When I build my next one, I'll remember to take pictures
along the way so I can show how I constructed it. I'll try to explain it as
best I can below.
A side view of the antenna. You can see it's zip tied to
the railing around the "fire escape" from the basement apartment. The window
top just barely in view in the bottom center of the picture (by the yellow
coax cable) is one of the windows from my apartment. The ground plane elements
of the antenna are roughly 4 1/2 feet off the ground.
Here we see a close-up of the "mount" for the antenna,
and the coax. It looks like alot more than it needs to be, but I'll explain
why I did it this way below.
This view shows the coax connector unscrewed from the SO-239
butt splice connector.. The antenna can be removed for cleaning, coax replacement,
or whatever. The coax is Thick Ethernet cable, 52 ohm impedance, and double
shielded. It's stiff stuff, and should hold the antenna upright in a modest
Basically, this antenna cost me $9.19 US to build, and that included the PL-259's for the coax as well.
First I took a piece of coathanger,
about 21" long, and soldered it into one PL-259 from the coax side. The coathanger
sticks out the coax side of the PL-259 connector.
Next, I screwed the PL-259 into the dual SO-239 butt splice connector. Basically this is a "barrel" to join two pieces of coax. I had a different idea for this one. Once the PL-259 was securely screwed onto the barrel, I went on to the next step.
This was the "fun" part. I got out 4 more coathangers, and clipped the hanger part off with a pair of cutters, and straightened them out. I then took one end of each coathanger and bent it into a loop, so that it would fit snugly over the body of the PL-259. I made four of these, and staggered them so the two middle ones (from bottom to top) were 180 degrees opposed, and the top and bottom ones were 180 degrees opposed.
I then took my butane soldering pencil, with the "blowtorch" attachment, and heated up the body and the "rings" on the ground plane elements. I then laid in a healthy amount of solder to make a good electrical connection, and to hold them in place.
Once this whole assembly cooled down enough, I measured 20.5 inches from the radiating element, and cut the remaining coathanger off there.
When I put the antenna up to tune it, I found I had cut the radiating element too short. A good 2 inches was taken up inside the PL-259, and I'd forgotten to allow for that. I'm guessing the radiating element is shielded up until it clears the top (coax end) of the PL-259, so the system thinks that's part of the coax. I ended up stripping the "coating" off the top inch or so of the radiating element, and soldering a 5 inch piece of copper wire onto the end. I stripped about an inch and a half of insulation off the wire, wrapped it around the top of the coathanger and just soldered it on, leaving the insulation on the wire. The antenna was then too long, but still showed a 3:1 match AT WORST on 148.000. I trimmed the copper wire down until I got the match I wanted, as below.
I could trim it slightly shorter to "even up" the match,
but it's good enough for me right now. When I'm not such a "green" HAM (no
eggs, though), I'll probably work on this design to see if I can't get the
curve flatter, and the match more even.
73 de KC8RKQ - Chris
P.S. There's More! Click Here!