The Infamous Attic Dipole

Mac, AF4PS, FP –51

(Note:  This was installed at a previous QTH)

 

I will be the first (or millionth, remember, I’m from FL!) to affirm that the antenna is the determining factor for success when it comes to one’s station set-up.  The better your antenna, the more success you will have making contacts.  However, I also realize that you can have a lot of fun under less than ideal circumstances.  I was drawn to the recent article in QST where the guy loaded up the light bulb and made contacts.  Yes, almost anything can radiate!   This is important to me, because I live in a deed restricted covenant community that forbids outside antennas, and has a strict “enforcement” committee.  Further, Lori, my XYL only tolerates “wires and beeping” because she loves me, and each antenna experiment is a strain on that balance.  I’m aware that many hams operate under similar circumstances.  I simply want to encourage you!  I’ve been asked to write something about my indoor antenna, and I get asked about it a lot, so I agreed.

 

Honestly, the thing has a life of its own.

 

I began my HAM career as a Tech+ choosing to operate only CW because I am frugal (cheap!). I built the NorCal 40a for the Novice part of the band, and started looking at antenna options.  The first effort was an end fed wire out my garage window with a counterpoise winding around the floor.  My first contact was OH, the second was SC.  I was hooked.  But the wire all over the garage, and running at a low elevation out my window was not a permanent arrangement.  I looked at the trees (I am still working on a loop idea.), then I noticed that my attic is long… in fact, it’s just over 70 feet in length.

 


I grabbed a flashlight, climbed up among the rafters, saw a clear shot end to end, and grinned.  After climbing back down, I got out the ARRL Handbook and saw the measurements for a doublet cut for 40 meters.  I grinned again. (See the accompanying table.)  Lori looked in on me and asked what I was doing.  After I began my detailed explanation, midway, she just frowned, “turned her pretty head and walked away.”  I began humming the Joe Walsh song, and ventured on!

 

 

 

Dipole Dimensions for Amateur Bands

(Table 20.5 in the ARRL Handbook 2000)

 

FREQ

MHz

Overall

Length

Leg

Length

28.4

16’ 6”

8’ 3”

21.1

22’ 2”

11’ 1”

18.1

25’ 10”

12’ 11”

14.1

33’ 2”

16’ 7”

10.1

46’ 4”

23’ 2”

7.1

65’ 10”

32’ 11”

3.6

130’ 0”

65’ 0”

 

 

 

So, it began as a simple, coax fed doublet, right out of the ARRL Handbook: two 35’ equal legs of 14 gauge bare stranded copper wire, 35’ of Radio Shack RG58 coax, three of my son’s plastic blocks for insulators, and nylon rope.  I cut the connector off one end of the coax, drilled a hole through the ceiling in a “hidden” corner of my garage where my bench is (dangerous ground here, but we all take risks!) and fed the end of the coax up into the attic.

 

 

 

 

  I measured the copper wire to confirm 70 feet, coiled it up and gathered my other components including my soldering iron, solder, extension cord, cutters, flashlight, tape and hauled them up with me. I tied a piece of rope to the rafter on one end of the house, attached the copper wire to a plastic block and tied it off.  I stretched the wire out lengthwise, by swinging Tarzan-like from rafter to rafter.  Later, I noticed that there are braces I could have walked on.  That’s when the itching began.  I have 8-9 inches of loose, blown fiberglass insulation in my attic, which was then making its way inside my clothing in a MOST uncomfortable fashion.  I pictured Lori, lying on the bed, trying to read, shaking her head in disbelief, and decided not to seek sympathy from her.

 

 

 

After cutting the long wire in half, I fed the coax through two convenient holes in the plastic block I was using for the center insulator.  Next, I made an RF choke to keep RF from coming back down the outside of the coax by coiling it 8 turns 6” diameter just below the feed point.

 

 

 

 

 

 

 

 

 

 

 

 

 

I found myself wishing I had a better light source than the mini-flashlight I was holding in my mouth, but managed to solder on leg of my dipole to the coax braid, and the other to the center wire.  Then I thought about the battery powered clamp-on “book light” Lori was using down in the bedroom, and dropped my pliers.  Now, using the convenient braces to walk on, occasionally pausing to scratch, I pulled the copper wire through the trusses to the other end of the house. I suspended it about a foot from the apex using rope only at the center insulator and the ends.

 

I estimate that it is up about 17 feet from the ground.  It was done, and I was very proud, but never have found the pliers I dropped into the depths of the fiberglass insulation.  If you permit me to make a theological statement, that stuff is the work of the devil.

 

 

 

 

 

 

 

 

 

 

 

 

This antenna has served me very well, as I was able to get WAS QRP with it.  However, I’m not one to leave well enough alone!  I upgraded my license to General, and built three more rigs!  Although I used the ZM-2 tuner from Emtech, I wanted to tweak the antenna for better multi-band performance.  I added “fans” for 20 and 10 meters using the MFJ 259b to measure and cut.  I do not recommend this, unless you do not happen to have blown fiberglass insulation in your attic.  Enough about that.  After reading Maxwell’s “Reflections”, devouring L.B. Cebik’s web site (http://www.cebik.com/radio.html), and a host of other sources, I decided to transform it into a modified G5RV for multi-band use.  This decision was prompted by my purchase of the Elecraft K2, and my upgrade to Extra class.

 

The modifications are simple.  I purchased 450-ohm window line, a 4:1 balun, and a “Ladder Grabber” center insulator from Emtech.  (Thanks again for the coffee Scott!)  The coax runs up through the hole to the balun, and the window line from there to the center insulator.  When I was performing this modification, Lori finally noticed the hole.  However, by this time, I had collected so much “wires and junk” in the garage, the little slot in the ceiling was a non-issue! (Ask Diz, W8DIZ, he has seen my garage.)

 

Twenty meters is now the “best” band for the antenna, but it loads and works on 10 – 80 just fine, using the ZM-2 tuner.  (I got the internal ATU for the K2 for Christmas!)  I now have over 180 countries in the log, all QRP, with this antenna, 170 of them in this year.  I suppose I can conclude that it works pretty well, better than a lot of indoor antennas, I’m told.  Why? Some have speculated it has something to do with the groundwater, and proximity to the Gulf or Mexico.  Others have suggested that the particular arrangement of my air conditioning ducts and/or shingles boosts my signal like directing or reflecting elements. Lots of people simply refuse to believe that I run 4 watts.  I, truly, have no idea.

 

I will say, that I continue to try various stealth outdoor antennas.  I had a G5RV Jr. up outside hoping to improve my performance in the Fox season, but the last hurricane just TOOK it.  That was ok, because I’m sure that the “Code Enforcers” would have addressed it had the hurricane not. While vacationing on Sanibel Island, I threw a dipole up in a couple of trees, joined in on a Sprint and could not BELIEVE the signals!  On the other hand, I have conditioned myself to operate under less than ideal circumstances.  I’ve become comfortable with my set-up, and really don’t do any better when I use the big tri-band beam at the local clubhouse!

 

I do believe, that while I cannot claim to be a “good” operator, I am a BETTER one, simply because I get on the air… a LOT!  I’ve read and reread Bob Locher’s book, “The Complete DXer”, I practice listening, and try to improve my timing and placement of calls.  My bottom line advice is GET ON THE AIR!  Don’t let a less than ideal antenna situation keep you from having fun.  Call me if you hear me on the air, just don’t ask me to climb in your attic!

 

72 es oo

Mac - AF4PS

Odessa, FL

FP -51