Well, I was planning on a long bike ride for this afternoon, but was too tired ... SO I BUILT AN ANTENNA !! I didn't want to go whole hog and build this huge antenna only to find out it doesn't work, so I started off with a pair of 8 foot yagis, stacked side by side, just to test out the plans.
I stopped at a couple stores and bought three, 8 foot wooden 1x2's ($2 each), aluminum clothes line ($4), two U bolts ($0.99 each but only used one), and RG-6 (the most expensive part at $20!).
I followed the plans from the link above multiplying each dimension by 144/162 = 0.89. My 1x2's were 8 foot, so that allowed me to add a few elements to the 6 element plan. I continued with the same spacing and director length as the last one in the 2 meter plan, so I ended up with 8 elements. The third 1x2 I cut in half (44 inches), screwed them together to form the cross member. 44 inches is close to 5/8 wavelength at 162mhz, so I figured that would be a 'pretty' good spacing and easy to make. A wider spacing might help a little, but for initial tests, it should work.
Little by little though the afternoon I cut and drilled wood and wire - and here's what I came up with! :
I've got it mounted on a flag pole just so I could work on it.
To mount the elements, I simply drilled a 1/8 inch hole through the boom and fed the wire through it. It fits pretty tight, so they won't fall out. I wasn't sure how to handle the driven elements. I didn't need anything as fancy as the original article, so I just used #14 solid copper wire, cut it in half and mounted each half as above. There are currently no connectors on each driven element, I just wound the wire right on each element half to be soldered later.
I tried to pay some attention to the phasing of each beam by using an electrical half wavelength of RG6 on each side of the splitter. That would at least repeat the impeadance of each beam at the splitter and not get some goofy, unknown impeadance that I could never match. I used .78 as the velocity factor of the line. ((468\162) x 12) / .78 = 44 inches of RG6 to feed each beam.
Hooking up the SWR analyzer showed resonance at 150.5 mhz (always make your elements LONG, then trim them shorter!). Little by little I trimmed the driven elements ... PRESTO - 1.4:1 SWR! Good enough for me !
Now it's time to see how it works ... *GULP!*
I tuned my receiver to 162.55, placed one of my little FRS walkie talkies by the speaker and carried the other one out to the antenna. They have "VOX", so nobody has to press the push to talk button to get it to transmit.
Starting with the antenna pointed south, I had Chicago, about 90 miles away. Swinging east, across Lake Michigan, Grand Rapids was full quieting, 100 miles distant. Turning the whole thing around, now aiming west, I've got Madison, WI, also about 90 miles away over some pretty hilly land ! Do you want to hear? (I was recording when I did my intial tests)
http://members.aol.com/j999w/NOAA.wav
With my attic vertical, all I could hear was Grand Rapids with no indication of any other station. So it DOES work !!
It's not quite as sharp as I would like, but it works a heck of a lot better than my little 3 element beam I had made. Rejection off the back and sides seems pretty good. While I'm typing this up, I've got Sheboygan and Green Bay (130 miles) booming in with it turned north. I will ~try~ to squeeze it in the attic, but if not there, then maybe on the roof or even on a dedicated mast of it's own, with a rotator of course.
Would I like to go BIGGER??? YEAH!! But honestly, I'm not sure where I would put it right now. Let's see how this one works out and take it from there.
73!
John K9RZZ
Milwaukee