huh?

I do still need to buy a hard-wired access point for our living room though for connecting the HDTV and Blu-Ray directly to the Internet, and that will come when we switch to from 1 mpbs DSL Internet access to 20 mbps cable Internet access.

Looks right at home in the shack too, doesn’t it?

Right now, at least, I can sit out in the lanai at the other end of the apartment at our dining room table and work on the laptop  if I want to ‘come out of the closet’ (where my Internet access point and radio shack are set up)! So instead of looking at plaster walls, I can watch the palm trees swaying in the sea breeze! Life is indeed sweet.


de K0GKJ

dit dit

2 Responses to “Homebrew Microwave Antennas That Perform!”

  1. Gene. I put together the WIA (Australia) Amateur Radio magazine and this month we are running a brief article about corrosion repairs to antennas. I caught your radio blog and the pic of the hub of your antenna ticks all the boxes. It’s complex, uses different metals, is in a marine environment and I presume that the boulevarde you live on is high traffic, pumping particulant matter into the air.

    Can I use the pic ( if space permits) with a caption along the lines of “ticks all….?

    BTW I have a Boomaroo 22, you would know it as a Catalina 22, I am building a 19 foot rowing dory for the surf and have floating around as my retirement project a 25 foot trailerable houseboat with an Atkins Rescue Minor type main hull and fold out outrigger hulls, its opened plan is similar to the plan view of a Maine lobster.
    I just recently stopped ocean racing in Bass Straight which has a bad reputation for very ordinary weather. On one delivery trip we went from being becalmed to up to 70 knots, its maximum read, over the anemometer in the space of about three hours. I’m too old for that… to quote some movie.
    John Nieman aka Capt’n Nemo

    • Cap’n Nemo, feel free to use pic. Thanks for asking. Salt air here is worst. After less than two months aloft, the small lock washers that lock the fiberglass spreaders to the hub plate virtually disintegrated. Not a structural issue, but salt air, wind working the joints and high UV sun damage all conspire against not only the continuity of electrical connections (for which I liberally employ Coax Seal, the messy bit that it is, it works), but mechanical joints as well. I’ve painted the antenna with Krylon Fusion (designed for plastics) to guard against the sun, and that seems to be working well. Stainless hardware just means that it rusts more slowly, but rust it does. Insidious & insistent. The best corrosion repair, however, is prevention, however nothing corrodes faster than a LOOSE electrical connection, as you well know, and the more RF energy that passes through such a connection, not only will your SWR vascillate, your connection will ‘oxidate’!

      Boomeroo = Catalina? Marvelous! Used to have a thirty. Great boat, but leaked splendidly. My thirty year old motorsailer (Island Trader), now nearly fully restored, had degraded more here in less than a year than the previous fourteen in Minnesota (no salt water or air, freezing temps and she sat “on the hard” for six months each year, which allowed her to dry out regularly as well as experience hundreds of freeze cracks (a different kind of ‘corrosion’).

      Sounds as if you’ve logged some interesting offshore miles. I’ve not sailed in 70 knots, but have found myself anchored in same with lightening all ’round. Exciting evening.

      LOVE the ‘downeaster’ lobster boat design! I’m sure she’s a lovely and stout craft.

      73 from salty and humid Florida. and thanks for checking out the blog(s?)

      dit dit

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