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Simple DIY Stealth Apartment Antenna for 20m and 40m!

I have no money for a HF antenna, and even if I did my apartment complex wouldn’t allow it! This is my story, and while I’m no expert I hope that sharing my experience will help encourage others to try crazy things in the spirit of invention. A friend loaned me a Century 21 HF CW-only transceiver which puts out ~20W. As far as an antenna, I was limited to what I could build. I tried a bunch of different designs, including a trash-brew 40m base-loaded vertical, but it didn’t work that well. I found that a “contorted dipole” (I heard it’s officially called a zig-zag design) strung up on my ceiling works surprisingly well. I’ve only had it up a few days, but from Florida I’ve talked to New York on 40m at 20W and Maine on 20m using 20W. Keep in mind that I’m brand new to CW, and that 99% of the conversations out there are way too fast for me to copy, so my greatest limitation is finding a CQ slow enough that I can respond to it.

The beauty of my antenna is four-fold. First, it’s super-cheap (a few bucks worth of parts). Second, it’s off the floor and out of the way (unlike my vertical). Third, it doesn’t require a tuner once it’s set up. Forth, it’s virtually invisible! Seriously, if you walk in my apartment you’d have no idea it’s there unless someone points it out. Check it out…

FROM MY FRONT DOOR:
dipole_apartment_1

THERE ARE 7 WIRES! CAN YOU SEE THEM? BARELY!
dipole_apartment_2

So, will this fly for you? That’s between you and your XYL. Here’s a diagram of my apartment and the antennas which hopefully should make a lot more sense…
apartment_dipole
The orange lines represent a 20m dipole with 2 ground radials rather than 1. The purple lines represent a 40m dipole. Dotted gray lines represent fishing line tied to the end of a wire to keep it stretched. Blue circles are plant hooks. Measurements are similar to regular dipoles (approx. quarter wavelength per leg), but I cut these long and used an antenna tuner to shorten them until I reached a 1:1 SWR. Once the SWR was set, I returned my borrowed antenna analyzer and the resulting antenna network seems pretty stable! I’m totally impressed with myself.
IMG_3091
not too shabby ‘eh?
IMG_3084

The physical assembly involved a package of ceiling-mount (screw-type) plant hooks and a couple packages of 50′ of picture hanging wire from Target (a few bucks total). The coax to the radio is pretty straightforward. Just a short patch of cable running up to the ceiling, then the shield goes one direction (to the 3 ground wires) and the center wire goes in the other direction (to the antenna elements). Both antennas are permanently soldered together, which is fine because SWR stays low and I don’t have to jumper things around when I want to change bands.

Here are some photos to show it more clearly…
IMG_3074
and, yes, that’s a sketch of a painting I haven’t painted yet
IMG_3075

DONT GET CONFUSED BY THOSE COILS! They’re not used for the antenna!!! They’re just there to help weigh down the wire to prevent it from wobbling due to the AC. Seriously, they do nothing, you don’t need them. They’re not even touching the antenna! Which reminds me, the two 20m radials were made from actual wire (because I had it lying around), so they’re coated in yellow. No biggie! No reason other than convenience that I didn’t use the picture hanging wire. Okay, that sums it up.

I hope this information helps! If you build a similar setup, let me know – I’d love to see it. If you have questions, feel free to email me. Remember, I didn’t put much math into this – I just went with approximately quarter wavelength legs and started cutting them until the SWR was down to 1:1, then I didn’t adjust it any more. It’s been several days and SWR seems stable, so no antenna analyzer is needed anymore. Good luck with your project, and with any luck I’ll work ya’ on the band. 73!
–Scott, AJ4VD

About the author

Scott W Harden

Scott Harden has had a lifelong passion for computer programming and electrical engineering, and recently has become interested in its relationship with biomolecular sciences. He has run a personal website since he was 15, which has changed names from HardenTechnologies.com, to KnightHacker.com, to ScottIsHot.com, to its current SWHarden.com. Scott has been in college for 10 years, with 3 more years to go. He has an AA in Biology (Valencia College), BS in Cell Biology (Union University), MS in Molecular Biology and Microbiology (University of Central Florida), and is currently in a combined DMD (doctor of dental medicine) / PhD (neuroscience) program through the collaboration of the College of Dentistry and College of Medicine (Interdisciplinary Program in Biomedical Science, IDP) at the University of Florida in Gainesville, Florida. In his spare time Scott builds small electrical devices (with an emphasis on radio frequency) and enjoys writing cross-platform open-source software.

Permanent link to this article: http://www.SWHarden.com/blog/2010-02-07-simple-diy-stealth-apartment-antenna-for-20m-and-40m/

12 comments

  1. morphix

    How is life in dental school?

  2. Scott

    Incredibly boring and unfulfilling right now. I hope it improves =o\

  3. Bill

    I just repaired my Century 21s power supply…
    Your a fine ham with the spirit…
    keep up the radio activity…
    I attached the web site to a sub culture of radio
    people…check it out maybe your hear a Phfer beacon some day.

    73

  4. Andy UU1CC

    Hi there. I’ve tried nearly the same antenna, but got too high level of indoor radiation from my 300 watts tube transmitter and, then moved radiator itself outdoor (leaved counterpoise on the floor). Well, it was an interesting experiment..

  5. DeathByRadio

    I hope you are not using that to transmit.

    Else, enjoy whatever the extreme level of RF will give you and your family/neighbours.

  6. Scott

    It’s obviously not for high power use. If you’re concerned about these amounts of RF, be sure not to use a HT anywhere near your head.

    1. steve

      Up to what power do you consider your zig zag dipole RF “safe”?

      1. munch

        @Steve, Looks like some people don’t know how to read. Or, if they know how to read, they fail to comprehend. It says the power used right in the article.

        20W, at the duty cycles typically found in CW, won’t even register in human flesh. Indeed, the operator will get more heating from the 60Hz AC in the wall.

        @Scott, Speaking of AC, I’d be far more worried about RFI. The last time I tried to use 5W on 6m indoors, I nearly blew the cones off my stereo speakers when I keyed. What steps do you take to mitigate RFI issues? Thanks.

  7. Greg

    http://www.comportco.com/~w5alt/antennas/index.php
    Try the URL above for inspiration.

    Also, check out http://www.southgatearc.org/articles/g0ftd/indoorantenna.htm
    It’s a loop, a very easy loop to build.

    I haven’t either of these, but I think you are up to the challenge.

    73
    Greg, K3ANG

  8. Jaakko, OH6FQI

    Hi there,

    I also live in an apartment, and getting a decent antenna outside seems a bit tricky at the moment. I’ve been using the G0FTD indoor loop, even got a few QSOs with it, but the performance could be better. At least the antenna works much better in a wood/brick house I recently visited than in the steel and concrete building where I live.

    I’m now considering trying something in the line of your above design. Can you tell me your best guess on the materials of your walls and roof before the solar panels? Perhaps your home is less of a faraday cage than mine…

    73,
    Jaakko, OH6FQI

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