2 Meter Antennas. Mechanical part.
See the “Tilt Tower” page for more about the tower where this antenna is mounted.
We live in kind of a ham-radio “void”. There’s almost no hams living around here, no hamfests around here, and no repeaters around here. The closest “useful” repeaters are in Duluth and St. Paul, both about 60-80 miles away.
So, to even get repeaters, let alone do any simplex work, a pretty good antenna is called for. After a few other experiments, this is what I’ve ended up using for the past few months….
The next time I tilt down the tower, I’ll shoot a better, close-up, picture of this beam.
The design criteria for this antenna were:
- must cover the whole 2m band with good matching
- good back and side rejection
- as much gain as I could get after satisfying the above two items
It’s an 8-element Yagi-Uda array, with approx. 10 dbd gain, an SWR under 1.5:1 all the way from 144 to 148, and about 25db F-B ratio. It’s constructed with a 1×2″ wood boom, #8 aluminum wire elements, and a bit of glue. This beam has survived all kinds of windstorms, thunderstorms, snow and ice storms, and hasn’t changed a bit. It’s amazing….
For matching the 18 ohm driven-element impedance to 50 ohm coax, I used a “gamma” match….
That’s #12 copper house wire with the insulation stripped off; an Arco mica compression trimmer, and a BNC female connector. The socket-head screw beside the BNC goes up into the boom and contacts the driven element at the exact center.
I expected some trouble from this arrangement, but apparently the springiness of the wood keeps the pressure applied, and the sharp ring at the end of the screw makes a gas-tight joint with the element. I’ve not had any intermittent operation whatsoever since putting this beam up 4 months ago. Probably just lucky though…